JTC1/SC22/WG14
N843
Programming languages -- C
1. Scope
[#1] This International Standard specifies the form and
establishes the interpretation of programs written in the C
programming language.1) It specifies
-- the representation of C programs;
-- the syntax and constraints of the C language;
-- the semantic rules for interpreting C programs;
-- the representation of input data to be processed by C
programs;
-- the representation of output data produced by C
programs;
-- the restrictions and limits imposed by a conforming
implementation of C.
[#2] This International Standard does not specify
-- the mechanism by which C programs are transformed for
use by a data-processing system;
-- the mechanism by which C programs are invoked for use
by a data-processing system;
-- the mechanism by which input data are transformed for
use by a C program;
-- the mechanism by which output data are transformed
after being produced by a C program;
-- the size or complexity of a program and its data that
will exceed the capacity of any specific data-
processing system or the capacity of a particular
processor;
-- all minimal requirements of a data-processing system
that is capable of supporting a conforming
implementation.
____________________
1) This International Standard is designed to promote the
portability of C programs among a variety of data-
processing systems. It is intended for use by
implementors and programmers.
1 General 1
2 Committee Draft -- August 3, 1998 WG14/N843
2. Normative references
[#1] The following normative documents contain provisions
which, through reference in this text, constitute provisions
of this International Standard. For dated references,
subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements
based on this International Standard are encouraged to
investigate the possibility of applying the most recent
editions of the normative documents indicated below. For
undated references, the latest edition of the normative
document referred to applies. Members of ISO and IEC
maintain registers of currently valid International
Standards.
[#2] ISO/IEC 646:1991, Information technology -- ISO 7-bit |
coded character set for information interchange.
[#3] ISO/IEC 2382-1:1993, Information technology --
Vocabulary -- Part 1: Fundamental terms.
[#4] ISO 4217:1995, Codes for the representation of
currencies and funds.
[#5] ISO 8601:1988, Data elements and interchange formats
-- Information interchange -- Representation of dates and
times.
[#6] ISO/IEC 10646:1993, Information technology -- |
Universal Multiple-Octet Coded Character Set (UCS). |
[#7] IEC 60559:1989, Binary floating-point arithmetic for |
microprocessor systems, second edition (previously |
designated IEC 559:1989).
3. Terms and definitions
[#1] For the purposes of this International Standard, the
following definitions apply. Other terms are defined where
they appear in italic type or on the left side of a syntax
rule. Terms explicitly defined in this International
Standard are not to be presumed to refer implicitly to
similar terms defined elsewhere. Terms not defined in this
International Standard are to be interpreted according to
ISO/IEC 2382-1.
3.1
[#1] alignment
requirement that objects of a particular type be located on
storage boundaries with addresses that are particular
multiples of a byte address
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WG14/N843 Committee Draft -- August 3, 1998 3
3.2
[#1] argument
actual argument
actual parameter (deprecated)
expression in the comma-separated list bounded by the
parentheses in a function call expression, or a sequence of
preprocessing tokens in the comma-separated list bounded by
the parentheses in a function-like macro invocation
3.3
[#1] bit
unit of data storage in the execution environment large
enough to hold an object that may have one of two values
[#2] NOTE It need not be possible to express the address of
each individual bit of an object.
3.4
[#1] byte
addressable unit of data storage large enough to hold any
member of the basic character set of the execution
environment
[#2] NOTE 1 It is possible to express the address of each
individual byte of an object uniquely.
[#3] NOTE 2 A byte is composed of a contiguous sequence of
bits, the number of which is implementation-defined. The
least significant bit is called the low-order bit; the most
significant bit is called the high-order bit.
3.5
[#1] character
bit representation that fits in a byte *
3.6
[#1] constraints
restrictions, both syntactic and semantic, by which the
exposition of language elements is to be interpreted
3.7
[#1] correctly rounded result
a representation in the result format that is nearest in
value, subject to the effective rounding mode, to what the
result would be given unlimited range and precision
3.8
[#1] diagnostic message
message belonging to an implementation-defined subset of the
implementation's message output
3.9
[#1] forward references
references to later subclauses of this International
3.2 General 3.9
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Standard that contain additional information relevant to
this subclause
3.10
[#1] implementation
a particular set of software, running in a particular
translation environment under particular control options,
that performs translation of programs for, and supports
execution of functions in, a particular execution
environment
3.11
[#1] implementation-defined behavior
unspecified behavior where each implementation documents how
the choice is made
[#2] EXAMPLE An example of implementation-defined behavior
is the propagation of the high-order bit when a signed
integer is shifted right.
3.12
[#1] implementation limits
restrictions imposed upon programs by the implementation
3.13
[#1] locale-specific behavior
behavior that depends on local conventions of nationality,
culture, and language that each implementation documents
[#2] EXAMPLE An example of locale-specific behavior is
whether the islower function returns true for characters
other than the 26 lowercase Latin letters.
3.14
[#1] multibyte character
sequence of one or more bytes representing a member of the
extended character set of either the source or the execution
environment
[#2] NOTE The extended character set is a superset of the
basic character set.
3.15
[#1] object
region of data storage in the execution environment, the
contents of which can represent values |
[#2] NOTE When referenced, an object may be interpreted as
having a particular type; see 6.3.2.1.
3.9 General 3.15
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3.16
[#1] parameter
formal parameter
formal argument (deprecated)
object declared as part of a function declaration or
definition that acquires a value on entry to the function,
or an identifier from the comma-separated list bounded by
the parentheses immediately following the macro name in a
function-like macro definition
3.17
[#1] recommended practice
specifications that are strongly recommended as being in
keeping with the intent of the standard, but that may be
impractical for some implementations
3.18
[#1] undefined behavior
behavior, upon use of a nonportable or erroneous program
construct, of erroneous data, or of indeterminately valued
objects, for which this International Standard imposes no
requirements
[#2] NOTE Possible undefined behavior ranges from ignoring |
the situation completely with unpredictable results, to
behaving during translation or program execution in a
documented manner characteristic of the environment (with or
without the issuance of a diagnostic message), to
terminating a translation or execution (with the issuance of
a diagnostic message).
[#3] EXAMPLE An example of undefined behavior is the
behavior on integer overflow.
3.19
[#1] unspecified behavior
behavior where this International Standard provides two or
more possibilities and imposes no requirements on which is
chosen in any instance
[#2] EXAMPLE An example of unspecified behavior is the
order in which the arguments to a function are evaluated.
Forward references: bitwise shift operators (6.5.7),
expressions (6.5), function calls (6.5.2.2), the islower
function (7.4.1.6), localization (7.11).
3.16 General 3.19
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4. Conformance
[#1] In this International Standard, ``shall'' is to be
interpreted as a requirement on an implementation or on a
program; conversely, ``shall not'' is to be interpreted as a
prohibition.
[#2] If a ``shall'' or ``shall not'' requirement that
appears outside of a constraint is violated, the behavior is
undefined. Undefined behavior is otherwise indicated in
this International Standard by the words ``undefined
behavior'' or by the omission of any explicit definition of
behavior. There is no difference in emphasis among these
three; they all describe ``behavior that is undefined''.
[#3] A program that is correct in all other aspects,
operating on correct data, containing unspecified behavior
shall be a correct program and act in accordance with
5.1.2.3.
[#4] The implementation shall not successfully translate a |
preprocessing translation unit containing a #error |
preprocessing directive unless it is part of a group skipped |
by conditional inclusion.
[#5] A strictly conforming program shall use only those
features of the language and library specified in this
International Standard.2) It shall not produce output
dependent on any unspecified, undefined, or implementation-
defined behavior, and shall not exceed any minimum
implementation limit.
[#6] The two forms of conforming implementation are hosted
and freestanding. A conforming hosted implementation shall
accept any strictly conforming program. A conforming
freestanding implementation shall accept any strictly
conforming program that does not use complex types and in
which the use of the features specified in the library
clause (clause 7) is confined to the contents of the
standard headers <float.h>, <iso646.h>, <limits.h>,
<stdarg.h>, <stdbool.h>, <stddef.h>, and <stdint.h>. A
conforming implementation may have extensions (including
additional library functions), provided they do not alter
____________________
2) A strictly conforming program can use conditional |
features (such as those in annex F) provided the use is |
guarded by a #ifdef directive with the appropriate macro. |
For example:
#ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
/* ... */
fesetround(FE_UPWARD);
/* ... */
#endif
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WG14/N843 Committee Draft -- August 3, 1998 7
the behavior of any strictly conforming program.3)
[#7] A conforming program is one that is acceptable to a
conforming implementation.4)
[#8] An implementation shall be accompanied by a document
that defines all implementation-defined and locale-specific
characteristics and all extensions.
Forward references: conditional inclusion (6.10.1), |
characteristics of floating types <float.h> (7.7), |
alternative spellings <iso646.h> (7.9), sizes of integer
types <limits.h> (7.10), variable arguments <stdarg.h>
(7.15), boolean type and values <stdbool.h> (7.16), common |
definitions <stddef.h> (7.17), integer types <stdint.h> |
(7.18).
____________________
3) This implies that a conforming implementation reserves no
identifiers other than those explicitly reserved in this
International Standard.
4) Strictly conforming programs are intended to be maximally
portable among conforming implementations. Conforming
programs may depend upon nonportable features of a
conforming implementation.
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5. Environment
[#1] An implementation translates C source files and
executes C programs in two data-processing-system
environments, which will be called the translation
environment and the execution environment in this
International Standard. Their characteristics define and
constrain the results of executing conforming C programs
constructed according to the syntactic and semantic rules
for conforming implementations.
Forward references: In this clause, only a few of many
possible forward references have been noted.
5.1 Conceptual models
5.1.1 Translation environment
5.1.1.1 Program structure
[#1] A C program need not all be translated at the same
time. The text of the program is kept in units called
source files, (or preprocessing files) in this International |
Standard. A source file together with all the headers and
source files included via the preprocessing directive
#include is known as a preprocessing translation unit. After
preprocessing, a preprocessing translation unit is called a
translation unit. Previously translated translation units
may be preserved individually or in libraries. The separate
translation units of a program communicate by (for example)
calls to functions whose identifiers have external linkage,
manipulation of objects whose identifiers have external
linkage, or manipulation of data files. Translation units
may be separately translated and then later linked to
produce an executable program.
Forward references: conditional inclusion (6.10.1),
linkages of identifiers (6.2.2), source file inclusion
(6.10.2), external definitions (6.9), preprocessing
directives (6.10).
5.1.1.2 Translation phases
[#1] The precedence among the syntax rules of translation is
specified by the following phases.5)
1. Physical source file multibyte characters are mapped
to the source character set (introducing new-line
characters for end-of-line indicators) if necessary. |
____________________
5) Implementations shall behave as if these separate phases
occur, even though many are typically folded together in
practice.
5 Environment 5.1.1.2
WG14/N843 Committee Draft -- August 3, 1998 9
Trigraph sequences are replaced by corresponding
single-character internal representations.
2. Each instance of a backslash character (\) immediately
followed by a new-line character is deleted, splicing
physical source lines to form logical source lines. |
If, as a result, a character sequence that matches the |
syntax of a universal character name is produced, the |
behavior is undefined. Only the last backslash on any
physical source line shall be eligible for being part
of such a splice. A source file that is not empty
shall end in a new-line character, which shall not be
immediately preceded by a backslash character before
any such splicing takes place.
3. The source file is decomposed into preprocessing
tokens6) and sequences of white-space characters
(including comments). A source file shall not end in
a partial preprocessing token or in a partial comment.
Each comment is replaced by one space character. New-
line characters are retained. Whether each nonempty
sequence of white-space characters other than new-line
is retained or replaced by one space character is
implementation-defined.
4. Preprocessing directives are executed, macro
invocations are expanded, and _Pragma unary operator |
expressions are executed. If a character sequence
that matches the syntax of a universal character name
is produced by token concatenation (6.10.3.3), the
behavior is undefined. A #include preprocessing
directive causes the named header or source file to be
processed from phase 1 through phase 4, recursively.
All preprocessing directives are then deleted.
5. Each source character set member, escape sequence, and
universal character name in character constants and
string literals is converted to the corresponding
member of the execution character set; if there is no
corresponding member, it is converted to an
implementation-defined member.
6. Adjacent string literal tokens are concatenated.
7. White-space characters separating tokens are no longer
significant. Each preprocessing token is converted
into a token. The resulting tokens are syntactically
and semantically analyzed and translated as a
____________________
6) As described in 6.4, the process of dividing a source
file's characters into preprocessing tokens is context-
dependent. For example, see the handling of < within a
#include preprocessing directive.
5.1.1.2 Environment 5.1.1.2
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translation unit.
8. All external object and function references are
resolved. Library components are linked to satisfy
external references to functions and objects not
defined in the current translation. All such
translator output is collected into a program image
which contains information needed for execution in its
execution environment.
Forward references: universal character names (6.4.3),
lexical elements (6.4), preprocessing directives (6.10),
trigraph sequences (5.2.1.1), external definitions (6.9).
5.1.1.3 Diagnostics
[#1] A conforming implementation shall produce at least one
diagnostic message (identified in an implementation-defined
manner) if a preprocessing translation unit or translation
unit contains a violation of any syntax rule or constraint,
even if the behavior is also explicitly specified as
undefined or implementation-defined. Diagnostic messages
need not be produced in other circumstances.7)
[#2] EXAMPLE An implementation shall issue a diagnostic for
the translation unit:
char i;
int i;
because in those cases where wording in this International
Standard describes the behavior for a construct as being
both a constraint error and resulting in undefined behavior,
the constraint error shall be diagnosed.
5.1.2 Execution environments
[#1] Two execution environments are defined: freestanding
and hosted. In both cases, program startup occurs when a
designated C function is called by the execution
environment. All objects in static storage shall be
initialized (set to their initial values) before program
startup. The manner and timing of such initialization are
otherwise unspecified. Program termination returns control
to the execution environment.
____________________
7) The intent is that an implementation should identify the
nature of, and where possible localize, each violation.
Of course, an implementation is free to produce any
number of diagnostics as long as a valid program is still
correctly translated. It may also successfully translate
an invalid program.
5.1.1.2 Environment 5.1.2
WG14/N843 Committee Draft -- August 3, 1998 11
Forward references: initialization (6.7.8).
5.1.2.1 Freestanding environment
[#1] In a freestanding environment (in which C program
execution may take place without any benefit of an operating
system), the name and type of the function called at program
startup are implementation-defined. Any library facilities |
available to a freestanding program, other than the minimal |
set required by clause 4, are implementation-defined.
[#2] The effect of program termination in a freestanding
environment is implementation-defined.
5.1.2.2 Hosted environment
[#1] A hosted environment need not be provided, but shall
conform to the following specifications if present.
5.1.2.2.1 Program startup
[#1] The function called at program startup is named main.
The implementation declares no prototype for this function.
It shall be defined with a return type of int and with no
parameters:
int main(void) { /* ... */ }
or with two parameters (referred to here as argc and argv,
though any names may be used, as they are local to the
function in which they are declared):
int main(int argc, char *argv[]) { /* ... */ }
or equivalent;8) or in some other implementation-defined
manner.
[#2] If they are declared, the parameters to the main
function shall obey the following constraints:
-- The value of argc shall be nonnegative.
-- argv[argc] shall be a null pointer.
-- If the value of argc is greater than zero, the array
members argv[0] through argv[argc-1] inclusive shall
contain pointers to strings, which are given
implementation-defined values by the host environment
prior to program startup. The intent is to supply to
____________________
8) Thus, int can be replaced by a typedef name defined as
int, or the type of argv can be written as char ** argv,
and so on.
5.1.2 Environment 5.1.2.2.1
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the program information determined prior to program
startup from elsewhere in the hosted environment. If
the host environment is not capable of supplying
strings with letters in both uppercase and lowercase,
the implementation shall ensure that the strings are
received in lowercase.
-- If the value of argc is greater than zero, the string
pointed to by argv[0] represents the program name;
argv[0][0] shall be the null character if the program
name is not available from the host environment. If
the value of argc is greater than one, the strings
pointed to by argv[1] through argv[argc-1] represent
the program parameters.
-- The parameters argc and argv and the strings pointed to
by the argv array shall be modifiable by the program,
and retain their last-stored values between program
startup and program termination.
5.1.2.2.2 Program execution
[#1] In a hosted environment, a program may use all the
functions, macros, type definitions, and objects described
in the library clause (clause 7).
5.1.2.2.3 Program termination
[#1] If the return type of the main function is a type |
compatible with int, a return from the initial call to the
main function is equivalent to calling the exit function
with the value returned by the main function as its |
argument;9) reaching the } that terminates the main function |
returns a value of 0. If the return type is not compatible |
with int, the termination status returned to the host
environment is unspecified.
Forward references: definition of terms (7.1.1), the exit
function (7.20.4.3).
5.1.2.3 Program execution
[#1] The semantic descriptions in this International
Standard describe the behavior of an abstract machine in
which issues of optimization are irrelevant.
[#2] Accessing a volatile object, modifying an object,
modifying a file, or calling a function that does any of
____________________
9) In accordance with 6.2.4, objects with automatic storage
duration declared in main will no longer have storage
guaranteed to be reserved in the former case even where
they would in the latter.
5.1.2.2.1 Environment 5.1.2.3
WG14/N843 Committee Draft -- August 3, 1998 13
those operations are all side effects,10) which are changes
in the state of the execution environment. Evaluation of an
expression may produce side effects. At certain specified
points in the execution sequence called sequence points, all
side effects of previous evaluations shall be complete and
no side effects of subsequent evaluations shall have taken
place. (A summary of the sequence points is given in annex
C.)
[#3] In the abstract machine, all expressions are evaluated
as specified by the semantics. An actual implementation
need not evaluate part of an expression if it can deduce
that its value is not used and that no needed side effects
are produced (including any caused by calling a function or
accessing a volatile object).
[#4] When the processing of the abstract machine is
interrupted by receipt of a signal, only the values of
objects as of the previous sequence point may be relied on.
Objects that may be modified between the previous sequence
point and the next sequence point need not have received
their correct values yet.
[#5] An instance of each object with automatic storage
duration is associated with each entry into its block. Such
an object exists and retains its last-stored value during
the execution of the block and while the block is suspended
(by a call of a function or receipt of a signal).
[#6] The least requirements on a conforming implementation
are:
-- At sequence points, volatile objects are stable in the |
sense that previous accesses are complete and |
subsequent accesses have not yet occurred.
-- At program termination, all data written into files
shall be identical to the result that execution of the
program according to the abstract semantics would have
produced.
____________________
10)The IEC 60559 standard for binary floating-point
arithmetic requires certain user-accessible status flags
and control modes. Floating-point operations implicitly
set the status flags; modes affect result values of
floating-point operations. Implementations that support
such floating-point state are required to regard changes
to it as side effects -- see annex F for details. The
floating-point environment library <fenv.h> provides a
programming facility for indicating when these side
effects matter, freeing the implementations in other
cases.
5.1.2.3 Environment 5.1.2.3
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-- The input and output dynamics of interactive devices
shall take place as specified in 7.19.3. The intent of
these requirements is that unbuffered or line-buffered
output appear as soon as possible, to ensure that
prompting messages actually appear prior to a program
waiting for input.
[#7] What constitutes an interactive device is
implementation-defined.
[#8] More stringent correspondences between abstract and
actual semantics may be defined by each implementation.
[#9] EXAMPLE 1 An implementation might define a one-to-one
correspondence between abstract and actual semantics: at
every sequence point, the values of the actual objects would
agree with those specified by the abstract semantics. The
keyword volatile would then be redundant.
[#10] Alternatively, an implementation might perform various
optimizations within each translation unit, such that the
actual semantics would agree with the abstract semantics
only when making function calls across translation unit
boundaries. In such an implementation, at the time of each
function entry and function return where the calling
function and the called function are in different
translation units, the values of all externally linked
objects and of all objects accessible via pointers therein
would agree with the abstract semantics. Furthermore, at
the time of each such function entry the values of the
parameters of the called function and of all objects
accessible via pointers therein would agree with the
abstract semantics. In this type of implementation, objects
referred to by interrupt service routines activated by the
signal function would require explicit specification of
volatile storage, as well as other implementation-defined
restrictions.
[#11] EXAMPLE 2 In executing the fragment
char c1, c2;
/* ... */
c1 = c1 + c2;
the ``integer promotions'' require that the abstract machine
promote the value of each variable to int size and then add
the two ints and truncate the sum. Provided the addition of
two chars can be done without overflow, or with overflow
wrapping silently to produce the correct result, the actual
execution need only produce the same result, possibly
omitting the promotions.
5.1.2.3 Environment 5.1.2.3
WG14/N843 Committee Draft -- August 3, 1998 15
[#12] EXAMPLE 3 Similarly, in the fragment
float f1, f2;
double d;
/* ... */
f1 = f2 * d;
the multiplication may be executed using single-precision
arithmetic if the implementation can ascertain that the
result would be the same as if it were executed using
double-precision arithmetic (for example, if d were replaced
by the constant 2.0, which has type double).
[#13] EXAMPLE 4 Implementations employing wide registers
have to take care to honor appropriate semantics. Values
are independent of whether they are represented in a
register or in memory. For example, an implicit spilling of
a register is not permitted to alter the value. Also, an
explicit store and load is required to round to the
precision of the storage type. In particular, casts and
assignments are required to perform their specified
conversion. For the fragment
double d1, d2;
float f;
d1 = f = expression;
d2 = (float) expressions;
the values assigned to d1 and d2 are required to have been
converted to float.
[#14] EXAMPLE 5 Rearrangement for floating-point expressions
is often restricted because of limitations in precision as
well as range. The implementation cannot generally apply
the mathematical associative rules for addition or
multiplication, nor the distributive rule, because of
roundoff error, even in the absence of overflow and
underflow. Likewise, implementations cannot generally
replace decimal constants in order to rearrange expressions.
In the following fragment, rearrangements suggested by
mathematical rules for real numbers are often not valid (see
F.8).
double x, y, z;
/* ... */
x = (x * y) * z; // not equivalent to x *= y * z;
z = (x - y) + y ; // not equivalent to z = x;
z = x + x * y; // not equivalent to z = x * (1.0 + y);
y = x / 5.0; // not equivalent to y = x * 0.2; |
5.1.2.3 Environment 5.1.2.3
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[#15] EXAMPLE 6 To illustrate the grouping behavior of
expressions, in the following fragment
int a, b;
/* ... */
a = a + 32760 + b + 5;
the expression statement behaves exactly the same as
a = (((a + 32760) + b) + 5);
due to the associativity and precedence of these operators.
Thus, the result of the sum (a + 32760) is next added to b,
and that result is then added to 5 which results in the
value assigned to a. On a machine in which overflows
produce an explicit trap and in which the range of values
representable by an int is [-32768, +32767], the
implementation cannot rewrite this expression as
a = ((a + b) + 32765);
since if the values for a and b were, respectively, -32754
and -15, the sum a + b would produce a trap while the
original expression would not; nor can the expression be
rewritten either as
a = ((a + 32765) + b);
or
a = (a + (b + 32765));
since the values for a and b might have been, respectively,
4 and -8 or -17 and 12. However, on a machine in which
overflow silently generates some value and where positive
and negative overflows cancel, the above expression
statement can be rewritten by the implementation in any of
the above ways because the same result will occur.
[#16] EXAMPLE 7 The grouping of an expression does not
completely determine its evaluation. In the following
fragment
#include <stdio.h>
int sum;
char *p;
/* ... */
sum = sum * 10 - '0' + (*p++ = getchar());
the expression statement is grouped as if it were written as
sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
but the actual increment of p can occur at any time between
the previous sequence point and the next sequence point (the
5.1.2.3 Environment 5.1.2.3
WG14/N843 Committee Draft -- August 3, 1998 17
;), and the call to getchar can occur at any point prior to
the need of its returned value.
Forward references: compound statement, or block (6.8.2),
expressions (6.5), files (7.19.3), sequence points (6.5,
6.8), the signal function (7.14), type qualifiers (6.7.3).
5.1.2.3 Environment 5.1.2.3
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5.2 Environmental considerations
5.2.1 Character sets
[#1] Two sets of characters and their associated collating
sequences shall be defined: the set in which source files
are written, and the set interpreted in the execution
environment. The values of the members of the execution
character set are implementation-defined; any additional
members beyond those required by this subclause are locale-
specific.
[#2] In a character constant or string literal, members of
the execution character set shall be represented by
corresponding members of the source character set or by
escape sequences consisting of the backslash \ followed by
one or more characters. A byte with all bits set to 0,
called the null character, shall exist in the basic
execution character set; it is used to terminate a character
string.
[#3] Both the basic source and basic execution character
sets shall have at least the following members: the 26
uppercase letters of the Latin alphabet
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z
the 26 lowercase letters of the Latin alphabet
a b c d e f g h i j k l m
n o p q r s t u v w x y z
the 10 decimal digits
0 1 2 3 4 5 6 7 8 9
the following 29 graphic characters
! " # % & ' ( ) * + , - . / :
; < = > ? [ \ ] ^ _ { | } ~
the space character, and control characters representing
horizontal tab, vertical tab, and form feed. The |
representation of each member of the source and execution |
basic character sets shall fit in a byte. In both the
source and execution basic character sets, the value of each
character after 0 in the above list of decimal digits shall
be one greater than the value of the previous. In source
files, there shall be some way of indicating the end of each
line of text; this International Standard treats such an
end-of-line indicator as if it were a single new-line
character. In the execution character set, there shall be
control characters representing alert, backspace, carriage
5.2 Environment 5.2.1
WG14/N843 Committee Draft -- August 3, 1998 19
return, and new line. If any other characters are
encountered in a source file (except in an identifier, a |
character constant, a string literal, a header name, a
comment, or a preprocessing token that is never converted to
a token), the behavior is undefined.
[#4] The universal character name construct provides a way
to name other characters.
Forward references: universal character names (6.4.3),
character constants (6.4.4.4), preprocessing directives
(6.10), string literals (6.4.5), comments (6.4.9), string
(7.1.1).
5.2.1.1 Trigraph sequences
[#1] All occurrences in a source file of the following
sequences of three characters (called trigraph sequences11))
are replaced with the corresponding single character. |
??= # ??) ] ??! |
??( [ ??' ^ ??> }
??/ \ ??< { ??- ~
No other trigraph sequences exist. Each ? that does not
begin one of the trigraphs listed above is not changed.
[#2] EXAMPLE The following source line
printf("Eh???/n");
becomes (after replacement of the trigraph sequence ??/)
printf("Eh?\n");
5.2.1.2 Multibyte characters
[#1] The source character set may contain multibyte
characters, used to represent members of the extended
character set. The execution character set may also contain
multibyte characters, which need not have the same encoding
as for the source character set. For both character sets,
the following shall hold:
-- The single-byte characters defined in 5.2.1 shall be
present.
____________________
11)The trigraph sequences enable the input of characters
that are not defined in the Invariant Code Set as
described in ISO/IEC 646, which is a subset of the seven- |
bit US ASCII code set. |
5.2.1 Environment 5.2.1.2
20 Committee Draft -- August 3, 1998 WG14/N843
-- The presence, meaning, and representation of any
additional members is locale-specific.
-- A multibyte character set may have a state-dependent |
encoding, wherein each sequence of multibyte characters
begins in an initial shift state and enters other
locale-specific shift states when specific multibyte
characters are encountered in the sequence. While in
the initial shift state, all single-byte characters
retain their usual interpretation and do not alter the
shift state. The interpretation for subsequent bytes
in the sequence is a function of the current shift
state.
-- A byte with all bits zero shall be interpreted as a
null character independent of shift state.
-- A byte with all bits zero shall not occur in the second
or subsequent bytes of a multibyte character.
[#2] For source files, the following shall hold: |
-- An identifier, comment, string literal, character |
constant, or header name shall begin and end in the
initial shift state.
-- An identifier, comment, string literal, character |
constant, or header name shall consist of a sequence of
valid multibyte characters.
5.2.2 Character display semantics
[#1] The active position is that location on a display
device where the next character output by the fputc or |
fputwc function would appear. The intent of writing a
printable character (as defined by the isprint or iswprint |
function) to a display device is to display a graphic
representation of that character at the active position and
then advance the active position to the next position on the
current line. The direction of writing is locale-specific.
If the active position is at the final position of a line
(if there is one), the behavior is unspecified.
[#2] Alphabetic escape sequences representing nongraphic
characters in the execution character set are intended to
produce actions on display devices as follows:
\a (alert) Produces an audible or visible alert. The active
position shall not be changed.
\b (backspace) Moves the active position to the previous
position on the current line. If the active position is
at the initial position of a line, the behavior is
unspecified.
5.2.1.2 Environment 5.2.2
WG14/N843 Committee Draft -- August 3, 1998 21
\f (form feed) Moves the active position to the initial
position at the start of the next logical page.
\n (new line) Moves the active position to the initial
position of the next line.
\r (carriage return) Moves the active position to the
initial position of the current line.
\t (horizontal tab) Moves the active position to the next
horizontal tabulation position on the current line. If
the active position is at or past the last defined
horizontal tabulation position, the behavior is
unspecified.
\v (vertical tab) Moves the active position to the initial
position of the next vertical tabulation position. If
the active position is at or past the last defined
vertical tabulation position, the behavior is
unspecified.
[#3] Each of these escape sequences shall produce a unique
implementation-defined value which can be stored in a single
char object. The external representations in a text file
need not be identical to the internal representations, and
are outside the scope of this International Standard.
Forward references: the isprint function (7.4.1.7), the
fputc function (7.19.7.3), the fputwc functions (7.24.3.3), |
the iswprint function (7.25.2.1.7).
5.2.3 Signals and interrupts
[#1] Functions shall be implemented such that they may be
interrupted at any time by a signal, or may be called by a
signal handler, or both, with no alteration to earlier, but
still active, invocations' control flow (after the
interruption), function return values, or objects with
automatic storage duration. All such objects shall be
maintained outside the function image (the instructions that |
compose the executable representation of a function) on a
per-invocation basis.
5.2.4 Environmental limits
[#1] Both the translation and execution environments
constrain the implementation of language translators and
libraries. The following summarizes the language-related |
environmental limits on a conforming implementation; the |
library-related limits are discussed in clause 7.
5.2.2 Environment 5.2.4
22 Committee Draft -- August 3, 1998 WG14/N843
5.2.4.1 Translation limits
[#1] The implementation shall be able to translate and
execute at least one program that contains at least one
instance of every one of the following limits:12)
-- 127 nesting levels of compound statements, iteration
statements, and selection statements
-- 63 nesting levels of conditional inclusion
-- 12 pointer, array, and function declarators (in any
combinations) modifying an arithmetic, structure,
union, or incomplete type in a declaration
-- 63 nesting levels of parenthesized declarators within a
full declarator
-- 63 nesting levels of parenthesized expressions within a
full expression
-- 63 significant initial characters in an internal
identifier or a macro name (each universal character |
name or extended source character is considered a |
single character)
-- 31 significant initial characters in an external
identifier (each universal character name specifying a |
character short identifier of 0000FFFF or less is |
considered 6 characters, each universal character name |
specifying a character short identifier of 00010000 or |
more is considered 10 characters, and each extended |
source character is considered the same number of |
characters as the corresponding universal character |
name, if any)
-- 4095 external identifiers in one translation unit
-- 511 identifiers with block scope declared in one block
-- 4095 macro identifiers simultaneously defined in one
preprocessing translation unit
-- 127 parameters in one function definition
-- 127 arguments in one function call
-- 127 parameters in one macro definition
____________________
12)Implementations should avoid imposing fixed translation
limits whenever possible.
5.2.4.1 Environment 5.2.4.1
WG14/N843 Committee Draft -- August 3, 1998 23
-- 127 arguments in one macro invocation
-- 4095 characters in a logical source line
-- 4095 characters in a character string literal or wide
string literal (after concatenation)
-- 65535 bytes in an object (in a hosted environment only)
-- 15 nesting levels for #included files
-- 1023 case labels for a switch statement (excluding
those for any nested switch statements)
-- 1023 members in a single structure or union
-- 1023 enumeration constants in a single enumeration
-- 63 levels of nested structure or union definitions in a
single struct-declaration-list
5.2.4.2 Numerical limits
[#1] A conforming implementation shall document all the
limits specified in this subclause, which are specified in |
the headers <limits.h> and <float.h>. Additional limits are |
specified in <stdint.h>.
5.2.4.2.1 Sizes of integer types <limits.h>
[#1] The values given below shall be replaced by constant
expressions suitable for use in #if preprocessing
directives. Moreover, except for CHAR_BIT and MB_LEN_MAX,
the following shall be replaced by expressions that have the
same type as would an expression that is an object of the
corresponding type converted according to the integer
promotions. Their implementation-defined values shall be
equal or greater in magnitude (absolute value) to those
shown, with the same sign.
-- number of bits for smallest object that is not a bit-
field (byte)
CHAR_BIT 8
-- minimum value for an object of type signed char
SCHAR_MIN -127 // -(27-1)
-- maximum value for an object of type signed char
SCHAR_MAX +127 // 27-1
-- maximum value for an object of type unsigned char
UCHAR_MAX 255 // 28-1
5.2.4.1 Environment 5.2.4.2.1
24 Committee Draft -- August 3, 1998 WG14/N843
-- minimum value for an object of type char
CHAR_MIN see below
-- maximum value for an object of type char
CHAR_MAX see below
-- maximum number of bytes in a multibyte character, for
any supported locale
MB_LEN_MAX 1
-- minimum value for an object of type short int
SHRT_MIN -32767 // -(215-1)
-- maximum value for an object of type short int
SHRT_MAX +32767 // 215-1
-- maximum value for an object of type unsigned short int
USHRT_MAX 65535 // 216-1
-- minimum value for an object of type int
INT_MIN -32767 // -(215-1)
-- maximum value for an object of type int
INT_MAX +32767 // 215-1
-- maximum value for an object of type unsigned int
UINT_MAX 65535 // 216-1
-- minimum value for an object of type long int
LONG_MIN -2147483647 // -(231-1)
-- maximum value for an object of type long int
LONG_MAX +2147483647 // 231-1
-- maximum value for an object of type unsigned long int
ULONG_MAX 4294967295 // 232-1
-- minimum value for an object of type long long int
LLONG_MIN -9223372036854775807 // -(263-1)
-- maximum value for an object of type long long int
LLONG_MAX +9223372036854775807 // 263-1
-- maximum value for an object of type unsigned long long
int
ULLONG_MAX 18446744073709551615 // 264-1
[#2] If the value of an object of type char is treated as a
signed integer when used in an expression, the value of
CHAR_MIN shall be the same as that of SCHAR_MIN and the
value of CHAR_MAX shall be the same as that of SCHAR_MAX.
Otherwise, the value of CHAR_MIN shall be 0 and the value of
CHAR_MAX shall be the same as that of UCHAR_MAX.13) The
value UCHAR_MAX+1 shall equal 2 raised to the power
5.2.4.2.1 Environment 5.2.4.2.1
WG14/N843 Committee Draft -- August 3, 1998 25
CHAR_BIT.
5.2.4.2.2 Characteristics of floating types <float.h>
[#1] The characteristics of floating types are defined in
terms of a model that describes a representation of
floating-point numbers and values that provide information
about an implementation's floating-point arithmetic.14) The
following parameters are used to define the model for each
floating-point type:
s sign (±1)
b base or radix of exponent representation (an integer > 1)
e exponent (an integer between a minimum emin and a maximum emax)
p precision (the number of base-b digits in the significand)
fk nonnegative integers less than b (the significand digits)
[#2] A normalized floating-point number x (f1 > 0 if x != 0)
is defined by the following model:
x=s×be×k=1fk×b-k,emin<=e<=emax
[#3] Floating types may include values that are not
normalized floating-point numbers, for example subnormal |
floating-point numbers (x!=0,e=emin,f1=0), infinities, and |
NaNs.15) A NaN is an encoding signifying Not-a-Number. A
quiet NaN propagates through almost every arithmetic
operation without raising an exception; a signaling NaN
generally raises an exception when occurring as an
arithmetic operand.16)
[#4] The accuracy of the floating-point operations (+, -, *,
/) and of the library functions in <math.h> and <complex.h> |
that return floating-point results is implementation |
defined. The implementation may state that the accuracy is |
unknown.
[#5] All integer values in the <float.h> header, except
____________________
13)See 6.2.5.
14)The floating-point model is intended to clarify the
description of each floating-point characteristic and
does not require the floating-point arithmetic of the
implementation to be identical.
15)Although they are stored in floating types, infinities
and NaNs are not floating-point numbers.
16)IEC 60559:1989 specifies quiet and signaling NaNs. For
implementations that do not support IEC 60559:1989, the
terms quiet NaN and signaling NaN are intended to apply
to encodings with similar behavior.
5.2.4.2.1 Environment 5.2.4.2.2
26 Committee Draft -- August 3, 1998 WG14/N843
FLT_ROUNDS, shall be constant expressions suitable for use
in #if preprocessing directives; all floating values shall
be constant expressions. All except DECIMAL_DIG, |
FLT_EVAL_METHOD, FLT_RADIX, and FLT_ROUNDS have separate
names for all three floating-point types. The floating-
point model representation is provided for all values except
FLT_EVAL_METHOD and FLT_ROUNDS.
[#6] The rounding mode for floating-point addition is
characterized by the value of FLT_ROUNDS:17)
-1 indeterminable
0 toward zero
1 to nearest
2 toward positive infinity
3 toward negative infinity
All other values for FLT_ROUNDS characterize implementation-
defined rounding behavior.
[#7] The values of operations with floating operands and
values subject to the usual arithmetic conversions and of
floating constants are evaluated to a format whose range and
precision may be greater than required by the type. The use
of evaluation formats is characterized by the value of
FLT_EVAL_METHOD:18)
-1 indeterminable;
0 evaluate all operations and constants just
to the range and precision of the type;
1 evaluate operations and constants of type
float and double to the range and precision
of the double type, evaluate long double
operations and constants to the range and
precision of the long double type;
2 evaluate all operations and constants to the
range and precision of the long double type.
All other negative values for FLT_EVAL_METHOD characterize
implementation-defined behavior.
____________________
17)Evaluation of FLT_ROUNDS correctly reflects any
execution-time change of rounding mode through the
function fesetround in <fenv.h>.
18)The evaluation method determines evaluation formats of
expressions involving all floating types, not just real
types. For example, if FLT_EVAL_METHOD is 1, then the
product of two float _Complex operands is represented in
the double _Complex format, and its parts are evaluated
to double.
5.2.4.2.2 Environment 5.2.4.2.2
WG14/N843 Committee Draft -- August 3, 1998 27
[#8] The values given in the following list shall be
replaced by implementation-defined constant expressions with
values that are greater or equal in magnitude (absolute
value) to those shown, with the same sign:
-- radix of exponent representation, b
FLT_RADIX 2
-- number of base-FLT_RADIX digits in the floating-point
significand, p
FLT_MANT_DIG
DBL_MANT_DIG
LDBL_MANT_DIG
-- number of decimal digits, n, such that any floating- |
point number in the widest supported floating type with |
pmax radix b digits can be rounded to a floating-point |
number with n decimal digits and back again without |
changpmax×log10blueif b is a power of 10 |
|1+pmax×log10b|otherwise
DECIMAL_DIG 10
-- number of decimal digits, q, such that any floating-
point number with q decimal digits can be rounded into
a floating-point number with p radix b digits and back
again without change to the q decimal digits, |
5.2.4.2.2 Environment 5.2.4.2.2
28 Committee Draft -- August 3, 1998 WG14/N843
p×log10b if b is a power of 10
|(p-1)×log10b|otherwise
FLT_DIG 6
DBL_DIG 10
LDBL_DIG 10
-- minimum negative integer such that FLT_RADIX raised to
one less than that power is a normalized floating-point
number, emin
FLT_MIN_EXP
DBL_MIN_EXP
LDBL_MIN_EXP
-- minimum negative integer such that 10 raised to that
power is in the range of normalized floating-point
numbers, |log10bemin-1|
FLT_MIN_10_EXP -37
DBL_MIN_10_EXP -37
LDBL_MIN_10_EXP -37
-- maximum integer such that FLT_RADIX raised to one less
than that power is a representable finite floating-
point number, emax
FLT_MAX_EXP
DBL_MAX_EXP
LDBL_MAX_EXP
-- maximum integer such that 10 raised to that power is in
the range of representable finite floating-point
numbers, |log10((1-b-p)×bemax)|
5.2.4.2.2 Environment 5.2.4.2.2
WG14/N843 Committee Draft -- August 3, 1998 29
FLT_MAX_10_EXP +37
DBL_MAX_10_EXP +37
LDBL_MAX_10_EXP +37
[#9] The values given in the following list shall be
replaced by implementation-defined constant expressions with
values that are greater than or equal to those shown:
-- maximum representable finite floating-point number,
(1-b-p)×bemax
FLT_MAX 1E+37
DBL_MAX 1E+37
LDBL_MAX 1E+37
[#10] The values given in the following list shall be
replaced by implementation-defined constant expressions with
(positive) values that are less than or equal to those
shown:
-- the difference between 1 and the least value greater
than 1 that is representable in the given floating
point type, b1-p
FLT_EPSILON 1E-5
DBL_EPSILON 1E-9
LDBL_EPSILON 1E-9
-- minimum normalized positive floating-point number,
bemin-1
FLT_MIN 1E-37
DBL_MIN 1E-37
LDBL_MIN 1E-37
[#11] EXAMPLE 1 The following describes an artificial
floating-point representation that meets the minimum
requirements of this International Standard, and the
appropriate values in a <float.h> header for type float:
x=s×16e×k=1fk×16-k,-31<=e<=+32
FLT_RADIX 16
FLT_MANT_DIG 6
FLT_EPSILON 9.53674316E-07F
FLT_DIG 6
FLT_MIN_EXP -31
FLT_MIN 2.93873588E-39F
FLT_MIN_10_EXP -38
FLT_MAX_EXP +32
FLT_MAX 3.40282347E+38F
FLT_MAX_10_EXP +38
5.2.4.2.2 Environment 5.2.4.2.2
30 Committee Draft -- August 3, 1998 WG14/N843
[#12] EXAMPLE 2 The following describes floating-point
representations that also meet the requirements for single-
precision and double-precision normalized numbers in IEC
60559,19) and the appropriate values in a <float.h> header
for types float and double:
xf=s×2e×k=1fk×2-k,-125<=e<=+128
xd=s×2e×k=1fk×2-k,-1021<=e<=+1024
FLT_RADIX 2
DECIMAL_DIG 17 |
FLT_MANT_DIG 24
FLT_EPSILON 1.19209290E-07F // decimal constant
FLT_EPSILON 0X1P-23F // hex constant
FLT_DIG 6
FLT_MIN_EXP -125
FLT_MIN 1.17549435E-38F // decimal constant
FLT_MIN 0X1P-126F // hex constant
FLT_MIN_10_EXP -37
FLT_MAX_EXP +128
FLT_MAX 3.40282347E+38F // decimal constant
FLT_MAX 0X1.fffffeP127F // hex constant
FLT_MAX_10_EXP +38
DBL_MANT_DIG 53
DBL_EPSILON 2.2204460492503131E-16 // decimal constant
DBL_EPSILON 0X1P-52 // hex constant
DBL_DIG 15
DBL_MIN_EXP -1021
DBL_MIN 2.2250738585072014E-308 // decimal constant
DBL_MIN 0X1P-1022 // hex constant
DBL_MIN_10_EXP -307
DBL_MAX_EXP +1024
DBL_MAX 1.7976931348623157E+308 // decimal constant
DBL_MAX 0X1.ffffffffffffeP1023 // hex constant
DBL_MAX_10_EXP +308
If a type wider than double were supported, then DECIMAL_DIG |
would be greater than 17. For example, if the widest type |
were to use the minimal-width IEC 60559 double-extended |
format (64 bits of precision), then DECIMAL_DIG would be 21.
Forward references: conditional inclusion (6.10.1), complex |
arithmetic <complex.h> (7.3), mathematics <math.h> (7.12), |
integer types <stdint.h> (7.18).
____________________
19)The floating-point model in that standard sums powers of
b from zero, so the values of the exponent limits are one
less than shown here.
5.2.4.2.2 Environment 5.2.4.2.2
WG14/N843 Committee Draft -- August 3, 1998 31
6. Language
6.1 Notation
[#1] In the syntax notation used in this clause, syntactic
categories (nonterminals) are indicated by italic type, and
literal words and character set members (terminals) by bold
type. A colon (:) following a nonterminal introduces its
definition. Alternative definitions are listed on separate
lines, except when prefaced by the words ``one of''. An
optional symbol is indicated by the suffix ``-opt'', so that
{ expression-opt }
indicates an optional expression enclosed in braces.
[#2] A summary of the language syntax is given in annex A.
6.2 Concepts
6.2.1 Scopes of identifiers
[#1] An identifier can denote an object; a function; a tag |
or a member of a structure, union, or enumeration; a typedef |
name; a label name; a macro name; or a macro parameter. The |
same identifier can denote different entities at different |
points in the program. A member of an enumeration is called |
an enumeration constant. Macro names and macro parameters |
are not considered further here, because prior to the |
semantic phase of program translation any occurrences of |
macro names in the source file are replaced by the |
preprocessing token sequences that constitute their macro |
definitions. |
[#2] For each different entity that an identifier
designates, the identifier is visible (i.e., can be used)
only within a region of program text called its scope.
Different entities designated by the same identifier either |
have different scopes, or are in different name spaces.
There are four kinds of scopes: function, file, block, and
function prototype. (A function prototype is a declaration
of a function that declares the types of its parameters.)
[#3] A label name is the only kind of identifier that has
function scope. It can be used (in a goto statement)
anywhere in the function in which it appears, and is
declared implicitly by its syntactic appearance (followed by
a : and a statement). Label names shall be unique within a
function.
[#4] Every other identifier has scope determined by the
placement of its declaration (in a declarator or type
specifier). If the declarator or type specifier that
declares the identifier appears outside of any block or list
6 Language 6.2.1
32 Committee Draft -- August 3, 1998 WG14/N843
of parameters, the identifier has file scope, which
terminates at the end of the translation unit. If the
declarator or type specifier that declares the identifier
appears inside a block or within the list of parameter
declarations in a function definition, the identifier has
block scope, which terminates at the } that closes the
associated block. If the declarator or type specifier that
declares the identifier appears within the list of parameter
declarations in a function prototype (not part of a function
definition), the identifier has function prototype scope,
which terminates at the end of the function declarator. If
an identifier designates two different entities in the same
name space, the scopes might overlap. If so, the scope of
one entity (the inner scope) will be a strict subset of the
scope of the other entity (the outer scope). Within the
inner scope, the identifier designates the entity declared
in the inner scope; the entity declared in the outer scope
is hidden (and not visible) within the inner scope.
[#5] Unless explicitly stated otherwise, where this
International Standard uses the term identifier to refer to
some entity (as opposed to the syntactic construct), it
refers to the entity in the relevant name space whose
declaration is visible at the point the identifier occurs.
[#6] Two identifiers have the same scope if and only if
their scopes terminate at the same point.
[#7] Structure, union, and enumeration tags have scope that
begins just after the appearance of the tag in a type
specifier that declares the tag. Each enumeration constant
has scope that begins just after the appearance of its
defining enumerator in an enumerator list. Any other
identifier has scope that begins just after the completion
of its declarator.
Forward references: compound statement, or block (6.8.2),
declarations (6.7), enumeration specifiers (6.7.2.2),
function calls (6.5.2.2), function declarators (including
prototypes) (6.7.5.3), function definitions (6.9.1), the
goto statement (6.8.6.1), labeled statements (6.8.1), name
spaces of identifiers (6.2.3), scope of macro definitions
(6.10.3.5), source file inclusion (6.10.2), tags (6.7.2.3),
type specifiers (6.7.2).
6.2.2 Linkages of identifiers
[#1] An identifier declared in different scopes or in the
same scope more than once can be made to refer to the same
object or function by a process called linkage. There are
three kinds of linkage: external, internal, and none.
[#2] In the set of translation units and libraries that
constitutes an entire program, each declaration of a |
6.2.1 Language 6.2.2
WG14/N843 Committee Draft -- August 3, 1998 33
particular identifier with external linkage denotes the same
object or function. Within one translation unit, each |
declaration of an identifier with internal linkage denotes
the same object or function. Each declaration of an |
identifier with no linkage denotes a unique entity. |
[#3] If the declaration of a file scope identifier for an
object or a function contains the storage-class specifier
static, the identifier has internal linkage.20)
[#4] For an identifier declared with the storage-class
specifier extern in a scope in which a prior declaration of
that identifier is visible,21) if the prior declaration
specifies internal or external linkage, the linkage of the
identifier at the later declaration is the same as the |
linkage specified at the prior declaration. If no prior
declaration is visible, or if the prior declaration
specifies no linkage, then the identifier has external
linkage.
[#5] If the declaration of an identifier for a function has
no storage-class specifier, its linkage is determined
exactly as if it were declared with the storage-class
specifier extern. If the declaration of an identifier for
an object has file scope and no storage-class specifier, its
linkage is external.
[#6] The following identifiers have no linkage: an
identifier declared to be anything other than an object or a
function; an identifier declared to be a function parameter;
a block scope identifier for an object declared without the
storage-class specifier extern.
[#7] If, within a translation unit, the same identifier
appears with both internal and external linkage, the
behavior is undefined.
Forward references: compound statement, or block (6.8.2),
declarations (6.7), expressions (6.5), external definitions
(6.9).
____________________
20)A function declaration can contain the storage-class
specifier static only if it is at file scope; see 6.7.1.
21)As specified in 6.2.1, the later declaration might hide
the prior declaration.
6.2.2 Language 6.2.2
34 Committee Draft -- August 3, 1998 WG14/N843
6.2.3 Name spaces of identifiers
[#1] If more than one declaration of a particular identifier
is visible at any point in a translation unit, the syntactic
context disambiguates uses that refer to different entities.
Thus, there are separate name spaces for various categories
of identifiers, as follows:
-- label names (disambiguated by the syntax of the label
declaration and use);
-- the tags of structures, unions, and enumerations
(disambiguated by following any22) of the keywords
struct, union, or enum);
-- the members of structures or unions; each structure or
union has a separate name space for its members
(disambiguated by the type of the expression used to
access the member via the . or -> operator);
-- all other identifiers, called ordinary identifiers
(declared in ordinary declarators or as enumeration
constants).
Forward references: enumeration specifiers (6.7.2.2),
labeled statements (6.8.1), structure and union specifiers
(6.7.2.1), structure and union members (6.5.2.3), tags
(6.7.2.3).
6.2.4 Storage durations of objects
[#1] An object has a storage duration that determines its
lifetime. There are three storage durations: static,
automatic, and allocated. Allocated storage is described in
7.20.3.
[#2] An object whose identifier is declared with external or
internal linkage, or with the storage-class specifier static
has static storage duration. For such an object, storage is
reserved and its stored value is initialized only once,
prior to program startup. The object exists, has a constant
address, and retains its last-stored value throughout the
execution of the entire program.23)
[#3] An object whose identifier is declared with no linkage
and without the storage-class specifier static has automatic
storage duration. For objects that do not have a variable |
length array type, storage is guaranteed to be reserved for |
a new instance of the object on each entry into the block |
with which it is associated; the initial value of the object |
is indeterminate. If an initialization is specified for the |
object, it is performed each time the declaration is reached |
in the execution of the block; otherwise, the value becomes |
indeterminate each time the declaration is reached. Storage
for the object is no longer guaranteed to be reserved when
execution of the block ends in any way. (Entering an |
enclosed block or calling a function suspends, but does not |
end, execution of the current block.) |
WG14/N843 Committee Draft -- August 3, 1998 35
[#4] For objects that do have a variable length array type, |
storage is guaranteed to be reserved for a new instance of |
the object each time the declaration is reached in the |
execution of the program. The initial value of the object |
is indeterminate. Storage for the object is no longer |
guaranteed to be reserved when the execution of the program |
leaves the scope of the declaration.24) |
[#5] If an object is referred to when storage is not |
reserved for it, the behavior is undefined. The value of a
pointer that referred to an object whose storage is no |
longer reserved is indeterminate. During the time that its |
storage is reserved, an object has a constant address.
Forward references: compound statement, or block (6.8.2),
function calls (6.5.2.2), declarators (6.7.5), array
declarators (6.7.5.2), initialization (6.7.8).
6.2.5 Types
[#1] The meaning of a value stored in an object or returned
by a function is determined by the type of the expression
used to access it. (An identifier declared to be an object
is the simplest such expression; the type is specified in
the declaration of the identifier.) Types are partitioned
into object types (types that describe objects), function
types (types that describe functions), and incomplete types
(types that describe objects but lack information needed to
determine their sizes).
[#2] An object declared as type _Bool is large enough to |
store the values 0 and 1. |
[#3] An object declared as type char is large enough to
store any member of the basic execution character set. If a
member of the required source character set enumerated in
5.2.1 is stored in a char object, its value is guaranteed to
____________________
22)There is only one name space for tags even though three
are possible.
23)The term constant address means that two pointers to the
object constructed at possibly different times will
compare equal. The address may be different during two
different executions of the same program.
In the case of a volatile object, the last store need not
be explicit in the program.
24)Leaving the innermost block containing the declaration,
or jumping to a point in that block or an embedded block
prior to the declaration, leaves the scope of the
declaration.
6.2.4 Language 6.2.5
36 Committee Draft -- August 3, 1998 WG14/N843
be positive. If any other character is stored in a char
object, the resulting value is implementation-defined but
shall be within the range of values that can be represented
in that type.
[#4] There are five standard signed integer types,
designated as signed char, short int, int, long int, and
long long int. (These and other types may be designated in
several additional ways, as described in 6.7.2.) There may
also be implementation-defined extended signed integer
types.25) The standard and extended signed integer types
are collectively called signed integer types.26) |
[#5] An object declared as type signed char occupies the
same amount of storage as a ``plain'' char object. A
``plain'' int object has the natural size suggested by the
architecture of the execution environment (large enough to
contain any value in the range INT_MIN to INT_MAX as defined
in the header <limits.h>).
[#6] For each of the signed integer types, there is a
corresponding (but different) unsigned integer type
(designated with the keyword unsigned) that uses the same
amount of storage (including sign information) and has the
same alignment requirements. The type _Bool and the |
unsigned integer types that correspond to the standard |
signed integer types are the standard unsigned integer
types. The unsigned integer types that correspond to the
extended signed integer types are the extended unsigned
integer types.
[#7] The standard signed integer types and standard unsigned |
integer types are collectively called the standard integer |
types, the extended signed integer types and extended |
unsigned integer types are collectively called the extended
integer types.
[#8] For any two types with the same signedness and
different integer conversion rank (see 6.3.1.1), the range |
of values of the type with smaller integer conversion rank
is a subrange of the values of the other type.
[#9] The range of nonnegative values of a signed integer
type is a subrange of the corresponding unsigned integer
type, and the representation of the same value in each type
is the same.27) A computation involving unsigned operands
____________________
25)Implementation-defined keywords shall have the form of an
identifier reserved for any use as described in 7.1.3.
26)Therefore, any statement in this Standard about signed
integer types also applies to the extended signed integer
types.
6.2.5 Language 6.2.5
WG14/N843 Committee Draft -- August 3, 1998 37
can never overflow, because a result that cannot be
represented by the resulting unsigned integer type is
reduced modulo the number that is one greater than the
largest value that can be represented by the resulting
unsigned integer type.
[#10] There are three real floating types, designated as
float, double, and long double. The set of values of the
type float is a subset of the set of values of the type
double; the set of values of the type double is a subset of
the set of values of the type long double.
[#11] There are three complex types, designated as float
_Complex, double _Complex, and long double _Complex.28) The
real floating and complex types are collectively called the
floating types.
[#12] For each floating type there is a corresponding real
type, which is always a real floating type. For real
floating types, it is the same type. For complex types, it
is the type given by deleting the keyword _Complex from the
type name.
[#13] Each complex type has the same representation and
alignment requirements as an array type containing exactly
two elements of the corresponding real type; the first
element is equal to the real part, and the second element to
the imaginary part, of the complex number.
[#14] The type char, the signed and unsigned integer types,
and the floating types are collectively called the basic
types. Even if the implementation defines two or more basic
types to have the same representation, they are nevertheless
different types.29)
[#15] The three types char, signed char, and unsigned char
are collectively called the character types. The
implementation shall define char to have the same range,
____________________
27)The same representation and alignment requirements are
meant to imply interchangeability as arguments to
functions, return values from functions, and members of
unions.
28)A specification for imaginary types is in informative
annex G.
29)An implementation may define new keywords that provide
alternative ways to designate a basic (or any other)
type; this does not violate the requirement that all
basic types be different. Implementation-defined
keywords shall have the form of an identifier reserved
for any use as described in 7.1.3.
6.2.5 Language 6.2.5
38 Committee Draft -- August 3, 1998 WG14/N843
representation, and behavior as either signed char or
unsigned char.30)
[#16] An enumeration comprises a set of named integer
constant values. Each distinct enumeration constitutes a
different enumerated type.
[#17] The type char, the signed and unsigned integer types, |
and the enumerated types are collectively called integer |
types. The integer and real floating types are collectively |
called real types. |
[#18] The void type comprises an empty set of values; it is
an incomplete type that cannot be completed.
[#19] Any number of derived types can be constructed from
the object, function, and incomplete types, as follows:
-- An array type describes a contiguously allocated
nonempty set of objects with a particular member object
type, called the element type.31) Array types are
characterized by their element type and by the number
of elements in the array. An array type is said to be
derived from its element type, and if its element type
is T, the array type is sometimes called ``array of
T''. The construction of an array type from an element
type is called ``array type derivation''.
-- A structure type describes a sequentially allocated |
nonempty set of member objects (and, in certain |
circumstances, an incomplete array), each of which has
an optionally specified name and possibly distinct
type.
-- A union type describes an overlapping nonempty set of
member objects, each of which has an optionally
specified name and possibly distinct type.
-- A function type describes a function with specified
return type. A function type is characterized by its
return type and the number and types of its parameters.
A function type is said to be derived from its return
type, and if its return type is T, the function type is
sometimes called ``function returning T''. The
____________________
30)CHAR_MIN, defined in <limits.h>, will have one of the
values 0 or SCHAR_MIN, and this can be used to
distinguish the two options. Irrespective of the choice
made, char is a separate type from the other two and is
not compatible with either.
31)Since object types do not include incomplete types, an
array of incomplete type cannot be constructed.
6.2.5 Language 6.2.5
WG14/N843 Committee Draft -- August 3, 1998 39
construction of a function type from a return type is
called ``function type derivation''.
-- A pointer type may be derived from a function type, an
object type, or an incomplete type, called the
referenced type. A pointer type describes an object
whose value provides a reference to an entity of the
referenced type. A pointer type derived from the
referenced type T is sometimes called ``pointer to T''.
The construction of a pointer type from a referenced
type is called ``pointer type derivation''.
[#20] These methods of constructing derived types can be
applied recursively.
[#21] Integer and floating types are collectively called *
arithmetic types. Arithmetic types and pointer types are
collectively called scalar types. Array and structure types
are collectively called aggregate types.32)
[#22] Each arithmetic type belongs to one typedomain. The |
real type domain comprises the real types. The complex type |
domain comprises the complex types.
[#23] An array type of unknown size is an incomplete type.
It is completed, for an identifier of that type, by
specifying the size in a later declaration (with internal or
external linkage). A structure or union type of unknown
content (as described in 6.7.2.3) is an incomplete type. It
is completed, for all declarations of that type, by
declaring the same structure or union tag with its defining
content later in the same scope. A structure type |
containing a flexible array member is an incomplete type |
that cannot be completed.
[#24] Array, function, and pointer types are collectively
called derived declarator types. A declarator type
derivation from a type T is the construction of a derived
declarator type from T by the application of an array-type,
a function-type, or a pointer-type derivation to T.
[#25] A type is characterized by its type category, which is
either the outermost derivation of a derived type (as noted
above in the construction of derived types), or the type
itself if the type consists of no derived types.
[#26] Any type so far mentioned is an unqualified type. Each
unqualified type has several qualified versions of its
type,33) corresponding to the combinations of one, two, or
____________________
32)Note that aggregate type does not include union type
because an object with union type can only contain one
member at a time.
6.2.5 Language 6.2.5
40 Committee Draft -- August 3, 1998 WG14/N843
all three of the const, volatile, and restrict qualifiers.
The qualified or unqualified versions of a type are distinct
types that belong to the same type category and have the
same representation and alignment requirements.27) A
derived type is not qualified by the qualifiers (if any) of
the type from which it is derived.
[#27] A pointer to void shall have the same representation
and alignment requirements as a pointer to a character type.
Similarly, pointers to qualified or unqualified versions of
compatible types shall have the same representation and
alignment requirements.27) All pointers to structure types
shall have the same representation and alignment
requirements as each other. All pointers to union types
shall have the same representation and alignment
requirements as each other. Pointers to other types need
not have the same representation or alignment requirements.
[#28] EXAMPLE 1 The type designated as ``float *'' has type
``pointer to float''. Its type category is pointer, not a
floating type. The const-qualified version of this type is
designated as ``float * const'' whereas the type designated
as ``const float *'' is not a qualified type -- its type is
``pointer to const-qualified float'' and is a pointer to a
qualified type.
[#29] EXAMPLE 2 The type designated as ``struct tag
(*[5])(float)'' has type ``array of pointer to function
returning struct tag''. The array has length five and the
function has a single parameter of type float. Its type
category is array.
Forward references: character constants (6.4.4.4),
compatible type and composite type (6.2.7), declarations *
(6.7), tags (6.7.2.3), type qualifiers (6.7.3).
6.2.6 Representations of types
[#1] The representations of all types are unspecified except
as stated in this subclause.
6.2.6.1 General
[#1] Except for bit-fields, objects are composed of |
contiguous sequences of one or more bytes, the number, |
order, and encoding of which are either explicitly specified |
or implementation-defined. |
[#2] Values stored in objects of type unsigned char shall be
____________________
33)See 6.7.3 regarding qualified array and function types.
6.2.5 Language 6.2.6.1
WG14/N843 Committee Draft -- August 3, 1998 41
represented using a pure binary notation.34)
[#3] Values stored in objects of any other object type |
consist of n×CHAR_BIT bits, where n is the size of an object |
of that type, in bytes. The value may be copied into an
object of type unsigned char [n] (e.g., by memcpy); the
resulting set of bytes is called the object representation
of the value. Two values (other than NaNs) with the same |
object representation compare equal, but values that compare |
equal may have different object representations.
[#4] Certain object representations need not represent a |
value of the object type. If the stored value of an object
has such a representation and is accessed by an lvalue
expression that does not have character type, the behavior
is undefined. If such a representation is produced by a
side effect that modifies all or any part of the object by
an lvalue expression that does not have character type, the
behavior is undefined.35) Such a representation is called a
trap representation.
[#5] When a value is stored in an object of structure or
union type, including in a member object, the bytes of the
object representation that correspond to any padding bytes
take unspecified values.36) The values of padding bytes
shall not affect whether the value of such an object is a
trap representation. Those bits of a structure or union
object that are in the same byte as a bit-field member, but
are not part of that member, shall similarly not affect
whether the value of such an object is a trap
representation.
[#6] When a value is stored in a member of an object of
union type, the bytes of the object representation that do
not correspond to that member but do correspond to other
____________________
34)A positional representation for integers that uses the
binary digits 0 and 1, in which the values represented by
successive bits are additive, begin with 1, and are
multiplied by successive integral powers of 2, except
perhaps the bit with the highest position. (Adapted from
the American National Dictionary for Information
Processing Systems.) A byte contains CHAR_BIT bits, and
the values of type unsigned char range from 0 to
2CHAR_BIT-1.
35)Thus an automatic variable can be initialized to a trap
representation without causing undefined behavior, but
the value of the variable cannot be used until a proper
value is stored in it.
36)Thus, for example, structure assignment may be
implemented element-at-a-time or via memcpy.
6.2.6.1 Language 6.2.6.1
42 Committee Draft -- August 3, 1998 WG14/N843
members take unspecified values, but the value of the union
object shall not thereby become a trap representation.
[#7] Where an operator is applied to a value which has more
than one object representation, which object representation
is used shall not affect the value of the result. Where a
value is stored in an object using a type that has more than
one object representation for that value, it is unspecified
which representation is used, but a trap representation
shall not be generated.
6.2.6.2 Integer types
[#1] For unsigned integer types other than unsigned char,
the bits of the object representation shall be divided into
two groups: value bits and padding bits (there need not be
any of the latter). If there are N value bits, each bit
shall represent a different power of 2 between 1 and 2N-1,
so that objects of that type shall be capable of
representing values from 0 to 2N-1 using a pure binary
representation; this shall be known as the value
representation. The values of any padding bits are
unspecified.37)
[#2] For signed integer types, the bits of the object
representation shall be divided into three groups: value
bits, padding bits, and the sign bit. There need not be any
padding bits; there shall be exactly one sign bit. Each bit
that is a value bit shall have the same value as the same
bit in the object representation of the corresponding
unsigned type (if there are M value bits in the signed type
and N in the unsigned type, then M<=N). If the sign bit is
zero, it shall not affect the resulting value. If the sign
bit is one, then the value shall be modified in one of the
following ways:
-- the corresponding value with sign bit 0 is negated;
-- the sign bit has the value -2N;
-- the sign bit has the value 1-2N.
[#3] The values of any padding bits are unspecified.37) A
valid (non-trap) object representation of a signed integer
____________________
37)Some combinations of padding bits might generate trap
representations, for example, if one padding bit is a
parity bit. Regardless, no arithmetic operation on valid
values can generate a trap representation other than as
part of an exception such as an overflow, and this cannot
occur with unsigned types. All other combinations of
padding bits are alternative object representations of
the value specified by the value bits.
6.2.6.1 Language 6.2.6.2
WG14/N843 Committee Draft -- August 3, 1998 43
type where the sign bit is zero is a valid object
representation of the corresponding unsigned type, and shall
represent the same value.
[#4] The precision of an integer type is the number of bits
it uses to represent values, excluding any sign and padding
bits. The width of an integer type is the same but
including any sign bit; thus for unsigned integer types the
two values are the same, while for signed integer types the
width is one greater than the precision.
6.2.7 Compatible type and composite type
[#1] Two types have compatible type if their types are the
same. Additional rules for determining whether two types
are compatible are described in 6.7.2 for type specifiers,
in 6.7.3 for type qualifiers, and in 6.7.5 for
declarators.38) Moreover, two structure, union, or
enumerated types declared in separate translation units are
compatible if their tags and members satisfy the following
requirements: If one is declared with a tag, the other
shall be declared with the same tag. If both are completed
types, then the following additional requirements apply:
there shall be a one-to-one correspondence between their
members such that each pair of corresponding members are
declared with compatible types, and such that if one member
of a corresponding pair is declared with a name, the other
member is declared with the same name. For two structures,
corresponding members shall be declared in the same order.
For two structures or unions, corresponding bit-fields shall
have the same widths. For two enumerations, corresponding
members shall have the same values.
[#2] All declarations that refer to the same object or
function shall have compatible type; otherwise, the behavior
is undefined.
[#3] A composite type can be constructed from two types that
are compatible; it is a type that is compatible with both of
the two types and satisfies the following conditions:
-- If one type is an array of known constant size, the
composite type is an array of that size; otherwise, if
one type is a variable length array, the composite type
is that type.
-- If only one type is a function type with a parameter
type list (a function prototype), the composite type is
a function prototype with the parameter type list.
____________________
38)Two types need not be identical to be compatible.
6.2.6.2 Language 6.2.7
44 Committee Draft -- August 3, 1998 WG14/N843
-- If both types are function types with parameter type
lists, the type of each parameter in the composite
parameter type list is the composite type of the
corresponding parameters.
These rules apply recursively to the types from which the
two types are derived.
[#4] For an identifier with internal or external linkage
declared in a scope in which a prior declaration of that
identifier is visible,39) if the prior declaration specifies
internal or external linkage, the type of the identifier at
the later declaration becomes the composite type.
[#5] EXAMPLE Given the following two file scope
declarations:
int f(int (*)(), double (*)[3]);
int f(int (*)(char *), double (*)[]);
The resulting composite type for the function is:
int f(int (*)(char *), double (*)[3]);
Forward references: declarators (6.7.5), enumeration
specifiers (6.7.2.2), structure and union specifiers
(6.7.2.1), type definitions (6.7.7), type qualifiers
(6.7.3), type specifiers (6.7.2).
____________________
39)As specified in 6.2.1, the later declaration might hide
the prior declaration.
6.2.7 Language 6.2.7
WG14/N843 Committee Draft -- August 3, 1998 45
6.3 Conversions
[#1] Several operators convert operand values from one type
to another automatically. This subclause specifies the
result required from such an implicit conversion, as well as
those that result from a cast operation (an explicit
conversion). The list in 6.3.1.8 summarizes the conversions
performed by most ordinary operators; it is supplemented as
required by the discussion of each operator in 6.5.
[#2] Conversion of an operand value to a compatible type
causes no change to the value or the representation.
Forward references: cast operators (6.5.4).
6.3.1 Arithmetic operands
6.3.1.1 Boolean, characters, and integers |
[#1] Every integer type has an integer conversion rank
defined as follows:
-- No two signed integer types shall have the same rank,
even if they have the same representation.
-- The rank of a signed integer type shall be greater than
the rank of any signed integer type with less
precision.
-- The rank of long long int shall be greater than the *
rank of long int, which shall be greater than the rank
of int, which shall be greater than the rank of short
int, which shall be greater than the rank of signed
char.
-- The rank of any unsigned integer type shall equal the
rank of the corresponding signed integer type, if any. |
-- The rank of any standard integer type shall be greater |
than the rank of any extended integer type with the |
same width.
-- The rank of char shall equal the rank of signed char
and unsigned char.
-- The rank of _Bool shall be less than the rank of all |
other standard integer types. |
-- The rank of any enumerated type shall equal the rank of
the compatible integer type.
-- The rank of any extended signed integer type relative
to another extended signed integer type with the same
precision is implementation-defined, but still subject
6.3 Language 6.3.1.1
46 Committee Draft -- August 3, 1998 WG14/N843
to the other rules for determining the integer
conversion rank.
-- For all integer types T1, T2, and T3, if T1 has greater
rank than T2 and T2 has greater rank than T3, then T1
has greater rank than T3.
[#2] The following may be used in an expression wherever an
int or unsigned int may be used:
-- An object or expression with an integer type whose
integer conversion rank is less than the rank of int
and unsigned int.
-- A bit-field of type _Bool, int, signed int, or unsigned |
int.
If an int can represent all values of the original type, the |
value is converted to an int; otherwise, it is converted to
an unsigned int. These are called the integer
promotions.40) All other types are unchanged by the integer
promotions.
[#3] The integer promotions preserve value including sign.
As discussed earlier, whether a ``plain'' char is treated as
signed is implementation-defined.
Forward references: enumeration specifiers (6.7.2.2),
structure and union specifiers (6.7.2.1). |
6.3.1.2 Boolean type |
[#1] When any scalar value is converted to _Bool, the result |
is 0 if the value compares equal to 0; otherwise, the result |
is 1.
6.3.1.3 Signed and unsigned integers
[#1] When a value with integer type is converted to another |
integer type other than _Bool, if the value can be
represented by the new type, it is unchanged.
[#2] Otherwise, if the new type is unsigned, the value is
converted by repeatedly adding or subtracting one more than
the maximum value that can be represented in the new type
until the value is in the range of the new type.
____________________
40)The integer promotions are applied only: as part of the |
usual arithmetic conversions, to certain argument
expressions, to the operands of the unary +, -, and ~
operators, and to both operands of the shift operators,
as specified by their respective subclauses.
6.3.1.1 Language 6.3.1.3
WG14/N843 Committee Draft -- August 3, 1998 47
[#3] Otherwise, the new type is signed and the value cannot
be represented in it; the result is implementation-defined.
6.3.1.4 Real floating and integer
[#1] When a finite value of real floating type is converted |
to integer type other than _Bool, the fractional part is |
discarded (i.e., the value is truncated toward zero). If
the value of the integral part cannot be represented by the
integer type, the behavior is undefined.41)
[#2] When a value of integer type is converted to real
floating type, if the value being converted is in the range
of values that can be represented but cannot be represented
exactly, the result is either the nearest higher or nearest
lower value, chosen in an implementation-defined manner. If
the value being converted is outside the range of values
that can be represented, the behavior is undefined.
6.3.1.5 Real floating types
[#1] When a float is promoted to double or long double, or a
double is promoted to long double, its value is unchanged.
[#2] When a double is demoted to float or a long double to
double or float, if the value being converted is outside the
range of values that can be represented, the behavior is
undefined. If the value being converted is in the range of
values that can be represented but cannot be represented
exactly, the result is either the nearest higher or nearest
lower value, chosen in an implementation-defined manner.
6.3.1.6 Complex types
[#1] When a value of complex type is converted to another
complex type, both the real and imaginary parts follow the
conversion rules for the corresponding real types.
6.3.1.7 Real and complex
[#1] When a value of real type is converted to a complex
type, the real part of the complex result value is
determined by the rules of conversion to the corresponding
real type and the imaginary part of the complex result value
is a positive zero or an unsigned zero.
[#2] When a value of complex type is converted to a real
____________________
41)The remaindering operation performed when a value of
integer type is converted to unsigned type need not be
performed when a value of real floating type is converted
to unsigned type. Thus, the range of portable real
floating values is (-1, Utype_MAX+1).
6.3.1.3 Language 6.3.1.7
48 Committee Draft -- August 3, 1998 WG14/N843
type, the imaginary part of the complex value is discarded
and the value of the real part is converted according to the
conversion rules for the corresponding real type.
6.3.1.8 Usual arithmetic conversions
[#1] Many operators that expect operands of arithmetic type
cause conversions and yield result types in a similar way.
The purpose is to determine a common real type for the
operands and result. For the specified operands, each
operand is converted, without change of type domain, to a |
type whose corresponding real type is the common real type.
Unless explicitly stated otherwise, the common real type is
also the corresponding real type of the result, whose type |
domain is determined by the operator. This pattern is
called the usual arithmetic conversions:
First, if the corresponding real type of either operand
is long double, the other operand is converted, without
change of type domain, to a type whose corresponding |
real type is long double.
Otherwise, if the corresponding real type of either
operand is double, the other operand is converted,
without change of type domain, to a type whose |
corresponding real type is double.
Otherwise, if the corresponding real type of either
operand is float, the other operand is converted, |
without change of type domain, to a type whose
corresponding real type is float.42)
Otherwise, the integer promotions are performed on both
operands. Then the following rules are applied to the
promoted operands:
If both operands have the same type, then no
further conversion is needed.
Otherwise, if both operands have signed integer
types or both have unsigned integer types, the
operand with the type of lesser integer conversion
rank is converted to the type of the operand with
greater rank.
Otherwise, if the operand that has unsigned
integer type has rank greater or equal to the rank
of the type of the other operand, then the operand
with signed integer type is converted to the type
____________________
42)For example, addition of a double _Complex and a float
entails just the conversion of the float operand to
double (and yields a double _Complex result).
6.3.1.7 Language 6.3.1.8
WG14/N843 Committee Draft -- August 3, 1998 49
of the operand with unsigned integer type.
Otherwise, if the type of the operand with signed
integer type can represent all of the values of
the type of the operand with unsigned integer
type, then the operand with unsigned integer type
is converted to the type of the operand with
signed integer type.
Otherwise, both operands are converted to the
unsigned integer type corresponding to the type of
the operand with signed integer type.
[#2] The values of floating operands and of the results of
floating expressions may be represented in greater precision
and range than that required by the type; the types are not
changed thereby.43)
6.3.2 Other operands
6.3.2.1 Lvalues and function designators
[#1] An lvalue is an expression with an object type or an |
incomplete type other than void;44) if an lvalue does not |
designate an object when it is evaluated, the behavior is |
undefined. When an object is said to have a particular
type, the type is specified by the lvalue used to designate
the object. A modifiable lvalue is an lvalue that does not
have array type, does not have an incomplete type, does not
have a const-qualified type, and if it is a structure or
union, does not have any member (including, recursively, any
member or element of all contained aggregates or unions)
with a const-qualified type.
[#2] Except when it is the operand of the sizeof operator,
the unary & operator, the ++ operator, the -- operator, or
____________________
43)The cast and assignment operators are still required to
perform their specified conversions as described in
6.3.1.4 and 6.3.1.5.
44)The name ``lvalue'' comes originally from the assignment
expression E1 = E2, in which the left operand E1 is
required to be a (modifiable) lvalue. It is perhaps
better considered as representing an object ``locator
value''. What is sometimes called ``rvalue'' is in this
International Standard described as the ``value of an
expression''.
An obvious example of an lvalue is an identifier of an
object. As a further example, if E is a unary expression
that is a pointer to an object, *E is an lvalue that
designates the object to which E points.
6.3.1.8 Language 6.3.2.1
50 Committee Draft -- August 3, 1998 WG14/N843
the left operand of the . operator or an assignment
operator, an lvalue that does not have array type is
converted to the value stored in the designated object (and
is no longer an lvalue). If the lvalue has qualified type,
the value has the unqualified version of the type of the
lvalue; otherwise, the value has the type of the lvalue. If
the lvalue has an incomplete type and does not have array
type, the behavior is undefined.
[#3] Except when it is the operand of the sizeof operator or
the unary & operator, or is a string literal used to |
initialize an array, an expression that has type ``array of |
type'' is converted to an expression with type ``pointer to |
type'' that points to the initial element of the array
object and is not an lvalue. If the array object has
register storage class, the behavior is undefined.
[#4] A function designator is an expression that has
function type. Except when it is the operand of the sizeof
operator45) or the unary & operator, a function designator
with type ``function returning type'' is converted to an
expression that has type ``pointer to function returning
type''.
Forward references: address and indirection operators
(6.5.3.2), assignment operators (6.5.16), common definitions
<stddef.h> (7.17), initialization (6.7.8), postfix increment
and decrement operators (6.5.2.4), prefix increment and
decrement operators (6.5.3.1), the sizeof operator
(6.5.3.4), structure and union members (6.5.2.3).
6.3.2.2 void
[#1] The (nonexistent) value of a void expression (an
expression that has type void) shall not be used in any way,
and implicit or explicit conversions (except to void) shall
not be applied to such an expression. If an expression of
any other type is evaluated as a void expression, its value |
or designator is discarded. (A void expression is evaluated
for its side effects.)
6.3.2.3 Pointers
[#1] A pointer to void may be converted to or from a pointer
to any incomplete or object type. A pointer to any
incomplete or object type may be converted to a pointer to
void and back again; the result shall compare equal to the
original pointer.
____________________
45)Because this conversion does not occur, the operand of
the sizeof operator remains a function designator and
violates the constraint in 6.5.3.4.
6.3.2.1 Language 6.3.2.3
WG14/N843 Committee Draft -- August 3, 1998 51
[#2] For any qualifier q, a pointer to a non-q-qualified
type may be converted to a pointer to the q-qualified
version of the type; the values stored in the original and
converted pointers shall compare equal.
[#3] An integer constant expression with the value 0, or
such an expression cast to type void *, is called a null
pointer constant.46) If a null pointer constant is assigned
to or compared for equality to a pointer, the constant is
converted to a pointer of that type. Such a pointer, called
a null pointer, is guaranteed to compare unequal to a
pointer to any object or function.
[#4] Conversion of a null pointer to another pointer type
yields a null pointer of that type. Any two null pointers
shall compare equal.
[#5] An integer may be converted to any pointer type. The
result is implementation-defined, might not be properly
aligned, and might not point to an entity of the referenced
type.47)
[#6] Any pointer type may be converted to an integer type;
the result is implementation-defined. If the result cannot
be represented in the integer type, the behavior is
undefined. The result need not be in the range of values of |
any integer type.
[#7] A pointer to an object or incomplete type may be
converted to a pointer to a different object or incomplete
type. If the resulting pointer is not correctly aligned48)
for the pointed-to type, the behavior is undefined. |
Otherwise, when converted back again, the result shall
compare equal to the original pointer. When a pointer to an |
object is converted to a pointer to a character type, the |
result points to the lowest addressed byte of the object. |
Successive increments of the result, up to the size of the |
object, yield pointers to the remaining bytes of the object.
____________________
46)The macro NULL is defined in <stddef.h> as a null pointer
constant; see 7.17.
47)The mapping functions for converting a pointer to an
integer or an integer to a pointer are intended to be
consistent with the addressing structure of the execution
environment.
48)In general, the concept ``correctly aligned'' is |
transitive: if a pointer to type A is correctly aligned
for a pointer to type B, which in turn is correctly
aligned for a pointer to type C, then a pointer to type A
is correctly aligned for a pointer to type C.
6.3.2.3 Language 6.3.2.3
52 Committee Draft -- August 3, 1998 WG14/N843
[#8] A pointer to a function of one type may be converted to
a pointer to a function of another type and back again; the
result shall compare equal to the original pointer. If a |
converted pointer is used to call a function whose type is |
not compatible with the pointed-to type, the behavior is |
undefined.
Forward references: cast operators (6.5.4), equality
operators (6.5.9), simple assignment (6.5.16.1).
6.3.2.3 Language 6.3.2.3
WG14/N843 Committee Draft -- August 3, 1998 53
6.4 Lexical elements
Syntax
[#1]
token:
keyword
identifier
constant
string-literal
punctuator
preprocessing-token:
header-name
identifier
pp-number
character-constant
string-literal
punctuator
each universal-character-name that cannot be one of the above|
each non-white-space character that cannot be one of the above
Constraints
[#2] Each preprocessing token that is converted to a token
shall have the lexical form of a keyword, an identifier, a
constant, a string literal, or a punctuator.
Semantics
[#3] A token is the minimal lexical element of the language
in translation phases 7 and 8. The categories of tokens
are: keywords, identifiers, constants, string literals, and
punctuators. A preprocessing token is the minimal lexical
element of the language in translation phases 3 through 6.
The categories of preprocessing token are: header names,
identifiers, preprocessing numbers, character constants,
string literals, punctuators, and single non-white-space
characters that do not lexically match the other
preprocessing token categories.49) If a ' or a " character
matches the last category, the behavior is undefined.
Preprocessing tokens can be separated by white space; this
consists of comments (described later), or white-space
characters (space, horizontal tab, new-line, vertical tab,
and form-feed), or both. As described in 6.10, in certain
circumstances during translation phase 4, white space (or
the absence thereof) serves as more than preprocessing token
separation. White space may appear within a preprocessing
____________________
49)An additional category, placemarkers, is used internally
in translation phase 4 (see 6.10.3.3); it cannot occur in
source files.
6.4 Language 6.4
54 Committee Draft -- August 3, 1998 WG14/N843
token only as part of a header name or between the quotation
characters in a character constant or string literal.
[#4] If the input stream has been parsed into preprocessing
tokens up to a given character, the next preprocessing token
is the longest sequence of characters that could constitute
a preprocessing token. There is one exception to this rule:
a header name preprocessing token is only recognized within
a #include preprocessing directive, and within such a
directive, a sequence of characters that could be either a
header name or a string literal is recognized as the former.
[#5] EXAMPLE 1 The program fragment 1Ex is parsed as a
preprocessing number token (one that is not a valid floating
or integer constant token), even though a parse as the pair
of preprocessing tokens 1 and Ex might produce a valid
expression (for example, if Ex were a macro defined as +1).
Similarly, the program fragment 1E1 is parsed as a
preprocessing number (one that is a valid floating constant
token), whether or not E is a macro name.
[#6] EXAMPLE 2 The program fragment x+++++y is parsed as
x+++++y, which violates a constraint on increment operators,
even though the parse x+++++y might yield a correct
expression.
Forward references: character constants (6.4.4.4), comments
(6.4.9), expressions (6.5), floating constants (6.4.4.2),
header names (6.4.7), macro replacement (6.10.3), postfix
increment and decrement operators (6.5.2.4), prefix
increment and decrement operators (6.5.3.1), preprocessing
directives (6.10), preprocessing numbers (6.4.8), string
literals (6.4.5).
6.4.1 Keywords
Syntax
[#1]
keyword: one of
auto enum restrict unsigned
break extern return void
case float short volatile
char for signed while
const goto sizeof _Bool |
continue if static _Complex
default inline struct _Imaginary
do int switch
double long typedef
else register union
6.4 Language 6.4.1
WG14/N843 Committee Draft -- August 3, 1998 55
Semantics
[#2] The above tokens (case sensitive) are reserved (in |
translation phases 7 and 8) for use as keywords, and shall
not be used otherwise.
6.4.2 Identifiers
6.4.2.1 General
Syntax
[#1]
identifier: |
identifier-nondigit ||
identifier identifier-nondigit ||
identifier digit ||
identifier-nondigit: |
nondigit
universal-character-name |
other implementation-defined characters |
nondigit: one of
_ a b c d e f g h i j k l m *
n o p q r s t u v w x y z
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z
digit: one of
0 1 2 3 4 5 6 7 8 9
Semantics |
[#2] An identifier is a sequence of nondigit characters
(including the underscore _, the lowercase and uppercase
Latin letters, and other characters) and digits, which |
designates one or more entities as described in 6.2.1. |
Lower-case and upper-case letters are distinct. There is no |
specific limit on the maximum length of an identifier. |
[#3] Each universal character name in an identifier shall
designate a character whose encoding in ISO/IEC 10646 falls |
into one of the ranges specified in annex I.50) The initial
____________________
50)On systems in which linkers cannot accept extended
characters, an encoding of the universal character name
may be used in forming valid external identifiers. For
example, some otherwise unused character or sequence of
characters may be used to encode the \u in a universal
character name. Extended characters may produce a long
external identifier.
6.4.1 Language 6.4.2.1
56 Committee Draft -- August 3, 1998 WG14/N843
nondigit character shall not be a universal character name
designating a digit. An implementation may allow multibyte |
characters that are not part of the required source |
character set to appear in identifiers; which characters and |
their correspondence to universal character names is |
implementation defined.
[#4] When preprocessing tokens are converted to tokens
during translation phase 7, if a preprocessing token could
be converted to either a keyword or an identifier, it is
converted to a keyword.
Implementation limits
[#5] As discussed in 5.2.4.1, an implementation may limit |
the number of significant initial characters in an |
identifier; the limit for an external name (an identifier
that has external linkage) may be more restrictive than that |
for an internal name (a macro name or an identifier that |
does not have external linkage). The number of significant
characters in an identifier is implementation-defined.
[#6] Any identifiers that differ in a significant character
are different identifiers. If two identifiers differ only
in nonsignificant characters, the behavior is undefined.
Forward references: universal character names (6.4.3), *
macro replacement (6.10.3).
6.4.2.2 Predefined identifiers
Semantics
[#1] The identifier __func__ shall be implicitly declared by
the translator as if, immediately following the opening
brace of each function definition, the declaration
static const char __func__[] = "function-name";
appeared, where function-name is the name of the lexically-
enclosing function.51) *
[#2] This name is encoded as if the implicit declaration had
been written in the source character set and then translated
into the execution character set as indicated in translation
phase 5.
[#3] EXAMPLE Consider the code fragment:
____________________
51)Note that since the name __func__ is reserved for any use
by the implementation (7.1.3), if any other identifier is
explicitly declared using the name __func__, the behavior
is undefined.
6.4.2.1 Language 6.4.2.2
WG14/N843 Committee Draft -- August 3, 1998 57
#include <stdio.h>
void myfunc(void)
{
printf("%s\n", __func__);
/* ... */
}
Each time the function is called, it will print to the
standard output stream:
myfunc
|
Forward references: function definitions (6.9.1).
6.4.3 Universal character names
Syntax
[#1]
universal-character-name:
\u hex-quad
\U hex-quad hex-quad
hex-quad:
hexadecimal-digit hexadecimal-digit
hexadecimal-digit hexadecimal-digit
Constraints
[#2] A universal character name shall not specify a
character short identifier in the range 00000000 through |
00000020, 0000007F through 0000009F, or 0000D800 through |
0000DFFF inclusive. A universal character name shall not
designate a character in the required character set. |
Description
[#3] Universal character names may be used in identifiers,
character constants, and string literals to designate
characters that are not in the required character set. |
Semantics
[#4] The universal character name \Unnnnnnnn designates the
character whose character short identifier (as specified by |
ISO/IEC 10646) is nnnnnnnn. Similarly, the universal
character name \unnnn designates the character whose
character short identifier is 0000nnnn.
6.4.2.2 Language 6.4.3
58 Committee Draft -- August 3, 1998 WG14/N843
6.4.4 Constants
Syntax
[#1]
constant:
integer-constant
floating-constant
enumeration-constant
character-constant
Constraints
[#2] The value of a constant shall be in the range of
representable values for its type.
Semantics
[#3] Each constant has a type, determined by its form and
value, as detailed later.
6.4.4.1 Integer constants
Syntax
[#1]
integer-constant:
decimal-constant integer-suffix-opt
octal-constant integer-suffix-opt
hexadecimal-constant integer-suffix-opt
decimal-constant:
nonzero-digit
decimal-constant digit
octal-constant:
0
octal-constant octal-digit
hexadecimal-constant:
hexadecimal-prefix hexadecimal-digit
hexadecimal-constant hexadecimal-digit
hexadecimal-prefix: one of
0x 0X
nonzero-digit: one of
1 2 3 4 5 6 7 8 9
octal-digit: one of
0 1 2 3 4 5 6 7
6.4.4 Language 6.4.4.1
WG14/N843 Committee Draft -- August 3, 1998 59
hexadecimal-digit: one of
0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
integer-suffix:
unsigned-suffix long-suffix-opt |
unsigned-suffix long-long-suffix |
long-suffix unsigned-suffix-opt |
long-long-suffix unsigned-suffix-opt |
unsigned-suffix: one of
u U
long-suffix: one of
l L
long-long-suffix: one of
ll LL
Description
[#2] An integer constant begins with a digit, but has no
period or exponent part. It may have a prefix that
specifies its base and a suffix that specifies its type.
[#3] A decimal constant begins with a nonzero digit and
consists of a sequence of decimal digits. An octal constant
consists of the prefix 0 optionally followed by a sequence
of the digits 0 through 7 only. A hexadecimal constant
consists of the prefix 0x or 0X followed by a sequence of
the decimal digits and the letters a (or A) through f (or F)
with values 10 through 15 respectively.
Semantics
[#4] The value of a decimal constant is computed base 10;
that of an octal constant, base 8; that of a hexadecimal
constant, base 16. The lexically first digit is the most
significant.
[#5] The type of an integer constant is the first of the
corresponding list in which its value can be represented.
6.4.4.1 Language 6.4.4.1
60 Committee Draft -- August 3, 1998 WG14/N843
|| |
|| | Octal or Hexadecimal
Suffix || Decimal Constant | Constant
-------------++-----------------------+------------------------
none ||int | int
||long int | unsigned int
||long long int | long int
|| | unsigned long int
|| | long long int
|| | unsigned long long int
-------------++-----------------------+------------------------
u or U ||unsigned int | unsigned int
||unsigned long int | unsigned long int
||unsigned long long int | unsigned long long int
-------------++-----------------------+------------------------
l or L ||long int | long int
||long long int | unsigned long int
|| | long long int
|| | unsigned long long int
-------------++-----------------------+------------------------
Both u or U ||unsigned long int | unsigned long int
and l or L ||unsigned long long int | unsigned long long int
-------------++-----------------------+------------------------
ll or LL ||long long int | long long int
|| | unsigned long long int
-------------++-----------------------+------------------------
Both u or U ||unsigned long long int | unsigned long long int
and ll or LL || |
If an integer constant cannot be represented by any type in
its list, it may have an extended integer type, if the
extended integer type can represent its value. If all of
the types in the list for the constant are signed, the
extended integer type shall be signed. If all of the types
in the list for the constant are unsigned, the extended
integer type shall be unsigned. If the list contains both
signed and unsigned types, the extended integer type may be
signed or unsigned.
6.4.4.2 Floating constants
Syntax
[#1]
floating-constant:
decimal-floating-constant
hexadecimal-floating-constant
decimal-floating-constant:
fractional-constant exponent-part-opt floating-suffix-opt
digit-sequence exponent-part floating-suffix-opt
6.4.4.1 Language 6.4.4.2
WG14/N843 Committee Draft -- August 3, 1998 61
hexadecimal-floating-constant:
hexadecimal-prefix hexadecimal-fractional-constant
binary-exponent-part floating-suffix-opt
hexadecimal-prefix hexadecimal-digit-sequence
binary-exponent-part floating-suffix-opt
fractional-constant:
digit-sequence-opt . digit-sequence
digit-sequence .
exponent-part:
e sign-opt digit-sequence
E sign-opt digit-sequence
sign: one of
+ -
digit-sequence:
digit
digit-sequence digit
hexadecimal-fractional-constant:
hexadecimal-digit-sequence-opt .
hexadecimal-digit-sequence
hexadecimal-digit-sequence .
binary-exponent-part:
p sign-opt digit-sequence
P sign-opt digit-sequence
hexadecimal-digit-sequence:
hexadecimal-digit
hexadecimal-digit-sequence hexadecimal-digit
floating-suffix: one of
f l F L
Description
[#2] A floating constant has a significand part that may be
followed by an exponent part and a suffix that specifies its
type. The components of the significand part may include a
digit sequence representing the whole-number part, followed
by a period (.), followed by a digit sequence representing
the fraction part. The components of the exponent part are
an e, E, p, or P followed by an exponent consisting of an
optionally signed digit sequence. Either the whole-number |
part or the fraction part has to be present; for decimal
floating constants, either the period or the exponent part |
has to be present.
Semantics
[#3] The significand part is interpreted as a (decimal or
6.4.4.2 Language 6.4.4.2
62 Committee Draft -- August 3, 1998 WG14/N843
hexadecimal) rational number; the digit sequence in the
exponent part is interpreted as a decimal integer. For
decimal floating constants, the exponent indicates the power
of 10 by which the significand part is to be scaled. For
hexadecimal floating constants, the exponent indicates the
power of 2 by which the significand part is to be scaled.
For decimal floating constants, and also for hexadecimal
floating constants when FLT_RADIX is not a power of 2, the |
result is either the nearest representable value, or the
larger or smaller representable value immediately adjacent
to the nearest representable value, chosen in an
implementation-defined manner. For hexadecimal floating |
constants when FLT_RADIX is a power of 2, the result is |
correctly rounded.
[#4] An unsuffixed floating constant has type double. If
suffixed by the letter f or F, it has type float. If
suffixed by the letter l or L, it has type long double.
Recommended practice
[#5] The implementation should produce a diagnostic message
if a hexadecimal constant cannot be represented exactly in
its evaluation format; the implementation should then |
proceed with the translation of the program.
[#6] The translation-time conversion of floating constants
should match the execution-time conversion of character
strings by library functions, such as strtod, given matching
inputs suitable for both conversions, the same result
format, and default execution-time rounding.52)
6.4.4.3 Enumeration constants
Syntax
[#1]
enumeration-constant:
identifier
Semantics
[#2] An identifier declared as an enumeration constant has
type int.
Forward references: enumeration specifiers (6.7.2.2).
____________________
52)The specification for the library functions recommends
more accurate conversion than required for floating
constants (see 7.20.1.3).
6.4.4.2 Language 6.4.4.3
WG14/N843 Committee Draft -- August 3, 1998 63
6.4.4.4 Character constants
Syntax
[#1]
character-constant:
'c-char-sequence'
L'c-char-sequence'
c-char-sequence:
c-char
c-char-sequence c-char
c-char: *
any member of the source character set except
the single-quote ', backslash \, or new-line character
escape-sequence
escape-sequence:
simple-escape-sequence
octal-escape-sequence
hexadecimal-escape-sequence
universal-character-name |
simple-escape-sequence: one of
\' \" \? \\
\a \b \f \n \r \t \v
octal-escape-sequence:
\ octal-digit
\ octal-digit octal-digit
\ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence:
\x hexadecimal-digit
hexadecimal-escape-sequence hexadecimal-digit
Description
[#2] An integer character constant is a sequence of one or
more multibyte characters enclosed in single-quotes, as in
'x' or 'ab'. A wide character constant is the same, except
prefixed by the letter L. With a few exceptions detailed
later, the elements of the sequence are any members of the
source character set; they are mapped in an implementation-
defined manner to members of the execution character set.
[#3] The single-quote ', the double-quote ", the question-
mark ?, the backslash \, and arbitrary integer values, are
representable according to the following table of escape
sequences:
6.4.4.4 Language 6.4.4.4
64 Committee Draft -- August 3, 1998 WG14/N843
single quote ' \'
double quote " \"
question mark ? \?
backslash \ \\
octal character \octal digits
hexadecimal character \xhexadecimal digits
[#4] The double-quote " and question-mark ? are
representable either by themselves or by the escape
sequences \" and \?, respectively, but the single-quote '
and the backslash \ shall be represented, respectively, by
the escape sequences \' and \\.
[#5] The octal digits that follow the backslash in an octal
escape sequence are taken to be part of the construction of
a single character for an integer character constant or of a
single wide character for a wide character constant. The
numerical value of the octal integer so formed specifies the
value of the desired character or wide character.
[#6] The hexadecimal digits that follow the backslash and
the letter x in a hexadecimal escape sequence are taken to
be part of the construction of a single character for an
integer character constant or of a single wide character for
a wide character constant. The numerical value of the
hexadecimal integer so formed specifies the value of the
desired character or wide character.
[#7] Each octal or hexadecimal escape sequence is the
longest sequence of characters that can constitute the
escape sequence.
[#8] In addition, graphic characters not in the required |
character set are representable by universal character names |
and certain nongraphic characters are representable by
escape sequences consisting of the backslash \ followed by a
lowercase letter: \a, \b, \f, \n, \r, \t, and \v.53)
Constraints
[#9] The value of an octal or hexadecimal escape sequence
shall be in the range of representable values for the type
unsigned char for an integer character constant, or the
unsigned type corresponding to wchar_t for a wide character
constant.
____________________
53)The semantics of these characters were discussed in
5.2.2. If any other character follows a backslash, the
result is not a token and a diagnostic is required. See
``future language directions'' (6.11.1).
6.4.4.4 Language 6.4.4.4
WG14/N843 Committee Draft -- August 3, 1998 65
Semantics
[#10] An integer character constant has type int. The value
of an integer character constant containing a single
character that maps to a member of the basic execution
character set is the numerical value of the representation
of the mapped character interpreted as an integer. The
value of an integer character constant containing more than
one character, or containing a character or escape sequence
not represented in the basic execution character set, is
implementation-defined. If an integer character constant
contains a single character or escape sequence, its value is
the one that results when an object with type char whose
value is that of the single character or escape sequence is
converted to type int.
[#11] A wide character constant has type wchar_t, an integer
type defined in the <stddef.h> header. The value of a wide
character constant containing a single multibyte character
that maps to a member of the extended execution character
set is the wide character (code) corresponding to that
multibyte character, as defined by the mbtowc function, with
an implementation-defined current locale. The value of a
wide character constant containing more than one multibyte
character, or containing a multibyte character or escape
sequence not represented in the extended execution character
set, is implementation-defined.
[#12] EXAMPLE 1 The construction '\0' is commonly used to
represent the null character.
[#13] EXAMPLE 2 Consider implementations that use two's-
complement representation for integers and eight bits for
objects that have type char. In an implementation in which
type char has the same range of values as signed char, the
integer character constant '\xFF' has the value -1; if type
char has the same range of values as unsigned char, the
character constant '\xFF' has the value +255 .
[#14] EXAMPLE 3 Even if eight bits are used for objects that
have type char, the construction '\x123' specifies an
integer character constant containing only one character,
since a hexadecimal escape sequence is terminated only by a
non-hexadecimal character. To specify an integer character
constant containing the two characters whose values are
'\x12' and '3', the construction '\0223' may be used, since
an octal escape sequence is terminated after three octal
digits. (The value of this two-character integer character
constant is implementation-defined.)
[#15] EXAMPLE 4 Even if 12 or more bits are used for objects
6.4.4.4 Language 6.4.4.4
66 Committee Draft -- August 3, 1998 WG14/N843
that have type wchar_t, the construction L'\1234' specifies
the implementation-defined value that results from the
combination of the values 0123 and '4'.
Forward references: common definitions <stddef.h> (7.17), *
the mbtowc function (7.20.7.2).
6.4.5 String literals
Syntax
[#1]
string-literal:
"s-char-sequence-opt"
L"s-char-sequence-opt"
s-char-sequence:
s-char
s-char-sequence s-char
s-char: *
any member of the source character set except
the double-quote ", backslash \, or new-line character
escape-sequence
Description
[#2] A character string literal is a sequence of zero or
more multibyte characters enclosed in double-quotes, as in
"xyz". A wide string literal is the same, except prefixed
by the letter L.
[#3] The same considerations apply to each element of the
sequence in a character string literal or a wide string
literal as if it were in an integer character constant or a
wide character constant, except that the single-quote ' is
representable either by itself or by the escape sequence \',
but the double-quote " shall be represented by the escape
sequence \".
Semantics
[#4] In translation phase 6, the multibyte character
sequences specified by any sequence of adjacent character
and wide string literal tokens are concatenated into a
single multibyte character sequence. If any of the tokens
are wide string literal tokens, the resulting multibyte
character sequence is treated as a wide string literal;
otherwise, it is treated as a character string literal.
[#5] In translation phase 7, a byte or code of value zero is
appended to each multibyte character sequence that results
6.4.4.4 Language 6.4.5
WG14/N843 Committee Draft -- August 3, 1998 67
from a string literal or literals.54) The multibyte
character sequence is then used to initialize an array of
static storage duration and length just sufficient to
contain the sequence. For character string literals, the
array elements have type char, and are initialized with the
individual bytes of the multibyte character sequence; for
wide string literals, the array elements have type wchar_t,
and are initialized with the sequence of wide characters |
corresponding to the multibyte character sequence, as |
defined by the mbstowcs function with an implementation- |
defined current locale. The value of a string literal |
containing a multibyte character or escape sequence not |
represented in the execution character set is |
implementation-defined.
[#6] It is unspecified whether these arrays are distinct |
provided their elements have the appropriate values. If the
program attempts to modify such an array, the behavior is
undefined.
[#7] EXAMPLE This pair of adjacent character string
literals
"\x12" "3"
produces a single character string literal containing the
two characters whose values are '\x12' and '3', because
escape sequences are converted into single members of the
execution character set just prior to adjacent string
literal concatenation.
Forward references: common definitions <stddef.h> (7.17).
6.4.6 Punctuators
Syntax
[#1]
punctuator: one of
[ ] ( ) { } . ->
++ -- & * + - ~ !
/ % << >> < > <= >= == != ^ | && ||
? : ; ...
= *= /= %= += -= <<= >>= &= ^= |=
, # ## |
<: :> <% %> %: %:%: |
____________________
54)A character string literal need not be a string (see
7.1.1), because a null character may be embedded in it by
a \0 escape sequence.
6.4.5 Language 6.4.6
68 Committee Draft -- August 3, 1998 WG14/N843
Semantics
[#2] A punctuator is a symbol that has independent syntactic
and semantic significance. Depending on context, it may
specify an operation to be performed (which in turn may |
yield a value or a function designator, produce a side
effect, or some combination thereof) in which case it is
known as an operator (other forms of operator also exist in
some contexts). An operand is an entity on which an
operator acts.
[#3] In all aspects of the language, these six tokens
<: :> <% %> %: %:%:
behave, respectively, the same as these six tokens
[ ] { } # ##
except for their spelling.55)
Forward references: expressions (6.5), declarations (6.7),
preprocessing directives (6.10), statements (6.8).
6.4.7 Header names
Syntax
[#1]
header-name:
<h-char-sequence>
"q-char-sequence"
h-char-sequence:
h-char
h-char-sequence h-char
h-char:
any member of the source character set except
the new-line character and >
q-char-sequence:
q-char
q-char-sequence q-char
q-char:
any member of the source character set except
the new-line character and "
____________________
55)Thus [ and <: behave differently when ``stringized'' (see
6.10.3.2), but can otherwise be freely interchanged.
6.4.6 Language 6.4.7
WG14/N843 Committee Draft -- August 3, 1998 69
Semantics
[#2] The sequences in both forms of header names are mapped
in an implementation-defined manner to headers or external
source file names as specified in 6.10.2.
[#3] If the characters ', \, ", //, or /* occur in the
sequence between the < and > delimiters, the behavior is
undefined. Similarly, if the characters ', \, //, or /*
occur in the sequence between the " delimiters, the behavior
is undefined.56) A header name preprocessing token is
recognized only within a #include preprocessing directive.
[#4] EXAMPLE The following sequence of characters:
0x3<1/a.h>1e2
#include <1/a.h>
#define const.member@$
forms the following sequence of preprocessing tokens (with
each individual preprocessing token delimited by a { on the
left and a } on the right).
{0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
{#}{include} {<1/a.h>}
{#}{define} {const}{.}{member}{@}{$}
Forward references: source file inclusion (6.10.2).
6.4.8 Preprocessing numbers
Syntax
[#1]
pp-number:
digit
. digit
pp-number digit
pp-number identifier-nondigit |
pp-number e sign
pp-number E sign
pp-number p sign
pp-number P sign
pp-number .
Description
____________________
56)Thus, sequences of characters that resemble escape
sequences cause undefined behavior.
6.4.7 Language 6.4.8
70 Committee Draft -- August 3, 1998 WG14/N843
[#2] A preprocessing number begins with a digit optionally
preceded by a period (.) and may be followed by letters,
underscores, digits, periods, and e+, e-, E+, E-, p+, p-,
P+, or P- character sequences.
[#3] Preprocessing number tokens lexically include all
floating and integer constant tokens.
Semantics
[#4] A preprocessing number does not have type or a value;
it acquires both after a successful conversion (as part of
translation phase 7) to a floating constant token or an
integer constant token.
6.4.9 Comments
[#1] Except within a character constant, a string literal,
or a comment, the characters /* introduce a comment. The
contents of a comment are examined only to identify
multibyte characters and to find the characters */ that
terminate it.57)
[#2] Except within a character constant, a string literal,
or a comment, the characters // introduce a comment that
includes all multibyte characters up to, but not including,
the next new-line character. The contents of such a comment
are examined only to identify multibyte characters and to
find the terminating new-line character.
[#3] EXAMPLE 1
"a//b" // four-character string literal|
#include "//e" // undefined behavior |
// */ // comment, not syntax error|
f = g/**//h; // equivalent to f = g / h; |
//\ |
i(); // part of a two-line comment|
/\ |
/ j(); // part of a two-line comment|
#define glue(x,y) x##y
glue(/,/) k(); // syntax error, not comment|
/*//*/ l(); // equivalent to l(); |
m = n//**/o
+ p; // equivalent to m = n + p; |
____________________
57)Thus, /* ... */ comments do not nest.
6.4.8 Language 6.4.9
WG14/N843 Committee Draft -- August 3, 1998 71
6.5 Expressions
[#1] An expression is a sequence of operators and operands
that specifies computation of a value, or that designates an
object or a function, or that generates side effects, or
that performs a combination thereof.
[#2] Between the previous and next sequence point an object
shall have its stored value modified at most once by the
evaluation of an expression. Furthermore, the prior value
shall be accessed only to determine the value to be |
stored.58) Informative annex D presents an algorithm for |
determining whether an expression or set of expressions |
meets these requirements.
[#3] The grouping of operators and operands is indicated by |
the syntax.59) Except as specified later (for the function- |
call (), &&, ||, ?:, and comma operators), the order of
evaluation of subexpressions and the order in which side
effects take place are both unspecified.
[#4] Some operators (the unary operator ~, and the binary
operators <<, >>, &, ^, and |, collectively described as
bitwise operators) are required to have operands that have |
integer type. These operators return values that depend on
the internal representations of integers, and have
implementation-defined and undefined aspects for signed
____________________
58)This paragraph renders undefined statement expressions
such as
i = ++i + 1;
a[i++] = i; |
while allowing
i = i + 1;
a[i] = i; |
59)The syntax specifies the precedence of operators in the
evaluation of an expression, which is the same as the
order of the major subclauses of this subclause, highest
precedence first. Thus, for example, the expressions
allowed as the operands of the binary + operator (6.5.6) |
are those expressions defined in 6.5.1 through 6.5.6.
The exceptions are cast expressions (6.5.4) as operands
of unary operators (6.5.3), and an operand contained
between any of the following pairs of operators: grouping
parentheses () (6.5.1), subscripting brackets []
(6.5.2.1), function-call parentheses () (6.5.2.2), and
the conditional operator ?: (6.5.15).
Within each major subclause, the operators have the same
precedence. Left- or right-associativity is indicated in
each subclause by the syntax for the expressions
discussed therein.
6.5 Language 6.5
72 Committee Draft -- August 3, 1998 WG14/N843
types.
[#5] If an exception occurs during the evaluation of an
expression (that is, if the result is not mathematically
defined or not in the range of representable values for its
type), the behavior is undefined.
[#6] The effective type of an object for an access to its
stored value is the declared type of the object, if any.60) |
If a value is stored into an object having no declared type
through an lvalue having a type that is not a character
type, then the type of the lvalue becomes the effective type
of the object for that access and for subsequent accesses
that do not modify the stored value. If a value is copied
into an object having no declared type using memcpy or
memmove, or is copied as an array of character type, then
the effective type of the modified object for that access
and for subsequent accesses that do not modify the value is
the effective type of the object from which the value is
copied, if it has one. For all other accesses to an object
having no declared type, the effective type of the object is
simply the type of the lvalue used for the access.
[#7] An object shall have its stored value accessed only by
an lvalue expression that has one of the following types:61)
-- a type compatible with the effective type of the
object,
-- a qualified version of a type compatible with the
effective type of the object,
-- a type that is the signed or unsigned type
corresponding to the effective type of the object,
-- a type that is the signed or unsigned type
corresponding to a qualified version of the effective
type of the object,
-- an aggregate or union type that includes one of the
aforementioned types among its members (including,
recursively, a member of a subaggregate or contained
union), or
-- a character type.
[#8] A floating expression may be contracted, that is,
evaluated as though it were an atomic operation, thereby
____________________
60)Allocated objects have no declared type.
61)The intent of this list is to specify those circumstances
in which an object may or may not be aliased.
6.5 Language 6.5
WG14/N843 Committee Draft -- August 3, 1998 73
omitting rounding errors implied by the source code and the
expression evaluation method.62) The FP_CONTRACT pragma in
<math.h> provides a way to disallow contracted expressions.
Otherwise, whether and how expressions are contracted is
implementation-defined.63)
6.5.1 Primary expressions
Syntax
[#1]
primary-expr:
identifier
constant
string-literal
( expression )
Semantics
[#2] An identifier is a primary expression, provided it has
been declared as designating an object (in which case it is
an lvalue) or a function (in which case it is a function
designator).64)
[#3] A constant is a primary expression. Its type depends
on its form and value, as detailed in 6.4.4.
[#4] A string literal is a primary expression. It is an
lvalue with type as detailed in 6.4.5.
[#5] A parenthesized expression is a primary expression.
Its type and value are identical to those of the
unparenthesized expression. It is an lvalue, a function
designator, or a void expression if the unparenthesized
expression is, respectively, an lvalue, a function
designator, or a void expression.
____________________
62)A contracted expression might also omit the raising of
floating-point exception flags.
63)This license is specifically intended to allow
implementations to exploit fast machine instructions that
combine multiple C operators. As contractions
potentially undermine predictability, and can even
decrease accuracy for containing expressions, their use
needs to be well-defined and clearly documented.
64)Thus, an undeclared identifier is a violation of the
syntax.
6.5 Language 6.5.1
74 Committee Draft -- August 3, 1998 WG14/N843
Forward references: declarations (6.7).
6.5.2 Postfix operators
Syntax
[#1]
postfix-expr:
primary-expr
postfix-expr [ expression ]
postfix-expr ( argument-expression-list-opt )
postfix-expr . identifier
postfix-expr -> identifier
postfix-expr ++
postfix-expr --
( type-name ) { initializer-list }
( type-name ) { initializer-list , }
argument-expression-list:
assignment-expr
argument-expression-list , assignment-expr
6.5.2.1 Array subscripting
Constraints
[#1] One of the expressions shall have type ``pointer to
object type'', the other expression shall have integer type,
and the result has type ``type''.
Semantics
[#2] A postfix expression followed by an expression in
square brackets [] is a subscripted designation of an
element of an array object. The definition of the subscript
operator [] is that E1[E2] is identical to (*((E1)+(E2))). |
Because of the conversion rules that apply to the binary +
operator, if E1 is an array object (equivalently, a pointer
to the initial element of an array object) and E2 is an
integer, E1[E2] designates the E2-th element of E1 (counting
from zero).
[#3] Successive subscript operators designate an element of
a multidimensional array object. If E is an n-dimensional
array (n>=2) with dimensions i×j× ... ×k, then E (used as
other than an lvalue) is converted to a pointer to an
(n-1)-dimensional array with dimensions j× ... ×k. If the
unary * operator is applied to this pointer explicitly, or
implicitly as a result of subscripting, the result is the
pointed-to (n-1)-dimensional array, which itself is
converted into a pointer if used as other than an lvalue.
It follows from this that arrays are stored in row-major
order (last subscript varies fastest).
6.5.1 Language 6.5.2.1
WG14/N843 Committee Draft -- August 3, 1998 75
[#4] EXAMPLE Consider the array object defined by the
declaration
int x[3][5];
Here x is a 3×5 array of ints; more precisely, x is an array
of three element objects, each of which is an array of five
ints. In the expression x[i], which is equivalent to |
(*((x)+(i))), x is first converted to a pointer to the
initial array of five ints. Then i is adjusted according to
the type of x, which conceptually entails multiplying i by
the size of the object to which the pointer points, namely
an array of five int objects. The results are added and
indirection is applied to yield an array of five ints. When
used in the expression x[i][j], that array is in turn |
converted to a pointer to the first of the ints, so x[i][j]
yields an int.
Forward references: additive operators (6.5.6), address and
indirection operators (6.5.3.2), array declarators
(6.7.5.2).
6.5.2.2 Function calls
Constraints
[#1] The expression that denotes the called function65)
shall have type pointer to function returning void or
returning an object type other than an array type.
[#2] If the expression that denotes the called function has
a type that includes a prototype, the number of arguments
shall agree with the number of parameters. Each argument
shall have a type such that its value may be assigned to an
object with the unqualified version of the type of its
corresponding parameter.
Semantics
[#3] A postfix expression followed by parentheses ()
containing a possibly empty, comma-separated list of
expressions is a function call. The postfix expression
denotes the called function. The list of expressions
specifies the arguments to the function.
[#4] An argument may be an expression of any object type.
In preparing for the call to a function, the arguments are
evaluated, and each parameter is assigned the value of the |
corresponding argument.66) |
____________________
65)Most often, this is the result of converting an
identifier that is a function designator.
6.5.2.1 Language 6.5.2.2
76 Committee Draft -- August 3, 1998 WG14/N843
[#5] If the expression that denotes the called function has
type pointer to function returning an object type, the
function call expression has the same type as that object
type, and has the value determined as specified in 6.8.6.4.
Otherwise, the function call has type void. If an attempt |
is made to modify the result of a function call or to access |
it after the next sequence point, the behavior is undefined.
[#6] If the expression that denotes the called function has
a type that does not include a prototype, the integer
promotions are performed on each argument, and arguments
that have type float are promoted to double. These are
called the default argument promotions. If the number of
arguments does not agree with the number of parameters, the
behavior is undefined. If the function is defined with a
type that includes a prototype, and either the prototype
ends with an ellipsis (, ...) or the types of the arguments
after promotion are not compatible with the types of the
parameters, the behavior is undefined. If the function is
defined with a type that does not include a prototype, and
the types of the arguments after promotion are not
compatible with those of the parameters after promotion, the
behavior is undefined, except for the following cases:
-- one promoted type is a signed integer type, the other
promoted type is the corresponding unsigned integer
type, and the value is representable in both types;
-- one type is pointer to void and the other is a pointer
to a character type.
[#7] If the expression that denotes the called function has |
a type that does include a prototype, the arguments are
implicitly converted, as if by assignment, to the types of
the corresponding parameters, taking the type of each
parameter to be the unqualified version of its declared
type. The ellipsis notation in a function prototype
declarator causes argument type conversion to stop after the
last declared parameter. The default argument promotions
are performed on trailing arguments.
[#8] No other conversions are performed implicitly; in
particular, the number and types of arguments are not
compared with those of the parameters in a function
definition that does not include a function prototype
____________________
66)A function may change the values of its parameters, but
these changes cannot affect the values of the arguments.
On the other hand, it is possible to pass a pointer to an
object, and the function may change the value of the
object pointed to. A parameter declared to have array or
function type is converted to a parameter with a pointer
type as described in 6.9.1.
6.5.2.2 Language 6.5.2.2
WG14/N843 Committee Draft -- August 3, 1998 77
declarator.
[#9] If the function is defined with a type that is not
compatible with the type (of the expression) pointed to by
the expression that denotes the called function, the
behavior is undefined.
[#10] The order of evaluation of the function designator, |
the actual arguments, and subexpressions within the actual |
arguments is unspecified, but there is a sequence point
before the actual call.
[#11] Recursive function calls shall be permitted, both
directly and indirectly through any chain of other
functions.
[#12] EXAMPLE In the function call
(*pf[f1()]) (f2(), f3() + f4())
the functions f1, f2, f3, and f4 may be called in any order. |
All side effects have to be completed before the function
pointed to by pf[f1()] is called. |
Forward references: function declarators (including
prototypes) (6.7.5.3), function definitions (6.9.1), the
return statement (6.8.6.4), simple assignment (6.5.16.1).
6.5.2.3 Structure and union members
Constraints
[#1] The first operand of the . operator shall have a
qualified or unqualified structure or union type, and the
second operand shall name a member of that type.
[#2] The first operand of the -> operator shall have type
``pointer to qualified or unqualified structure'' or
``pointer to qualified or unqualified union'', and the
second operand shall name a member of the type pointed to.
Semantics
[#3] A postfix expression followed by the . operator and an
identifier designates a member of a structure or union
object. The value is that of the named member, and is an
lvalue if the first expression is an lvalue. If the first
expression has qualified type, the result has the so-
qualified version of the type of the designated member.
[#4] A postfix expression followed by the -> operator and an
identifier designates a member of a structure or union
object. The value is that of the named member of the object
6.5.2.2 Language 6.5.2.3
78 Committee Draft -- August 3, 1998 WG14/N843
to which the first expression points, and is an lvalue.67)
If the first expression is a pointer to a qualified type,
the result has the so-qualified version of the type of the
designated member.
[#5] With one exception, if the value of a member of a union
object is used when the most recent store to the object was
to a different member, the behavior is
implementation-defined.68) One special guarantee is made in
order to simplify the use of unions: If a union contains
several structures that share a common initial sequence (see
below), and if the union object currently contains one of
these structures, it is permitted to inspect the common
initial part of any of them anywhere that a declaration of
the completed type of the union is visible. Two structures
share a common initial sequence if corresponding members
have compatible types (and, for bit-fields, the same widths)
for a sequence of one or more initial members.
[#6] EXAMPLE 1 If f is a function returning a structure or
union, and x is a member of that structure or union, f().x
is a valid postfix expression but is not an lvalue.
[#7] EXAMPLE 2 In: |
struct s { int i; const int ci; };
struct s s;
const struct s cs;
volatile struct s vs;
the various members have the types: |
s.i int
s.ci const int
cs.i const int
cs.ci const int
vs.i volatile int
vs.ci volatile const int
|
____________________
67)If &E is a valid pointer expression (where & is the
``address-of'' operator, which generates a pointer to its
operand), the expression (&E)->MOS is the same as E.MOS.
68)The ``byte orders'' for scalar types are invisible to
isolated programs that do not indulge in type punning
(for example, by assigning to one member of a union and
inspecting the storage by accessing another member that
is an appropriately sized array of character type), but
have to be accounted for when conforming to externally
imposed storage layouts.
6.5.2.3 Language 6.5.2.3
WG14/N843 Committee Draft -- August 3, 1998 79
[#8] EXAMPLE 3 The following is a valid fragment:
union {
struct {
int alltypes;
} n;
struct {
int type;
int intnode;
} ni;
struct {
int type;
double doublenode;
} nf;
} u;
u.nf.type = 1;
u.nf.doublenode = 3.14;
/* ... */
if (u.n.alltypes == 1)
if (sin(u.nf.doublenode) == 0.0)
/* ... */
The following is not a valid fragment (because the union *
type is not visible within function f):
struct t1 { int m; };
struct t2 { int m; };
int f(struct t1 * p1, struct t2 * p2)
{
if (p1->m < 0)
p2->m = -p2->m;
return p1->m;
}
int g()
{
union {
struct t1 s1;
struct t2 s2;
} u;
/* ... */
return f(&u.s1, &u.s2);
}
Forward references: address and indirection operators
(6.5.3.2), structure and union specifiers (6.7.2.1).
6.5.2.3 Language 6.5.2.3
80 Committee Draft -- August 3, 1998 WG14/N843
6.5.2.4 Postfix increment and decrement operators
Constraints
[#1] The operand of the postfix increment or decrement
operator shall have qualified or unqualified real or pointer
type and shall be a modifiable lvalue.
Semantics
[#2] The result of the postfix ++ operator is the value of
the operand. After the result is obtained, the value of the
operand is incremented. (That is, the value 1 of the
appropriate type is added to it.) See the discussions of
additive operators and compound assignment for information
on constraints, types, and conversions and the effects of
operations on pointers. The side effect of updating the
stored value of the operand shall occur between the previous
and the next sequence point.
[#3] The postfix -- operator is analogous to the postfix ++
operator, except that the value of the operand is
decremented (that is, the value 1 of the appropriate type is
subtracted from it).
Forward references: additive operators (6.5.6), compound
assignment (6.5.16.2).
6.5.2.5 Compound literals
Constraints
[#1] The type name shall specify an object type or an array
of unknown size.
[#2] No initializer shall attempt to provide a value for an
object not contained within the entire unnamed object
specified by the compound literal.
[#3] If the compound literal occurs outside the body of a
function, the initializer list shall consist of constant
expressions.
Semantics
[#4] A postfix expression that consists of a parenthesized
type name followed by a brace-enclosed list of initializers
is a compound literal. It provides an unnamed object whose
value is given by the initializer list.69)
[#5] If the type name specifies an array of unknown size,
the size is determined by the initializer list as specified
in 6.7.7, and the type of the compound literal is that of
the completed array type. Otherwise (when the type name
specifies an object type), the type of the compound literal
is that specified by the type name. In either case, the
result is an lvalue.
[#6] The value of the compound literal is that of an unnamed
WG14/N843 Committee Draft -- August 3, 1998 81
object initialized by the initializer list. The object has
static storage duration if and only if the compound literal
occurs outside the body of a function; otherwise, it has
automatic storage duration associated with the enclosing
block.
[#7] All the semantic rules and constraints for initializer
lists in 6.7.8 are applicable to compound literals.70)
[#8] String literals, and compound literals with const-
qualified types, need not designate distinct objects.71)
[#9] EXAMPLE 1 The file scope definition
int *p = (int []){2, 4};
initializes p to point to the first element of an array of
two ints, the first having the value two and the second,
four. The expressions in this compound literal are required
to be constant. The unnamed object has static storage
duration.
[#10] EXAMPLE 2 In contrast, in
void f(void)
{
int *p;
/*...*/
p = (int [2]){*p};
/*...*/
}
p is assigned the address of the first element of an array
of two ints, the first having the value previously pointed
to by p and the second, zero. The expressions in this
compound literal need not be constant. The unnamed object
has automatic storage duration.
[#11] EXAMPLE 3 Initializers with designations can be
____________________
69)Note that this differs from a cast expression. For
example, a cast specifies a conversion to scalar types or
void only, and the result of a cast expression is not an
lvalue.
70)For example, subobjects without explicit initializers are
initialized to zero.
71)This allows implementations to share storage for string
literals and constant compound literals with the same or
overlapping representations.
6.5.2.5 Language 6.5.2.5
82 Committee Draft -- August 3, 1998 WG14/N843
combined with compound literals. Structure objects created
using compound literals can be passed to functions without
depending on member order:
drawline((struct point){.x=1, .y=1},
(struct point){.x=3, .y=4});
Or, if drawline instead expected pointers to struct point:
drawline(&(struct point){.x=1, .y=1},
&(struct point){.x=3, .y=4});
[#12] EXAMPLE 4 A read-only compound literal can be
specified through constructions like:
(const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
[#13] EXAMPLE 5 The following three expressions have
different meanings:
"/tmp/fileXXXXXX"
(char []){"/tmp/fileXXXXXX"}
(const char []){"/tmp/fileXXXXXX"}
The first always has static storage duration and has type
array of char, but need not be modifiable; the last two have
automatic storage duration when they occur within the body
of a function, and the first of these two is modifiable.
[#14] EXAMPLE 6 Like string literals, const-qualified
compound literals can be placed into read-only memory and
can even be shared. For example,
(const char []){"abc"} == "abc"
might yield 1 if the literals' storage is shared.
[#15] EXAMPLE 7 Since compound literals are unnamed, a
single compound literal cannot specify a circularly linked
object. For example, there is no way to write a self-
referential compound literal that could be used as the
function argument in place of the named object endless_zeros
below:
struct int_list { int car; struct int_list *cdr; };
struct int_list endless_zeros = {0, &endless_zeros};
eval(endless_zeros);
6.5.2.5 Language 6.5.2.5
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[#16] EXAMPLE 8 Each compound literal creates only a single *
object in a given scope:
struct s { int i; };
int f (void)
{
struct s *p = 0, *q;
int j = 0; |
while (j < 2) |
q = p, p = &((struct s){ j++ }); |
return p == q && q->i == 1; |
}
The function f() always returns the value 1.
[#17] Note that if a for loop were used instead of a while |
loop, the lifetime of the unnamed object would be the body
of the loop only, and on entry next time around p would be
pointing to an object which is no longer guaranteed to |
exist, which would result in undefined behavior.
6.5.3 Unary operators
Syntax
[#1]
unary-expr:
postfix-expr
++ unary-expr
-- unary-expr
unary-operator cast-expr
sizeof unary-expr
sizeof ( type-name )
unary-operator: one of
& * + - ~ !
6.5.3.1 Prefix increment and decrement operators
Constraints
[#1] The operand of the prefix increment or decrement
operator shall have qualified or unqualified real or pointer
type and shall be a modifiable lvalue.
Semantics
[#2] The value of the operand of the prefix ++ operator is
6.5.2.5 Language 6.5.3.1
84 Committee Draft -- August 3, 1998 WG14/N843
incremented. The result is the new value of the operand
after incrementation. The expression ++E is equivalent to
(E+=1). See the discussions of additive operators and
compound assignment for information on constraints, types,
side effects, and conversions and the effects of operations
on pointers.
[#3] The prefix -- operator is analogous to the prefix ++
operator, except that the value of the operand is
decremented.
Forward references: additive operators (6.5.6), compound
assignment (6.5.16.2).
6.5.3.2 Address and indirection operators
Constraints
[#1] The operand of the unary & operator shall be either a
function designator, the result of a [] or unary * operator,
or an lvalue that designates an object that is not a bit-
field and is not declared with the register storage-class
specifier.
[#2] The operand of the unary * operator shall have pointer
type.
Semantics
[#3] The result of the unary & (address-of) operator is a
pointer to the object or function designated by its operand.
If the operand has type ``type'', the result has type
``pointer to type''. If the operand is the result of a
unary * operator, neither that operator nor the & operator |
is evaluated, and the result is as if both were omitted, |
except that the constraints on the operators still apply and |
the result is not an lvalue. Similarly, if the operand is
the result of a [] operator, neither the & operator nor the
unary * that is implied by the [] is evaluated, and the |
result is as if the & operator were removed and the [] |
operator were changed to a + operator.
[#4] The unary * operator denotes indirection. If the
operand points to a function, the result is a function
designator; if it points to an object, the result is an
lvalue designating the object. If the operand has type
``pointer to type'', the result has type ``type''. If an
invalid value has been assigned to the pointer, the behavior
of the unary * operator is undefined.72)
Forward references: storage-class specifiers (6.7.1),
structure and union specifiers (6.7.2.1).
6.5.3.1 Language 6.5.3.2
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6.5.3.3 Unary arithmetic operators
Constraints
[#1] The operand of the unary + or - operator shall have
arithmetic type; of the ~ operator, integer type; of the !
operator, scalar type.
Semantics
[#2] The result of the unary + operator is the value of its |
(promoted) operand. The integer promotions are performed on
the operand, and the result has the promoted type.
[#3] The result of the unary - operator is the negative of |
its (promoted) operand. The integer promotions are
performed on the operand, and the result has the promoted
type.
[#4] The result of the ~ operator is the bitwise complement |
of its (promoted) operand (that is, each bit in the result
is set if and only if the corresponding bit in the converted
operand is not set). The integer promotions are performed
on the operand, and the result has the promoted type. If |
the promoted type is an unsigned type, the expression ~E is |
equivalent to the maximum value representable in that type |
minus E.
[#5] The result of the logical negation operator ! is 0 if
the value of its operand compares unequal to 0, 1 if the
value of its operand compares equal to 0. The result has
type int. The expression !E is equivalent to (0==E).
Forward references: characteristics of floating types
<float.h> (7.7), sizes of integer types <limits.h> (7.10).
____________________
72)Thus, &*E is equivalent to E (even if E is a null |
pointer), and &(E1[E2]) to ((E1)+(E2)). It is always |
true that if E is a function designator or an lvalue that
is a valid operand of the unary & operator, *&E is a
function designator or an lvalue equal to E. If *P is an
lvalue and T is the name of an object pointer type, *(T)P
is an lvalue that has a type compatible with that to
which T points.
Among the invalid values for dereferencing a pointer by
the unary * operator are a null pointer, an address
inappropriately aligned for the type of object pointed
to, and the address of an automatic storage duration
object when execution of the block with which the object
is associated has terminated.
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6.5.3.4 The sizeof operator
Constraints
[#1] The sizeof operator shall not be applied to an
expression that has function type or an incomplete type, to
the parenthesized name of such a type, or to an lvalue that
designates a bit-field object.
Semantics
[#2] The sizeof operator yields the size (in bytes) of its
operand, which may be an expression or the parenthesized
name of a type. The size is determined from the type of the
operand. The result is an integer. If the type of the
operand is a variable length array type, the operand is
evaluated; otherwise, the operand is not evaluated and the
result is an integer constant.
[#3] When applied to an operand that has type char, unsigned
char, or signed char, (or a qualified version thereof) the
result is 1. When applied to an operand that has array
type, the result is the total number of bytes in the
array.73) When applied to an operand that has structure or
union type, the result is the total number of bytes in such
an object, including internal and trailing padding.
[#4] The value of the result is implementation-defined, and
its type (an unsigned integer type) is size_t, defined in |
the <stddef.h> header.
[#5] EXAMPLE 1 A principal use of the sizeof operator is in
communication with routines such as storage allocators and
I/O systems. A storage-allocation function might accept a
size (in bytes) of an object to allocate and return a
pointer to void. For example:
extern void *alloc(size_t);
double *dp = alloc(sizeof *dp);
The implementation of the alloc function should ensure that
its return value is aligned suitably for conversion to a
pointer to double.
[#6] EXAMPLE 2 Another use of the sizeof operator is to
compute the number of elements in an array:
____________________
73)When applied to a parameter declared to have array or
function type, the sizeof operator yields the size of the
pointer obtained by converting as in 6.3.2.1; see 6.9.1.
6.5.3.3 Language 6.5.3.4
WG14/N843 Committee Draft -- August 3, 1998 87
sizeof array / sizeof array[0]
[#7] EXAMPLE 3 In this example, the size of a variable-
length array is computed and returned from a function:
size_t fsize3 (int n)
{
char b[n+3]; // Variable length array.
return sizeof b; // Execution time sizeof.
}
int main()
{
size_t size;
size = fsize3(10); // fsize3 returns 13.
return 0;
}
Forward references: common definitions <stddef.h> (7.17),
declarations (6.7), structure and union specifiers
(6.7.2.1), type names (6.7.6), array declarators (6.7.5.2).
6.5.4 Cast operators
Syntax
[#1]
cast-expr:
unary-expr
( type-name ) cast-expr
Constraints
[#2] Unless the type name specifies a void type, the type
name shall specify qualified or unqualified scalar type and
the operand shall have scalar type.
[#3] Conversions that involve pointers, other than where
permitted by the constraints of 6.5.16.1, shall be specified
by means of an explicit cast.
Semantics
[#4] Preceding an expression by a parenthesized type name
converts the value of the expression to the named type.
This construction is called a cast.74) A cast that
specifies no conversion has no effect on the type or value
of an expression.75)
Forward references: equality operators (6.5.9), function
declarators (including prototypes) (6.7.5.3), simple
assignment (6.5.16.1), type names (6.7.6).
88 Committee Draft -- August 3, 1998 WG14/N843
6.5.5 Multiplicative operators
Syntax
[#1]
multiplicative-expr:
cast-expr
multiplicative-expr * cast-expr
multiplicative-expr / cast-expr
multiplicative-expr % cast-expr
Constraints
[#2] Each of the operands shall have arithmetic type. The
operands of the % operator shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands. If either operand has complex type, the result
has complex type.
[#4] The result of the binary * operator is the product of
the operands.
[#5] The result of the / operator is the quotient from the
division of the first operand by the second; the result of
the % operator is the remainder. In both operations, if the
value of the second operand is zero, the behavior is
undefined.
[#6] When integers are divided, the result of the / operator
is the algebraic quotient with any fractional part
discarded.76) If the quotient a/b is representable, the
expression (a/b)*b + a%b shall equal a.
____________________
75)If the value of the expression is represented with
greater precision or range than required by the type
named by the cast (6.3.1.8), then the cast specifies a
conversion even if the type of the expression is the same
as the named type.
76)This is often called ``truncation toward zero''.
6.5.5 Language 6.5.5
WG14/N843 Committee Draft -- August 3, 1998 89
6.5.6 Additive operators
Syntax
[#1]
additive-expr:
multiplicative-expr
additive-expr + multiplicative-expr
additive-expr - multiplicative-expr
Constraints
[#2] For addition, either both operands shall have
arithmetic type, or one operand shall be a pointer to an
object type and the other shall have integer type.
(Incrementing is equivalent to adding 1.)
[#3] For subtraction, one of the following shall hold:
-- both operands have arithmetic type;
-- both operands are pointers to qualified or unqualified
versions of compatible object types; or
-- the left operand is a pointer to an object type and the
right operand has integer type. *
(Decrementing is equivalent to subtracting 1.) |
Semantics
[#4] If both operands have arithmetic type, the usual
arithmetic conversions are performed on them. If either
operand has complex type, the result has complex type.
[#5] The result of the binary + operator is the sum of the
operands.
[#6] The result of the binary - operator is the difference
resulting from the subtraction of the second operand from
the first.
[#7] For the purposes of these operators, a pointer to a
nonarray object behaves the same as a pointer to the first
element of an array of length one with the type of the
object as its element type.
[#8] When an expression that has integer type is added to or
subtracted from a pointer, the result has the type of the
pointer operand. If the pointer operand points to an
element of an array object, and the array is large enough,
the result points to an element offset from the original
element such that the difference of the subscripts of the
6.5.6 Language 6.5.6
90 Committee Draft -- August 3, 1998 WG14/N843
resulting and original array elements equals the integer
expression. In other words, if the expression P points to
the i-th element of an array object, the expressions (P)+N
(equivalently, N+(P)) and (P)-N (where N has the value n)
point to, respectively, the i+n-th and i-n-th elements of
the array object, provided they exist. Moreover, if the
expression P points to the last element of an array object,
the expression (P)+1 points one past the last element of the
array object, and if the expression Q points one past the
last element of an array object, the expression (Q)-1 points
to the last element of the array object. If both the
pointer operand and the result point to elements of the same
array object, or one past the last element of the array
object, the evaluation shall not produce an overflow;
otherwise, the behavior is undefined. If the result points |
one past the last element of the array object, it shall not |
be used as the operand of a unary * operator that is |
evaluated.
[#9] When two pointers are subtracted, both shall point to |
elements of the same array object, or one past the last |
element of the array object; the result is the difference of
the subscripts of the two array elements. The size of the
result is implementation-defined, and its type (a signed
integer type) is ptrdiff_t defined in the <stddef.h> header.
If the result is not representable in an object of that
type, the behavior is undefined. In other words, if the
expressions P and Q point to, respectively, the i-th and j-
th elements of an array object, the expression (P)-(Q) has
the value i-j provided the value fits in an object of type
ptrdiff_t. Moreover, if the expression P points either to
an element of an array object or one past the last element
of an array object, and the expression Q points to the last
element of the same array object, the expression ((Q)+1)-(P)
has the same value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and
has the value zero if the expression P points one past the
last element of the array object, even though the expression
(Q)+1 does not point to an element of the array object.77) |
____________________
77)Another way to approach pointer arithmetic is first to
convert the pointer(s) to character pointer(s): In this
scheme the integer expression added to or subtracted from
the converted pointer is first multiplied by the size of
the object originally pointed to, and the resulting
pointer is converted back to the original type. For
pointer subtraction, the result of the difference between
the character pointers is similarly divided by the size
of the object originally pointed to.
When viewed in this way, an implementation need only
provide one extra byte (which may overlap another object
in the program) just after the end of the object in order
to satisfy the ``one past the last element''
requirements.
6.5.6 Language 6.5.6
WG14/N843 Committee Draft -- August 3, 1998 91
[#10] EXAMPLE Pointer arithmetic is well defined with
pointers to variable length array types.
{
int n = 4, m = 3;
int a[n][m];
int (*p)[m] = a; // p == &a[0]
p += 1; // p == &a[1]
(*p)[2] = 99; // a[1][2] == 99
n = p - a; // n == 1
}
[#11] If array a in the above example were declared to be an |
array of known constant size, and pointer p were declared to |
be a pointer to an array of the same known constant size |
(pointing to a), the results would be the same.
Forward references: array declarators (6.7.5.2), common
definitions <stddef.h> (7.17).
6.5.7 Bitwise shift operators
Syntax
[#1]
shift-expr:
additive-expr
shift-expr << additive-expr
shift-expr >> additive-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The integer promotions are performed on each of the
operands. The type of the result is that of the promoted
left operand. If the value of the right operand is negative |
or is greater than or equal to the width of the promoted
left operand, the behavior is undefined.
[#4] The result of E1 << E2 is E1 left-shifted E2 bit
positions; vacated bits are filled with zeros. If E1 has an
unsigned type, the value of the result is E1×2E2, reduced |
modulo one more than the maximum value representable in the |
result type. If E1 has a signed type and nonnegative value,
and E1×2E2 is representable in the result type, then that is |
the resulting value; otherwise, the behavior is undefined.
[#5] The result of E1 >> E2 is E1 right-shifted E2 bit
positions. If E1 has an unsigned type or if E1 has a signed
6.5.6 Language 6.5.7
92 Committee Draft -- August 3, 1998 WG14/N843
type and a nonnegative value, the value of the result is the
integral part of the quotient of E1 divided by the quantity,
2 raised to the power E2. If E1 has a signed type and a
negative value, the resulting value is implementation-
defined.
6.5.8 Relational operators
Syntax
[#1]
relational-expr:
shift-expr
relational-expr < shift-expr
relational-expr > shift-expr
relational-expr <= shift-expr
relational-expr >= shift-expr
Constraints
[#2] One of the following shall hold:
-- both operands have real type;
-- both operands are pointers to qualified or unqualified
versions of compatible object types; or
-- both operands are pointers to qualified or unqualified
versions of compatible incomplete types.
Semantics
[#3] If both of the operands have arithmetic type, the usual
arithmetic conversions are performed.
[#4] For the purposes of these operators, a pointer to a
nonarray object behaves the same as a pointer to the first
element of an array of length one with the type of the
object as its element type.
[#5] When two pointers are compared, the result depends on
the relative locations in the address space of the objects
pointed to. If two pointers to object or incomplete types
both point to the same object, or both point one past the
last element of the same array object, they compare equal.
If the objects pointed to are members of the same aggregate
object, pointers to structure members declared later compare
greater than pointers to members declared earlier in the
structure, and pointers to array elements with larger
subscript values compare greater than pointers to elements
of the same array with lower subscript values. All pointers
to members of the same union object compare equal. If the
expression P points to an element of an array object and the
6.5.7 Language 6.5.8
WG14/N843 Committee Draft -- August 3, 1998 93
expression Q points to the last element of the same array
object, the pointer expression Q+1 compares greater than P.
In all other cases, the behavior is undefined.
[#6] Each of the operators < (less than), > (greater than),
<= (less than or equal to), and >= (greater than or equal
to) shall yield 1 if the specified relation is true and 0 if
it is false.78) The result has type int.
6.5.9 Equality operators
Syntax
[#1]
equality-expr:
relational-expr
equality-expr == relational-expr
equality-expr != relational-expr
Constraints
[#2] One of the following shall hold:
-- both operands have arithmetic type;
-- both operands are pointers to qualified or unqualified
versions of compatible types;
-- one operand is a pointer to an object or incomplete
type and the other is a pointer to a qualified or
unqualified version of void; or
-- one operand is a pointer and the other is a null
pointer constant.
Semantics
[#3] The == (equal to) and != (not equal to) operators are |
analogous to the relational operators except for their lower
precedence.79) Each of the operators yields 1 if the |
specified relation is true and 0 if it is false. The result |
has type int. For any pair of operands, exactly one of the |
relations is true.
____________________
78)The expression a<b<c is not interpreted as in ordinary
mathematics. As the syntax indicates, it means (a<b)<c;
in other words, ``if a is less than b, compare 1 to c; |
otherwise, compare 0 to c''.
79)Because of the precedences, a<b == c<d is 1 whenever a<b
and c<d have the same truth-value.
6.5.8 Language 6.5.9
94 Committee Draft -- August 3, 1998 WG14/N843
[#4] If both of the operands have arithmetic type, the usual |
arithmetic conversions are performed. Values of complex
types are equal if and only if both their real parts are
equal and also their imaginary parts are equal. Any two |
values of arithmetic types from different type domains are
equal if and only if the results of their conversion to the
complex type corresponding to the common real type
determined by the usual arithmetic conversions are equal. |
[#5] Otherwise, at least one operand is a pointer. If one |
operand is a null pointer constant, it is converted to the |
type of the other operand. If one operand is a pointer to |
an object or incomplete type and the other is a pointer to a |
qualified or unqualified version of void, the former is |
converted to the type of the latter. |
[#6] Two pointers compare equal if both are null pointers, |
both are pointers to the same object (including a pointer to |
an object and a subobject at its beginning) or function, |
both are pointers to one past the last element of the same |
array object, or one is a pointer to one past the end of one |
array object and the other is a pointer to the start of a |
different array object that happens to immediately follow |
the first array object in the address space.80)
6.5.10 Bitwise AND operator
Syntax
[#1]
AND-expr:
equality-expr
AND-expr & equality-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands.
____________________
80)Two objects may be adjacent in memory because they are
adjacent elements of a larger array or adjacent members
of a structure with no padding between them, or because
the implementation chose to place them so, even though
they are unrelated. If prior invalid pointer operations,
such as accesses outside array bounds, produced undefined
behavior, the effect of subsequent comparisons is also
undefined.
6.5.9 Language 6.5.10
WG14/N843 Committee Draft -- August 3, 1998 95
[#4] The result of the binary & operator is the bitwise AND
of the operands (that is, each bit in the result is set if
and only if each of the corresponding bits in the converted
operands is set).
6.5.11 Bitwise exclusive OR operator
Syntax
[#1]
exclusive-OR-expr:
AND-expr
exclusive-OR-expr ^ AND-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands.
[#4] The result of the ^ operator is the bitwise exclusive
OR of the operands (that is, each bit in the result is set
if and only if exactly one of the corresponding bits in the
converted operands is set).
6.5.12 Bitwise inclusive OR operator
Syntax
[#1]
inclusive-OR-expr:
exclusive-OR-expr
inclusive-OR-expr | exclusive-OR-expr
Constraints
[#2] Each of the operands shall have integer type.
Semantics
[#3] The usual arithmetic conversions are performed on the
operands.
[#4] The result of the | operator is the bitwise inclusive
OR of the operands (that is, each bit in the result is set
if and only if at least one of the corresponding bits in the
converted operands is set).
6.5.10 Language 6.5.12
96 Committee Draft -- August 3, 1998 WG14/N843
6.5.13 Logical AND operator
Syntax
[#1]
logical-AND-expr:
inclusive-OR-expr
logical-AND-expr && inclusive-OR-expr
Constraints
[#2] Each of the operands shall have scalar type.
Semantics
[#3] The && operator shall yield 1 if both of its operands
compare unequal to 0; otherwise, it yields 0. The result
has type int.
[#4] Unlike the bitwise binary & operator, the && operator
guarantees left-to-right evaluation; there is a sequence
point after the evaluation of the first operand. If the
first operand compares equal to 0, the second operand is not
evaluated.
6.5.14 Logical OR operator
Syntax
[#1]
logical-OR-expr:
logical-AND-expr
logical-OR-expr || logical-AND-expr
Constraints
[#2] Each of the operands shall have scalar type.
Semantics
[#3] The || operator shall yield 1 if either of its operands
compare unequal to 0; otherwise, it yields 0. The result
has type int.
[#4] Unlike the bitwise | operator, the || operator
guarantees left-to-right evaluation; there is a sequence
point after the evaluation of the first operand. If the
first operand compares unequal to 0, the second operand is
not evaluated.
6.5.13 Language 6.5.14
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6.5.15 Conditional operator
Syntax
[#1]
conditional-expr:
logical-OR-expr
logical-OR-expr ? expr : conditional-expr
Constraints
[#2] The first operand shall have scalar type.
[#3] One of the following shall hold for the second and
third operands:
-- both operands have arithmetic type;
-- both operands have compatible structure or union types;
-- both operands have void type;
-- both operands are pointers to qualified or unqualified
versions of compatible types;
-- one operand is a pointer and the other is a null
pointer constant; or
-- one operand is a pointer to an object or incomplete
type and the other is a pointer to a qualified or
unqualified version of void.
Semantics
[#4] The first operand is evaluated; there is a sequence
point after its evaluation. The second operand is evaluated
only if the first compares unequal to 0; the third operand
is evaluated only if the first compares equal to 0; the
result is the value of the second or third operand
(whichever is evaluated), converted to the type described
below.81) If an attempt is made to modify the result of a |
conditional operator or to access it after the next sequence |
point, the behavior is undefined.
[#5] If both the second and third operands have arithmetic
type, the type that the usual arithmetic conversions would
yield if applied to those two operands is the type of the
result. If both the operands have structure or union type,
the result has that type. If both operands have void type,
the result has void type.
____________________
81)A conditional expression does not yield an lvalue.
6.5.15 Language 6.5.15
98 Committee Draft -- August 3, 1998 WG14/N843
[#6] If both the second and third operands are pointers or
one is a null pointer constant and the other is a pointer,
the result type is a pointer to a type qualified with all
the type qualifiers of the types pointed-to by both
operands. Furthermore, if both operands are pointers to
compatible types or to differently qualified versions of
compatible types, the result type is a pointer to an
appropriately qualified version of the composite type; if
one operand is a null pointer constant, the result has the
type of the other operand; otherwise, one operand is a
pointer to void or a qualified version of void, in which
case the result type is a pointer to an appropriately
qualified version of void.
[#7] EXAMPLE The common type that results when the second
and third operands are pointers is determined in two
independent stages. The appropriate qualifiers, for
example, do not depend on whether the two pointers have
compatible types.
[#8] Given the declarations
const void *c_vp;
void *vp;
const int *c_ip;
volatile int *v_ip;
int *ip;
const char *c_cp;
the third column in the following table is the common type
that is the result of a conditional expression in which the
first two columns are the second and third operands (in
either order):
c_vp c_ip const void *
v_ip 0 volatile int *
c_ip v_ip const volatile int *
vp c_cp const void *
ip c_ip const int *
vp ip void *
6.5.16 Assignment operators
Syntax
[#1]
assignment-expr:
conditional-expr
unary-expr assignment-operator assignment-expr
6.5.15 Language 6.5.16
WG14/N843 Committee Draft -- August 3, 1998 99
assignment-operator: one of
= *= /= %= += -= <<= >>= &= ^= |=
Constraints
[#2] An assignment operator shall have a modifiable lvalue
as its left operand.
Semantics
[#3] An assignment operator stores a value in the object
designated by the left operand. An assignment expression
has the value of the left operand after the assignment, but
is not an lvalue. The type of an assignment expression is
the type of the left operand unless the left operand has
qualified type, in which case it is the unqualified version
of the type of the left operand. The side effect of
updating the stored value of the left operand shall occur
between the previous and the next sequence point.
[#4] The order of evaluation of the operands is unspecified. |
If an attempt is made to modify the result of an assignment |
operator or to access it after the next sequence point, the |
behavior is undefined.
6.5.16.1 Simple assignment
Constraints
[#1] One of the following shall hold:82)
-- the left operand has qualified or unqualified
arithmetic type and the right has arithmetic type;
-- the left operand has a qualified or unqualified version
of a structure or union type compatible with the type
of the right;
-- both operands are pointers to qualified or unqualified
versions of compatible types, and the type pointed to
by the left has all the qualifiers of the type pointed
to by the right;
-- one operand is a pointer to an object or incomplete
type and the other is a pointer to a qualified or
unqualified version of void, and the type pointed to by
the left has all the qualifiers of the type pointed to
____________________
82)The asymmetric appearance of these constraints with
respect to type qualifiers is due to the conversion
(specified in 6.3.2.1) that changes lvalues to ``the
value of the expression'' which removes any type
qualifiers from the type category of the expression.
6.5.16 Language 6.5.16.1
100 Committee Draft -- August 3, 1998 WG14/N843
by the right; or
-- the left operand is a pointer and the right is a null
pointer constant.
Semantics
[#2] In simple assignment (=), the value of the right
operand is converted to the type of the assignment
expression and replaces the value stored in the object
designated by the left operand.
[#3] If the value being stored in an object is accessed from
another object that overlaps in any way the storage of the
first object, then the overlap shall be exact and the two
objects shall have qualified or unqualified versions of a
compatible type; otherwise, the behavior is undefined.
[#4] EXAMPLE 1 In the program fragment
int f(void);
char c;
/* ... */
if ((c = f()) == -1)
/* ... */
the int value returned by the function may be truncated when
stored in the char, and then converted back to int width
prior to the comparison. In an implementation in which
``plain'' char has the same range of values as unsigned char
(and char is narrower than int), the result of the
conversion cannot be negative, so the operands of the
comparison can never compare equal. Therefore, for full
portability, the variable c should be declared as int.
[#5] EXAMPLE 2 In the fragment:
char c;
int i;
long l;
l = (c = i);
the value of i is converted to the type of the assignment-
expression c = i, that is, char type. The value of the
expression enclosed in parentheses is then converted to the
type of the outer assignment-expression, that is, long int
type.
|
[#6] EXAMPLE 3 Consider the fragment: |
6.5.16.1 Language 6.5.16.1
WG14/N843 Committee Draft -- August 3, 1998 101
const char **cpp;
char *p;
const char c = 'A';
cpp = &p; // constraint violation
*cpp = &c; // valid
*p = 0; // valid
The first assignment is unsafe because it would allow the |
following valid code to attempt to change the value of the |
const object c. |
6.5.16.2 Compound assignment
Constraints
[#1] For the operators += and -= only, either the left
operand shall be a pointer to an object type and the right
shall have integer type, or the left operand shall have
qualified or unqualified arithmetic type and the right shall
have arithmetic type.
[#2] For the other operators, each operand shall have
arithmetic type consistent with those allowed by the
corresponding binary operator.
Semantics
[#3] A compound assignment of the form E1 op= E2 differs
from the simple assignment expression E1 = E1 op (E2) only
in that the lvalue E1 is evaluated only once.
6.5.17 Comma operator
Syntax
[#1]
expression:
assignment-expr
expression , assignment-expr
Semantics
[#2] The left operand of a comma operator is evaluated as a
void expression; there is a sequence point after its
evaluation. Then the right operand is evaluated; the result
has its type and value.83) If an attempt is made to modify |
the result of a comma operator or to access it after the |
next sequence point, the behavior is undefined.
____________________
83)A comma operator does not yield an lvalue.
6.5.16.1 Language 6.5.17
102 Committee Draft -- August 3, 1998 WG14/N843
[#3] EXAMPLE As indicated by the syntax, the comma operator
(as described in this subclause) cannot appear in contexts
where a comma is used to separate items in a list (such as
arguments to functions or lists of initializers). On the
other hand, it can be used within a parenthesized expression
or within the second expression of a conditional operator in
such contexts. In the function call
f(a, (t=3, t+2), c)
the function has three arguments, the second of which has
the value 5.
Forward references: initialization (6.7.8).
6.5.17 Language 6.5.17
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6.6 Constant expressions
Syntax
[#1]
constant-expression:
conditional-expression
Description
[#2] A constant expression can be evaluated during
translation rather than runtime, and accordingly may be used
in any place that a constant may be.
Constraints
[#3] Constant expressions shall not contain assignment,
increment, decrement, function-call, or comma operators, |
except when they are contained within a subexpression that |
is not evaluated.84)
[#4] Each constant expression shall evaluate to a constant
that is in the range of representable values for its type.
Semantics
[#5] An expression that evaluates to a constant is required
in several contexts. If a floating expression is evaluated
in the translation environment, the arithmetic precision and
range shall be at least as great as if the expression were
being evaluated in the execution environment.
[#6] An integer constant expression85) shall have integer
type and shall only have operands that are integer
constants, enumeration constants, character constants,
sizeof expressions whose results are integer constants, and |
floating constants that are the immediate operands of casts.
Cast operators in an integer constant expression shall only
convert arithmetic types to integer types, except as part of
an operand to the sizeof operator.
____________________
84)The operand of a sizeof operator is usually not evaluated |
(6.5.3.4).
85)An integer constant expression is used to specify the
size of a bit-field member of a structure, the value of
an enumeration constant, the size of an array, or the
value of a case constant. Further constraints that apply
to the integer constant expressions used in conditional-
inclusion preprocessing directives are discussed in
6.10.1.
6.6 Language 6.6
104 Committee Draft -- August 3, 1998 WG14/N843
[#7] More latitude is permitted for constant expressions in
initializers. Such a constant expression shall be, or
evaluate to, one of the following:
-- an arithmetic constant expression,
-- a null pointer constant,
-- an address constant, or
-- an address constant for an object type plus or minus an
integer constant expression.
[#8] An arithmetic constant expression shall have arithmetic
type and shall only have operands that are integer
constants, floating constants, enumeration constants,
character constants, and sizeof expressions. Cast operators
in an arithmetic constant expression shall only convert
arithmetic types to arithmetic types, except as part of an
operand to the sizeof operator.
[#9] An address constant is a null pointer, a pointer to an
lvalue designating an object of static storage duration, or
to a function designator; it shall be created explicitly
using the unary & operator or an integer constant cast to
pointer type, or implicitly by the use of an expression of
array or function type. The array-subscript [] and member-
access . and -> operators, the address & and indirection *
unary operators, and pointer casts may be used in the
creation of an address constant, but the value of an object
shall not be accessed by use of these operators.
[#10] An implementation may accept other forms of constant
expressions.
[#11] The semantic rules for the evaluation of a constant
expression are the same as for nonconstant expressions.86)
Forward references: array declarators (6.7.5.2),
initialization (6.7.8).
____________________
86)Thus, in the following initialization,
static int i = 2 || 1 / 0;
the expression is a valid integer constant expression
with value one.
6.6 Language 6.6
WG14/N843 Committee Draft -- August 3, 1998 105
6.7 Declarations
Syntax
[#1]
declaration:
declaration-specifiers init-declarator-list-opt ;
declaration-specifiers:
storage-class-specifier declaration-specifiers-opt
type-specifier declaration-specifiers-opt
type-qualifier declaration-specifiers-opt
function-specifier declaration-specifiers-opt
init-declarator-list:
init-declarator
init-declarator-list , init-declarator
init-declarator:
declarator
declarator = initializer
Constraints
[#2] A declaration shall declare at least a declarator |
(other than the parameters of a function or the members of a
structure or union), a tag, or the members of an
enumeration.
[#3] If an identifier has no linkage, there shall be no more
than one declaration of the identifier (in a declarator or
type specifier) with the same scope and in the same name
space, except for tags as specified in 6.7.2.3.
[#4] All declarations in the same scope that refer to the
same object or function shall specify compatible types.
Semantics
[#5] A declaration specifies the interpretation and
attributes of a set of identifiers. A definition of an
identifier is a declaration for that identifier that:
-- for an object, causes storage to be reserved for that
object;
-- for a function, includes the function body;87)
____________________
87)Function definitions have a different syntax, described
in 6.9.1.
6.7 Language 6.7
106 Committee Draft -- August 3, 1998 WG14/N843
-- for an enumeration constant or typedef name, is the
(only) declaration of the identifier.
[#6] The declaration specifiers consist of a sequence of
specifiers that indicate the linkage, storage duration, and
part of the type of the entities that the declarators
denote. The init-declarator-list is a comma-separated
sequence of declarators, each of which may have additional
type information, or an initializer, or both. The
declarators contain the identifiers (if any) being declared.
[#7] If an identifier for an object is declared with no
linkage, the type for the object shall be complete by the
end of its declarator, or by the end of its init-declarator
if it has an initializer.
Forward references: declarators (6.7.5), enumeration
specifiers (6.7.2.2), initialization (6.7.8), tags
(6.7.2.3).
6.7.1 Storage-class specifiers
Syntax
[#1]
storage-class-specifier:
typedef
extern
static
auto
register
Constraints
[#2] At most, one storage-class specifier may be given in
the declaration specifiers in a declaration.88)
Semantics
[#3] The typedef specifier is called a ``storage-class
specifier'' for syntactic convenience only; it is discussed
in 6.7.7. The meanings of the various linkages and storage
durations were discussed in 6.2.2 and 6.2.4.
[#4] A declaration of an identifier for an object with
storage-class specifier register suggests that access to the
object be as fast as possible. The extent to which such
suggestions are effective is implementation-defined.89)
[#5] The declaration of an identifier for a function that
____________________
88)See ``future language directions'' (6.11.2).
6.7 Language 6.7.1
WG14/N843 Committee Draft -- August 3, 1998 107
has block scope shall have no explicit storage-class
specifier other than extern.
[#6] If an aggregate or union object is declared with a
storage-class specifier other than typedef, the properties
resulting from the storage-class specifier, except with
respect to linkage, also apply to the members of the object,
and so on recursively for any aggregate or union member
objects.
Forward references: type definitions (6.7.7).
6.7.2 Type specifiers
Syntax
[#1]
type-specifier:
void
char
short
int
long
float
double
signed
unsigned
_Bool |
_Complex
_Imaginary
struct-or-union-specifier
enum-specifier
typedef-name
Constraints
[#2] At least one type specifier shall be given in the
declaration specifiers in each declaration, and in the |
specifier-qualifier list in each struct declaration and type |
name. Each list of type specifiers shall be one of the
following sets (delimited by commas, when there is more than
____________________
89)The implementation may treat any register declaration
simply as an auto declaration. However, whether or not
addressable storage is actually used, the address of any
part of an object declared with storage-class specifier
register cannot be computed, either explicitly (by use of
the unary & operator as discussed in 6.5.3.2) or
implicitly (by converting an array name to a pointer as
discussed in 6.3.2.1). Thus the only operator that can
be applied to an array declared with storage-class
specifier register is sizeof.
6.7.1 Language 6.7.2
108 Committee Draft -- August 3, 1998 WG14/N843
one set on a line); the type specifiers may occur in any
order, possibly intermixed with the other declaration
specifiers.
-- void
-- char
-- signed char
-- unsigned char
-- short, signed short, short int, or signed short int
-- unsigned short, or unsigned short int
-- int, signed, or signed int
-- unsigned, or unsigned int
-- long, signed long, long int, or signed long int
-- unsigned long, or unsigned long int
-- long long, signed long long, long long int, or signed
long long int
-- unsigned long long, or unsigned long long int
-- float
-- double
-- long double
-- _Bool |
-- float _Complex
-- double _Complex
-- long double _Complex
-- float _Imaginary
-- double _Imaginary
-- long double _Imaginary
-- struct or union specifier |
-- enum specifier |
6.7.2 Language 6.7.2
WG14/N843 Committee Draft -- August 3, 1998 109
-- typedef name |
[#3] The type specifiers _Complex and _Imaginary shall not
be used if the implementation does not provide those
types.90)
Semantics
[#4] Specifiers for structures, unions, and enumerations are
discussed in 6.7.2.1 through 6.7.2.3. Declarations of
typedef names are discussed in 6.7.7. The characteristics
of the other types are discussed in 6.2.5.
[#5] Each of the comma-separated sets designates the same
type, except that for bit-fields, it is implementation-
defined whether the specifier int designates the same type
as signed int or the same type as unsigned int.
Forward references: enumeration specifiers (6.7.2.2),
structure and union specifiers (6.7.2.1), tags (6.7.2.3),
type definitions (6.7.7).
6.7.2.1 Structure and union specifiers
Syntax
[#1]
struct-or-union-specifier:
struct-or-union identifier-opt { struct-declaration-list }
struct-or-union identifier
struct-or-union:
struct
union
struct-declaration-list:
struct-declaration
struct-declaration-list struct-declaration
struct-declaration:
specifier-qualifier-list struct-declarator-list ;
specifier-qualifier-list:
type-specifier specifier-qualifier-list-opt
type-qualifier specifier-qualifier-list-opt
____________________
90)Implementations are not required to provide imaginary
types. Freestanding implementations are not required to
provide complex types.
6.7.2 Language 6.7.2.1
110 Committee Draft -- August 3, 1998 WG14/N843
struct-declarator-list:
struct-declarator
struct-declarator-list , struct-declarator
struct-declarator:
declarator
declarator-opt : constant-expression
Constraints
[#2] A structure or union shall not contain a member with |
incomplete or function type (hence, a structure shall not |
contain an instance of itself, but may contain a pointer to |
an instance of itself), except that the last member of a |
structure with more than one named member may have |
incomplete array type; such a structure (and any union |
containing, possibly recursively, a member that is such a |
structure) shall not be a member of a structure or an |
element of an array.
[#3] The expression that specifies the width of a bit-field
shall be an integer constant expression that has nonnegative
value that shall not exceed the number of bits in an object
of the type that is specified if the colon and expression
are omitted. If the value is zero, the declaration shall
have no declarator.
Semantics
[#4] As discussed in 6.2.5, a structure is a type consisting
of a sequence of members, whose storage is allocated in an
ordered sequence, and a union is a type consisting of a
sequence of members whose storage overlap.
[#5] Structure and union specifiers have the same form.
[#6] The presence of a struct-declaration-list in a struct-
or-union-specifier declares a new type, within a translation
unit. The struct-declaration-list is a sequence of
declarations for the members of the structure or union. If
the struct-declaration-list contains no named members, the
behavior is undefined. The type is incomplete until after
the } that terminates the list.
[#7] A member of a structure or union may have any object
type other than a variably modified type.91) In addition, a
member may be declared to consist of a specified number of
bits (including a sign bit, if any). Such a member is
called a bit-field;92) its width is preceded by a colon.
____________________
91)A structure or union can not contain a member with a
variably modified type because member names are not
ordinary identifiers as defined in 6.2.3.
6.7.2.1 Language 6.7.2.1
WG14/N843 Committee Draft -- August 3, 1998 111
[#8] A bit-field shall have a type that is a qualified or
unqualified version of _Bool, signed int, or unsigned int. |
A bit-field is interpreted as a signed or unsigned integer
type consisting of the specified number of bits.93) If the |
value 0 or 1 is stored into a nonzero-width bit-field of |
type _Bool, the value of the bit-field shall compare equal |
to the value stored.
[#9] An implementation may allocate any addressable storage
unit large enough to hold a bit-field. If enough space
remains, a bit-field that immediately follows another bit-
field in a structure shall be packed into adjacent bits of
the same unit. If insufficient space remains, whether a
bit-field that does not fit is put into the next unit or
overlaps adjacent units is implementation-defined. The
order of allocation of bit-fields within a unit (high-order
to low-order or low-order to high-order) is implementation-
defined. The alignment of the addressable storage unit is
unspecified.
[#10] A bit-field declaration with no declarator, but only a
colon and a width, indicates an unnamed bit-field.94) As a |
special case, a bit-field structure member with a width of 0
indicates that no further bit-field is to be packed into the
unit in which the previous bit-field, if any, was placed.
[#11] Each non-bit-field member of a structure or union
object is aligned in an implementation-defined manner
appropriate to its type.
[#12] Within a structure object, the non-bit-field members
and the units in which bit-fields reside have addresses that
increase in the order in which they are declared. A pointer
to a structure object, suitably converted, points to its
initial member (or if that member is a bit-field, then to
the unit in which it resides), and vice versa. There may be
unnamed padding within a structure object, but not at its
beginning.
[#13] The size of a union is sufficient to contain the
largest of its members. The value of at most one of the
____________________
92)The unary & (address-of) operator cannot be applied to a
bit-field object; thus, there are no pointers to or
arrays of bit-field objects.
93)As specified in 6.7.2 above, if the actual type specifier
used is int or a typedef-name defined as int, then it is
implementation-defined whether the bit-field is signed or
unsigned.
94)An unnamed bit-field structure member is useful for
padding to conform to externally imposed layouts.
6.7.2.1 Language 6.7.2.1
112 Committee Draft -- August 3, 1998 WG14/N843
members can be stored in a union object at any time. A
pointer to a union object, suitably converted, points to
each of its members (or if a member is a bit-field, then to
the unit in which it resides), and vice versa.
[#14] There may be unnamed padding at the end of a structure |
or union.
[#15] As a special case, the last element of a structure |
with more than one named member may have an incomplete array |
type. This is called a flexible array member, and the size
of the structure shall be equal to the offset of the last
element of an otherwise identical structure that replaces
the flexible array member with an array of unspecified |
length.95) When an lvalue whose type is a structure with a
flexible array member is used to access an object, it
behaves as if that member were replaced with the longest |
array, with the same element type, that would not make the |
structure larger than the object being accessed; the offset |
of the array shall remain that of the flexible array member, |
even if this would differ from that of the replacement |
array. If this array would have no elements, then it |
behaves as if it had one element, but the behavior is
undefined if any attempt is made to access that element or |
to generate a pointer one past it.
[#16] EXAMPLE Assuming that all array members are aligned |
the same, after the declarations:
struct s { int n; double d[]; };
struct ss { int n; double d[1]; };
the three expressions:
sizeof (struct s)
offsetof(struct s, d)
offsetof(struct ss, d)
have the same value. The structure struct s has a flexible
array member d.
[#17] If sizeof (double) is 8, then after the following code
is executed:
struct s *s1;
struct s *s2;
s1 = malloc(sizeof (struct s) + 64);
s2 = malloc(sizeof (struct s) + 46);
____________________
95)The length is unspecified to allow for the fact that
implementations may give array members different
alignments according to their lengths.
6.7.2.1 Language 6.7.2.1
WG14/N843 Committee Draft -- August 3, 1998 113
and assuming that the calls to malloc succeed, the objects |
pointed to by s1 and s2 behave as if the identifiers had |
been declared as:
struct { int n; double d[8]; } *s1;
struct { int n; double d[5]; } *s2;
[#18] Following the further successful assignments:
s1 = malloc(sizeof (struct s) + 10);
s2 = malloc(sizeof (struct s) + 6);
they then behave as if the declarations were: |
struct { int n; double d[1]; } *s1, *s2;
and:
double *dp;
dp = &(s1->d[0]); // Permitted
*dp = 42; // Permitted
dp = &(s2->d[0]); // Permitted
*dp = 42; // Undefined behavior
Forward references: tags (6.7.2.3).
6.7.2.2 Enumeration specifiers
Syntax
[#1]
enum-specifier:
enum identifier-opt { enumerator-list }
enum identifier-opt { enumerator-list , }
enum identifier
enumerator-list:
enumerator
enumerator-list , enumerator
enumerator:
enumeration-constant
enumeration-constant = constant-expression
Constraints
[#2] The expression that defines the value of an enumeration
constant shall be an integer constant expression that has a
value representable as an int.
6.7.2.1 Language 6.7.2.2
114 Committee Draft -- August 3, 1998 WG14/N843
Semantics
[#3] The identifiers in an enumerator list are declared as
constants that have type int and may appear wherever such
are permitted.96) An enumerator with = defines its
enumeration constant as the value of the constant
expression. If the first enumerator has no =, the value of
its enumeration constant is 0. Each subsequent enumerator
with no = defines its enumeration constant as the value of
the constant expression obtained by adding 1 to the value of
the previous enumeration constant. (The use of enumerators
with = may produce enumeration constants with values that
duplicate other values in the same enumeration.) The
enumerators of an enumeration are also known as its members.
[#4] Each enumerated type shall be compatible with an
integer type. The choice of type is |
implementation-defined,97) but shall be capable of
representing the values of all the members of the
enumeration. The enumerated type is incomplete until after *
the } that terminates the list of enumerator declarations.
[#5] EXAMPLE The following fragment: |
enum hue { chartreuse, burgundy, claret=20, winedark };
enum hue col, *cp;
col = claret;
cp = &col;
if (*cp != burgundy)
/* ... */
makes hue the tag of an enumeration, and then declares col
as an object that has that type and cp as a pointer to an
object that has that type. The enumerated values are in the
set {0, 1, 20, 21}.
Forward references: tags (6.7.2.3).
6.7.2.3 Tags
Constraints
[#1] A specific type shall have its content defined at most
once.
____________________
96)Thus, the identifiers of enumeration constants declared
in the same scope shall all be distinct from each other
and from other identifiers declared in ordinary
declarators.
97)An implementation may delay the choice of which integer
type until all enumeration constants have been seen.
6.7.2.2 Language 6.7.2.3
WG14/N843 Committee Draft -- August 3, 1998 115
[#2] A type specifier of the form
enum identifier
without an enumerator list shall only appear after the type
it specifies is completed.
Semantics
[#3] All declarations of structure, union, or enumerated
types that have the same scope and use the same tag declare
the same type. The type is incomplete98) until the closing
brace of the list defining the content, and complete
thereafter.
[#4] Two declarations of structure, union, or enumerated
types which are in different scopes or use different tags
declare distinct types. Each declaration of a structure,
union, or enumerated type which does not include a tag
declares a distinct type.
[#5] A type specifier of the form
struct-or-union identifier-opt { struct-declaration-list }
or
enum identifier { enumerator-list }
or
enum identifier { enumerator-list , }
declares a structure, union, or enumerated type. The list
defines the structure content, union content, or enumeration
content. If an identifier is provided,99) the type
specifier also declares the identifier to be the tag of that
type.
[#6] A declaration of the form
____________________
98)An incomplete type may only by used when the size of an
object of that type is not needed. It is not needed, for
example, when a typedef name is declared to be a
specifier for a structure or union, or when a pointer to
or a function returning a structure or union is being
declared. (See incomplete types in 6.2.5.) The |
specification has to be complete before such a function
is called or defined.
99)If there is no identifier, the type can, within the
translation unit, only be referred to by the declaration
of which it is a part. Of course, when the declaration
is of a typedef name, subsequent declarations can make
use of that typedef name to declare objects having the
specified structure, union, or enumerated type.
6.7.2.3 Language 6.7.2.3
116 Committee Draft -- August 3, 1998 WG14/N843
struct-or-union identifier ;
specifies a structure or union type and declares the
identifier as a tag of that type.100)
[#7] If a type specifier of the form
struct-or-union identifier
occurs other than as part of one of the above forms, and no
other declaration of the identifier as a tag is visible,
then it declares an incomplete structure or union type, and
declares the identifier as the tag of that type.100)
[#8] If a type specifier of the form
struct-or-union identifier
or
enum identifier
occurs other than as part of one of the above forms, and a
declaration of the identifier as a tag is visible, then it
specifies the same type as that other declaration, and does
not redeclare the tag.
[#9] EXAMPLE 1 This mechanism allows declaration of a self-
referential structure.
struct tnode {
int count;
struct tnode *left, *right;
};
specifies a structure that contains an integer and two
pointers to objects of the same type. Once this declaration
has been given, the declaration
struct tnode s, *sp;
declares s to be an object of the given type and sp to be a
pointer to an object of the given type. With these
declarations, the expression sp->left refers to the left
struct tnode pointer of the object to which sp points; the
expression s.right->count designates the count member of the
right struct tnode pointed to from s.
[#10] The following alternative formulation uses the typedef
mechanism:
____________________
100A similar construction with enum does not exist.
6.7.2.3 Language 6.7.2.3
WG14/N843 Committee Draft -- August 3, 1998 117
typedef struct tnode TNODE;
struct tnode {
int count;
TNODE *left, *right;
};
TNODE s, *sp;
[#11] EXAMPLE 2 To illustrate the use of prior declaration
of a tag to specify a pair of mutually referential
structures, the declarations
struct s1 { struct s2 *s2p; /* ... */ }; // D1
struct s2 { struct s1 *s1p; /* ... */ }; // D2
specify a pair of structures that contain pointers to each
other. Note, however, that if s2 were already declared as a
tag in an enclosing scope, the declaration D1 would refer to
it, not to the tag s2 declared in D2. To eliminate this
context sensitivity, the declaration
struct s2;
may be inserted ahead of D1. This declares a new tag s2 in
the inner scope; the declaration D2 then completes the
specification of the new type.
*
Forward references: declarators (6.7.5), array declarators
(6.7.5.2), type definitions (6.7.7).
6.7.3 Type qualifiers
Syntax
[#1]
type-qualifier:
const
restrict
volatile
Constraints
[#2] Types other than pointer types derived from object or
incomplete types shall not be restrict-qualified.
Semantics
[#3] The properties associated with qualified types are
meaningful only for expressions that are lvalues.101)
[#4] If the same qualifier appears more than once in the
6.7.2.3 Language 6.7.3
118 Committee Draft -- August 3, 1998 WG14/N843
same specifier-qualifier-list, either directly or via one or
more typedefs, the behavior is the same as if it appeared
only once.
[#5] If an attempt is made to modify an object defined with
a const-qualified type through use of an lvalue with non-
const-qualified type, the behavior is undefined. If an
attempt is made to refer to an object defined with a
volatile-qualified type through use of an lvalue with non-
volatile-qualified type, the behavior is undefined.102)
[#6] An object that has volatile-qualified type may be
modified in ways unknown to the implementation or have other
unknown side effects. Therefore any expression referring to
such an object shall be evaluated strictly according to the
rules of the abstract machine, as described in 5.1.2.3.
Furthermore, at every sequence point the value last stored
in the object shall agree with that prescribed by the
abstract machine, except as modified by the unknown factors
mentioned previously.103) What constitutes an access to an
object that has volatile-qualified type is implementation-
defined.
[#7] An object that is accessed through a restrict-qualified |
pointer has a special association with that pointer. This
association, defined in 6.7.3.1 below, requires that all |
accesses to that object use, directly or indirectly, the |
value of that particular pointer.104) The intended use of
the restrict qualifier (like the register storage class) is
to promote optimization, and deleting all instances of the
qualifier from a conforming program does not change its
____________________
101The implementation may place a const object that is not
volatile in a read-only region of storage. Moreover, the
implementation need not allocate storage for such an
object if its address is never used.
102This applies to those objects that behave as if they were
defined with qualified types, even if they are never
actually defined as objects in the program (such as an
object at a memory-mapped input/output address).
103A volatile declaration may be used to describe an object
corresponding to a memory-mapped input/output port or an
object accessed by an asynchronously interrupting
function. Actions on objects so declared shall not be
``optimized out'' by an implementation or reordered
except as permitted by the rules for evaluating
expressions.
104For example, a statement that assigns a value returned by |
malloc to a single pointer establishes this association |
between the allocated object and the pointer. ||
6.7.3 Language 6.7.3
WG14/N843 Committee Draft -- August 3, 1998 119
meaning (i.e., observable behavior).
[#8] If the specification of an array type includes any type
qualifiers, the element type is so-qualified, not the array
type. If the specification of a function type includes any
type qualifiers, the behavior is undefined.105)
[#9] For two qualified types to be compatible, both shall
have the identically qualified version of a compatible type;
the order of type qualifiers within a list of specifiers or
qualifiers does not affect the specified type.
[#10] EXAMPLE 1 An object declared
extern const volatile int real_time_clock;
may be modifiable by hardware, but cannot be assigned to,
incremented, or decremented.
[#11] EXAMPLE 2 The following declarations and expressions
illustrate the behavior when type qualifiers modify an
aggregate type:
const struct s { int mem; } cs = { 1 };
struct s ncs; // the object ncs is modifiable
typedef int A[2][3];
const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of
// const int
int *pi;
const int *pci;
ncs = cs; // valid
cs = ncs; // violates modifiable lvalue constraint for =
pi = &ncs.mem; // valid
pi = &cs.mem; // violates type constraints for =
pci = &cs.mem; // valid
pi = a[0]; // invalid: a[0] has type ``const int *''
6.7.3.1 Formal definition of restrict
[#1] Let D be a declaration of an ordinary identifier that
provides a means of designating an object P as a restrict-
qualified pointer.
[#2] If D appears inside a block and does not have storage
class extern, let B denote the block. If D appears in the
list of parameter declarations of a function definition, let
B denote the associated block. Otherwise, let B denote the
____________________ |
105Both of these can occur through the use of typedefs. ||
6.7.3 Language 6.7.3.1
120 Committee Draft -- August 3, 1998 WG14/N843
block of main (or the block of whatever function is called
at program startup in a freestanding environment).
[#3] In what follows, a pointer expression E is said to be
based on object P if (at some sequence point in the
execution of B prior to the evaluation of E) modifying P to
point to a copy of the array object into which it formerly
pointed would change the value of E.106) Note that |
``based'' is defined only for expressions with pointer
types.
[#4] During each execution of B, let A be the array object
that is determined dynamically by all accesses through |
pointer expressions based on P. Then all accesses to values |
of A shall be through pointer expressions based on P.
Furthermore, if P is assigned the value of a pointer
expression E that is based on another restricted pointer
object P2, associated with block B2, then either the
execution of B2 shall begin before the execution of B, or
the execution of B2 shall end prior to the assignment. If
these requirements are not met, then the behavior is
undefined.
[#5] Here an execution of B means that portion of the
execution of the program during which storage is guaranteed
to be reserved for an instance of an object that is
associated with B and that has automatic storage duration. |
An access to a value means either fetching it or modifying |
it; expressions that are not evaluated do not access values.
[#6] A translator is free to ignore any or all aliasing
implications of uses of restrict.
[#7] EXAMPLE 1 The file scope declarations
int * restrict a;
int * restrict b;
extern int c[];
assert that if an object is accessed using the value of one |
of a, b, or c, then it is never accessed using the value of |
either of the other two.
[#8] EXAMPLE 2 The function parameter declarations in the
following example
____________________ |
106In other words, E depends on the value of P itself rather ||
than on the value of an object referenced indirectly ||
through P. For example, if identifier p has type (int ||
**restrict), then the pointer expressions p and p+1 are ||
based on the restricted pointer object designated by p, ||
but the pointer expressions *p and p[1] are not. ||
6.7.3.1 Language 6.7.3.1
WG14/N843 Committee Draft -- August 3, 1998 121
void f(int n, int * restrict p, int * restrict q)
{
while (n-- > 0)
*p++ = *q++;
}
assert that, during each execution of the function, if an |
object is accessed through one of the pointer parameters, |
then it is not also accessed through the other.
[#9] The benefit of the restrict qualifiers is that they
enable a translator to make an effective dependence analysis
of function f without examining any of the calls of f in the
program. The cost is that the programmer has to examine all
of those calls to ensure that none give undefined behavior.
For example, the second call of f in g has undefined
behavior because each of d[1] through d[49] is accessed |
through both p and q.
void g(void)
{
extern int d[100]; |
f(50, d + 50, d); // ok
f(50, d + 1, d); // undefined behavior
}
[#10] EXAMPLE 3 The function parameter declarations
void h(int n, int * const restrict p,
int * const q, int * const r)
{
int i;
for (i = 0; i < n; i++)
p[i] = q[i] + r[i];
}
show how const can be used in conjunction with restrict.
The const qualifiers imply, without the need to examine the
body of h, that q and r cannot become based on p. The fact
that p is restrict-qualified therefore implies that an |
object accessed through p is never accessed through either |
of q or r. This is the precise assertion required to
optimize the loop. Note that a call of the form h(100, a,
b, b) has defined behavior, which would not be true if all
three of p, q, and r were restrict-qualified.
[#11] EXAMPLE 4 The rule limiting assignments between
restricted pointers does not distinguish between a function
call and an equivalent nested block. With one exception,
only ``outer-to-inner'' assignments between restricted
pointers declared in nested blocks have defined behavior.
6.7.3.1 Language 6.7.3.1
122 Committee Draft -- August 3, 1998 WG14/N843
{
int * restrict p1;
int * restrict q1;
p1 = q1; // undefined behavior
{
int * restrict p2 = p1; // ok
int * restrict q2 = q1; // ok
p1 = q2; // undefined behavior
p2 = q2; // undefined behavior
}
}
The exception allows the value of a restricted pointer to be
carried out of the block in which it (or, more precisely,
the ordinary identifier used to designate it) is declared
when that block finishes execution. For example, this
permits new_vector to return a vector.
typedef struct { int n; float * restrict v; } vector;
vector new_vector(int n)
{
vector t;
t.n = n;
t.v = malloc(n * sizeof (float));
return t;
}
6.7.4 Function specifiers
Syntax
[#1]
function-specifier:
inline
Constraints
[#2] Function specifiers shall be used only in the
declaration of an identifier for a function.
[#3] An inline definition of a function with external |
linkage shall not contain a definition of a modifiable |
object with static storage duration, and shall not contain a |
reference to an identifier with internal linkage.
[#4] The inline function specifier shall not appear in a
declaration of main.
Semantics
[#5] A function declared with an inline function specifier
6.7.3.1 Language 6.7.4
WG14/N843 Committee Draft -- August 3, 1998 123
is an inline function. (The function specifier may appear |
more than once; the behavior is the same as if it appeared |
only once.) Making a function an inline function suggests
that calls to the function be as fast as possible.107) The |
extent to which such suggestions are effective is
implementation-defined.108)
[#6] Any function with internal linkage can be an inline
function. For a function with external linkage, the
following restrictions apply: If a function is declared with |
an inline function specifier, then it shall also be defined
in the same translation unit. If all of the file scope
declarations for a function in a translation unit include
the inline function specifier without extern, then the
definition in that translation unit is an inline definition.
An inline definition does not provide an external definition
for the function, and does not forbid an external definition
in another translation unit. An inline definition provides
an alternative to an external definition, which a translator
may use to implement any call to the function in the same
translation unit. It is unspecified whether a call to the
function uses the inline definition or the external |
definition.109)
[#7] EXAMPLE The declaration of an inline function with
external linkage can result in either an external
definition, or a definition available for use only within
the translation unit. A file scope declaration with extern
creates an external definition. The following example shows
an entire translation unit.
____________________
107By using, for example, an alternative to the usual |
function call mechanism, such as ``inline substitution''. |
Inline substitution is not textual substitution, nor does
it create a new function. Therefore, for example, the
expansion of a macro used within the body of the function
uses the definition it had at the point the function body
appears, and not where the function is called; and
identifiers refer to the declarations in scope where the
body occurs. Similarly, the address of the function is
not affected by the function's being inlined.
108For example, an implementation might never perform inline
substitution, or might only perform inline substitutions
to calls in the scope of an inline declaration.
109Since an inline definition is distinct from the
corresponding external definition, and from any other
corresponding inline definition in another translation
unit, all corresponding objects with static storage
duration are also distinct in each of the definitions.
6.7.4 Language 6.7.4
124 Committee Draft -- August 3, 1998 WG14/N843
inline double fahr(double t)
{
return (9.0 * t) / 5.0 + 32.0;
}
inline double cels(double t)
{
return (5.0 * (t - 32.0)) / 9.0;
}
extern double fahr(double); // creates an external definition|
double convert(int is_fahr, double temp)
{
/* A translator may perform inline substitutions. */
return is_fahr ? cels(temp) : fahr(temp);
}
[#8] Note that the definition of fahr is an external
definition because fahr is also declared with extern, but
the definition of cels is an inline definition. Because |
cels has external linkage and is referenced, an external |
definition has to appear in another translation unit (see |
6.9); the inline definition and the external definition are |
distinct and either may be used for the call.
6.7.5 Declarators
Syntax
[#1]
declarator:
pointer-opt direct-declarator
direct-declarator:
identifier
( declarator )
direct-declarator [ assignment-expression-opt ]
direct-declarator [ * ]
direct-declarator ( parameter-type-list )
direct-declarator ( identifier-list-opt )
pointer:
* type-qualifier-list-opt
* type-qualifier-list-opt pointer
type-qualifier-list:
type-qualifier
type-qualifier-list type-qualifier
6.7.4 Language 6.7.5
WG14/N843 Committee Draft -- August 3, 1998 125
parameter-type-list:
parameter-list
parameter-list , ...
parameter-list:
parameter-declaration
parameter-list , parameter-declaration
parameter-declaration:
declaration-specifiers declarator
declaration-specifiers abstract-declarator-opt
identifier-list:
identifier
identifier-list , identifier
Semantics
[#2] Each declarator declares one identifier, and asserts
that when an operand of the same form as the declarator
appears in an expression, it designates a function or object
with the scope, storage duration, and type indicated by the
declaration specifiers.
[#3] A full declarator is a declarator that is not part of
another declarator. The end of a full declarator is a
sequence point. If the nested sequence of declarators in a
full declarator contains a variable length array type, the
type specified by the full declarator is said to be variably
modified.
[#4] In the following subclauses, consider a declaration
T D1
where T contains the declaration specifiers that specify a
type T (such as int) and D1 is a declarator that contains an
identifier ident. The type specified for the identifier
ident in the various forms of declarator is described
inductively using this notation.
[#5] If, in the declaration ``T D1'', D1 has the form
identifier
then the type specified for ident is T.
[#6] If, in the declaration ``T D1'', D1 has the form
( D )
then ident has the type specified by the declaration ``T
D''. Thus, a declarator in parentheses is identical to the
unparenthesized declarator, but the binding of complicated
6.7.5 Language 6.7.5
126 Committee Draft -- August 3, 1998 WG14/N843
declarators may be altered by parentheses.
Implementation limits
[#7] As discussed in 5.2.4.1, an implementation may limit |
the number of pointer, array, and function declarators that |
modify an arithmetic, structure, union, or incomplete type,
either directly or via one or more typedefs.
Forward references: array declarators (6.7.5.2), type
definitions (6.7.7).
6.7.5.1 Pointer declarators
Semantics
[#1] If, in the declaration ``T D1'', D1 has the form
* type-qualifier-list-opt D
and the type specified for ident in the declaration ``T D''
is ``derived-declarator-type-list T'', then the type
specified for ident is ``derived-declarator-type-list type-
qualifier-list pointer to T''. For each type qualifier in
the list, ident is a so-qualified pointer.
[#2] For two pointer types to be compatible, both shall be
identically qualified and both shall be pointers to
compatible types.
[#3] EXAMPLE The following pair of declarations
demonstrates the difference between a ``variable pointer to
a constant value'' and a ``constant pointer to a variable
value''.
const int *ptr_to_constant;
int *const constant_ptr;
The contents of any object pointed to by ptr_to_constant |
shall not be modified through that pointer, but
ptr_to_constant itself may be changed to point to another
object. Similarly, the contents of the int pointed to by
constant_ptr may be modified, but constant_ptr itself shall
always point to the same location.
[#4] The declaration of the constant pointer constant_ptr
may be clarified by including a definition for the type
``pointer to int''.
typedef int *int_ptr;
const int_ptr constant_ptr;
declares constant_ptr as an object that has type ``const-
qualified pointer to int''.
6.7.5 Language 6.7.5.1
WG14/N843 Committee Draft -- August 3, 1998 127
6.7.5.2 Array declarators
Constraints
[#1] The [ and ] may delimit an expression or *. If [ and ]
delimit an expression (which specifies the size of an
array), it shall have an integer type. If the expression is
a constant expression then it shall have a value greater
than zero. The element type shall not be an incomplete or
function type.
[#2] Only ordinary identifiers (as defined in 6.2.3) with |
both block scope or function prototype scope and no linkage |
shall have a variably modified type. If an identifier is
declared to be an object with static storage duration, it
shall not have a variable length array type.
Semantics
[#3] If, in the declaration ``T D1'', D1 has the form
D[assignment-expr-opt]
or
D[*]
and the type specified for ident in the declaration ``T D''
is ``derived-declarator-type-list T'', then the type
specified for ident is ``derived-declarator-type-list array
of T''.110) If the size is not present, the array type is
an incomplete type. If * is used instead of a size
expression, the array type is a variable length array type
of unspecified size, which can only be used in declarations |
with function prototype scope.111) If the size expression
is an integer constant expression and the element type has a
known constant size, the array type is not a variable length
array type; otherwise, the array type is a variable length |
array type. If the size expression is not a constant
expression, and it is evaluated at program execution time,
it shall evaluate to a value greater than zero. It is
unspecified whether side effects are produced when the size
expression is evaluated. The size of each instance of a
variable length array type does not change during its
lifetime.
____________________
110When several ``array of'' specifications are adjacent, a
multidimensional array is declared.
111Thus, * can be used only in function declarations that
are not definitions (see 6.7.5.3).
6.7.5.1 Language 6.7.5.2
128 Committee Draft -- August 3, 1998 WG14/N843
[#4] For two array types to be compatible, both shall have
compatible element types, and if both size specifiers are
present, and are integer constant expressions, then both
size specifiers shall have the same constant value. If the
two array types are used in a context which requires them to
be compatible, it is undefined behavior if the two size
specifiers evaluate to unequal values.
[#5] EXAMPLE 1
float fa[11], *afp[17];
declares an array of float numbers and an array of pointers
to float numbers.
[#6] EXAMPLE 2 Note the distinction between the declarations
extern int *x;
extern int y[];
The first declares x to be a pointer to int; the second
declares y to be an array of int of unspecified size (an
incomplete type), the storage for which is defined
elsewhere.
[#7] EXAMPLE 3 The following declarations demonstrate the
compatibility rules for variably modified types.
extern int n;
extern int m;
void fcompat(void)
{
int a[n][6][m];
int (*p)[4][n+1];
int c[n][n][6][m];
int (*r)[n][n][n+1];
p = a; // Error - not compatible because 4 != 6.
r = c; // Compatible, but defined behavior
// only if n == 6 and m == n+1.
}
[#8] EXAMPLE 4 All declarations of variably modified (VM)
types have to be at either block scope or function prototype
scope. Array objects declared with the static or extern
storage class specifier cannot have a variable length array
(VLA) type. However, an object declared with the static
storage class specifier can have a VM type (that is, a
pointer to a VLA type). Finally, all identifiers declared |
with a VM type have to be ordinary identifiers and cannot, |
therefore, be members of structures or unions.
6.7.5.2 Language 6.7.5.2
WG14/N843 Committee Draft -- August 3, 1998 129
extern int n;
int A[n]; // Error - file scope VLA.
extern int (*p2)[n]; // Error - file scope VM.
int B[100]; // OK - file scope but not VM.
void fvla(int m, int C[m][m]) // OK - VLA with prototype scope.
{
typedef int VLA[m][m] // OK - block scope typedef VLA.
struct tag {
int (*y)[n]; // Error - y not ordinary identifier.
int z[n]; // Error - z not ordinary identifier.
};
int D[m]; // OK - auto VLA.
static int E[m]; // Error - static block scope VLA.
extern int F[m]; // Error - F has linkage and is VLA.
int (*s)[m]; // OK - auto pointer to VLA.
extern int (*r)[m]; // Error - r had linkage and is
// a pointer to VLA.
static int (*q)[m] = &B; // OK - q is a static block
// pointer to VLA.
}
Forward references: function declarators (6.7.5.3), |
function definitions (6.9.1), initialization (6.7.8).
6.7.5.3 Function declarators (including prototypes)
Constraints
[#1] A function declarator shall not specify a return type
that is a function type or an array type.
[#2] The only storage-class specifier that shall occur in a
parameter declaration is register.
[#3] An identifier list in a function declarator that is not |
part of a definition of that function shall be empty.
[#4] After adjustment, the parameters in a parameter type |
list in a function declarator that is part of a definition |
of that function shall not have incomplete type.112)
Semantics
[#5] If, in the declaration ``T D1'', D1 has the form
____________________
112Arrays and functions are rewritten as pointers.
6.7.5.2 Language 6.7.5.3
130 Committee Draft -- August 3, 1998 WG14/N843
D(parameter-type-list)
or
D(identifier-list-opt)
and the type specified for ident in the declaration ``T D''
is ``derived-declarator-type-list T'', then the type
specified for ident is ``derived-declarator-type-list
function returning T''.
[#6] A parameter type list specifies the types of, and may
declare identifiers for, the parameters of the function. A |
declaration of a parameter as ``array of type'' shall be |
adjusted to ``pointer to type'', and a declaration of a |
parameter as ``function returning type'' shall be adjusted |
to ``pointer to function returning type'', as in 6.3.2.1.
If the list terminates with an ellipsis (, ...), no
information about the number or types of the parameters
after the comma is supplied.113) The special case of an
unnamed parameter of type void as the only item in the list
specifies that the function has no parameters.
[#7] If, in a parameter declaration, an identifier can be
treated as a typedef name or as a parameter name, it shall
be taken as a typedef name.
[#8] If the function declarator is not part of a definition |
of that function, parameters may have incomplete type and |
may use the [*] notation in their sequences of declarator |
specifiers to specify variable length array types.
[#9] The storage-class specifier in the declaration
specifiers for a parameter declaration, if present, is
ignored unless the declared parameter is one of the members
of the parameter type list for a function definition.
[#10] An identifier list declares only the identifiers of
the parameters of the function. An empty list in a function
declarator that is part of a definition of that function |
specifies that the function has no parameters. The empty
list in a function declarator that is not part of a |
definition of that function specifies that no information
about the number or types of the parameters is
supplied.114)
[#11] For two function types to be compatible, both shall
specify compatible return types.115) Moreover, the
parameter type lists, if both are present, shall agree in
the number of parameters and in use of the ellipsis
terminator; corresponding parameters shall have compatible
types. If one type has a parameter type list and the other
type is specified by a function declarator that is not part
of a function definition and that contains an empty
identifier list, the parameter list shall not have an
ellipsis terminator and the type of each parameter shall be
compatible with the type that results from the application
of the default argument promotions. If one type has a
parameter type list and the other type is specified by a
function definition that contains a (possibly empty)
identifier list, both shall agree in the number of
WG14/N843 Committee Draft -- August 3, 1998 131
parameters, and the type of each prototype parameter shall
be compatible with the type that results from the
application of the default argument promotions to the type
of the corresponding identifier. (In the determination of
type compatibility and of a composite type, each parameter
declared with function or array type is taken as having the |
adjusted type and each parameter declared with qualified
type is taken as having the unqualified version of its
declared type.)
[#12] EXAMPLE 1 The declaration
int f(void), *fip(), (*pfi)();
declares a function f with no parameters returning an int, a
function fip with no parameter specification returning a
pointer to an int, and a pointer pfi to a function with no
parameter specification returning an int. It is especially
useful to compare the last two. The binding of *fip() is
*(fip()), so that the declaration suggests, and the same
construction in an expression requires, the calling of a
function fip, and then using indirection through the pointer
result to yield an int. In the declarator (*pfi)(), the
extra parentheses are necessary to indicate that indirection
through a pointer to a function yields a function
designator, which is then used to call the function; it
returns an int.
[#13] If the declaration occurs outside of any function, the
identifiers have file scope and external linkage. If the
declaration occurs inside a function, the identifiers of the
functions f and fip have block scope and either internal or
external linkage (depending on what file scope declarations
for these identifiers are visible), and the identifier of
the pointer pfi has block scope and no linkage.
[#14] EXAMPLE 2 The declaration
int (*apfi[3])(int *x, int *y);
declares an array apfi of three pointers to functions
returning int. Each of these functions has two parameters
that are pointers to int. The identifiers x and y are
declared for descriptive purposes only and go out of scope
____________________
113The macros defined in the <stdarg.h> header (7.15) may be
used to access arguments that correspond to the ellipsis.
114See ``future language directions'' (6.11.3).
115If both function types are ``old style'', parameter types
are not compared.
6.7.5.3 Language 6.7.5.3
132 Committee Draft -- August 3, 1998 WG14/N843
at the end of the declaration of apfi.
[#15] EXAMPLE 3 The declaration
int (*fpfi(int (*)(long), int))(int, ...);
declares a function fpfi that returns a pointer to a
function returning an int. The function fpfi has two
parameters: a pointer to a function returning an int (with
one parameter of type long int), and an int. The pointer
returned by fpfi points to a function that has one int
parameter and accepts zero or more additional arguments of
any type.
[#16] EXAMPLE 4 The following prototype has a variably
modified parameter.
void addscalar(int n, int m,
double a[n][n*m+300], double x);
int main()
{
double b[4][308];
addscalar(4, 2, b, 2.17);
return 0;
}
void addscalar(int n, int m,
double a[n][n*m+300], double x)
{
for (int i = 0; i < n; i++)
for (int j = 0, k = n*m+300; j < k; j++)
// a is a pointer to a VLA
// with n*m+300 elements
a[i][j] += x;
}
[#17] EXAMPLE 5 The following are all compatible function
prototype declarators.
double maximum(int n, int m, double a[n][m]);
double maximum(int n, int m, double a[*][*]);
double maximum(int n, int m, double a[ ][*]);
double maximum(int n, int m, double a[ ][m]);
Forward references: function definitions (6.9.1), type
names (6.7.6).
6.7.5.3 Language 6.7.5.3
WG14/N843 Committee Draft -- August 3, 1998 133
6.7.6 Type names
Syntax
[#1]
type-name:
specifier-qualifier-list abstract-declarator-opt
abstract-declarator:
pointer
pointer-opt direct-abstract-declarator
direct-abstract-declarator:
( abstract-declarator )
direct-abstract-declarator-opt [ assignment-expression-opt ]
direct-abstract-declarator-opt [ * ]
direct-abstract-declarator-opt ( parameter-type-list-opt )
Semantics
[#2] In several contexts, it is necessary to specify a type. |
This is accomplished using a type name, which is
syntactically a declaration for a function or an object of
that type that omits the identifier.116)
[#3] EXAMPLE The constructions
(a) int
(b) int *
(c) int *[3]
(d) int (*)[3]
(e) int (*)[*] |
(f) int *() |
(g) int (*)(void) |
(h) int (*const [])(unsigned int, ...) |
name respectively the types (a) int, (b) pointer to int, (c)
array of three pointers to int, (d) pointer to an array of
three ints, (e) pointer to a variable length array of an |
unspecified number of ints, (f) function with no parameter
specification returning a pointer to int, (g) pointer to |
function with no parameters returning an int, and (h) array |
of an unspecified number of constant pointers to functions,
each with one parameter that has type unsigned int and an
unspecified number of other parameters, returning an int.
____________________
116As indicated by the syntax, empty parentheses in a type
name are interpreted as ``function with no parameter
specification'', rather than redundant parentheses around
the omitted identifier.
6.7.6 Language 6.7.6
134 Committee Draft -- August 3, 1998 WG14/N843
6.7.7 Type definitions
Syntax
[#1]
typedef-name:
identifier
Constraints
[#2] If a typedef name specifies a variably modified type
then it shall have block scope.
Semantics
[#3] In a declaration whose storage-class specifier is
typedef, each declarator defines an identifier to be a |
typedef name that denotes the type specified for the
identifier in the way described in 6.7.5. Any array size
expressions associated with variable length array |
declarators are evaluated each time the declaration of the |
typedef name is reached in the order of execution. A
typedef declaration does not introduce a new type, only a
synonym for the type so specified. That is, in the
following declarations:
typedef T type_ident;
type_ident D;
type_ident is defined as a typedef name with the type
specified by the declaration specifiers in T (known as T),
and the identifier in D has the type ``derived-declarator-
type-list T'' where the derived-declarator-type-list is
specified by the declarators of D. A typedef name shares
the same name space as other identifiers declared in
ordinary declarators. *
[#4] EXAMPLE 1 After
typedef int MILES, KLICKSP();
typedef struct { double hi, lo; } range;
the constructions
MILES distance;
extern KLICKSP *metricp;
range x;
range z, *zp;
are all valid declarations. The type of distance is int,
that of metricp is ``pointer to function with no parameter
specification returning int'', and that of x and z is the
specified structure; zp is a pointer to such a structure.
6.7.7 Language 6.7.7
WG14/N843 Committee Draft -- August 3, 1998 135
The object distance has a type compatible with any other int
object.
[#5] EXAMPLE 2 After the declarations
typedef struct s1 { int x; } t1, *tp1;
typedef struct s2 { int x; } t2, *tp2;
type t1 and the type pointed to by tp1 are compatible. Type
t1 is also compatible with type struct s1, but not
compatible with the types struct s2, t2, the type pointed to
by tp2, or int. |
[#6] EXAMPLE 3 The following obscure constructions
typedef signed int t;
typedef int plain;
struct tag {
unsigned t:4;
const t:5;
plain r:5;
};
declare a typedef name t with type signed int, a typedef
name plain with type int, and a structure with three bit-
field members, one named t that contains values in the range
[0, 15], an unnamed const-qualified bit-field which (if it
could be accessed) would contain values in at least the
range [-15, +15], and one named r that contains values in
the range [0, 31] or values in at least the range [-15,
+15]. (The choice of range is implementation-defined.) The
first two bit-field declarations differ in that unsigned is
a type specifier (which forces t to be the name of a
structure member), while const is a type qualifier (which
modifies t which is still visible as a typedef name). If
these declarations are followed in an inner scope by
t f(t (t));
long t;
then a function f is declared with type ``function returning
signed int with one unnamed parameter with type pointer to
function returning signed int with one unnamed parameter
with type signed int'', and an identifier t with type long
int.
[#7] EXAMPLE 4 On the other hand, typedef names can be used
to improve code readability. All three of the following
declarations of the signal function specify exactly the same
type, the first without making use of any typedef names.
6.7.7 Language 6.7.7
136 Committee Draft -- August 3, 1998 WG14/N843
typedef void fv(int), (*pfv)(int);
void (*signal(int, void (*)(int)))(int);
fv *signal(int, fv *);
pfv signal(int, pfv);
[#8] EXAMPLE 5 If a typedef name denotes a variable length |
array type, the length of the array is fixed at the time the |
typedef name is defined, not each time it is used:
void copyt(int n)
{
typedef int B[n]; // B is n ints, n evaluated now.|
n += 1;
B a; // a is n ints, n without += 1.|
int b[n]; // a and b are different sizes|
for (int i = 1; i < n; i++) |
a[i-1] = b[i]; |
}
Forward references: the signal function (7.14.1.1).
6.7.8 Initialization
Syntax
[#1]
initializer:
assignment-expression
{ initializer-list }
{ initializer-list , }
initializer-list:
designation-opt initializer
initializer-list , designation-opt initializer
designation:
designator-list =
designator-list:
designator
designator-list designator
designator:
[ constant-expression ]
. identifier
Constraints
6.7.7 Language 6.7.8
WG14/N843 Committee Draft -- August 3, 1998 137
[#2] No initializer shall attempt to provide a value for an
object not contained within the entity being initialized.
[#3] The type of the entity to be initialized shall be an
array of unknown size or an object type that is not a
variable length array type.
[#4] All the expressions in an initializer for an object
that has static storage duration shall be constant
expressions or string literals.
[#5] If the declaration of an identifier has block scope,
and the identifier has external or internal linkage, the
declaration shall have no initializer for the identifier.
[#6] If a designator has the form
[ constant-expression ]
then the current object (defined below) shall have array
type and the expression shall be an integer constant
expression. If the array is of unknown size, any
nonnegative value is valid.
[#7] If a designator has the form
. identifier
then the current object (defined below) shall have structure
or union type and the identifier shall be the name of a |
member of that type.
Semantics
[#8] An initializer specifies the initial value stored in an
object.
[#9] Except where explicitly stated otherwise, for the
purposes of this subclause unnamed members of objects of
structure and union type do not participate in
initialization. Unnamed members of structure objects have
indeterminate value even after initialization. *
[#10] If an object that has automatic storage duration is
not initialized explicitly, its value is indeterminate. If
an object that has static storage duration is not
initialized explicitly, then:
-- if it has pointer type, it is initialized to a null
pointer;
-- if it has arithmetic type, it is initialized to |
(positive or unsigned) zero;
6.7.8 Language 6.7.8
138 Committee Draft -- August 3, 1998 WG14/N843
-- if it is an aggregate, every member is initialized
(recursively) according to these rules;
-- if it is a union, the first named member is initialized
(recursively) according to these rules.
[#11] The initializer for a scalar shall be a single
expression, optionally enclosed in braces. The initial
value of the object is that of the expression (after
conversion); the same type constraints and conversions as
for simple assignment apply, taking the type of the scalar
to be the unqualified version of its declared type.
[#12] The rest of this subclause deals with initializers for |
objects that have aggregate or union type. |
[#13] The initializer for a structure or union object that |
has automatic storage duration shall be either an |
initializer list as described below, or a single expression |
that has compatible structure or union type. In the latter |
case, the initial value of the object, including unnamed |
members, is that of the expression. |
[#14] An array of character type may be initialized by a |
character string literal, optionally enclosed in braces. |
Successive characters of the character string literal |
(including the terminating null character if there is room |
or if the array is of unknown size) initialize the elements |
of the array. |
[#15] An array with element type compatible with wchar_t may |
be initialized by a wide string literal, optionally enclosed |
in braces. Successive wide characters of the wide string |
literal (including the terminating null wide character if |
there is room or if the array is of unknown size) initialize |
the elements of the array. |
[#16] Otherwise, the initializer for an object that has |
aggregate or union type shall be a brace-enclosed list of |
initializers for the elements or named members. |
[#17] Each brace-enclosed initializer list has an associated
current object. When no designations are present, subobjects
of the current object are initialized in order according to
the type of the current object: array elements in increasing
subscript order, structure members in declaration order, and
the first named member of a union.117) In contrast, a
designation causes the following initializer to begin
initialization of the subobject described by the designator.
Initialization then continues forward in order, beginning
with the next subobject after that described by the
designator.118)
[#18] Each designator list begins its description with the
current object associated with the closest surrounding brace
pair. Each item in the designator list (in order) specifies
a particular member of its current object and changes the
current object for the next designator (if any) to be that
member.119) The current object that results at the end of
WG14/N843 Committee Draft -- August 3, 1998 139
the designator list is the subobject to be initialized by
the following initializer.
[#19] The initialization shall occur in initializer list
order, each initializer provided for a particular subobject
overriding any previously listed initializer for the same
subobject; all subobjects that are not initialized
explicitly shall be initialized implicitly the same as
objects that have static storage duration.
[#20] If the aggregate contains elements or members that are |
aggregates or unions, or if the first member of a union is
an aggregate or union, these rules apply recursively to the |
subaggregates or contained unions. If the initializer of a
subaggregate or contained union begins with a left brace,
the initializers enclosed by that brace and its matching
right brace initialize the elements or members of the |
subaggregate or the first member of the contained union.
Otherwise, only enough initializers from the list are taken
to account for the elements or members of the subaggregate |
or the first member of the contained union; any remaining
initializers are left to initialize the next element or |
member of the aggregate of which the current subaggregate or
contained union is a part.
[#21] If there are fewer initializers in a brace-enclosed
list than there are elements or members of an aggregate, or |
fewer characters in a string literal used to initialize an
array of known size than there are elements in the array,
the remainder of the aggregate shall be initialized
implicitly the same as objects that have static storage
duration.
[#22] If an array of unknown size is initialized, its size
is determined by the largest indexed element with an
explicit initializer. At the end of its initializer list,
the array no longer has incomplete type.
[#23] The order in which any side effects occur among the
initialization list expressions is unspecified.120)
____________________
118After a union member is initialized, the next object is
not the next member of the union; instead, it is the next
subobject of an object containing the union.
119Thus, a designator can only specify a strict subobject of
the aggregate or union that is associated with the
surrounding brace pair. Note, too, that each separate
designator list is independent.
120In particular, the evaluation order need not be the same
as the order of subobject initialization.
6.7.8 Language 6.7.8
140 Committee Draft -- August 3, 1998 WG14/N843
[#24] EXAMPLE 1 Provided that <complex.h> has been
#included, the declarations
int i = 3.5;
complex c = 5 + 3 * I;
define and initialize i with the value 3 and c with the
value 5.0+3.0i.
[#25] EXAMPLE 2 The declaration
int x[] = { 1, 3, 5 };
defines and initializes x as a one-dimensional array object
that has three elements, as no size was specified and there
are three initializers.
[#26] EXAMPLE 3 The declaration
int y[4][3] = {
{ 1, 3, 5 },
{ 2, 4, 6 },
{ 3, 5, 7 },
};
is a definition with a fully bracketed initialization: 1, 3,
and 5 initialize the first row of y (the array object y[0]),
namely y[0][0], y[0][1], and y[0][2]. Likewise the next two
lines initialize y[1] and y[2]. The initializer ends early,
so y[3] is initialized with zeros. Precisely the same
effect could have been achieved by
int y[4][3] = {
1, 3, 5, 2, 4, 6, 3, 5, 7
};
The initializer for y[0] does not begin with a left brace,
so three items from the list are used. Likewise the next
three are taken successively for y[1] and y[2].
[#27] EXAMPLE 4 The declaration
int z[4][3] = {
{ 1 }, { 2 }, { 3 }, { 4 }
};
initializes the first column of z as specified and
initializes the rest with zeros.
[#28] EXAMPLE 5 The declaration
6.7.8 Language 6.7.8
WG14/N843 Committee Draft -- August 3, 1998 141
struct { int a[3], b; } w[] = { { 1 }, 2 };
is a definition with an inconsistently bracketed
initialization. It defines an array with two element
structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other
elements are zero.
[#29] EXAMPLE 6 The declaration
short q[4][3][2] = {
{ 1 },
{ 2, 3 },
{ 4, 5, 6 }
};
contains an incompletely but consistently bracketed
initialization. It defines a three-dimensional array
object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3,
and 4, 5, and 6 initialize q[2][0][0], q[2][0][1], and
q[2][1][0], respectively; all the rest are zero. The
initializer for q[0][0] does not begin with a left brace, so
up to six items from the current list may be used. There is
only one, so the values for the remaining five elements are
initialized with zero. Likewise, the initializers for
q[1][0] and q[2][0] do not begin with a left brace, so each
uses up to six items, initializing their respective two-
dimensional subaggregates. If there had been more than six
items in any of the lists, a diagnostic message would have
been issued. The same initialization result could have been
achieved by:
short q[4][3][2] = {
1, 0, 0, 0, 0, 0,
2, 3, 0, 0, 0, 0,
4, 5, 6
};
or by:
short q[4][3][2] = {
{
{ 1 },
},
{
{ 2, 3 },
},
{
{ 4, 5 },
{ 6 },
}
};
in a fully bracketed form.
6.7.8 Language 6.7.8
142 Committee Draft -- August 3, 1998 WG14/N843
[#30] Note that the fully bracketed and minimally bracketed
forms of initialization are, in general, less likely to
cause confusion.
[#31] EXAMPLE 7 One form of initialization that completes
array types involves typedef names. Given the declaration
typedef int A[]; // OK - declared with block scope
the declaration
A a = { 1, 2 }, b = { 3, 4, 5 };
is identical to
int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
due to the rules for incomplete types.
[#32] EXAMPLE 8 The declaration
char s[] = "abc", t[3] = "abc";
defines ``plain'' char array objects s and t whose elements
are initialized with character string literals. This
declaration is identical to
char s[] = { 'a', 'b', 'c', '\0' },
t[] = { 'a', 'b', 'c' };
The contents of the arrays are modifiable. On the other
hand, the declaration
char *p = "abc";
defines p with type ``pointer to char'' and initializes it |
to point to an object with type ``array of char'' with
length 4 whose elements are initialized with a character
string literal. If an attempt is made to use p to modify
the contents of the array, the behavior is undefined.
[#33] EXAMPLE 9 Arrays can be initialized to correspond to
the elements of an enumeration by using designators:
enum { member_one, member_two };
const char *nm[] = {
[member_two] = "member two",
[member_one] = "member one",
};
6.7.8 Language 6.7.8
WG14/N843 Committee Draft -- August 3, 1998 143
[#34] EXAMPLE 10 Structure members can be initialized to
nonzero values without depending on their order:
div_t answer = { .quot = 2, .rem = -1 };
[#35] EXAMPLE 11 Designators can be used to provide explicit
initialization when unadorned initializer lists might be
misunderstood:
struct { int a[3], b; } w[] =
{ [0].a = {1}, [1].a[0] = 2 };
[#36] EXAMPLE 12 Space can be ``allocated'' from both ends
of an array by using a single designator:
int a[MAX] = {
1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
};
[#37] In the above, if MAX is greater than ten, there will
be some zero-valued elements in the middle; if it is less
than ten, some of the values provided by the first five
initializers will be overridden by the second five.
[#38] EXAMPLE 13 Any member of a union can be initialized:
union { /* ... */ } u = { .any_member = 42 };
Forward references: common definitions <stddef.h> (7.17).
6.7.8 Language 6.7.8
144 Committee Draft -- August 3, 1998 WG14/N843
6.8 Statements
Syntax
[#1]
statement:
labeled-statement
compound-statement
expression-statement
selection-statement
iteration-statement
jump-statement
Semantics
[#2] A statement specifies an action to be performed.
Except as indicated, statements are executed in sequence.
[#3] A full expression is an expression that is not part of |
another expression or declarator. Each of the following is
a full expression: an initializer; the expression in an
expression statement; the controlling expression of a
selection statement (if or switch); the controlling
expression of a while or do statement; each of the
(optional) expressions of a for statement; the (optional)
expression in a return statement. The end of a full
expression is a sequence point.
Forward references: expression and null statements (6.8.3),
selection statements (6.8.4), iteration statements (6.8.5),
the return statement (6.8.6.4).
6.8.1 Labeled statements
Syntax
[#1]
labeled-statement:
identifier : statement
case constant-expr : statement
default : statement
Constraints
[#2] A case or default label shall appear only in a switch
statement. Further constraints on such labels are discussed
under the switch statement.
Semantics
[#3] Any statement may be preceded by a prefix that declares
an identifier as a label name. Labels in themselves do not
6.8 Language 6.8.1
WG14/N843 Committee Draft -- August 3, 1998 145
alter the flow of control, which continues unimpeded across
them.
Forward references: the goto statement (6.8.6.1), the
switch statement (6.8.4.2).
6.8.2 Compound statement, or block
Syntax
[#1]
compound-statement:
{ block-item-list-opt }
block-item-list:
block-item
block-item-list block-item
block-item:
declaration
statement
Semantics
[#2] A compound statement (also called a block) allows a set |
of declarations and statements to be grouped into one |
syntactic unit. The initializers of objects that have
automatic storage duration, and the variable length array
declarators of ordinary identifiers with block scope are
evaluated and the values are stored in the objects
(including storing an indeterminate value in objects without
an initializer) each time that the declaration is reached in
the order of execution, as if it were a statement, and
within each declaration in the order that declarators
appear.
6.8.3 Expression and null statements
Syntax
[#1]
expression-statement:
expression-opt ;
Semantics
[#2] The expression in an expression statement is evaluated
as a void expression for its side effects.121)
____________________
121Such as assignments, and function calls which have side
effects.
6.8.1 Language 6.8.3
146 Committee Draft -- August 3, 1998 WG14/N843
[#3] A null statement (consisting of just a semicolon)
performs no operations.
[#4] EXAMPLE 1 If a function call is evaluated as an
expression statement for its side effects only, the
discarding of its value may be made explicit by converting
the expression to a void expression by means of a cast:
int p(int);
/* ... */
(void)p(0);
[#5] EXAMPLE 2 In the program fragment
char *s;
/* ... */
while (*s++ != '\0')
;
a null statement is used to supply an empty loop body to the
iteration statement.
[#6] EXAMPLE 3 A null statement may also be used to carry a
label just before the closing } of a compound statement.
while (loop1) {
/* ... */
while (loop2) {
/* ... */
if (want_out)
goto end_loop1;
/* ... */
}
/* ... */
end_loop1: ;
}
Forward references: iteration statements (6.8.5).
6.8.4 Selection statements
Syntax
[#1]
6.8.3 Language 6.8.4
WG14/N843 Committee Draft -- August 3, 1998 147
selection-statement:
if ( expression ) statement
if ( expression ) statement else statement
switch ( expression ) statement
Semantics
[#2] A selection statement selects among a set of statements
depending on the value of a controlling expression.
6.8.4.1 The if statement
Constraints
[#1] The controlling expression of an if statement shall
have scalar type.
Semantics
[#2] In both forms, the first substatement is executed if
the expression compares unequal to 0. In the else form, the
second substatement is executed if the expression compares
equal to 0. If the first substatement is reached via a
label, the second substatement is not executed.
[#3] An else is associated with the lexically nearest
preceding if that is allowed by the syntax.
6.8.4.2 The switch statement
Constraints
[#1] The controlling expression of a switch statement shall |
have integer type. |
[#2] If the switch statement causes a jump to within the |
scope of an identifier with a variably modified type, the |
entire switch statement shall be within the scope of that |
identifier.122) |
[#3] The expression of each case label shall be an integer |
constant expression and no two of the case constant
expressions in the same switch statement shall have the same
value after conversion. There may be at most one default
label in a switch statement. (Any enclosed switch statement
may have a default label or case constant expressions with
values that duplicate case constant expressions in the
enclosing switch statement.)
____________________
122That is, the declaration either precedes the switch
statement, or it follows the last case or default label
associated with the switch that is in the block
containing the declaration.
6.8.4 Language 6.8.4.2
148 Committee Draft -- August 3, 1998 WG14/N843
Semantics
[#4] A switch statement causes control to jump to, into, or
past the statement that is the switch body, depending on the
value of a controlling expression, and on the presence of a
default label and the values of any case labels on or in the
switch body. A case or default label is accessible only
within the closest enclosing switch statement.
[#5] The integer promotions are performed on the controlling
expression. The constant expression in each case label is
converted to the promoted type of the controlling
expression. If a converted value matches that of the
promoted controlling expression, control jumps to the
statement following the matched case label. Otherwise, if
there is a default label, control jumps to the labeled
statement. If no converted case constant expression matches
and there is no default label, no part of the switch body is
executed.
Implementation limits
[#6] As discussed in 5.2.4.1, the implementation may limit |
the number of case values in a switch statement.
[#7] EXAMPLE In the artificial program fragment
switch (expr)
{
int i = 4;
f(i);
case 0:
i = 17;
/* falls through into default code */
default:
printf("%d\n", i);
}
the object whose identifier is i exists with automatic
storage duration (within the block) but is never
initialized, and thus if the controlling expression has a
nonzero value, the call to the printf function will access
an indeterminate value. Similarly, the call to the function
f cannot be reached.
6.8.4.2 Language 6.8.4.2
WG14/N843 Committee Draft -- August 3, 1998 149
6.8.5 Iteration statements
Syntax
[#1]
iteration-statement:
while ( expression ) statement
do statement while ( expression ) ;
for ( expr-opt ; expr-opt ; expr-opt ) statement
for ( declaration ; expr-opt ; expr-opt ) statement
Constraints
[#2] The controlling expression of an iteration statement
shall have scalar type.
[#3] The declaration part of a for statement shall only
declare identifiers for objects having storage class auto or
register.
Semantics
[#4] An iteration statement causes a statement called the
loop body to be executed repeatedly until the controlling
expression compares equal to 0.
6.8.5.1 The while statement
[#1] The evaluation of the controlling expression takes
place before each execution of the loop body.
6.8.5.2 The do statement
[#1] The evaluation of the controlling expression takes
place after each execution of the loop body.
6.8.5.3 The for statement
[#1] Except for the behavior of a continue statement in the |
loop body, the statement
for ( clause-1 ; expr-2 ; expr-3 ) statement
and the sequence of statements
{
clause-1 ;
while ( expr-2 ) {
statement
expr-3 ;
}
}
6.8.5 Language 6.8.5.3
150 Committee Draft -- August 3, 1998 WG14/N843
are equivalent (where clause-1 can be an expression or a
declaration).123) Unlike the other iteration statements, |
the for statement introduces new blocks that limit the scope |
of declarations and compound literals occurring in the loop.
[#2] Both clause-1 and expr-3 can be omitted. If clause-1 |
is an expression, it is evaluated as a void expression, as |
is expr-3. An omitted expr-2 is replaced by a nonzero
constant.
Forward references: the continue statement (6.8.6.2).
6.8.6 Jump statements
Syntax
[#1]
jump-statement:
goto identifier ;
continue ;
break ;
return expression-opt ;
Semantics
[#2] A jump statement causes an unconditional jump to
another place.
____________________
123Thus, clause-1 specifies initialization for the loop,
possibly declaring one or more variables for use in the
loop; expr-2, the controlling expression, specifies an
evaluation made before each iteration, such that
execution of the loop continues until the expression
compares equal to 0; expr-3 specifies an operation (such
as incrementing) that is performed after each iteration.
If clause-1 is a declaration, then the scope of any
variable it declares is the remainder of the declaration
and the entire loop, including the other two expressions.
6.8.5.3 Language 6.8.6
WG14/N843 Committee Draft -- August 3, 1998 151
6.8.6.1 The goto statement
Constraints
[#1] The identifier in a goto statement shall name a label
located somewhere in the enclosing function. A goto |
statement shall not jump from outside the scope of an |
identifier having a variably modified type to inside the |
scope of that identifier.
Semantics
[#2] A goto statement causes an unconditional jump to the
statement prefixed by the named label in the enclosing
function.
[#3] EXAMPLE 1 It is sometimes convenient to jump into the
middle of a complicated set of statements. The following
outline presents one possible approach to a problem based on
these three assumptions:
1. The general initialization code accesses objects only
visible to the current function.
2. The general initialization code is too large to
warrant duplication.
3. The code to determine the next operation is at the
head of the loop. (To allow it to be reached by
continue statements, for example.)
/* ... */
goto first_time;
for (;;) {
// determine next operation
/* ... */
if (need to reinitialize) {
// reinitialize-only code
/* ... */
first_time:
// general initialization code
/* ... */
continue;
}
// handle other operations
/* ... */
}
[#4] EXAMPLE 2 A goto statement is not allowed to jump past
any declarations of objects with variably modified types. A |
jump within the scope, however, is permitted.
6.8.6 Language 6.8.6.1
152 Committee Draft -- August 3, 1998 WG14/N843
goto lab3; // Error: going INTO scope of VLA.
{
double a[n];
a[j] = 4.4;
lab3:
a[j] = 3.3;
goto lab4; // OK, going WITHIN scope of VLA.
a[j] = 5.5;
lab4:
a[j] = 6.6;
}
goto lab4; // Error: going INTO scope of VLA.
6.8.6.2 The continue statement
Constraints
[#1] A continue statement shall appear only in or as a loop
body.
Semantics
[#2] A continue statement causes a jump to the loop-
continuation portion of the smallest enclosing iteration
statement; that is, to the end of the loop body. More
precisely, in each of the statements
while (/* ... */) { do { for (/* ... */) {
/* ... */ /* ... */ /* ... */
continue; continue; continue;
/* ... */ /* ... */ /* ... */
contin: ; contin: ; contin: ;
} } while (/* ... */); }
unless the continue statement shown is in an enclosed
iteration statement (in which case it is interpreted within
that statement), it is equivalent to goto contin;.124)
____________________
124Following the contin: label is a null statement.
6.8.6.1 Language 6.8.6.2
WG14/N843 Committee Draft -- August 3, 1998 153
6.8.6.3 The break statement
Constraints
[#1] A break statement shall appear only in or as a switch
body or loop body.
Semantics
[#2] A break statement terminates execution of the smallest
enclosing switch or iteration statement.
6.8.6.4 The return statement
Constraints
[#1] A return statement with an expression shall not appear
in a function whose return type is void. A return statement
without an expression shall only appear in a function whose
return type is void.
Semantics
[#2] A return statement terminates execution of the current
function and returns control to its caller. A function may
have any number of return statements.
[#3] If a return statement with an expression is executed,
the value of the expression is returned to the caller as the
value of the function call expression. If the expression
has a type different from the return type of the function in
which it appears, the value is converted as if by assignment
to an object having the return type of the function.125) *
[#4] EXAMPLE In:
____________________
125The return statement is not an assignment. The overlap
restriction of subclause 6.5.16.1 does not apply to the
case of function return.
6.8.6.2 Language 6.8.6.4
154 Committee Draft -- August 3, 1998 WG14/N843
struct s { double i; } f(void);
union {
struct {
int f1;
struct s f2;
} u1;
struct {
struct s f3;
int f4;
} u2;
} g;
struct s f(void)
{
return g.u1.f2;
}
/* ... */
g.u2.f3 = f();
there is no undefined behavior, although there would be if |
the assignment were done directly (without using a function |
call to fetch the value).
6.8.6.4 Language 6.8.6.4
WG14/N843 Committee Draft -- August 3, 1998 155
6.9 External definitions
Syntax
[#1]
translation-unit:
external-declaration
translation-unit external-declaration
external-declaration:
function-definition
declaration
Constraints
[#2] The storage-class specifiers auto and register shall
not appear in the declaration specifiers in an external
declaration.
[#3] There shall be no more than one external definition for
each identifier declared with internal linkage in a
translation unit. Moreover, if an identifier declared with
internal linkage is used in an expression (other than as a
part of the operand of a sizeof operator), there shall be
exactly one external definition for the identifier in the
translation unit.
Semantics
[#4] As discussed in 5.1.1.1, the unit of program text after
preprocessing is a translation unit, which consists of a
sequence of external declarations. These are described as
``external'' because they appear outside any function (and
hence have file scope). As discussed in 6.7, a declaration
that also causes storage to be reserved for an object or a
function named by the identifier is a definition.
[#5] An external definition is an external declaration that
is also a definition of a function or an object. If an
identifier declared with external linkage is used in an
expression (other than as part of the operand of a sizeof
operator), somewhere in the entire program there shall be
exactly one external definition for the identifier;
otherwise, there shall be no more than one.126)
____________________
126Thus, if an identifier declared with external linkage is
not used in an expression, there need be no external
definition for it.
6.9 Language 6.9
156 Committee Draft -- August 3, 1998 WG14/N843
6.9.1 Function definitions
Syntax
[#1]
function-definition:
declaration-specifiers declarator declaration-list-opt compound-statement
declaration-list:
declaration
declaration-list declaration
Constraints
[#2] The identifier declared in a function definition (which
is the name of the function) shall have a function type, as
specified by the declarator portion of the function
definition.127)
[#3] The return type of a function shall be void or an
object type other than array type.
[#4] The storage-class specifier, if any, in the declaration
specifiers shall be either extern or static.
[#5] If the declarator includes a parameter type list, the |
declaration of each parameter shall include an identifier, |
except for the special case of a parameter list consisting
of a single parameter of type void, in which case there |
shall not be an identifier. No declaration list shall
follow.
[#6] If the declarator includes an identifier list, each
declaration in the declaration list shall have at least one
declarator, those declarators shall declare only identifiers
from the identifier list, and every identifier in the
identifier list shall be declared. An identifier declared
as a typedef name shall not be redeclared as a parameter.
The declarations in the declaration list shall contain no
____________________
127The intent is that the type category in a function
definition cannot be inherited from a typedef:
typedef int F(void); /* type F is ``function of no arguments returning int'' */
F f, g; /* f and g both have type compatible with F */
F f { /* ... */ } /* WRONG: syntax/constraint error */
F g() { /* ... */ } /* WRONG: declares that g returns a function */
int f(void) { /* ... */ } /* RIGHT: f has type compatible with F */
int g() { /* ... */ } /* RIGHT: g has type compatible with F */
F *e(void) { /* ... */ } /* e returns a pointer to a function */
F *((e))(void) { /* ... */ } /* same: parentheses irrelevant */
int (*fp)(void); /* fp points to a function that has type F */
F *Fp; /* Fp points to a function that has type F */
6.9.1 Language 6.9.1
WG14/N843 Committee Draft -- August 3, 1998 157
storage-class specifier other than register and no
initializations.
Semantics
[#7] The declarator in a function definition specifies the
name of the function being defined and the identifiers of
its parameters. If the declarator includes a parameter type
list, the list also specifies the types of all the
parameters; such a declarator also serves as a function
prototype for later calls to the same function in the same
translation unit. If the declarator includes an identifier
list,128) the types of the parameters shall be declared in a
following declaration list. In either case, the type of |
each parameter is adjusted as described in 6.7.5.3 for a |
parameter type list; the resulting type shall be an object |
type.
[#8] If a function that accepts a variable number of
arguments is defined without a parameter type list that ends
with the ellipsis notation, the behavior is undefined.
[#9] Each parameter has automatic storage duration. Its |
identifier is an lvalue, which is in effect declared at the
head of the compound statement that constitutes the function |
body (and therefore cannot be redeclared in the function |
body except in an enclosed block). The layout of the
storage for parameters is unspecified.
[#10] On entry to the function, all size expressions of |
variably modified parameters are evaluated and the value of |
each argument expression is converted to the type of the |
corresponding parameter as if by assignment. (Array |
expressions and function designators as arguments were |
converted to pointers before the call.) *
[#11] After all parameters have been assigned, the compound
statement that constitutes the body of the function
definition is executed.
[#12] If the } that terminates a function is reached, and
the value of the function call is used by the caller, the
behavior is undefined.
[#13] EXAMPLE 1 In the following:
extern int max(int a, int b)
{
return a > b ? a : b;
}
____________________
128See ``future language directions'' (6.11.4).
6.9.1 Language 6.9.1
158 Committee Draft -- August 3, 1998 WG14/N843
extern is the storage-class specifier and int is the type
specifier; max(int a, int b) is the function declarator; and
{ return a > b ? a : b; }
is the function body. The following similar definition uses
the identifier-list form for the parameter declarations:
extern int max(a, b)
int a, b;
{
return a > b ? a : b;
}
Here int a, b; is the declaration list for the parameters.
The difference between these two definitions is that the
first form acts as a prototype declaration that forces
conversion of the arguments of subsequent calls to the
function, whereas the second form does not. |
[#14] EXAMPLE 2 To pass one function to another, one might
say
int f(void);
/* ... */
g(f);
Then the definition of g might read
void g(int (*funcp)(void))
{
/* ... */ (*funcp)() /* or funcp() ... */
}
or, equivalently,
void g(int func(void))
{
/* ... */ func() /* or (*func)() ... */
}
6.9.2 External object definitions
Semantics
[#1] If the declaration of an identifier for an object has
file scope and an initializer, the declaration is an
external definition for the identifier.
[#2] A declaration of an identifier for an object that has
file scope without an initializer, and without a storage-
6.9.1 Language 6.9.2
WG14/N843 Committee Draft -- August 3, 1998 159
class specifier or with the storage-class specifier static,
constitutes a tentative definition. If a translation unit
contains one or more tentative definitions for an
identifier, and the translation unit contains no external
definition for that identifier, then the behavior is exactly
as if the translation unit contains a file scope declaration
of that identifier, with the composite type as of the end of
the translation unit, with an initializer equal to 0.
[#3] If the declaration of an identifier for an object is a
tentative definition and has internal linkage, the declared
type shall not be an incomplete type.
[#4] EXAMPLE 1
int i1 = 1; // definition, external linkage
static int i2 = 2; // definition, internal linkage
extern int i3 = 3; // definition, external linkage
int i4; // tentative definition, external linkage
static int i5; // tentative definition, internal linkage
int i1; // valid tentative definition, refers to previous
int i2; // 6.2.2 renders undefined, linkage disagreement
int i3; // valid tentative definition, refers to previous
int i4; // valid tentative definition, refers to previous
int i5; // 6.2.2 renders undefined, linkage disagreement
extern int i1; // refers to previous, whose linkage is external
extern int i2; // refers to previous, whose linkage is internal
extern int i3; // refers to previous, whose linkage is external
extern int i4; // refers to previous, whose linkage is external
extern int i5; // refers to previous, whose linkage is internal
[#5] EXAMPLE 2 If at the end of the translation unit
containing
int i[];
the array i still has incomplete type, the implicit |
initializer causes it to have one element, which is set to |
zero on program startup.
6.9.2 Language 6.9.2
160 Committee Draft -- August 3, 1998 WG14/N843
6.10 Preprocessing directives
Syntax
[#1]
preprocessing-file:
group-opt
group:
group-part
group group-part
group-part:
pp-tokens-opt new-line
if-section
control-line
if-section:
if-group elif-groups-opt else-group-opt endif-line
if-group:
# if constant-expr new-line group-opt
# ifdef identifier new-line group-opt
# ifndef identifier new-line group-opt
elif-groups:
elif-group
elif-groups elif-group
elif-group:
# elif constant-expr new-line group-opt
else-group:
# else new-line group-opt
endif-line:
# endif new-line
control-line:
# include pp-tokens new-line
# define identifier replacement-list new-line
# define identifier lparen identifier-list-opt )
replacement-list new-line
# define identifier lparen ... ) replacement-list new-line
# define identifier lparen identifier-list , ... )
replacement-list new-line
# undef identifier new-line
# line pp-tokens new-line
# error pp-tokens-opt new-line
# pragma pp-tokens-opt new-line
# new-line
6.10 Language 6.10
WG14/N843 Committee Draft -- August 3, 1998 161
lparen: |
a ( character not immediately preceded by white-space|
replacement-list:
pp-tokens-opt
pp-tokens:
preprocessing-token
pp-tokens preprocessing-token
new-line:
the new-line character
Description
[#2] A preprocessing directive consists of a sequence of
preprocessing tokens that begins with a # preprocessing
token that (at the start of translation phase 4) is either
the first character in the source file (optionally after
white space containing no new-line characters) or that
follows white space containing at least one new-line
character, and is ended by the next new-line character.129)
A new-line character ends the preprocessing directive even
if it occurs within what would otherwise be an invocation of
a function-like macro.
Constraints
[#3] The only white-space characters that shall appear
between preprocessing tokens within a preprocessing
directive (from just after the introducing # preprocessing
token through just before the terminating new-line
character) are space and horizontal-tab (including spaces
that have replaced comments or possibly other white-space
characters in translation phase 3). *
Semantics
[#4] The implementation can process and skip sections of
source files conditionally, include other source files, and
replace macros. These capabilities are called
preprocessing, because conceptually they occur before
translation of the resulting translation unit.
[#5] The preprocessing tokens within a preprocessing
directive are not subject to macro expansion unless
____________________
129Thus, preprocessing directives are commonly called
``lines''. These ``lines'' have no other syntactic
significance, as all white space is equivalent except in
certain situations during preprocessing (see the #
character string literal creation operator in 6.10.3.2,
for example).
6.10 Language 6.10
162 Committee Draft -- August 3, 1998 WG14/N843
otherwise stated.
[#6] EXAMPLE In:
#define EMPTY
EMPTY # include <file.h>
the sequence of preprocessing tokens on the second line is
not a preprocessing directive, because it does not begin
with a # at the start of translation phase 4, even though it
will do so after the macro EMPTY has been replaced.
6.10.1 Conditional inclusion
Constraints
[#1] The expression that controls conditional inclusion
shall be an integer constant expression except that: it
shall not contain a cast; identifiers (including those
lexically identical to keywords) are interpreted as
described below;130) and it may contain unary operator
expressions of the form
defined identifier
or
defined ( identifier )
which evaluate to 1 if the identifier is currently defined
as a macro name (that is, if it is predefined or if it has
been the subject of a #define preprocessing directive
without an intervening #undef directive with the same
subject identifier), 0 if it is not.
Semantics
[#2] Preprocessing directives of the forms
# if constant-expr new-line group-opt
# elif constant-expr new-line group-opt
check whether the controlling constant expression evaluates
to nonzero.
[#3] Prior to evaluation, macro invocations in the list of
preprocessing tokens that will become the controlling
constant expression are replaced (except for those macro
names modified by the defined unary operator), just as in
____________________
130Because the controlling constant expression is evaluated
during translation phase 4, all identifiers either are or
are not macro names -- there simply are no keywords,
enumeration constants, etc.
6.10 Language 6.10.1
WG14/N843 Committee Draft -- August 3, 1998 163
normal text. If the token defined is generated as a result
of this replacement process or use of the defined unary
operator does not match one of the two specified forms prior
to macro replacement, the behavior is undefined. After all
replacements due to macro expansion and the defined unary
operator have been performed, all remaining identifiers are
replaced with the pp-number 0, and then each preprocessing
token is converted into a token. The resulting tokens
compose the controlling constant expression which is
evaluated according to the rules of 6.6, except that all
signed integer types and all unsigned integer types act as
if they have the same representation as, respectively, the
types intmax_t and uintmax_t defined in the header
<stdint.h>. This includes interpreting character constants,
which may involve converting escape sequences into execution
character set members. Whether the numeric value for these
character constants matches the value obtained when an
identical character constant occurs in an expression (other
than within a #if or #elif directive) is
implementation-defined.131) Also, whether a single-
character character constant may have a negative value is
implementation-defined.
[#4] Preprocessing directives of the forms
# ifdef identifier new-line group-opt
# ifndef identifier new-line group-opt
check whether the identifier is or is not currently defined
as a macro name. Their conditions are equivalent to #if
defined identifier and #if !defined identifier respectively.
[#5] Each directive's condition is checked in order. If it
evaluates to false (zero), the group that it controls is
skipped: directives are processed only through the name that
determines the directive in order to keep track of the level
of nested conditionals; the rest of the directives'
preprocessing tokens are ignored, as are the other
preprocessing tokens in the group. Only the first group
whose control condition evaluates to true (nonzero) is
processed. If none of the conditions evaluates to true, and
there is a #else directive, the group controlled by the
#else is processed; lacking a #else directive, all the
groups until the #endif are skipped.132)
____________________
131Thus, the constant expression in the following #if
directive and if statement is not guaranteed to evaluate
to the same value in these two contexts.
#if 'z' - 'a' == 25
if ('z' - 'a' == 25)
6.10.1 Language 6.10.1
164 Committee Draft -- August 3, 1998 WG14/N843
Forward references: macro replacement (6.10.3), source file
inclusion (6.10.2), largest integer types (7.18.1.5).
6.10.2 Source file inclusion
Constraints
[#1] A #include directive shall identify a header or source
file that can be processed by the implementation.
Semantics
[#2] A preprocessing directive of the form
# include <h-char-sequence> new-line
searches a sequence of implementation-defined places for a
header identified uniquely by the specified sequence between
the < and > delimiters, and causes the replacement of that
directive by the entire contents of the header. How the
places are specified or the header identified is
implementation-defined.
[#3] A preprocessing directive of the form
# include "q-char-sequence" new-line
causes the replacement of that directive by the entire
contents of the source file identified by the specified
sequence between the " delimiters. The named source file is
searched for in an implementation-defined manner. If this
search is not supported, or if the search fails, the
directive is reprocessed as if it read
# include <h-char-sequence> new-line
with the identical contained sequence (including >
characters, if any) from the original directive.
[#4] A preprocessing directive of the form
# include pp-tokens new-line
(that does not match one of the two previous forms) is
permitted. The preprocessing tokens after include in the
directive are processed just as in normal text. (Each
identifier currently defined as a macro name is replaced by
____________________
132As indicated by the syntax, a preprocessing token shall
not follow a #else or #endif directive before the
terminating new-line character. However, comments may
appear anywhere in a source file, including within a
preprocessing directive.
6.10.1 Language 6.10.2
WG14/N843 Committee Draft -- August 3, 1998 165
its replacement list of preprocessing tokens.) The
directive resulting after all replacements shall match one
of the two previous forms.133) The method by which a
sequence of preprocessing tokens between a < and a >
preprocessing token pair or a pair of " characters is
combined into a single header name preprocessing token is
implementation-defined.
[#5] The implementation shall provide unique mappings for
sequences consisting of one or more letters or digits (as
defined in 5.2.1) followed by a period (.) and a single
letter. The first character shall be a letter. The
implementation may ignore the distinctions of alphabetical
case and restrict the mapping to eight significant
characters before the period.
[#6] A #include preprocessing directive may appear in a
source file that has been read because of a #include
directive in another file, up to an implementation-defined
nesting limit (see 5.2.4.1).
[#7] EXAMPLE 1 The most common uses of #include
preprocessing directives are as in the following:
#include <stdio.h>
#include "myprog.h"
[#8] EXAMPLE 2 This illustrates macro-replaced #include
directives:
#if VERSION == 1
#define INCFILE "vers1.h"
#elif VERSION == 2
#define INCFILE "vers2.h" // and so on
#else
#define INCFILE "versN.h"
#endif
#include INCFILE
Forward references: macro replacement (6.10.3).
____________________
133Note that adjacent string literals are not concatenated
into a single string literal (see the translation phases
in 5.1.1.2); thus, an expansion that results in two
string literals is an invalid directive.
6.10.2 Language 6.10.2
166 Committee Draft -- August 3, 1998 WG14/N843
6.10.3 Macro replacement
Constraints
[#1] Two replacement lists are identical if and only if the
preprocessing tokens in both have the same number, ordering,
spelling, and white-space separation, where all white-space
separations are considered identical.
[#2] An identifier currently defined as a macro without use
of lparen (an object-like macro) shall not be redefined by
another #define preprocessing directive unless the second
definition is an object-like macro definition and the two
replacement lists are identical.
[#3] An identifier currently defined as a macro using lparen
(a function-like macro) shall not be redefined by another
#define preprocessing directive unless the second definition
is a function-like macro definition that has the same number
and spelling of parameters, and the two replacement lists
are identical.
[#4] If the identifier-list in the macro definition does not
end with an ellipsis, the number of arguments, including
those arguments consisting of no preprocessing tokens, in an
invocation of a function-like macro shall agree with the
number of parameters in the macro definition. Otherwise,
there shall be more arguments in the invocation than there
are parameters in the macro definition (excluding the ...).
There shall exist a ) preprocessing token that terminates
the invocation.
[#5] The identifier __VA_ARGS__ shall only occur in the
replacement-list of a #define preprocessing directive using
the ellipsis notation in the arguments.
[#6] A parameter identifier in a function-like macro shall
be uniquely declared within its scope.
Semantics
[#7] The identifier immediately following the define is
called the macro name. There is one name space for macro
names. Any white-space characters preceding or following
the replacement list of preprocessing tokens are not
considered part of the replacement list for either form of
macro.
[#8] If a # preprocessing token, followed by an identifier,
occurs lexically at the point at which a preprocessing
directive could begin, the identifier is not subject to
macro replacement.
[#9] A preprocessing directive of the form
6.10.3 Language 6.10.3
WG14/N843 Committee Draft -- August 3, 1998 167
# define identifier replacement-list new-line
defines an object-like macro that causes each subsequent
instance of the macro name134) to be replaced by the
replacement list of preprocessing tokens that constitute the
remainder of the directive. *
[#10] A preprocessing directive of the form
# define identifier lparen identifier-list-opt ) replacement-list new-line
# define identifier lparen ... ) replacement-list new-line
# define identifier lparen identifier-list , ... ) replacement-list new-line
defines a function-like macro with arguments, similar
syntactically to a function call. The parameters are
specified by the optional list of identifiers, whose scope
extends from their declaration in the identifier list until
the new-line character that terminates the #define
preprocessing directive. Each subsequent instance of the
function-like macro name followed by a ( as the next
preprocessing token introduces the sequence of preprocessing
tokens that is replaced by the replacement list in the
definition (an invocation of the macro). The replaced
sequence of preprocessing tokens is terminated by the
matching ) preprocessing token, skipping intervening matched
pairs of left and right parenthesis preprocessing tokens.
Within the sequence of preprocessing tokens making up an
invocation of a function-like macro, new-line is considered
a normal white-space character.
[#11] The sequence of preprocessing tokens bounded by the
outside-most matching parentheses forms the list of
arguments for the function-like macro. The individual
arguments within the list are separated by comma
preprocessing tokens, but comma preprocessing tokens between
matching inner parentheses do not separate arguments. If
there are sequences of preprocessing tokens within the list
of arguments that would otherwise act as preprocessing
directives, the behavior is undefined.
[#12] If there is a ... in the identifier-list in the macro
definition, then the trailing arguments, including any
separating comma preprocessing tokens, are merged to form a
single item: the variable arguments. The number of arguments
so combined is such that, following merger, the number of
arguments is one more than the number of parameters in the
macro definition (excluding the ...).
____________________
134Since, by macro-replacement time, all character constants
and string literals are preprocessing tokens, not
sequences possibly containing identifier-like
subsequences (see 5.1.1.2, translation phases), they are
never scanned for macro names or parameters.
6.10.3 Language 6.10.3
168 Committee Draft -- August 3, 1998 WG14/N843
6.10.3.1 Argument substitution
[#1] After the arguments for the invocation of a function-
like macro have been identified, argument substitution takes
place. A parameter in the replacement list, unless preceded
by a # or ## preprocessing token or followed by a ##
preprocessing token (see below), is replaced by the
corresponding argument after all macros contained therein
have been expanded. Before being substituted, each
argument's preprocessing tokens are completely macro
replaced as if they formed the rest of the preprocessing
file; no other preprocessing tokens are available.
[#2] An identifier __VA_ARGS__ that occurs in the
replacement list shall be treated as if it were a parameter,
and the variable arguments shall form the preprocessing
tokens used to replace it.
6.10.3.2 The # operator
Constraints
[#1] Each # preprocessing token in the replacement list for
a function-like macro shall be followed by a parameter as
the next preprocessing token in the replacement list.
Semantics
[#2] If, in the replacement list, a parameter is immediately
preceded by a # preprocessing token, both are replaced by a
single character string literal preprocessing token that
contains the spelling of the preprocessing token sequence
for the corresponding argument. Each occurrence of white
space between the argument's preprocessing tokens becomes a
single space character in the character string literal.
White space before the first preprocessing token and after
the last preprocessing token composing the argument is |
deleted. Otherwise, the original spelling of each
preprocessing token in the argument is retained in the
character string literal, except for special handling for
producing the spelling of string literals and character
constants: a \ character is inserted before each " and \
character of a character constant or string literal
(including the delimiting " characters), except that it is |
unspecified whether a \ character is inserted before the \ |
character beginning a universal character name. If the
replacement that results is not a valid character string
literal, the behavior is undefined. The character string
literal corresponding to an empty argument is "". The order
of evaluation of # and ## operators is unspecified.
6.10.3 Language 6.10.3.2
WG14/N843 Committee Draft -- August 3, 1998 169
6.10.3.3 The ## operator
Constraints
[#1] A ## preprocessing token shall not occur at the
beginning or at the end of a replacement list for either
form of macro definition.
Semantics
[#2] If, in the replacement list of a function-like macro, a |
parameter is immediately preceded or followed by a ##
preprocessing token, the parameter is replaced by the
corresponding argument's preprocessing token sequence;
however, if an argument consists of no preprocessing tokens,
the parameter is replaced by a placemarker preprocessing
token instead.
[#3] For both object-like and function-like macro
invocations, before the replacement list is reexamined for
more macro names to replace, each instance of a ##
preprocessing token in the replacement list (not from an
argument) is deleted and the preceding preprocessing token
is concatenated with the following preprocessing token. |
Placemarker preprocessing tokens are handled specially:
concatenation of two placemarkers results in a single
placemarker preprocessing token, and concatenation of a |
placemarker with a non-placemarker preprocessing token
results in the non-placemarker preprocessing token. If the |
result is not a valid preprocessing token, the behavior is
undefined. The resulting token is available for further
macro replacement. The order of evaluation of ## operators
is unspecified.
[#4] EXAMPLE In the following fragment: |
#define hash_hash # ## #
#define mkstr(a) # a
#define in_between(a) mkstr(a)
#define join(c, d) in_between(c hash_hash d)
char p[] = join(x, y); // equivalent to
// char p[] = "x ## y";
The expansion produces, at various stages:
6.10.3.2 Language 6.10.3.3
170 Committee Draft -- August 3, 1998 WG14/N843
join(x, y)
in_between(x hash_hash y)
in_between(x ## y)
mkstr(x ## y)
"x ## y"
In other words, expanding hash_hash produces a new token,
consisting of two adjacent sharp signs, but this new token |
is not the ## operator.
6.10.3.4 Rescanning and further replacement
[#1] After all parameters in the replacement list have been
substituted and # and ## processing has taken place, all
placemarker preprocessing tokens are removed. Then, the |
resulting preprocessing token sequence is rescanned, along |
with all subsequent preprocessing tokens of the source file, |
for more macro names to replace.
[#2] If the name of the macro being replaced is found during
this scan of the replacement list (not including the rest of
the source file's preprocessing tokens), it is not replaced.
Further, if any nested replacements encounter the name of
the macro being replaced, it is not replaced. These
nonreplaced macro name preprocessing tokens are no longer
available for further replacement even if they are later
(re)examined in contexts in which that macro name
preprocessing token would otherwise have been replaced.
[#3] The resulting completely macro-replaced preprocessing
token sequence is not processed as a preprocessing directive
even if it resembles one, but all pragma unary operator
expressions within it are then processed as specified in
6.10.9 below.
6.10.3.5 Scope of macro definitions
[#1] A macro definition lasts (independent of block
structure) until a corresponding #undef directive is
encountered or (if none is encountered) until the end of
translation phase 4.
[#2] A preprocessing directive of the form
# undef identifier new-line
causes the specified identifier no longer to be defined as a
macro name. It is ignored if the specified identifier is
not currently defined as a macro name.
6.10.3.3 Language 6.10.3.5
WG14/N843 Committee Draft -- August 3, 1998 171
[#3] EXAMPLE 1 The simplest use of this facility is to
define a ``manifest constant'', as in
#define TABSIZE 100
int table[TABSIZE];
[#4] EXAMPLE 2 The following defines a function-like macro
whose value is the maximum of its arguments. It has the
advantages of working for any compatible types of the
arguments and of generating in-line code without the
overhead of function calling. It has the disadvantages of
evaluating one or the other of its arguments a second time
(including side effects) and generating more code than a
function if invoked several times. It also cannot have its
address taken, as it has none.
#define max(a, b) ((a) > (b) ? (a) : (b))
The parentheses ensure that the arguments and the resulting
expression are bound properly.
[#5] EXAMPLE 3 To illustrate the rules for redefinition and
reexamination, the sequence
#define x 3
#define f(a) f(x * (a))
#undef x
#define x 2
#define g f
#define z z[0]
#define h g(~
#define m(a) a(w)
#define w 0,1
#define t(a) a
#define p() int
#define q(x) x
#define r(x,y) x ## y
#define str(x) # x
f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
g(x+(3,4)-w) | h 5) & m
(f)^m(m);
p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
char c[2][6] = { str(hello), str() };
results in
6.10.3.5 Language 6.10.3.5
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f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
int i[] = { 1, 23, 4, 5, };
char c[2][6] = { "hello", "" };
[#6] EXAMPLE 4 To illustrate the rules for creating
character string literals and concatenating tokens, the
sequence
#define str(s) # s
#define xstr(s) str(s)
#define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
x ## s, x ## t)
#define INCFILE(n) vers ## n // from previous #include example
#define glue(a, b) a ## b
#define xglue(a, b) glue(a, b)
#define HIGHLOW "hello"
#define LOW LOW ", world"
debug(1, 2);
fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
== 0) str(: @\n), s);
#include xstr(INCFILE(2).h)
glue(HIGH, LOW);
xglue(HIGH, LOW)
results in
printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
fputs(
"strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
s);
#include "vers2.h" (after macro replacement, before file access)
"hello";
"hello" ", world"
or, after concatenation of the character string literals,
printf("x1= %d, x2= %s", x1, x2);
fputs(
"strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
s);
#include "vers2.h" (after macro replacement, before file access)
"hello";
"hello, world"
Space around the # and ## tokens in the macro definition is
optional.
[#7] EXAMPLE 5 To illustrate the rules for
6.10.3.5 Language 6.10.3.5
WG14/N843 Committee Draft -- August 3, 1998 173
placemarker ## placemarker
the sequence
#define t(x,y,z) x ## y ## z
int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
t(10,,), t(,11,), t(,,12), t(,,) };
results in
int j[] = { 123, 45, 67, 89,
10, 11, 12, };
[#8] EXAMPLE 6 To demonstrate the redefinition rules, the
following sequence is valid.
#define OBJ_LIKE (1-1)
#define OBJ_LIKE /* white space */ (1-1) /* other */
#define FUNC_LIKE(a) ( a )
#define FUNC_LIKE( a )( /* note the white space */ \
a /* other stuff on this line
*/ )
But the following redefinitions are invalid:
#define OBJ_LIKE (0) /* different token sequence */
#define OBJ_LIKE (1 - 1) /* different white space */
#define FUNC_LIKE(b) ( a ) /* different parameter usage */
#define FUNC_LIKE(b) ( b ) /* different parameter spelling */
[#9] EXAMPLE 7 Finally, to show the variable argument list
macro facilities:
#define debug(...) fprintf(stderr, __VA_ARGS__)
#define showlist(...) puts(#__VA_ARGS__)
#define report(test, ...) ((test)?puts(#test):\
printf(__VA_ARGS__))
debug("Flag");
debug("X = %d\n", x);
showlist(The first, second, and third items.);
report(x>y, "x is %d but y is %d", x, y);
results in
fprintf(stderr, "Flag" );
fprintf(stderr, "X = %d\n", x );
puts( "The first, second, and third items." );
((x>y)?puts("x>y"):
printf("x is %d but y is %d", x, y));
6.10.3.5 Language 6.10.3.5
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6.10.4 Line control
Constraints
[#1] The string literal of a #line directive, if present,
shall be a character string literal.
Semantics
[#2] The line number of the current source line is one
greater than the number of new-line characters read or
introduced in translation phase 1 (5.1.1.2) while processing
the source file to the current token.
[#3] A preprocessing directive of the form
# line digit-sequence new-line
causes the implementation to behave as if the following
sequence of source lines begins with a source line that has
a line number as specified by the digit sequence
(interpreted as a decimal integer). The digit sequence
shall not specify zero, nor a number greater than
2147483647.
[#4] A preprocessing directive of the form
# line digit-sequence "s-char-sequence-opt" new-line
sets the presumed line number similarly and changes the |
presumed name of the source file to be the contents of the
character string literal.
[#5] A preprocessing directive of the form
# line pp-tokens new-line
(that does not match one of the two previous forms) is
permitted. The preprocessing tokens after line on the
directive are processed just as in normal text (each
identifier currently defined as a macro name is replaced by
its replacement list of preprocessing tokens). The
directive resulting after all replacements shall match one
of the two previous forms and is then processed as
appropriate.
6.10.3.5 Language 6.10.4
WG14/N843 Committee Draft -- August 3, 1998 175
6.10.5 Error directive
Semantics
[#1] A preprocessing directive of the form
# error pp-tokens-opt new-line
causes the implementation to produce a diagnostic message
that includes the specified sequence of preprocessing
tokens.
6.10.6 Pragma directive
Semantics
[#1] A preprocessing directive of the form
# pragma pp-tokens-opt new-line
where the preprocessing token STDC does not immediately
follow pragma in the directive (prior to any macro
replacement)135) causes the implementation to behave in a
manner which it shall document. The behavior might cause |
translation to fail or cause the translator or the resulting |
program to behave in a non-conforming manner. Any such
pragma that is not recognized by the implementation is
ignored.
[#2] If the preprocessing token STDC does immediately follow
pragma in the directive (prior to any macro replacement),
then no macro replacement is performed on the directive, and
the directive shall have one of the following forms whose
meanings are described elsewhere:
#pragma STDC FP_CONTRACT on-off-switch
#pragma STDC FENV_ACCESS on-off-switch
#pragma STDC CX_LIMITED_RANGE on-off-switch
on-off-switch: one of
ON OFF DEFAULT
____________________
135An implementation is not required to perform macro
replacement in pragmas, but it is permitted except for in
standard pragmas (where STDC immediately follows pragma).
If the result of macro replacement in a non-standard
pragma has the same form as a standard pragma, the
behavior is still implementation-defined; an
implementation is permitted to behave as if it were the
standard pragma, but is not required to.
6.10.5 Language 6.10.6
176 Committee Draft -- August 3, 1998 WG14/N843
Forward references: the FP_CONTRACT pragma (7.12.2), the
FENV_ACCESS pragma (7.6.1), the CX_LIMITED_RANGE pragma
(7.3.4).
6.10.7 Null directive
Semantics
[#1] A preprocessing directive of the form
# new-line
has no effect.
6.10.8 Predefined macro names
[#1] The following macro names shall be defined by the
implementation:
__LINE__ The presumed line number (within the current source |
file) of the current source line (a decimal |
constant).136)
__FILE__ The presumed name of the current source file (a |
character string literal).136)
__DATE__ The date of translation of the source file: a |
character string literal of the form "Mmm dd yyyy",
where the names of the months are the same as those
generated by the asctime function, and the first
character of dd is a space character if the value |
is less than 10. If the date of translation is not
available, an implementation-defined valid date
shall be supplied.
__TIME__ The time of translation of the source file: a |
character string literal of the form "hh:mm:ss" as
in the time generated by the asctime function. If |
the time of translation is not available, an
implementation-defined valid time shall be
supplied.
__STDC__ The decimal constant 1, intended to indicate a
conforming implementation.
__STDC_VERSION__ The decimal constant 199901L.137)
____________________
136The presumed line number and source file name can be
changed by the #line directive.
137This macro was not specified in ISO/IEC 9899:1990 and was |
specified as 199409L in ISO/IEC 9899:AMD1:1995
6.10.6 Language 6.10.8
WG14/N843 Committee Draft -- August 3, 1998 177
[#2] The following macro names are conditionally defined by
the implementation: |
__STDC_ISO_10646__ A decimal constant of the form yyyymmL |
(for example, 199712L), intended to |
indicate that values of type wchar_t are |
the coded representations of the |
characters defined by ISO/IEC 10646, |
along with all amendments and technical |
corrigenda as of the specified year and |
month.
__STDC_IEC_559__ The decimal constant 1, intended to
indicate conformance to the
specifications in annex F (IEC 60559
floating-point arithmetic).
__STDC_IEC_559_COMPLEX__ The decimal constant 1, intended to
indicate adherence to the specifications
in informative annex G (IEC 60559
compatible complex arithmetic).
[#3] The values of the predefined macros (except for
__LINE__ and __FILE__) remain constant throughout the
translation unit.
[#4] None of these macro names, nor the identifier defined,
shall be the subject of a #define or a #undef preprocessing
directive. Any other predefined macro names shall begin |
with a leading underscore followed by an uppercase letter or
a second underscore.
Forward references: the asctime function (7.23.3.1).
6.10.9 Pragma operator
Semantics
[#1] A unary operator expression of the form:
_Pragma ( string-literal )
is processed as follows: The string literal is destringized
by deleting the L prefix, if present, deleting the leading
and trailing double-quotes, replacing each escape sequence |
\" by a double-quote, and replacing each escape sequence \\ |
by a single backslash. The resulting sequence of characters
is processed through translation phase 3 to produce
preprocessing tokens that are executed as if they were the
pp-tokens in a pragma directive. The original four
preprocessing tokens in the unary operator expression are
removed.
[#2] EXAMPLE A directive of the form:
6.10.8 Language 6.10.9
178 Committee Draft -- August 3, 1998 WG14/N843
#pragma listing on "..\listing.dir" |
can also be expressed as:
_Pragma ( "listing on \"..\\listing.dir\"" ) |
The latter form is processed in the same way whether it
appears literally as shown, or results from macro
replacement, as in:
#define LISTING(x) PRAGMA(listing on #x)
#define PRAGMA(x) _Pragma(#x)
LISTING ( ..\listing.dir ) |
6.10.9 Language 6.10.9
WG14/N843 Committee Draft -- August 3, 1998 179
6.11 Future language directions
6.11.1 Character escape sequences
[#1] Lowercase letters as escape sequences are reserved for
future standardization. Other characters may be used in
extensions.
6.11.2 Storage-class specifiers
[#1] The placement of a storage-class specifier other than
at the beginning of the declaration specifiers in a
declaration is an obsolescent feature.
6.11.3 Function declarators
[#1] The use of function declarators with empty parentheses
(not prototype-format parameter type declarators) is an
obsolescent feature.
6.11.4 Function definitions
[#1] The use of function definitions with separate parameter
identifier and declaration lists (not prototype-format
parameter type and identifier declarators) is an obsolescent
feature.
6.11.5 Pragma directives
[#1] Pragmas whose first pp-token is STDC are reserved for
future standardization.
6.11 Language 6.11.5
180 Committee Draft -- August 3, 1998 WG14/N843
7. Library
7.1 Introduction
7.1.1 Definitions of terms
[#1] A string is a contiguous sequence of characters
terminated by and including the first null character. The |
term multibyte string is sometimes used instead to emphasize |
special processing given to multibyte characters contained |
in the string or to avoid confusion with a wide string. A
pointer to a string is a pointer to its initial (lowest
addressed) character. The length of a string is the number
of characters preceding the null character and the value of
a string is the sequence of the values of the contained
characters, in order.
[#2] A letter is a printing character in the execution
character set corresponding to any of the 52 required
lowercase and uppercase letters in the source character set,
listed in 5.2.1.
[#3] The decimal-point character is the character used by
functions that convert floating-point numbers to or from
character sequences to denote the beginning of the
fractional part of such character sequences.138) It is
represented in the text and examples by a period, but may be
changed by the setlocale function.
[#4] A wide character is a code value (a binary encoded
integer) of an object of type wchar_t that corresponds to a
member of the extended character set.139)
[#5] A null wide character is a wide character with code
value zero.
[#6] A wide string is a contiguous sequence of wide
characters terminated by and including the first null wide
character. A pointer to a wide string is a pointer to its
initial (lowest addressed) wide character. The length of a
wide string is the number of wide characters preceding the
null wide character and the value of a wide string is the
sequence of code values of the contained wide characters, in
____________________
138The functions that make use of the decimal-point
character are the string conversion functions (7.20.1),
the wide-string numeric conversion functions (7.24.4.1),
the formatted input/output functions (7.19.6), and the
formatted wide-character input/output functions (7.24.2).
139An equivalent definition can be found in 6.4.4.4.
7 Library 7.1.1
WG14/N843 Committee Draft -- August 3, 1998 181
order.
[#7] A shift sequence is a contiguous sequence of bytes
within a multibyte string that (potentially) causes a change
in shift state (see 5.2.1.2). A shift sequence shall not
have a corresponding wide character; it is instead taken to
be an adjunct to an adjacent multibyte character.140)
Forward references: character handling (7.4), the setlocale
function (7.11.1.1).
7.1.2 Standard headers
[#1] Each library function is declared, with a type that
includes a prototype, in a header,141) whose contents are
made available by the #include preprocessing directive. The
header declares a set of related functions, plus any
necessary types and additional macros needed to facilitate
their use. Declarations of types described in this clause
shall not include type qualifiers, unless explicitly stated
otherwise.
[#2] The standard headers are
<assert.h> <inttypes.h> <signal.h> <stdlib.h>
<complex.h> <iso646.h> <stdarg.h> <string.h>
<ctype.h> <limits.h> <stdbool.h> <tgmath.h>
<errno.h> <locale.h> <stddef.h> <time.h>
<fenv.h> <math.h> <stdint.h> <wchar.h>
<float.h> <setjmp.h> <stdio.h> <wctype.h>
[#3] If a file with the same name as one of the above < and
> delimited sequences, not provided as part of the
implementation, is placed in any of the standard places that |
are searched for included source files, the behavior is |
undefined.
[#4] Standard headers may be included in any order; each may
be included more than once in a given scope, with no effect
different from being included only once, except that the
effect of including <assert.h> depends on the definition of |
NDEBUG (see 7.2). If used, a header shall be included
____________________
140For state-dependent encodings, the values for MB_CUR_MAX
and MB_LEN_MAX shall thus be large enough to count all
the bytes in any complete multibyte character plus at
least one adjacent shift sequence of maximum length.
Whether these counts provide for more than one shift
sequence is the implementation's choice.
141A header is not necessarily a source file, nor are the <
and > delimited sequences in header names necessarily
valid source file names.
7.1.1 Library 7.1.2
182 Committee Draft -- August 3, 1998 WG14/N843
outside of any external declaration or definition, and it
shall first be included before the first reference to any of
the functions or objects it declares, or to any of the types
or macros it defines. However, if an identifier is declared
or defined in more than one header, the second and
subsequent associated headers may be included after the
initial reference to the identifier. The program shall not
have any macros with names lexically identical to keywords
currently defined prior to the inclusion.
[#5] Any definition of an object-like macro described in
this clause shall expand to code that is fully protected by
parentheses where necessary, so that it groups in an
arbitrary expression as if it were a single identifier.
[#6] Any declaration of a library function shall have
external linkage.
[#7] A summary of the contents of the standard headers is
given in annex B.
Forward references: diagnostics (7.2).
7.1.3 Reserved identifiers
[#1] Each header declares or defines all identifiers listed
in its associated subclause, and optionally declares or
defines identifiers listed in its associated future library
directions subclause and identifiers which are always
reserved either for any use or for use as file scope
identifiers.
-- All identifiers that begin with an underscore and
either an uppercase letter or another underscore are
always reserved for any use.
-- All identifiers that begin with an underscore are
always reserved for use as identifiers with file scope
in both the ordinary and tag name spaces.
-- Each macro name in any of the following subclauses
(including the future library directions) is reserved
for use as specified if any of its associated headers
is included; unless explicitly stated otherwise (see
7.1.4).
-- All identifiers with external linkage in any of the
following subclauses (including the future library
directions) are always reserved for use as identifiers
with external linkage.142)
____________________
142The list of reserved identifiers with external linkage
includes errno, setjmp, and va_end.
7.1.2 Library 7.1.3
WG14/N843 Committee Draft -- August 3, 1998 183
-- Each identifier with file scope listed in any of the
following subclauses (including the future library
directions) is reserved for use as macro and as an
identifier with file scope in the same name space if
any of its associated headers is included.
[#2] No other identifiers are reserved. If the program
declares or defines an identifier in a context in which it |
is reserved (other than as allowed by 7.1.4), or defines a
reserved identifier as a macro name, the behavior is
undefined.
[#3] If the program removes (with #undef) any macro
definition of an identifier in the first group listed above,
the behavior is undefined.
7.1.4 Use of library functions
[#1] Each of the following statements applies unless
explicitly stated otherwise in the detailed descriptions |
that follow: If an argument to a function has an invalid
value (such as a value outside the domain of the function,
or a pointer outside the address space of the program, or a
null pointer) or a type (after promotion) not expected by a
function with variable number of arguments, the behavior is
undefined. If a function argument is described as being an
array, the pointer actually passed to the function shall
have a value such that all address computations and accesses
to objects (that would be valid if the pointer did point to
the first element of such an array) are in fact valid. Any
function declared in a header may be additionally
implemented as a function-like macro defined in the header,
so if a library function is declared explicitly when its
header is included, one of the techniques shown below can be
used to ensure the declaration is not affected by such a
macro. Any macro definition of a function can be suppressed
locally by enclosing the name of the function in
parentheses, because the name is then not followed by the
left parenthesis that indicates expansion of a macro
function name. For the same syntactic reason, it is
permitted to take the address of a library function even if
it is also defined as a macro.143) The use of #undef to
remove any macro definition will also ensure that an actual
function is referred to. Any invocation of a library
function that is implemented as a macro shall expand to code
that evaluates each of its arguments exactly once, fully
protected by parentheses where necessary, so it is generally
safe to use arbitrary expressions as arguments.144)
Likewise, those function-like macros described in the
____________________
143This means that an implementation shall provide an actual
function for each library function, even if it also
provides a macro for that function.
7.1.3 Library 7.1.4
184 Committee Draft -- August 3, 1998 WG14/N843
following subclauses may be invoked in an expression
anywhere a function with a compatible return type could be
called.145) All object-like macros listed as expanding to
integer constant expressions shall additionally be suitable
for use in #if preprocessing directives.
[#2] Provided that a library function can be declared
without reference to any type defined in a header, it is
also permissible to declare the function and use it without
including its associated header.
[#3] There is a sequence point immediately before a library
function returns.
[#4] The functions in the standard library are not
guaranteed to be reentrant and may modify objects with
static storage duration.146)
[#5] EXAMPLE The function atoi may be used in any of
several ways:
-- by use of its associated header (possibly generating a
macro expansion)
#include <stdlib.h>
const char *str;
/* ... */
i = atoi(str);
____________________
144Such macros might not contain the sequence points that
the corresponding function calls do.
145Because external identifiers and some macro names
beginning with an underscore are reserved,
implementations may provide special semantics for such
names. For example, the identifier _BUILTIN_abs could be
used to indicate generation of in-line code for the abs
function. Thus, the appropriate header could specify
#define abs(x) _BUILTIN_abs(x)
for a compiler whose code generator will accept it.
In this manner, a user desiring to guarantee that a given
library function such as abs will be a genuine function
may write
#undef abs
whether the implementation's header provides a macro
implementation of abs or a built-in implementation. The
prototype for the function, which precedes and is hidden
by any macro definition, is thereby revealed also.
146Thus, a signal handler cannot, in general, call standard
library functions.
7.1.4 Library 7.1.4
WG14/N843 Committee Draft -- August 3, 1998 185
-- by use of its associated header (assuredly generating a
true function reference)
#include <stdlib.h>
#undef atoi
const char *str;
/* ... */
i = atoi(str);
or
#include <stdlib.h>
const char *str;
/* ... */
i = (atoi)(str);
-- by explicit declaration
extern int atoi(const char *);
const char *str;
/* ... */
i = atoi(str);
7.1.4 Library 7.1.4
186 Committee Draft -- August 3, 1998 WG14/N843
7.2 Diagnostics <assert.h>
[#1] The header <assert.h> defines the assert macro and
refers to another macro,
NDEBUG
which is not defined by <assert.h>. If NDEBUG is defined as
a macro name at the point in the source file where
<assert.h> is included, the assert macro is defined simply
as
#define assert(ignore) ((void)0)
The assert macro is redefined according to the current state |
of NDEBUG each time that <assert.h> is included.
[#2] The assert macro shall be implemented as a macro, not
as an actual function. If the macro definition is
suppressed in order to access an actual function, the
behavior is undefined.
7.2.1 Program diagnostics
7.2.1.1 The assert macro
Synopsis
[#1]
#include <assert.h>
void assert(_Bool expression); |
Description
[#2] The assert macro puts diagnostic tests into programs.
When it is executed, if expression is false (that is,
compares equal to 0), the assert macro writes information
about the particular call that failed (including the text of
the argument, the name of the source file, the source line
number, and the name of the enclosing function -- the
latter are respectively the values of the preprocessing
macros __FILE__ and __LINE__ and of the identifier __func__) |
on the standard error file in an implementation-defined
format.147) It then calls the abort function.
Returns
____________________
147The message written might be of the form: |
Assertion failed: expression, function abc, file xyz, |
line nnn . |
7.2 Library 7.2.1.1
WG14/N843 Committee Draft -- August 3, 1998 187
[#3] The assert macro returns no value.
Forward references: the abort function (7.20.4.1).
7.2.1.1 Library 7.2.1.1
188 Committee Draft -- August 3, 1998 WG14/N843
7.3 Complex arithmetic <complex.h>
7.3.1 Introduction
[#1] The header <complex.h> defines macros and declares
functions that support complex arithmetic.148) Each
synopsis specifies a family of functions consisting of a
principal function with one or more double complex
parameters and a double complex or double return value; and
other functions with same name but with f and l suffixes
which are corresponding functions with float and long double
parameters and return values.
[#2] The macro
complex
expands to _Complex; the macro
_Complex_I
expands to a constant expression of type const float
_Complex, with the value of the imaginary unit.149)
[#3] The macros
imaginary
and
_Imaginary_I
are defined if and only if the implementation supports
imaginary types;150) if defined, they expand to _Imaginary
and a constant expression of type const float _Imaginary
with the value of the imaginary unit.
[#4] The macro
I
expands to either _Imaginary_I or _Complex_I. If
_Imaginary_I is not defined, I shall expand to _Complex_I.
[#5] Notwithstanding the provisions of 7.1.3, a program is
permitted to undefine and perhaps then redefine the macros
____________________
148See ``future library directions'' (7.26.1).
149The imaginary unit is a number i such that i2=-1. |
150A specification for imaginary types is in informative
annex G.
7.3 Library 7.3.1
WG14/N843 Committee Draft -- August 3, 1998 189
complex, imaginary, and I. |
Forward references: IEC 60559-compatible complex arithmetic |
(annex G).
7.3.2 Conventions
[#1] Values are interpreted as radians, not degrees. An
implementation may set errno but is not required to.
7.3.3 Branch cuts
[#1] Some of the functions below have branch cuts, across
which the function is discontinuous. For implementations
with a signed zero (including all IEC 60559 implementations)
that follow the specification of annex G, the sign of zero
distinguishes one side of a cut from another so the function
is continuous (except for format limitations) as the cut is
approached from either side. For example, for the square
root function, which has a branch cut along the negative
real axis, the top of the cut, with imaginary part +0, maps
to the positive imaginary axis, and the bottom of the cut,
with imaginary part -0, maps to the negative imaginary axis.
[#2] Implementations that do not support a signed zero (see
annex F) cannot distinguish the sides of branch cuts. These
implementations shall map a cut so the function is
continuous as the cut is approached coming around the finite
endpoint of the cut in a counter clockwise direction.
(Branch cuts for the functions specified here have just one
finite endpoint.) For example, for the square root
function, coming counter clockwise around the finite
endpoint of the cut along the negative real axis approaches
the cut from above, so the cut maps to the positive
imaginary axis.
7.3.4 The CX_LIMITED_RANGE pragma
Synopsis
[#1]
#include <complex.h>
#pragma STDC CX_LIMITED_RANGE on-off-switch
Description
[#2] The usual mathematical formula for complex multiply, |
divide, and absolute value are problematic because of their |
treatment of infinities and because of undue overflow and
underflow. The CX_LIMITED_RANGE pragma can be used to
inform the implementation that (where the state is on) the |
usual mathematical formulas are acceptable.151) The pragma
can occur either outside external declarations or preceding
7.3.1 Library 7.3.4
190 Committee Draft -- August 3, 1998 WG14/N843
all explicit declarations and statements inside a compound
statement. When outside external declarations, the pragma
takes effect from its occurrence until another
CX_LIMITED_RANGE pragma is encountered, or until the end of
the translation unit. When inside a compound statement, the
pragma takes effect from its occurrence until another
CX_LIMITED_RANGE pragma is encountered (within a nested
compound statement), or until the end of the compound
statement; at the end of a compound statement the state for
the pragma is restored to its condition just before the
compound statement. If this pragma is used in any other
context, the behavior is undefined. The default state for
the pragma is off.
7.3.5 Trigonometric functions
7.3.5.1 The cacos functions
Synopsis
[#1]
#include <complex.h>
double complex cacos(double complex z);
float complex cacosf(float complex z);
long double complex cacosl(long double complex z);
Description
[#2] The cacos functions compute the complex arc cosine of
z, with branch cuts outside the interval [-1, 1] along the
real axis.
Returns
[#3] The cacos functions return the complex arc cosine
value, in the range of a strip mathematically unbounded
along the imaginary axis and in the interval [0, pi] along
the real axis.
____________________
151The purpose of the pragma is to allow the implementation
to use the formulas: |
(x+iy)×(u+iv)=(xu-yv)+i(yu+xv) |
(x+iy)/(u+iv)=[(xu+yv)+i(yu-xv)]/(u2+v2) |
|x+iy|=x2+y2 |
where the programmer can determine they are safe.
7.3.4 Library 7.3.5.1
WG14/N843 Committee Draft -- August 3, 1998 191
7.3.5.2 The casin functions
Synopsis
[#1]
#include <complex.h>
double complex casin(double complex z);
float complex casinf(float complex z);
long double complex casinl(long double complex z);
Description
[#2] The casin functions compute the complex arc sine of z,
with branch cuts outside the interval [-1, 1] along the real
axis.
Returns
[#3] The casin functions return the complex arc sine value,
in the range of a strip mathematically unbounded along the
imaginary axis and in the interval [-pi/2, pi/2] along the
real axis.
7.3.5.3 The catan functions
Synopsis
[#1]
#include <complex.h>
double complex catan(double complex z);
float complex catanf(float complex z);
long double complex catanl(long double complex z);
Description
[#2] The catan functions compute the complex arc tangent of
z, with branch cuts outside the interval [-i, i] along the
imaginary axis.
Returns
[#3] The catan functions return the complex arc tangent
value, in the range of a strip mathematically unbounded
along the imaginary axis and in the interval [-pi/2, pi/2]
along the real axis.
7.3.5.1 Library 7.3.5.3
192 Committee Draft -- August 3, 1998 WG14/N843
7.3.5.4 The ccos functions
Synopsis
[#1]
#include <complex.h>
double complex ccos(double complex z);
float complex ccosf(float complex z);
long double complex ccosl(long double complex z);
Description
[#2] The ccos function computes the complex cosine of z.
Returns
[#3] The ccos functions return the complex cosine value.
7.3.5.5 The csin functions
Synopsis
[#1]
#include <complex.h>
double complex csin(double complex z);
float complex csinf(float complex z);
long double complex csinl(long double complex z);
Description
[#2] The csin functions compute the complex sine of z.
Returns
[#3] The csin functions return the complex sine value.
7.3.5.6 The ctan functions
Synopsis
[#1]
#include <complex.h>
double complex ctan(double complex z);
float complex ctanf(float complex z);
long double complex ctanl(long double complex z);
Description
[#2] The ctan functions compute the complex tangent of z.
7.3.5.3 Library 7.3.5.6
WG14/N843 Committee Draft -- August 3, 1998 193
Returns
[#3] The ctan functions return the complex tangent value.
7.3.6 Hyperbolic functions
7.3.6.1 The cacosh functions
Synopsis
[#1]
#include <complex.h>
double complex cacosh(double complex z);
float complex cacoshf(float complex z);
long double complex cacoshl(long double complex z);
Description
[#2] The cacosh functions compute the complex arc hyperbolic
cosine of z, with a branch cut at values less than 1 along
the real axis.
Returns
[#3] The cacosh functions return the complex arc hyperbolic
cosine value, in the range of a half-strip of non-negative
values along the real axis and in the interval [-ipi, ipi]
along the imaginary axis.
7.3.6.2 The casinh functions
Synopsis
[#1]
#include <complex.h>
double complex casinh(double complex z);
float complex casinhf(float complex z);
long double complex casinhl(long double complex z);
Description
[#2] The casinh functions compute the complex arc hyperbolic
sine of z, with branch cuts outside the interval [-i, i]
along the imaginary axis.
Returns
[#3] The casinh functions return the complex arc hyperbolic
sine value, in the range of a strip mathematically unbounded
along the real axis and in the interval [-ipi/2, ipi/2]
along the imaginary axis.
7.3.5.6 Library 7.3.6.2
194 Committee Draft -- August 3, 1998 WG14/N843
7.3.6.3 The catanh functions
Synopsis
[#1]
#include <complex.h>
double complex catanh(double complex z);
float complex catanhf(float complex z);
long double complex catanhl(long double complex z);
Description
[#2] The catanh functions compute the complex arc hyperbolic
tangent of z, with branch cuts outside the interval [-1, 1]
along the real axis.
Returns
[#3] The catanh functions return the complex arc hyperbolic
tangent value, in the range of a strip mathematically
unbounded along the real axis and in the interval
[-ipi/2, ipi/2] along the imaginary axis.
7.3.6.4 The ccosh functions
Synopsis
[#1]
#include <complex.h>
double complex ccosh(double complex z);
float complex ccoshf(float complex z);
long double complex ccoshl(long double complex z);
Description
[#2] The ccosh functions compute the complex hyperbolic
cosine of z.
Returns
[#3] The ccosh functions return the complex hyperbolic
cosine value.
7.3.6.2 Library 7.3.6.4
WG14/N843 Committee Draft -- August 3, 1998 195
7.3.6.5 The csinh functions
Synopsis
[#1]
#include <complex.h>
double complex csinh(double complex z);
float complex csinhf(float complex z);
long double complex csinhl(long double complex z);
Description
[#2] The csinh functions compute the complex hyperbolic sine
of z.
Returns
[#3] The csinh functions return the complex hyperbolic sine
value.
7.3.6.6 The ctanh functions
Synopsis
[#1]
#include <complex.h>
double complex ctanh(double complex z);
float complex ctanhf(float complex z);
long double complex ctanhl(long double complex z);
Description
[#2] The ctanh functions compute the complex hyperbolic
tangent of z.
Returns
[#3] The ctanh functions return the complex hyperbolic
tangent value.
7.3.7 Exponential and logarithmic functions
7.3.6.4 Library 7.3.7
196 Committee Draft -- August 3, 1998 WG14/N843
7.3.7.1 The cexp functions
Synopsis
[#1]
#include <complex.h>
double complex cexp(double complex z);
float complex cexpf(float complex z);
long double complex cexpl(long double complex z);
Description
[#2] The cexp functions compute the complex base-e
exponential of z.
Returns
[#3] The cexp functions return the complex base-e
exponential value.
7.3.7.2 The clog functions
Synopsis
[#1]
#include <complex.h>
double complex clog(double complex z);
float complex clogf(float complex z);
long double complex clogl(long double complex z);
Description
[#2] The clog functions compute the complex natural (base-e)
logarithm of z, with a branch cut along the negative real
axis.
Returns
[#3] The clog functions return the complex natural logarithm
value, in the range of a strip mathematically unbounded
along the real axis and in the interval [-ipi, ipi] along
the imaginary axis.
7.3.8 Power and absolute-value functions
7.3.7 Library 7.3.8
WG14/N843 Committee Draft -- August 3, 1998 197
7.3.8.1 The cabs functions
Synopsis
[#1]
#include <complex.h>
double cabs(double complex z);
float cabsf(float complex z);
long double cabsl(long double complex z);
Description
[#2] The cabs functions compute the complex absolute value
(also called norm, modulus, or magnitude) of z.
Returns
[#3] The cabs functions return the complex absolute value.
7.3.8.2 The cpow functions
Synopsis
[#1]
#include <complex.h>
double complex cpow(double complex x, double complex y);
float complex cpowf(float complex x, float complex y);
long double complex cpowl(long double complex x,
long double complex y);
Description
[#2] The cpow functions compute the complex power function
xy, with a branch cut for the first parameter along the
negative real axis.
Returns
[#3] The cpow functions return the complex power function
value.
7.3.8 Library 7.3.8.2
198 Committee Draft -- August 3, 1998 WG14/N843
7.3.8.3 The csqrt functions
Synopsis
[#1]
#include <complex.h>
double complex csqrt(double complex z);
float complex csqrtf(float complex z);
long double complex csqrtl(long double complex z);
Description
[#2] The csqrt functions compute the complex square root of
z, with a branch cut along the negative real axis.
Returns
[#3] The csqrt functions return the complex square root
value, in the range of the right half-plane (including the
imaginary axis).
7.3.9 Manipulation functions
7.3.9.1 The carg functions
Synopsis
[#1]
#include <complex.h>
double carg(double complex z);
float cargf(float complex z);
long double cargl(long double complex z);
Description
[#2] The carg functions compute the argument (also called
phase angle) of z, with a branch cut along the negative real
axis.
Returns
[#3] The carg functions return the value of the argument in
the range [-pi, pi].
7.3.8.2 Library 7.3.9.1
WG14/N843 Committee Draft -- August 3, 1998 199
7.3.9.2 The cimag functions
Synopsis
[#1]
#include <complex.h>
double cimag(double complex z);
float cimagf(float complex z);
long double cimagl(long double complex z);
Description
[#2] The cimag functions compute the imaginary part of
z.152)
Returns
[#3] The cimag functions return the imaginary part value (as
a real).
7.3.9.3 The conj functions
Synopsis
[#1]
#include <complex.h>
double complex conj(double complex z);
float complex conjf(float complex z);
long double complex conjl(long double complex z);
Description
[#2] The conj functions compute the complex conjugate of z,
by reversing the sign of its imaginary part.
Returns
[#3] The conj functions return the complex conjugate value.
____________________
152For a variable z of complex type, z == creal(z) +
cimag(z)*I.
7.3.9.1 Library 7.3.9.3
200 Committee Draft -- August 3, 1998 WG14/N843
7.3.9.4 The cproj functions
Synopsis
[#1]
#include <complex.h>
double complex cproj(double complex z);
float complex cprojf(float complex z);
long double complex cprojl(long double complex z);
Description
[#2] The cproj functions compute a projection of z onto the
Riemann sphere: z projects to z except that all complex
infinities (even those with one infinite part and one NaN
part) project to positive infinity on the real axis. If z
has an infinite part, then cproj(z) is equivalent to
INFINITY + I * copysign(0.0, cimag(z))
Returns
[#3] The cproj functions return the value of the projection
onto the Riemann sphere.
7.3.9.5 The creal functions
Synopsis
[#1]
#include <complex.h>
double creal(double complex z);
float crealf(float complex z);
long double creall(long double complex z);
Description
[#2] The creal functions compute the real part of z.153)
Returns
[#3] The creal functions return the real part value.
____________________
153For a variable z of complex type, z == creal(z) +
cimag(z)*I.
7.3.9.3 Library 7.3.9.5
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7.4 Character handling <ctype.h>
[#1] The header <ctype.h> declares several functions useful
for testing and mapping characters.154) In all cases the
argument is an int, the value of which shall be
representable as an unsigned char or shall equal the value
of the macro EOF. If the argument has any other value, the
behavior is undefined.
[#2] The behavior of these functions is affected by the
current locale. Those functions that have locale-specific
aspects only when not in the "C" locale are noted below.
[#3] The term printing character refers to a member of a
locale-specific set of characters, each of which occupies
one printing position on a display device; the term control
character refers to a member of a locale-specific set of
characters that are not printing characters.155)
Forward references: EOF (7.19.1), localization (7.11).
7.4.1 Character testing functions
[#1] The functions in this subclause return nonzero (true)
if and only if the value of the argument c conforms to that
in the description of the function.
7.4.1.1 The isalnum function
Synopsis
[#1]
#include <ctype.h>
int isalnum(int c);
Description
[#2] The isalnum function tests for any character for which
isalpha or isdigit is true.
____________________
154See ``future library directions'' (7.26.2).
155In an implementation that uses the seven-bit US ASCII |
character set, the printing characters are those whose
values lie from 0x20 (space) through 0x7E (tilde); the
control characters are those whose values lie from 0
(NUL) through 0x1F (US), and the character 0x7F (DEL).
7.4 Library 7.4.1.1
202 Committee Draft -- August 3, 1998 WG14/N843
7.4.1.2 The isalpha function
Synopsis
[#1]
#include <ctype.h>
int isalpha(int c);
Description
[#2] The isalpha function tests for any character for which
isupper or islower is true, or any character that is one of
a locale-specific set of alphabetic characters for which
none of iscntrl, isdigit, ispunct, or isspace is true.156)
In the "C" locale, isalpha returns true only for the
characters for which isupper or islower is true.
7.4.1.3 The iscntrl function
Synopsis
[#1]
#include <ctype.h>
int iscntrl(int c);
Description
[#2] The iscntrl function tests for any control character.
7.4.1.4 The isdigit function
Synopsis
[#1]
#include <ctype.h>
int isdigit(int c);
Description
[#2] The isdigit function tests for any decimal-digit
character (as defined in 5.2.1).
____________________
156The functions islower and isupper test true or false
separately for each of these additional characters; all
four combinations are possible.
7.4.1.1 Library 7.4.1.4
WG14/N843 Committee Draft -- August 3, 1998 203
7.4.1.5 The isgraph function
Synopsis
[#1]
#include <ctype.h>
int isgraph(int c);
Description
[#2] The isgraph function tests for any printing character
except space (' ').
7.4.1.6 The islower function
Synopsis
[#1]
#include <ctype.h>
int islower(int c);
Description
[#2] The islower function tests for any character that is a
lowercase letter or is one of a locale-specific set of
characters for which none of iscntrl, isdigit, ispunct, or
isspace is true. In the "C" locale, islower returns true
only for the characters defined as lowercase letters (as
defined in 5.2.1).
7.4.1.7 The isprint function
Synopsis
[#1]
#include <ctype.h>
int isprint(int c);
Description
[#2] The isprint function tests for any printing character
including space (' ').
7.4.1.4 Library 7.4.1.7
204 Committee Draft -- August 3, 1998 WG14/N843
7.4.1.8 The ispunct function
Synopsis
[#1]
#include <ctype.h>
int ispunct(int c);
Description
[#2] The ispunct function tests for any printing character
that is one of a locale-specific set of punctuation
characters for which neither isspace nor isalnum is true.
7.4.1.9 The isspace function
Synopsis
[#1]
#include <ctype.h>
int isspace(int c);
Description
[#2] The isspace function tests for any character that is a
standard white-space character or is one of a locale-
specific set of characters for which isalnum is false. The
standard white-space characters are the following: space
(' '), form feed ('\f'), new-line ('\n'), carriage return
('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In
the "C" locale, isspace returns true only for the standard
white-space characters.
7.4.1.10 The isupper function
Synopsis
[#1]
#include <ctype.h>
int isupper(int c);
Description
[#2] The isupper function tests for any character that is an
uppercase letter or is one of a locale-specific set of
characters for which none of iscntrl, isdigit, ispunct, or
isspace is true. In the "C" locale, isupper returns true
only for the characters defined as uppercase letters (as
defined in 5.2.1).
7.4.1.7 Library 7.4.1.10
WG14/N843 Committee Draft -- August 3, 1998 205
7.4.1.11 The isxdigit function
Synopsis
[#1]
#include <ctype.h>
int isxdigit(int c);
Description
[#2] The isxdigit function tests for any hexadecimal-digit
character (as defined in 6.4.4.2).
7.4.2 Character case mapping functions
7.4.2.1 The tolower function
Synopsis
[#1]
#include <ctype.h>
int tolower(int c);
Description
[#2] The tolower function converts an uppercase letter to a
corresponding lowercase letter.
Returns
[#3] If the argument is a character for which isupper is
true and there are one or more corresponding characters, as
specified by the current locale, for which islower is true,
the tolower function returns one of the corresponding
characters (always the same one for any given locale);
otherwise, the argument is returned unchanged.
7.4.2.2 The toupper function
Synopsis
[#1]
#include <ctype.h>
int toupper(int c);
Description
[#2] The toupper function converts a lowercase letter to a
corresponding uppercase letter.
7.4.1.10 Library 7.4.2.2
206 Committee Draft -- August 3, 1998 WG14/N843
Returns
[#3] If the argument is a character for which islower is
true and there are one or more corresponding characters, as
specified by the current locale, for which isupper is true,
the toupper function returns one of the corresponding
characters (always the same one for any given locale);
otherwise, the argument is returned unchanged.
7.4.2.2 Library 7.4.2.2
WG14/N843 Committee Draft -- August 3, 1998 207
7.5 Errors <errno.h>
[#1] The header <errno.h> defines several macros, all
relating to the reporting of error conditions.
[#2] The macros are
EDOM
EILSEQ
ERANGE
which expand to integer constant expressions with type int,
distinct positive values, and which are suitable for use in
#if preprocessing directives; and
errno
which expands to a modifiable lvalue157) that has type int,
the value of which is set to a positive error number by
several library functions. It is unspecified whether errno
is a macro or an identifier declared with external linkage.
If a macro definition is suppressed in order to access an
actual object, or a program defines an identifier with the
name errno, the behavior is undefined.
[#3] The value of errno is zero at program startup, but is
never set to zero by any library function.158) The value of
errno may be set to nonzero by a library function call
whether or not there is an error, provided the use of errno
is not documented in the description of the function in this
International Standard.
[#4] Additional macro definitions, beginning with E and a
digit or E and an uppercase letter,159) may also be
specified by the implementation.
____________________
157The macro errno need not be the identifier of an object.
It might expand to a modifiable lvalue resulting from a
function call (for example, *errno()).
158Thus, a program that uses errno for error checking should
set it to zero before a library function call, then
inspect it before a subsequent library function call. Of
course, a library function can save the value of errno on
entry and then set it to zero, as long as the original
value is restored if errno's value is still zero just
before the return.
159See ``future library directions'' (7.26.3).
7.5 Library 7.5
208 Committee Draft -- August 3, 1998 WG14/N843
7.6 Floating-point environment <fenv.h>
[#1] The header <fenv.h> declares two types and several
macros and functions to provide access to the floating-point
environment. The floating-point environment refers
collectively to any floating-point status flags and control
modes supported by the implementation.160) A floating-point
status flag is a system variable whose value is set as a
side effect of floating-point arithmetic to provide |
auxiliary information. A floating-point control mode is a
system variable whose value may be set by the user to affect
the subsequent behavior of floating-point arithmetic. |
[#2] Certain programming conventions support the intended
model of use for the floating-point environment:161)
-- a function call does not alter its caller's modes,
clear its caller's flags, nor depend on the state of
its caller's flags unless the function is so
documented;
-- a function call is assumed to require default modes,
unless its documentation promises otherwise or unless
the function is known not to use floating-point;
-- a function call is assumed to have the potential for
raising floating-point exceptions, unless its
documentation promises otherwise, or unless the
function is known not to use floating-point.
[#3] The type
fenv_t
represents the entire floating-point environment.
[#4] The type
fexcept_t
represents the floating-point exception flags collectively,
____________________
160This header is designed to support the exception status
flags and directed-rounding control modes required by IEC
60559, and other similar floating-point state
information. Also it is designed to facilitate code
portability among all systems.
161With these conventions, a programmer can safely assume
default modes (or be unaware of them). The
responsibilities associated with accessing the floating-
point environment fall on the programmer or program that
does so explicitly.
7.6 Library 7.6
WG14/N843 Committee Draft -- August 3, 1998 209
including any status the implementation associates with the
flags.
[#5] Each of the macros
FE_DIVBYZERO
FE_INEXACT
FE_INVALID
FE_OVERFLOW
FE_UNDERFLOW
is defined if and only if the implementation supports the
exception by means of the functions in 7.6.2. Additional |
floating-point exceptions, with macro definitions beginning |
with FE_ and an uppercase letter, may also be specified by |
the implementation. The defined macros expand to integer
constant expressions with values such that bitwise ORs of
all combinations of the macros result in distinct values.
[#6] The macro
FE_ALL_EXCEPT
is simply the bitwise OR of all exception macros defined by
the implementation.
[#7] Each of the macros
FE_DOWNWARD
FE_TONEAREST
FE_TOWARDZERO
FE_UPWARD
is defined if and only if the implementation supports
getting and setting the represented rounding direction by
means of the fegetround and fesetround functions. |
Additional rounding directions, with macro definitions |
beginning with FE_ and an uppercase letter, may also be |
specified by the implementation. The defined macros expand
to integer constant expressions whose values are distinct
nonnegative values.162)
[#8] The macro
FE_DFL_ENV
represents the default floating-point environment -- the
one installed at program startup -- and has type pointer
to const-qualified fenv_t. It can be used as an argument to
____________________
162Even though the rounding direction macros may expand to
constants corresponding to the values of FLT_ROUNDS, they
are not required to do so.
7.6 Library 7.6
210 Committee Draft -- August 3, 1998 WG14/N843
<fenv.h> functions that manage the floating-point
environment.
[#9] Additional macro definitions, beginning with FE_ and
having type pointer to const-qualified fenv_t, may also be
specified by the implementation.
7.6.1 The FENV_ACCESS pragma
Synopsis
[#1]
#include <fenv.h>
#pragma STDC FENV_ACCESS on-off-switch
Description
[#2] The FENV_ACCESS pragma provides a means to inform the
implementation when a program might access the floating-
point environment to test flags or run under non-default
modes.163) The pragma shall occur either outside external
declarations or preceding all explicit declarations and
statements inside a compound statement. When outside
external declarations, the pragma takes effect from its
occurrence until another FENV_ACCESS pragma is encountered,
or until the end of the translation unit. When inside a
compound statement, the pragma takes effect from its
occurrence until another FENV_ACCESS pragma is encountered
(within a nested compound statement), or until the end of
the compound statement; at the end of a compound statement
the state for the pragma is restored to its condition just
before the compound statement. If this pragma is used in
any other context, the behavior is undefined. If part of a
program tests flags or runs under non-default mode settings,
but was translated with the state for the FENV_ACCESS pragma
off, then the behavior is undefined. The default state (on
or off) for the pragma is implementation-defined.
[#3] EXAMPLE
____________________
163The purpose of the FENV_ACCESS pragma is to allow certain
optimizations, for example global common subexpression
elimination, code motion, and constant folding, that
could subvert flag tests and mode changes. In general,
if the state of FENV_ACCESS is off then the translator
can assume that default modes are in effect and the flags
are not tested.
7.6 Library 7.6.1
WG14/N843 Committee Draft -- August 3, 1998 211
#include <fenv.h>
void f(double x)
{
#pragma STDC FENV_ACCESS ON
void g(double);
void h(double);
/* ... */
g(x + 1);
h(x + 1);
/* ... */
}
[#4] If the function g might depend on status flags set as a
side effect of the first x + 1, or if the second x + 1 might
depend on control modes set as a side effect of the call to
function g, then the program shall contain an appropriately
placed invocation of #pragma STDC FENV_ACCESS ON.164)
7.6.2 Exceptions
[#1] The following functions provide access to the exception
flags.165) The int input argument for the functions
represents a subset of floating-point exceptions, and can be |
zero or the bitwise OR of one or more exception macros, for |
example FE_OVERFLOW | FE_INEXACT. For other argument values
the behavior of these functions is undefined.
____________________
164The side effects impose a temporal ordering that requires
two evaluations of x + 1. On the other hand, without the
#pragma STDC FENV_ACCESS ON pragma, and assuming the
default state is off, just one evaluation of x + 1 would
suffice.
165The functions fetestexcept, feraiseexcept, and
feclearexcept support the basic abstraction of flags that
are either set or clear. An implementation may endow
exception flags with more information -- for example,
the address of the code which first raised the exception;
the functions fegetexceptflag and fesetexceptflag deal
with the full content of flags.
7.6.1 Library 7.6.2
212 Committee Draft -- August 3, 1998 WG14/N843
7.6.2.1 The feclearexcept function
Synopsis
[#1]
#include <fenv.h>
void feclearexcept(int excepts);
Description
[#2] The feclearexcept function clears the supported
exceptions represented by its argument.
7.6.2.2 The fegetexceptflag function
Synopsis
[#1]
#include <fenv.h>
void fegetexceptflag(fexcept_t *flagp,
int excepts);
Description
[#2] The fegetexceptflag function stores an implementation-
defined representation of the exception flags indicated by
the argument excepts in the object pointed to by the
argument flagp.
7.6.2.3 The feraiseexcept function
Synopsis
[#1]
#include <fenv.h>
void feraiseexcept(int excepts);
Description
[#2] The feraiseexcept function raises the supported
exceptions represented by its argument.166) The order in
which these exceptions are raised is unspecified, except as
stated in F.7.6. Whether the feraiseexcept function
additionally raises the inexact exception whenever it raises
the overflow or underflow exception is implementation-
____________________
166The effect is intended to be similar to that of
exceptions raised by arithmetic operations. Hence,
enabled traps for exceptions raised by this function are
taken. The specification in F.7.6 is in the same spirit.
7.6.2 Library 7.6.2.3
WG14/N843 Committee Draft -- August 3, 1998 213
defined.
7.6.2.4 The fesetexceptflag function
Synopsis
[#1]
#include <fenv.h>
void fesetexceptflag(const fexcept_t *flagp,
int excepts);
Description
[#2] The fesetexceptflag function sets the complete status
for those exception flags indicated by the argument excepts,
according to the representation in the object pointed to by
flagp. The value of *flagp shall have been set by a
previous call to fegetexceptflag whose second argument
represented at least those exceptions represented by the
argument excepts. This function does not raise exceptions, |
but only sets the state of the flags.
7.6.2.5 The fetestexcept function
Synopsis
[#1]
#include <fenv.h>
int fetestexcept(int excepts);
Description
[#2] The fetestexcept function determines which of a
specified subset of the exception flags are currently set.
The excepts argument specifies the exception flags to be
queried.167)
Returns
[#3] The fetestexcept function returns the value of the
bitwise OR of the exception macros corresponding to the
currently set exceptions included in excepts.
[#4] EXAMPLE Call f if invalid is set, then g if overflow
is set:
____________________
167This mechanism allows testing several exceptions with
just one function call.
7.6.2.3 Library 7.6.2.5
214 Committee Draft -- August 3, 1998 WG14/N843
#include <fenv.h>
/* ... */
{
#pragma STDC FENV_ACCESS ON
int set_excepts;
// maybe raise exceptions
set_excepts =
fetestexcept(FE_INVALID | FE_OVERFLOW);
if (set_excepts & FE_INVALID) f();
if (set_excepts & FE_OVERFLOW) g();
/* ... */
}
7.6.3 Rounding
[#1] The fegetround and fesetround functions provide control
of rounding direction modes.
7.6.3.1 The fegetround function
Synopsis
[#1]
#include <fenv.h>
int fegetround(void);
Description
[#2] The fegetround function gets the current rounding
direction.
Returns
[#3] The fegetround function returns the value of the
rounding direction macro representing the current rounding
direction.
7.6.3.2 The fesetround function
Synopsis
[#1]
#include <fenv.h>
int fesetround(int round);
Description
[#2] The fesetround function establishes the rounding
direction represented by its argument round. If the |
argument is not equal to the value of a rounding direction
7.6.2.5 Library 7.6.3.2
WG14/N843 Committee Draft -- August 3, 1998 215
macro, the rounding direction is not changed.
Returns
[#3] The fesetround function returns a zero value if and |
only if the argument is equal to a rounding direction macro |
(that is, if and only if the requested rounding direction
can be established).
[#4] EXAMPLE 1 Save, set, and restore the rounding
direction. Report an error and abort if setting the
rounding direction fails.
#include <fenv.h>
#include <assert.h>
/* ... */
{
#pragma STDC FENV_ACCESS ON
int save_round;
int setround_ok;
save_round = fegetround();
setround_ok = fesetround(FE_UPWARD);
assert(setround_ok);
/* ... */
fesetround(save_round);
/* ... */
}
7.6.4 Environment
[#1] The functions in this section manage the floating-point
environment -- status flags and control modes -- as one
entity.
7.6.4.1 The fegetenv function
Synopsis
[#1]
#include <fenv.h>
void fegetenv(fenv_t *envp);
Description
[#2] The fegetenv function stores the current floating-point
environment in the object pointed to by envp.
7.6.3.2 Library 7.6.4.1
216 Committee Draft -- August 3, 1998 WG14/N843
7.6.4.2 The feholdexcept function
Synopsis
[#1]
#include <fenv.h>
int feholdexcept(fenv_t *envp);
Description
[#2] The feholdexcept function saves the current floating-
point environment in the object pointed to by envp, clears
the exception flags, and then installs a non-stop (continue
on exceptions) mode, if available, for all exceptions.168)
Returns
[#3] The feholdexcept function returns zero if and only if |
non-stop exception handling was successfully installed.
7.6.4.3 The fesetenv function
Synopsis
[#1]
#include <fenv.h>
void fesetenv(const fenv_t *envp);
Description
[#2] The fesetenv function establishes the floating-point
environment represented by the object pointed to by envp.
The argument envp shall point to an object set by a call to
fegetenv or feholdexcept, or equal the macro FE_DFL_ENV or
an implementation-defined environment macro. Note that
fesetenv merely installs the state of the exception flags
represented through its argument, and does not raise these
exceptions.
____________________
168IEC 60559 systems have a default non-stop mode, and
typically at least one other mode for trap handling or
aborting; if the system provides only the non-stop mode
then installing it is trivial. For such systems, the
feholdexcept function can be used in conjunction with the
feupdateenv function to write routines that hide spurious
exceptions from their callers.
7.6.4.1 Library 7.6.4.3
WG14/N843 Committee Draft -- August 3, 1998 217
7.6.4.4 The feupdateenv function
Synopsis
[#1]
#include <fenv.h>
void feupdateenv(const fenv_t *envp);
Description
[#2] The feupdateenv function saves the currently raised
exceptions in its automatic storage, installs the floating-
point environment represented by the object pointed to by
envp, and then raises the saved exceptions. The argument
envp shall point to an object set by a call to feholdexcept
or fegetenv, or equal the macro FE_DFL_ENV or an
implementation-defined environment macro.
[#3] EXAMPLE 1 Hide spurious underflow exceptions:
#include <fenv.h>
double f(double x)
{
#pragma STDC FENV_ACCESS ON
double result;
fenv_t save_env;
feholdexcept(&save_env);
// compute result
if (/* test spurious underflow */)
feclearexcept(FE_UNDERFLOW);
feupdateenv(&save_env);
return result;
}
7.6.4.3 Library 7.6.4.4
218 Committee Draft -- August 3, 1998 WG14/N843
7.7 Characteristics of floating types <float.h>
[#1] The header <float.h> defines several macros that expand
to various limits and parameters of the standard floating-
point types.
[#2] The macros, their meanings, and the constraints (or
restrictions) on their values are listed in 5.2.4.2.2.
7.7 Library 7.7
WG14/N843 Committee Draft -- August 3, 1998 219
7.8 Format conversion of integer types <inttypes.h>
[#1] The header <inttypes.h> includes the header <stdint.h>
and extends it with additional facilities provided by hosted
implementations.
[#2] It declares four functions for converting numeric
character strings to greatest-width integers and, for each
type declared in <stdint.h>, it defines corresponding macros
for conversion specifiers for use with the formatted
input/output functions.169)
Forward references: integer types <stdint.h> (7.18).
7.8.1 Macros for format specifiers
[#1] Each of the following object-like macros170) expands to |
a character string literal containing a conversion
specifier, possibly modified by a length modifier, suitable
for use within the format argument of a formatted
input/output function when converting the corresponding
integer type. These macro names have the general form of
PRI (character string literals for the fprintf family) or
SCN (character string literals for the fscanf family),171)
followed by the conversion specifier, followed by a name
corresponding to a similar type name in 7.18.1. For
example, PRIdFAST32 can be used in a format string to print
the value of an integer of type int_fast32_t.
[#2] The fprintf macros for signed integers are:
PRId8 PRId16 PRId32 PRId64
PRIdLEAST8 PRIdLEAST16 PRIdLEAST32 PRIdLEAST64
PRIdFAST8 PRIdFAST16 PRIdFAST32 PRIdFAST64
PRIdMAX PRIdPTR
PRIi8 PRIi16 PRIi32 PRIi64
PRIiLEAST8 PRIiLEAST16 PRIiLEAST32 PRIiLEAST64
PRIiFAST8 PRIiFAST16 PRIiFAST32 PRIiFAST64
PRIiMAX PRIiPTR
[#3] The fprintf macros for unsigned integers are:
____________________
169See ``future library directions'' (7.26.4).
170C++ implementations should define these macros only when
__STDC_FORMAT_MACROS is defined before <inttypes.h> is
included.
171Separate macros are given for use with fprintf and fscanf
functions because, in the general case, different format |
specifiers may be required for fprintf and fscanf, even |
when the type is the same.
7.8 Library 7.8.1
220 Committee Draft -- August 3, 1998 WG14/N843
PRIo8 PRIo16 PRIo32 PRIo64
PRIoLEAST8 PRIoLEAST16 PRIoLEAST32 PRIoLEAST64
PRIoFAST8 PRIoFAST16 PRIoFAST32 PRIoFAST64
PRIoMAX PRIoPTR
PRIu8 PRIu16 PRIu32 PRIu64
PRIuLEAST8 PRIuLEAST16 PRIuLEAST32 PRIuLEAST64
PRIuFAST8 PRIuFAST16 PRIuFAST32 PRIuFAST64
PRIuMAX PRIuPTR
PRIx8 PRIx16 PRIx32 PRIx64
PRIxLEAST8 PRIxLEAST16 PRIxLEAST32 PRIxLEAST64
PRIxFAST8 PRIxFAST16 PRIxFAST32 PRIxFAST64
PRIxMAX PRIxPTR
PRIX8 PRIX16 PRIX32 PRIX64
PRIXLEAST8 PRIXLEAST16 PRIXLEAST32 PRIXLEAST64
PRIXFAST8 PRIXFAST16 PRIXFAST32 PRIXFAST64
PRIXMAX PRIXPTR
[#4] The fscanf macros for signed integers are:
SCNd8 SCNd16 SCNd32 SCNd64
SCNdLEAST8 SCNdLEAST16 SCNdLEAST32 SCNdLEAST64
SCNdFAST8 SCNdFAST16 SCNdFAST32 SCNdFAST64
SCNdMAX SCNdPTR
SCNi8 SCNi16 SCNi32 SCNi64
SCNiLEAST8 SCNiLEAST16 SCNiLEAST32 SCNiLEAST64
SCNiFAST8 SCNiFAST16 SCNiFAST32 SCNiFAST64
SCNiMAX SCNiPTR
[#5] The fscanf macros for unsigned integers are:
SCNo8 SCNo16 SCNo32 SCNo64
SCNoLEAST8 SCNoLEAST16 SCNoLEAST32 SCNoLEAST64
SCNoFAST8 SCNoFAST16 SCNoFAST32 SCNoFAST64
SCNoMAX SCNoPTR
SCNu8 SCNu16 SCNu32 SCNu64
SCNuLEAST8 SCNuLEAST16 SCNuLEAST32 SCNuLEAST64
SCNuFAST8 SCNuFAST16 SCNuFAST32 SCNuFAST64
SCNuMAX SCNuPTR
SCNx8 SCNx16 SCNx32 SCNx64
SCNxLEAST8 SCNxLEAST16 SCNxLEAST32 SCNxLEAST64
SCNxFAST8 SCNxFAST16 SCNxFAST32 SCNxFAST64
SCNxMAX SCNxPTR
[#6] Because the default argument promotions do not affect
pointer parameters, there might not exist suitable fscanf
format specifiers for some of the types defined in this
header. Consequently, as a special exception to the
requirement that the implementation define all macros
7.8.1 Library 7.8.1
WG14/N843 Committee Draft -- August 3, 1998 221
associated with each type defined by this header, in such a
case the problematic fscanf macros may be left undefined.
[#7] EXAMPLE
#include <inttypes.h>
#include <wchar.h>
int main(void)
{
uintmax_t i = UINTMAX_MAX; // this type always exists
wprintf(L"The largest integer value is %020"
PRIxMAX "\n", i);
return 0;
}
7.8.2 Conversion functions for greatest-width integer types
7.8.2.1 The strtoimax and strtoumax functions |
Synopsis
[#1]
#include <inttypes.h>
intmax_t strtoimax(const char * restrict nptr,
char ** restrict endptr, int base);
uintmax_t strtoumax(const char * restrict nptr, |
char ** restrict endptr, int base); |
Description
[#2] The strtoimax and strtoumax functions are equivalent to |
the strtol, strtoll, strtoul, and strtoull functions, except |
that the initial portion of the string is converted to
intmax_t and uintmax_t representation, respectively. |
Returns
[#3] The strtoimax and strtoumax functions return the |
converted value, if any. If no conversion could be |
performed, zero is returned. If the correct value is
outside the range of representable values, INTMAX_MAX, |
INTMAX_MIN, or UINTMAX_MAX is returned (according to the |
return type and sign of the value, if any), and the value of
the macro ERANGE is stored in errno. |
7.8.2.2 The wcstoimax and wcstoumax functions |
Synopsis
[#1]
7.8.1 Library 7.8.2.2
222 Committee Draft -- August 3, 1998 WG14/N843
#include <stddef.h> // for wchar_t
#include <inttypes.h>
intmax_t wcstoimax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
uintmax_t wcstoumax(const wchar_t * restrict nptr, |
wchar_t ** restrict endptr, int base); |
Description
[#2] The wcstoimax and wcstoumax functions are equivalent to |
the wcstol, wcstoll, wcstoul, and wcstoull functions except |
that the initial portion of the wide string is converted to
intmax_t and uintmax_t representation, respectively. |
Returns
[#3] The wcstoimax function returns the converted value, if
any. If no conversion could be performed, zero is returned. |
If the correct value is outside the range of representable
values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned |
(according to the return type and sign of the value, if |
any), and the value of the macro ERANGE is stored in errno. *
7.8.2.2 Library 7.8.2.2
WG14/N843 Committee Draft -- August 3, 1998 223
7.9 Alternative spellings <iso646.h>
[#1] The header <iso646.h> defines the following eleven
macros (on the left) that expand to the corresponding tokens
(on the right):
and &&
and_eq &=
bitand &
bitor |
compl ~
not !
not_eq !=
or ||
or_eq |=
xor ^
xor_eq ^=
7.9 Library 7.9
224 Committee Draft -- August 3, 1998 WG14/N843
7.10 Sizes of integer types <limits.h>
[#1] The header <limits.h> defines several macros that
expand to various limits and parameters of the standard
integer types.
[#2] The macros, their meanings, and the constraints (or
restrictions) on their values are listed in 5.2.4.2.1.
7.10 Library 7.10
WG14/N843 Committee Draft -- August 3, 1998 225
7.11 Localization <locale.h>
[#1] The header <locale.h> declares two functions, one type,
and defines several macros.
[#2] The type is
struct lconv
which contains members related to the formatting of numeric
values. The structure shall contain at least the following
members, in any order. The semantics of the members and
their normal ranges are explained in 7.11.2.1. In the "C" |
locale, the members shall have the values specified in the
comments.
char *decimal_point; // "."
char *thousands_sep; // ""
char *grouping; // ""
char *mon_decimal_point; // "" *
char *mon_thousands_sep; // ""
char *mon_grouping; // ""
char *positive_sign; // ""
char *negative_sign; // ""
char *currency_symbol; // "" |
char frac_digits; // CHAR_MAX
char p_cs_precedes; // CHAR_MAX
char n_cs_precedes; // CHAR_MAX *
char p_sep_by_space; // CHAR_MAX |
char n_sep_by_space; // CHAR_MAX
char p_sign_posn; // CHAR_MAX
char n_sign_posn; // CHAR_MAX
char *int_curr_symbol; // "" |
char int_frac_digits; // CHAR_MAX |
char int_p_cs_precedes; // CHAR_MAX |
char int_n_cs_precedes; // CHAR_MAX |
char int_p_sep_by_space; // CHAR_MAX |
char int_n_sep_by_space; // CHAR_MAX |
char int_p_sign_posn; // CHAR_MAX |
char int_n_sign_posn; // CHAR_MAX |
[#3] The macros defined are NULL (described in 7.17); and
LC_ALL
LC_COLLATE
LC_CTYPE
LC_MONETARY
LC_NUMERIC
LC_TIME
which expand to integer constant expressions with distinct
values, suitable for use as the first argument to the
setlocale function.172) Additional macro definitions,
beginning with the characters LC_ and an uppercase
7.11 Library 7.11
226 Committee Draft -- August 3, 1998 WG14/N843
letter,173) may also be specified by the implementation.
7.11.1 Locale control
7.11.1.1 The setlocale function
Synopsis
[#1]
#include <locale.h>
char *setlocale(int category, const char *locale);
Description
[#2] The setlocale function selects the appropriate portion
of the program's locale as specified by the category and
locale arguments. The setlocale function may be used to
change or query the program's entire current locale or
portions thereof. The value LC_ALL for category names the
program's entire locale; the other values for category name
only a portion of the program's locale. LC_COLLATE affects
the behavior of the strcoll and strxfrm functions. LC_CTYPE
affects the behavior of the character handling functions174)
and the multibyte and wide-character functions. LC_MONETARY
affects the monetary formatting information returned by the
localeconv function. LC_NUMERIC affects the decimal-point
character for the formatted input/output functions and the
string conversion functions, as well as the nonmonetary
formatting information returned by the localeconv function.
LC_TIME affects the behavior of the strftime and strfxtime
functions.
[#3] A value of "C" for locale specifies the minimal
environment for C translation; a value of "" for locale
specifies the locale-specific native environment. Other
implementation-defined strings may be passed as the second
argument to setlocale.
[#4] At program startup, the equivalent of
setlocale(LC_ALL, "C");
is executed.
____________________
172ISO/IEC 9945-2 specifies locale and charmap formats that
may be used to specify locales for C.
173See ``future library directions'' (7.26.5).
174The only functions in 7.4 whose behavior is not affected
by the current locale are isdigit and isxdigit.
7.11 Library 7.11.1.1
WG14/N843 Committee Draft -- August 3, 1998 227
[#5] The implementation shall behave as if no library
function calls the setlocale function.
Returns
[#6] If a pointer to a string is given for locale and the
selection can be honored, the setlocale function returns a
pointer to the string associated with the specified category
for the new locale. If the selection cannot be honored, the
setlocale function returns a null pointer and the program's
locale is not changed.
[#7] A null pointer for locale causes the setlocale function
to return a pointer to the string associated with the
category for the program's current locale; the program's
locale is not changed.175)
[#8] The pointer to string returned by the setlocale
function is such that a subsequent call with that string
value and its associated category will restore that part of
the program's locale. The string pointed to shall not be
modified by the program, but may be overwritten by a
subsequent call to the setlocale function.
Forward references: formatted input/output functions
(7.19.6), the multibyte character functions (7.20.7), the
multibyte string functions (7.20.8), string conversion
functions (7.20.1), the strcoll function (7.21.4.3), the
strftime function (7.23.3.5), the strfxtime function
(7.23.3.6), the strxfrm function (7.21.4.5).
7.11.2 Numeric formatting convention inquiry
7.11.2.1 The localeconv function
Synopsis
[#1]
#include <locale.h>
struct lconv *localeconv(void);
Description
[#2] The localeconv function sets the components of an
object with type struct lconv with values appropriate for
the formatting of numeric quantities (monetary and
otherwise) according to the rules of the current locale.
____________________
175The implementation shall arrange to encode in a string
the various categories due to a heterogeneous locale when
category has the value LC_ALL.
7.11.1.1 Library 7.11.2.1
228 Committee Draft -- August 3, 1998 WG14/N843
[#3] The members of the structure with type char * are
pointers to strings, any of which (except decimal_point) can
point to "", to indicate that the value is not available in
the current locale or is of zero length. Apart from
grouping and mon_grouping, the strings shall start and end
in the initial shift state. The members with type char are
nonnegative numbers, any of which can be CHAR_MAX to
indicate that the value is not available in the current
locale. The members include the following:
char *decimal_point
The decimal-point character used to format
nonmonetary quantities.
char *thousands_sep
The character used to separate groups of digits
before the decimal-point character in formatted
nonmonetary quantities.
char *grouping
A string whose elements indicate the size of each
group of digits in formatted nonmonetary quantities. *
char *mon_decimal_point
The decimal-point used to format monetary quantities.
char *mon_thousands_sep
The separator for groups of digits before the
decimal-point in formatted monetary quantities.
char *mon_grouping
A string whose elements indicate the size of each
group of digits in formatted monetary quantities.
char *positive_sign
The string used to indicate a nonnegative-valued
formatted monetary quantity.
char *negative_sign
The string used to indicate a negative-valued
formatted monetary quantity. |
char *currency_symbol
The local currency symbol applicable to the current |
locale.
char frac_digits
The number of fractional digits (those after the
decimal-point) to be displayed in a locally formatted |
monetary quantity.
char p_cs_precedes
Set to 1 or 0 if the currency_symbol respectively
precedes or succeeds the value for a nonnegative |
7.11.2.1 Library 7.11.2.1
WG14/N843 Committee Draft -- August 3, 1998 229
locally formatted monetary quantity.
char n_cs_precedes
Set to 1 or 0 if the currency_symbol respectively
precedes or succeeds the value for a negative locally |
formatted monetary quantity. |
char p_sep_by_space |
Set to a value indicating the separation of the |
currency_symbol, the sign string, and the value for a |
nonnegative locally formatted monetary quantity.
char n_sep_by_space
Set to a value indicating the separation of the |
currency_symbol, the sign string, and the value for a |
negative locally formatted monetary quantity.
char p_sign_posn
Set to a value indicating the positioning of the
positive_sign for a nonnegative locally formatted |
monetary quantity.
char n_sign_posn
Set to a value indicating the positioning of the
negative_sign for a negative locally formatted |
monetary quantity. |
char *int_curr_symbol |
The international currency symbol applicable to the |
current locale. The first three characters contain |
the alphabetic international currency symbol in |
accordance with those specified in ISO 4217:1995. |
The fourth character (immediately preceding the null |
character) is the character used to separate the |
international currency symbol from the monetary |
quantity. |
char int_frac_digits |
The number of fractional digits (those after the |
decimal-point) to be displayed in an internationally |
formatted monetary quantity. |
char int_p_cs_precedes |
Set to 1 or 0 if the int_currency_symbol respectively |
precedes or succeeds the value for a nonnegative |
internationally formatted monetary quantity. |
char int_n_cs_precedes |
Set to 1 or 0 if the int_currency_symbol respectively |
precedes or succeeds the value for a negative |
internationally formatted monetary quantity. |
char int_p_sep_by_space |
Set to a value indicating the separation of the |
7.11.2.1 Library 7.11.2.1
230 Committee Draft -- August 3, 1998 WG14/N843
int_currency_symbol, the sign string, and the value |
for a nonnegative internationally formatted monetary |
quantity. |
char int_n_sep_by_space |
Set to a value indicating the separation of the |
int_currency_symbol, the sign string, and the value |
for a negative internationally formatted monetary |
quantity. |
char int_p_sign_posn |
Set to a value indicating the positioning of the |
positive_sign for a nonnegative internationally |
formatted monetary quantity. |
char int_n_sign_posn |
Set to a value indicating the positioning of the |
negative_sign for a negative internationally |
formatted monetary quantity.
[#4] The elements of grouping and mon_grouping are
interpreted according to the following:
CHAR_MAX No further grouping is to be performed.
0 The previous element is to be repeatedly used for
the remainder of the digits.
other The integer value is the number of digits that |
compose the current group. The next element is
examined to determine the size of the next group
of digits before the current group.
[#5] The values of p_sep_by_space, n_sep_by_space, |
int_p_sep_by_space, and int_n_sep_by_space are interpreted |
according to the following: |
0 No space separates the currency symbol and value. |
1 A space separates the currency symbol and value. |
2 A space separates the currency symbol and the sign |
string, if adjacent. |
[#6] The values of p_sign_posn, n_sign_posn, |
int_p_sign_posn, and int_n_sign_posn are interpreted |
according to the following:
0 Parentheses surround the quantity and currency symbol. |
1 The sign string precedes the quantity and currency |
symbol.
7.11.2.1 Library 7.11.2.1
WG14/N843 Committee Draft -- August 3, 1998 231
2 The sign string succeeds the quantity and currency |
symbol.
3 The sign string immediately precedes the currency symbol. |
4 The sign string immediately succeeds the currency symbol. |
[#7] The implementation shall behave as if no library
function calls the localeconv function.
Returns
[#8] The localeconv function returns a pointer to the
filled-in object. The structure pointed to by the return
value shall not be modified by the program, but may be
overwritten by a subsequent call to the localeconv function.
In addition, calls to the setlocale function with categories
LC_ALL, LC_MONETARY, or LC_NUMERIC may overwrite the
contents of the structure.
[#9] EXAMPLE The following table illustrates the rules
which may well be used by four countries to format monetary
quantities. |
|| |
|| Local format | International format |
|+--------------+----------------+--------------+--------------|
Country ||Positive | Negative | Positive | Negative|
------------++--------------+----------------+--------------+--------------|
Finland ||1.234,56 mk | -1.234,56 mk | FIM 1.234,56 | FIM -1.234,56|
Italy ||L.1.234 | -L.1.234 | ITL 1.234 | -ITL 1.234|
Netherlands ||f 1.234,56 | f -1.234,56 | NLG 1.234,56 | NLG -1.234,56|
Switzerland ||SFrs.1,234.56 | SFrs.1,234.56C | CHF 1,234.56 | CHF 1,234.56C|
[#10] For these four countries, the respective values for
the monetary members of the structure returned by localeconv
are:
7.11.2.1 Library 7.11.2.1
232 Committee Draft -- August 3, 1998 WG14/N843
|| | | |
||Finland | Italy | Netherlands | Switzerland|
-------------------++------------+-------------+-------------+------------|
mon_decimal_point ||"," | "" | "," | "."|
mon_thousands_sep ||"." | "." | "." | ","
mon_grouping ||"\3" | "\3" | "\3" | "\3"
positive_sign ||"" | "" | "" | ""
negative_sign ||"-" | "-" | "-" | "C"
currency_symbol ||"mk" | "L." | "\u0192 " | "SFrs."|
frac_digits ||2 | 0 | 2 | 2|
p_cs_precedes ||0 | 1 | 1 | 1|
n_cs_precedes ||0 | 1 | 1 | 1|
p_sep_by_space ||1 | 0 | 1 | 0|
n_sep_by_space ||1 | 0 | 1 | 0|
p_sign_posn ||1 | 1 | 1 | 1
n_sign_posn ||1 | 1 | 4 | 2|
int_curr_symbol ||"FIM " | "ITL " | "NLG " | "CHF "|
int_frac_digits ||2 | 0 | 2 | 2|
int_p_cs_precedes ||1 | 1 | 1 | 1|
int_n_cs_precedes ||1 | 1 | 1 | 1|
int_p_sep_by_space ||1 | 1 | 1 | 1|
int_n_sep_by_space ||1 | 1 | 1 | 1|
int_p_sign_posn ||1 | 1 | 1 | 1|
int_n_sign_posn ||4 | 1 | 4 | 2|
7.11.2.1 Library 7.11.2.1
WG14/N843 Committee Draft -- August 3, 1998 233
7.12 Mathematics <math.h>
[#1] The header <math.h> declares two types and several
mathematical functions and defines several macros. Most
synopses specify a family of functions consisting of a
principal function with one or more double parameters, a
double return value, or both; and other functions with the
same name but with f and l suffixes which are corresponding
functions with float and long double parameters, return
values, or both.176) Integer arithmetic functions and
conversion functions are discussed later.
[#2] The types
float_t
double_t
are floating types at least as wide as float and double,
respectively, and such that double_t is at least as wide as
float_t. If FLT_EVAL_METHOD equals 0, float_t and double_t
are float and double, respectively; if FLT_EVAL_METHOD
equals 1, they are both double; if FLT_EVAL_METHOD equals 2,
they are both long double; and for other values of
FLT_EVAL_METHOD, they are otherwise
implementation-defined.177)
[#3] The macro
HUGE_VAL
expands to a positive double constant expression, not
necessarily representable as a float. The macros
HUGE_VALF
HUGE_VALL
are respectively float and long double analogs of
HUGE_VAL.178)
____________________
176Particularly on systems with wide expression evaluation,
a <math.h> function might pass arguments and return
values in wider format than the synopsis prototype
indicates.
177The types float_t and double_t are intended to be the
implementation's most efficient types at least as wide as
float and double, respectively. For FLT_EVAL_METHOD
equal 0, 1, or 2, the type float_t is the narrowest type
used by the implementation to evaluate floating
expressions.
178HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive
infinities in an implementation that supports infinities.
7.12 Library 7.12
234 Committee Draft -- August 3, 1998 WG14/N843
[#4] The macro
INFINITY
expands to a constant expression of type float representing
an implementation-defined positive or unsigned infinity, if |
available; else to a positive constant of type float that |
overflows at translation time.179)
[#5] The macro
NAN
is defined if and only if the implementation supports quiet
NaNs for the float type. It expands to a constant
expression of type float representing an implementation-
defined quiet NaN.
[#6] The macros
FP_INFINITE
FP_NAN
FP_NORMAL
FP_SUBNORMAL
FP_ZERO
are for number classification. They represent the mutually
exclusive kinds of floating-point values. They expand to
integer constant expressions with distinct values.
[#7] The macro
FP_FAST_FMA
is optionally defined. If defined, it indicates that the |
fma function generally executes about as fast as, or faster |
than, a multiply and an add of double operands.180) The
macros
FP_FAST_FMAF
FP_FAST_FMAL
are, respectively, float and long double analogs of
FP_FAST_FMA.
____________________
179In this case, using INFINITY will violate the constraint
in 6.4.4 and thus require a diagnostic.
180Typically, the FP_FAST_FMA macro is defined if and only
if the fma function is implemented directly with a
hardware multiply-add instruction. Software
implementations are expected to be substantially slower.
7.12 Library 7.12
WG14/N843 Committee Draft -- August 3, 1998 235
[#8] The macros
FP_ILOGB0
FP_ILOGBNAN
expand to integer constant expressions whose values are
returned by ilogb(x) if x is zero or NaN, respectively. The
value of FP_ILOGB0 shall be either INT_MIN or -INT_MAX. The
value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN. *
Recommended practice
[#9] Conversion from (at least) double to decimal with |
DECIMAL_DIG digits and back should be the identity function |
(which assures that conversion from the widest supported IEC |
60559 format to decimal with DECIMAL_DIG digits and back is |
the identity function).
7.12.1 Treatment of error conditions
[#1] The behavior of each of the functions in <math.h> is
specified for all representable values of its input
arguments, except where stated otherwise.
[#2] For all functions, a domain error occurs if an input
argument is outside the domain over which the mathematical
function is defined. The description of each function lists
any required domain errors; an implementation may define
additional domain errors, provided that such errors are
consistent with the mathematical definition of the
function.181) On a domain error, the function returns an
implementation-defined value; whether the integer expression
errno acquires the value EDOM is implementation-defined.
[#3] Similarly, a range error occurs if the mathematical
result of the function cannot be represented in an object of
the specified type, due to extreme magnitude. A floating
result overflows if the magnitude of the mathematical result
is finite but so large that the mathematical result cannot
be represented, without extraordinary roundoff error, in an
object of the specified type. If a floating result
overflows and default rounding is in effect, or if the
mathematical result is an exact infinity (for example
log(0.0)), then the function returns the value of the macro
HUGE_VAL, HUGE_VALF, or HUGE_VALL according to the return
type, with the same sign as the correct value of the
function; whether errno acquires the value ERANGE when a
range error occurs is implementation-defined. The result
____________________
181In an implementation that supports infinities, this
allows an infinity as an argument to be a domain error if
the mathematical domain of the function does not include
the infinity.
7.12 Library 7.12.1
236 Committee Draft -- August 3, 1998 WG14/N843
underflows if the magnitude of the mathematical result is so
small that the mathematical result cannot be represented,
without extraordinary roundoff error, in an object of the
specified type.182) If the result underflows, the function
returns a value whose magnitude is no greater than the
smallest normalized positive number in the specified type
and is otherwise implementation-defined; whether errno
acquires the value ERANGE is implementation-defined.
7.12.2 The FP_CONTRACT pragma
Synopsis
[#1]
#include <math.h>
#pragma STDC FP_CONTRACT on-off-switch
Description
[#2] The FP_CONTRACT pragma can be used to allow (if the
state is on) or disallow (if the state is off) the
implementation to contract expressions (6.5). Each pragma
can occur either outside external declarations or preceding
all explicit declarations and statements inside a compound
statement. When outside external declarations, the pragma
takes effect from its occurrence until another FP_CONTRACT
pragma is encountered, or until the end of the translation
unit. When inside a compound statement, the pragma takes
effect from its occurrence until another FP_CONTRACT pragma
is encountered (within a nested compound statement), or
until the end of the compound statement; at the end of a
compound statement the state for the pragma is restored to
its condition just before the compound statement. If this
pragma is used in any other context, the behavior is
undefined. The default state (on or off) for the pragma is
implementation-defined.
7.12.3 Classification macros
[#1] In the synopses in this subclause, real-floating
indicates that the argument shall be an expression of real
floating type. The result is undefined if an argument is
not of real floating type.
____________________
182The term underflow here is intended to encompass both
gradual underflow as in IEC 60559 and also flush-to-zero
underflow.
7.12.1 Library 7.12.3
WG14/N843 Committee Draft -- August 3, 1998 237
7.12.3.1 The fpclassify macro
Synopsis
[#1]
#include <math.h>
int fpclassify(real-floating x);
Description
[#2] The fpclassify macro classifies its argument value as
NaN, infinite, normal, subnormal, or zero. First, an
argument represented in a format wider than its semantic
type is converted to its semantic type. Then classification
is based on the type of the argument.183)
Returns
[#3] The fpclassify macro returns the value of the number
classification macro appropriate to the value of its
argument.
[#4] EXAMPLE The fpclassify macro might be implemented in
terms of ordinary functions as
#define fpclassify(x) \ |
((sizeof (x) == sizeof (float)) ? \ |
__fpclassifyf(x) \ |
: (sizeof (x) == sizeof (double)) ? \ |
__fpclassifyd(x) \ |
: __fpclassifyl(x))
____________________
183Since an expression can be evaluated with more range and
precision than its type has, it is important to know the
type that classification is based on. For example, a
normal long double value might become subnormal when
converted to double, and zero when converted to float.
7.12.3 Library 7.12.3.1
238 Committee Draft -- August 3, 1998 WG14/N843
7.12.3.2 The isfinite macro
Synopsis
[#1]
#include <math.h>
int isfinite(real-floating x);
Description
[#2] The isfinite macro determines whether its argument has
a finite value (zero, subnormal, or normal, and not infinite
or NaN). First, an argument represented in a format wider
than its semantic type is converted to its semantic type.
Then determination is based on the type of the argument.
Returns
[#3] The isfinite macro returns a nonzero value if and only
if its argument has a finite value.
7.12.3.3 The isinf macro
Synopsis
[#1]
#include <math.h>
int isinf(real-floating x);
Description
[#2] The isinf macro determines whether its argument value
is an infinity (positive or negative). First, an argument
represented in a format wider than its semantic type is
converted to its semantic type. Then determination is based
on the type of the argument.
Returns
[#3] The isinf macro returns a nonzero value if and only if
its argument has an infinite value.
7.12.3.1 Library 7.12.3.3
WG14/N843 Committee Draft -- August 3, 1998 239
7.12.3.4 The isnan macro
Synopsis
[#1]
#include <math.h>
int isnan(real-floating x);
Description
[#2] The isnan macro determines whether its argument value
is a NaN. First, an argument represented in a format wider
than its semantic type is converted to its semantic type.
Then determination is based on the type of the argument.184)
Returns
[#3] The isnan macro returns a nonzero value if and only if
its argument has a NaN value.
7.12.3.5 The isnormal macro
Synopsis
[#1]
#include <math.h>
int isnormal(real-floating x);
Description
[#2] The isnormal macro determines whether its argument
value is normal (neither zero, subnormal, infinite, nor
NaN). First, an argument represented in a format wider than
its semantic type is converted to its semantic type. Then
determination is based on the type of the argument.
Returns
[#3] The isnormal macro returns a nonzero value if and only
if its argument has a normal value.
____________________
184For the isnan macro, the type for determination does not |
matter unless the implementation supports NaNs in the
evaluation type but not in the semantic type.
7.12.3.3 Library 7.12.3.5
240 Committee Draft -- August 3, 1998 WG14/N843
7.12.3.6 The signbit macro
Synopsis
[#1]
#include <math.h>
int signbit(real-floating x);
Description
[#2] The signbit macro determines whether the sign of its
argument value is negative.185)
Returns
[#3] The signbit macro returns a nonzero value if and only
if the sign of its argument value is negative.
7.12.4 Trigonometric functions
7.12.4.1 The acos functions
Synopsis
[#1]
#include <math.h>
double acos(double x);
float acosf(float x);
long double acosl(long double x);
Description
[#2] The acos functions compute the principal value of the
arc cosine of x. A domain error occurs for arguments not in
the range [-1, +1].
Returns
[#3] The acos functions return the arc cosine in the range
[0, pi] radians.
____________________
185The signbit macro reports the sign of all values,
including infinities, zeros, and NaNs.
7.12.3.5 Library 7.12.4.1
WG14/N843 Committee Draft -- August 3, 1998 241
7.12.4.2 The asin functions
Synopsis
[#1]
#include <math.h>
double asin(double x);
float asinf(float x);
long double asinl(long double x);
Description
[#2] The asin functions compute the principal value of the
arc sine of x. A domain error occurs for arguments not in
the range [-1, +1].
Returns
[#3] The asin functions return the arc sine in the range
[-pi/2, +pi/2] radians.
7.12.4.3 The atan functions
Synopsis
[#1]
#include <math.h>
double atan(double x);
float atanf(float x);
long double atanl(long double x);
Description
[#2] The atan functions compute the principal value of the
arc tangent of x.
Returns
[#3] The atan functions return the arc tangent in the range
[-pi/2, +pi/2] radians.
7.12.4.1 Library 7.12.4.3
242 Committee Draft -- August 3, 1998 WG14/N843
7.12.4.4 The atan2 functions
Synopsis
[#1]
#include <math.h>
double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
Description
[#2] The atan2 functions compute the principal value of the
arc tangent of y/x, using the signs of both arguments to
determine the quadrant of the return value. A domain error
may occur if both arguments are zero.
Returns
[#3] The atan2 functions return the arc tangent of y/x, in
the range [-pi, +pi] radians.
7.12.4.5 The cos functions
Synopsis
[#1]
#include <math.h>
double cos(double x);
float cosf(float x);
long double cosl(long double x);
Description
[#2] The cos functions compute the cosine of x (measured in
radians).
Returns
[#3] The cos functions return the cosine value.
7.12.4.3 Library 7.12.4.5
WG14/N843 Committee Draft -- August 3, 1998 243
7.12.4.6 The sin functions
Synopsis
[#1]
#include <math.h>
double sin(double x);
float sinf(float x);
long double sinl(long double x);
Description
[#2] The sin functions compute the sine of x (measured in
radians).
Returns
[#3] The sin functions return the sine value.
7.12.4.7 The tan functions
Synopsis
[#1]
#include <math.h>
double tan(double x);
float tanf(float x);
long double tanl(long double x);
Description
[#2] The tan functions return the tangent of x (measured in
radians).
Returns
[#3] The tan functions return the tangent value.
7.12.5 Hyperbolic functions
7.12.4.5 Library 7.12.5
244 Committee Draft -- August 3, 1998 WG14/N843
7.12.5.1 The acosh functions
Synopsis
[#1]
#include <math.h>
double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);
Description
[#2] The acosh functions compute the (nonnegative) arc
hyperbolic cosine of x. A domain error occurs for arguments
less than 1.
Returns
[#3] The acosh functions return the arc hyperbolic cosine in
the range [0, +].
7.12.5.2 The asinh functions
Synopsis
[#1]
#include <math.h>
double asinh(double x);
float asinhf(float x);
long double asinhl(long double x);
Description
[#2] The asinh functions compute the arc hyperbolic sine of
x.
Returns
[#3] The asinh functions return the arc hyperbolic sine
value.
7.12.5 Library 7.12.5.2
WG14/N843 Committee Draft -- August 3, 1998 245
7.12.5.3 The atanh functions
Synopsis
[#1]
#include <math.h>
double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
Description
[#2] The atanh functions compute the arc hyperbolic tangent
of x. A domain error occurs for arguments not in the range
[-1, +1]. A range error may occur if the argument equals -1
or +1.
Returns
[#3] The atanh functions return the arc hyperbolic tangent
value.
7.12.5.4 The cosh functions
Synopsis
[#1]
#include <math.h>
double cosh(double x);
float coshf(float x);
long double coshl(long double x);
Description
[#2] The cosh functions compute the hyperbolic cosine of x.
A range error occurs if the magnitude of x is too large.
Returns
[#3] The cosh functions return the hyperbolic cosine value.
7.12.5.2 Library 7.12.5.4
246 Committee Draft -- August 3, 1998 WG14/N843
7.12.5.5 The sinh functions
Synopsis
[#1]
#include <math.h>
double sinh(double x);
float sinhf(float x);
long double sinhl(long double x);
Description
[#2] The sinh functions compute the hyperbolic sine of x. A
range error occurs if the magnitude of x is too large.
Returns
[#3] The sinh functions return the hyperbolic sine value.
7.12.5.6 The tanh functions
Synopsis
[#1]
#include <math.h>
double tanh(double x);
float tanhf(float x);
long double tanhl(long double x);
Description
[#2] The tanh functions compute the hyperbolic tangent of x.
Returns
[#3] The tanh functions return the hyperbolic tangent value.
7.12.6 Exponential and logarithmic functions
7.12.5.4 Library 7.12.6
WG14/N843 Committee Draft -- August 3, 1998 247
7.12.6.1 The exp functions
Synopsis
[#1]
#include <math.h>
double exp(double x);
float expf(float x);
long double expl(long double x);
Description
[#2] The exp functions compute the base-e exponential of x:
ex. A range error occurs if the magnitude of x is too
large.
Returns
[#3] The exp functions return the exponential value.
7.12.6.2 The exp2 functions
Synopsis
[#1]
#include <math.h>
double exp2(double x);
float exp2f(float x);
long double exp2l(long double x);
Description
[#2] The exp2 functions compute the base-2 exponential of x:
2x. A range error occurs if the magnitude of x is too
large.
Returns
[#3] The exp2 functions return the base-2 exponential value.
7.12.6 Library 7.12.6.2
248 Committee Draft -- August 3, 1998 WG14/N843
7.12.6.3 The expm1 functions
Synopsis
[#1]
#include <math.h>
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
Description
[#2] The expm1 functions compute the base-e exponential of
the argument, minus 1: ex-1. A range error occurs if x is |
too large.186) *
Returns
[#3] The expm1 functions return the value of ex-1.
7.12.6.4 The frexp functions
Synopsis
[#1]
#include <math.h>
double frexp(double value, int *exp);
float frexpf(float value, int *exp);
long double frexpl(long double value, int *exp);
Description
[#2] The frexp functions break a floating-point number into
a normalized fraction and an integral power of 2. They
store the integer in the int object pointed to by exp.
Returns
[#3] The frexp functions return the value x, such that x has
a magnitude in the interval [1/2, 1) or zero, and value
equals x×2*exp. If value is zero, both parts of the result
are zero.
____________________
186For small magnitude x, expm1(x) is expected to be more
accurate than exp(x) - 1.
7.12.6.2 Library 7.12.6.4
WG14/N843 Committee Draft -- August 3, 1998 249
7.12.6.5 The ilogb functions
Synopsis
[#1]
#include <math.h>
int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
Description
[#2] The ilogb functions extract the exponent of x as a
signed int value. If x is zero they compute the value
FP_ILOGB0; if x is infinite they compute the value INT_MAX;
if x is a NaN they compute the value FP_ILOGBNAN; otherwise,
they are equivalent to calling the corresponding logb
function and casting the returned value to type int. A
range error may occur if x is 0.
Returns
[#3] The ilogb functions return the exponent of x as a
signed int value. |
Forward references: the logb functions (7.12.6.11).
7.12.6.6 The ldexp functions
Synopsis
[#1]
#include <math.h>
double ldexp(double x, int exp);
float ldexpf(float x, int exp);
long double ldexpl(long double x, int exp);
Description
[#2] The ldexp functions multiply a floating-point number by
an integral power of 2. A range error may occur.
Returns
[#3] The ldexp functions return the value of x×2exp.
7.12.6.4 Library 7.12.6.6
250 Committee Draft -- August 3, 1998 WG14/N843
7.12.6.7 The log functions
Synopsis
[#1]
#include <math.h>
double log(double x);
float logf(float x);
long double logl(long double x);
Description
[#2] The log functions compute the base-e (natural)
logarithm of x. A domain error occurs if the argument is
negative. A range error may occur if the argument is zero.
Returns
[#3] The log functions return the base-e logarithm value.
7.12.6.8 The log10 functions
Synopsis
[#1]
#include <math.h>
double log10(double x);
float log10f(float x);
long double log10l(long double x);
Description
[#2] The log10 functions compute the base-10 (common)
logarithm of x. A domain error occurs if the argument is
negative. A range error may occur if the argument is zero.
Returns
[#3] The log10 functions return the base-10 logarithm value.
7.12.6.6 Library 7.12.6.8
WG14/N843 Committee Draft -- August 3, 1998 251
7.12.6.9 The log1p functions
Synopsis
[#1]
#include <math.h>
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
Description
[#2] The log1p functions compute the base-e (natural)
logarithm of 1 plus the argument.187) A domain error occurs
if the argument is less than -1. A range error may occur if
the argument equals -1.
Returns
[#3] The log1p functions return the value of the base-e
logarithm of 1 plus the argument.
7.12.6.10 The log2 functions
Synopsis
[#1]
#include <math.h>
double log2(double x);
float log2f(float x);
long double log2l(long double x);
Description
[#2] The log2 functions compute the base-2 logarithm of x.
A domain error occurs if the argument is less than zero. A
range error may occur if the argument is zero.
Returns
[#3] The log2 functions return the base-2 logarithm value.
____________________
187For small magnitude x, log1p(x) is expected to be more
accurate than log(1 + x).
7.12.6.8 Library 7.12.6.10
252 Committee Draft -- August 3, 1998 WG14/N843
7.12.6.11 The logb functions
Synopsis
[#1]
#include <math.h>
double logb(double x);
float logbf(float x);
long double logbl(long double x);
Description
[#2] The logb functions extract the exponent of x, as a |
signed integer value in floating-point format. If x is
subnormal it is treated as though it were normalized; thus, |
for positive finite x,
1<=x×FLT_RADIX-logb(x)<FLT_RADIX
A domain error may occur if the argument is zero.
Returns
[#3] The logb functions return the signed exponent of x.
7.12.6.12 The modf functions
Synopsis
[#1]
#include <math.h>
double modf(double value, double *iptr);
float modff(float value, float *iptr);
long double modfl(long double value, long double *iptr);
Description
[#2] The modf functions break the argument value into
integral and fractional parts, each of which has the same
type and sign as the argument. They store the integral part |
(in floating-point format) in the object pointed to by iptr.
Returns
[#3] The modf functions return the value of the signed
fractional part of value. |
7.12.6.10 Library 7.12.6.12
WG14/N843 Committee Draft -- August 3, 1998 253
7.12.6.13 The scalbn and scalbln functions |
Synopsis
[#1]
#include <math.h>
double scalbn(double x, int n);
float scalbnf(float x, int n);
long double scalbnl(long double x, int n);
double scalbln(double x, long int n); |
float scalblnf(float x, long int n); |
long double scalblnl(long double x, long int n); |
Description
[#2] The scalbn and scalbln functions compute x×FLT_RADIXn |
efficiently, not normally by computing FLT_RADIXn
explicitly. A range error may occur.
Returns
[#3] The scalbn and scalbln functions return the value of |
x×FLT_RADIXn. *
7.12.7 Power and absolute-value functions
7.12.7.1 The cbrt functions
Synopsis
[#1]
#include <math.h>
double cbrt(double x);
float cbrtf(float x);
long double cbrtl(long double x);
Description
[#2] The cbrt functions compute the real cube root of x.
Returns
[#3] The cbrt functions return the value of the cube root.
7.12.6.13 Library 7.12.7.1
254 Committee Draft -- August 3, 1998 WG14/N843
7.12.7.2 The fabs functions
Synopsis
[#1]
#include <math.h>
double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);
Description
[#2] The fabs functions compute the absolute value of a
floating-point number x.
Returns
[#3] The fabs functions return the absolute value of x.
7.12.7.3 The hypot functions
Synopsis
[#1]
#include <math.h>
double hypot(double x, double y);
float hypotf(float x, float y);
long double hypotl(long double x, long double y);
Description
[#2] The hypot functions compute the square root of the sum
of the squares of x and y, without undue overflow or
underflow. A range error may occur.
[#3]
Returns
[#4] The hypot functions return the value of the square root
of the sum of the squares.
7.12.7.1 Library 7.12.7.3
WG14/N843 Committee Draft -- August 3, 1998 255
7.12.7.4 The pow functions
Synopsis
[#1]
#include <math.h>
double pow(double x, double y);
float powf(float x, float y);
long double powl(long double x, long double y);
Description
[#2] The pow functions compute x raised to the power y. A
domain error occurs if x is negative and y is finite and not
an integer value. A domain error occurs if the result
cannot be represented when x is zero and y is less than or
equal to zero. A range error may occur.
Returns
[#3] The pow functions return the value of x raised to the
power y.
7.12.7.5 The sqrt functions
Synopsis
[#1]
#include <math.h>
double sqrt(double x);
float sqrtf(float x);
long double sqrtl(long double x);
Description
[#2] The sqrt functions compute the nonnegative square root
of x. A domain error occurs if the argument is less than
zero.
Returns
[#3] The sqrt functions return the value of the square root.
7.12.8 Error and gamma functions
7.12.7.3 Library 7.12.8
256 Committee Draft -- August 3, 1998 WG14/N843
7.12.8.1 The erf functions
Synopsis
[#1]
#include <math.h>
double erf(double x);
float erff(float x);
long double erfl(long double x);
Description
[#2] The erf functions compute the error function of x: |
_0e-t2dt.
Returns
[#3] The erf functions return the error function value.
7.12.8.2 The erfc functions
Synopsis
[#1]
#include <math.h>
double erfc(double x);
float erfcf(float x);
long double erfcl(long double x);
Description
[#2] The erfc functions compute the complementary error
function of x: _xe-t2dt. A range error occurs if x is too |
large.
Returns
[#3] The erfc functions return the complementary error
function value.
7.12.8 Library 7.12.8.2
WG14/N843 Committee Draft -- August 3, 1998 257
7.12.8.3 The lgamma functions
Synopsis
[#1]
#include <math.h>
double lgamma(double x);
float lgammaf(float x);
long double lgammal(long double x);
Description
[#2] The lgamma functions compute the natural logarithm of
the absolute value of gamma of x: loge|(x)|. A range error |
occurs if x is too large or if x is a negative integer or
zero.
Returns
[#3] The lgamma functions return the value of the natural
logarithm of the absolute value of gamma of x. |
7.12.8.4 The tgamma functions |
Synopsis
[#1]
#include <math.h>
double tgamma(double x); |
float tgammaf(float x); |
long double tgammal(long double x); |
Description
[#2] The tgamma functions compute the gamma function of x: |
(x). A domain error occurs if x is a negative integer or
zero. A range error may occur if the magnitude of x is too
large or too small.
Returns
[#3] The tgamma functions return the gamma function value. |
7.12.9 Nearest integer functions
7.12.8.2 Library 7.12.9
258 Committee Draft -- August 3, 1998 WG14/N843
7.12.9.1 The ceil functions
Synopsis
[#1]
#include <math.h>
double ceil(double x);
float ceilf(float x);
long double ceill(long double x);
Description
[#2] The ceil functions compute the smallest integer value
not less than x: |x|. |
Returns
[#3] The ceil functions return the smallest integer value
not less than x, expressed as a floating-point number.
7.12.9.2 The floor functions
Synopsis
[#1]
#include <math.h>
double floor(double x);
float floorf(float x);
long double floorl(long double x);
Description
[#2] The floor functions compute the largest integer value
not greater than x: |x|. |
Returns
[#3] The floor functions return the largest integer value
not greater than x, expressed as a floating-point number.
7.12.9 Library 7.12.9.2
WG14/N843 Committee Draft -- August 3, 1998 259
7.12.9.3 The nearbyint functions
Synopsis
[#1]
#include <math.h>
double nearbyint(double x);
float nearbyintf(float x);
long double nearbyintl(long double x);
Description
[#2] The nearbyint functions round their argument to an |
integer value in floating-point format, using the current |
rounding direction and without raising the inexact |
exception.
Returns
[#3] The nearbyint functions return the rounded integer
value.
7.12.9.4 The rint functions
Synopsis
[#1]
#include <math.h>
double rint(double x);
float rintf(float x);
long double rintl(long double x);
Description
[#2] The rint functions differ from the nearbyint functions |
(7.12.9.3) only in that the rint functions do raise the |
inexact exception if the result differs in value from the |
argument (see F.9.6.3 and F.9.6.4).
Returns
[#3] The rint functions return the rounded integer value. |
7.12.9.5 The lrint and llrint functions |
Synopsis
[#1]
7.12.9.2 Library 7.12.9.5
260 Committee Draft -- August 3, 1998 WG14/N843
#include <math.h>
long int lrint(double x);
long int lrintf(float x);
long int lrintl(long double x);
long long int llrint(double x); |
long long int llrintf(float x); |
long long int llrintl(long double x); |
Description
[#2] The lrint and llrint functions round their argument to |
the nearest integer value, rounding according to the current
rounding direction. If the rounded value is outside the
range of the return type, the numeric result is unspecified. |
A range error may occur if the magnitude of x is too large.
Returns
[#3] The lrint and llrint functions return the rounded |
integer value. |
7.12.9.6 The round functions
Synopsis
[#1]
#include <math.h>
double round(double x);
float roundf(float x);
long double roundl(long double x);
Description
[#2] The round functions round their argument to the nearest
integer value in floating-point format, rounding halfway
cases away from zero, regardless of the current rounding
direction.
Returns
[#3] The round functions return the rounded integer value. |
7.12.9.7 The lround and llround functions |
Synopsis
[#1]
7.12.9.5 Library 7.12.9.7
WG14/N843 Committee Draft -- August 3, 1998 261
#include <math.h>
long int lround(double x);
long int lroundf(float x);
long int lroundl(long double x);
long long int llround(double x); |
long long int llroundf(float x); |
long long int llroundl(long double x); |
Description
[#2] The lround and llround functions round their argument |
to the nearest integer value, rounding halfway cases away
from zero, regardless of the current rounding direction. If
the rounded value is outside the range of the return type, |
the numeric result is unspecified. A range error may occur
if the magnitude of x is too large.
Returns
[#3] The lround and llround functions return the rounded |
integer value.
7.12.9.8 The trunc functions
Synopsis
[#1]
#include <math.h>
double trunc(double x);
float truncf(float x);
long double truncl(long double x);
Description
[#2] The trunc functions round their argument to the integer
value, in floating format, nearest to but no larger in
magnitude than the argument.
Returns
[#3] The trunc functions return the truncated integer value.
7.12.10 Remainder functions
7.12.9.7 Library 7.12.10
262 Committee Draft -- August 3, 1998 WG14/N843
7.12.10.1 The fmod functions
Synopsis
[#1]
#include <math.h>
double fmod(double x, double y);
float fmodf(float x, float y);
long double fmodl(long double x, long double y);
Description
[#2] The fmod functions compute the floating-point remainder
of x/y.
Returns
[#3] The fmod functions return the value x-ny, for some |
integer n such that, if y is nonzero, the result has the
same sign as x and magnitude less than the magnitude of y.
If y is zero, whether a domain error occurs or the fmod
functions return zero is implementation-defined.
7.12.10.2 The remainder functions
Synopsis
[#1]
#include <math.h>
double remainder(double x, double y);
float remainderf(float x, float y);
long double remainderl(long double x, long double y);
Description
[#2] The remainder functions compute the remainder x REM y |
required by IEC 60559.188)
Returns
[#3] The remainder functions return the value of x REM y. |
____________________
188``When y!=0, the remainder r=x REM y is defined |
regardless of the rounding mode by the mathematical
relation r=x-ny, where n is the integer nearest the exact |
value of x/y; whenever |n-x/y|=1/2, then n is even. |
Thus, the remainder is always exact. If r=0, its sign |
shall be that of x.'' This definition is applicable for
all implementations.
7.12.10 Library 7.12.10.2
WG14/N843 Committee Draft -- August 3, 1998 263
7.12.10.3 The remquo functions
Synopsis
[#1]
#include <math.h>
double remquo(double x, double y, int *quo);
float remquof(float x, float y, int *quo);
long double remquol(long double x, long double y,
int *quo);
Description
[#2] The remquo functions compute the same remainder as the |
remainder functions. In the object pointed to by quo they
store a value whose sign is the sign of x/y and whose |
magnitude is congruent modulo 2n to the magnitude of the
integral quotient of x/y, where n is an implementation- |
defined integer greater than or equal to 3.
Returns
[#3] The remquo functions return the value of x REM y. |
7.12.11 Manipulation functions
7.12.11.1 The copysign functions
Synopsis
[#1]
#include <math.h>
double copysign(double x, double y);
float copysignf(float x, float y);
long double copysignl(long double x, long double y);
Description
[#2] The copysign functions produce a value with the
magnitude of x and the sign of y. They produce a NaN (with
the sign of y) if x is a NaN. On implementations that
represent a signed zero but do not treat negative zero
consistently in arithmetic operations, the copysign
functions regard the sign of zero as positive.
Returns
[#3] The copysign functions return a value with the
magnitude of x and the sign of y.
7.12.10.2 Library 7.12.11.1
264 Committee Draft -- August 3, 1998 WG14/N843
7.12.11.2 The nan functions
Synopsis
[#1]
#include <math.h>
double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);
Description
[#2] The call nan("n-char-sequence") is equivalent to
strtod("NAN(n-char-sequence)", (char**) NULL); the call |
nan("") is equivalent to strtod("NAN()", (char**) NULL). If |
tagp does not point to an n-char sequence or an empty |
string, the call is equivalent to strtod("NAN", (char**) |
NULL). Calls to nanf and nanl are equivalent to the
corresponding calls to strtof and strtold.
Returns
[#3] The nan functions return a quiet NaN, if available,
with content indicated through tagp. If the implementation
does not support quiet NaNs, the functions return zero. |
Forward references: the strtod, strtof, and strtold
functions (7.20.1.3).
7.12.11.3 The nextafter functions
Synopsis
[#1]
#include <math.h>
double nextafter(double x, double y);
float nextafterf(float x, float y);
long double nextafterl(long double x, long double y);
Description
[#2] The nextafter functions determine the next
representable value, in the type of the function, after x in
the direction of y, where x and y are first converted to the
type of the function.189) The nextafter functions return y
if x equals y. A range error may occur if the magnitude of
x is the largest finite value representable in the type and
the result is infinite or not representable in the type.
____________________
189The argument values are converted to the type of the
function, even by a macro implementation of the function.
7.12.11.1 Library 7.12.11.3
WG14/N843 Committee Draft -- August 3, 1998 265
Returns
[#3] The nextafter functions return the next representable
value in the specified format after x in the direction of y.
7.12.11.4 The nextafterx functions
Synopsis
[#1]
#include <math.h>
double nextafterx(double x, long double y);
float nextafterxf(float x, long double y);
long double nextafterxl(long double x, long double y);
Description
[#2] The nextafterx functions are equivalent to the
nextafter functions except that the second parameter has
type long double.190)
7.12.12 Maximum, minimum, and positive difference functions
7.12.12.1 The fdim functions
Synopsis
[#1]
#include <math.h>
double fdim(double x, double y);
float fdimf(float x, float y);
long double fdiml(long double x, long double y);
Description
[#2] The fdim functions determine the positive difference
between their arguments:
____________________
190The result of the nextafterx functions is determined in
the type of the function, without loss of range or
precision in a floating second argument.
7.12.11.3 Library 7.12.12.1
266 Committee Draft -- August 3, 1998 WG14/N843
x-yif x>y
+0 if x<=y
A range error may occur.
Returns
[#3] The fdim functions return the positive difference
value.
7.12.12.2 The fmax functions
Synopsis
[#1]
#include <math.h>
double fmax(double x, double y);
float fmaxf(float x, float y);
long double fmaxl(long double x, long double y);
Description
[#2] The fmax functions determine the maximum numeric value
of their arguments.191)
Returns
[#3] The fmax functions return the maximum numeric value of
their arguments.
____________________
191NaN arguments are treated as missing data: if one
argument is a NaN and the other numeric, then the fmax
functions choose the numeric value. See F.9.9.2.
7.12.12.1 Library 7.12.12.2
WG14/N843 Committee Draft -- August 3, 1998 267
7.12.12.3 The fmin functions
Synopsis
[#1]
#include <math.h>
double fmin(double x, double y);
float fminf(float x, float y);
long double fminl(long double x, long double y);
Description
[#2] The fmin functions determine the minimum numeric value
of their arguments.192)
Returns
[#3] The fmin functions return the minimum numeric value of
their arguments.
7.12.13 Floating multiply-add
7.12.13.1 The fma functions
Synopsis
[#1]
#include <math.h>
double fma(double x, double y, double z);
float fmaf(float x, float y, float z);
long double fmal(long double x, long double y,
long double z);
Description
[#2] The fma functions compute the sum z plus the product x
times y, rounded as one ternary operation: they computes the
sum z plus the product x times y (as if) to infinite
precision and round once to the result format, according to
the rounding mode characterized by the value of FLT_ROUNDS.
Returns
[#3] The fma functions return the sum z plus the product x
times y, rounded as one ternary operation.
____________________
192The fmin functions are analogous to the fmax functions in
their treatment of NaNs.
7.12.12.2 Library 7.12.13.1
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7.12.14 Comparison macros
[#1] The relational and equality operators support the usual
mathematical relationships between numeric values. For any
ordered pair of numeric values exactly one of the
relationships -- less, greater, and equal
-- is true. Relational operators may raise the invalid
exception when argument values are NaNs. For a NaN and a
numeric value, or for two NaNs, just the unordered
relationship is true.193) The following subclauses provide
macros that are quiet (non exception raising) versions of
the relational operators, and other comparison macros that
facilitate writing efficient code that accounts for NaNs
without suffering the invalid exception. In the synopses in
this subclause, real-floating indicates that the argument
shall be an expression of real floating type.
7.12.14.1 The isgreater macro
Synopsis
[#1]
#include <math.h>
int isgreater(real-floating x, real-floating y);
Description
[#2] The isgreater macro determines whether its first
argument is greater than its second argument. The value of
isgreater(x,y) is always equal to (x) > (y); however, unlike
(x) > (y), isgreater(x,y) does not raise the invalid
exception when x and y are unordered.
Returns
[#3] The isgreater macro returns the value of (x) > (y).
____________________
193IEC 60559 requires that the built-in relational operators
raise the invalid exception if the operands compare
unordered, as an error indicator for programs written
without consideration of NaNs; the result in these cases
is false.
7.12.14 Library 7.12.14.1
WG14/N843 Committee Draft -- August 3, 1998 269
7.12.14.2 The isgreaterequal macro
Synopsis
[#1]
#include <math.h>
int isgreaterequal(real-floating x, real-floating y);
Description
[#2] The isgreaterequal macro determines whether its first
argument is greater than or equal to its second argument.
The value of isgreaterequal(x,y) is always equal to (x) >=
(y); however, unlike (x) >= (y), isgreaterequal(x,y) does
not raise the invalid exception when x and y are unordered.
Returns
[#3] The isgreaterequal macro returns the value of (x) >=
(y).
7.12.14.3 The isless macro
Synopsis
[#1]
#include <math.h>
int isless(real-floating x, real-floating y);
Description
[#2] The isless macro determines whether its first argument
is less than its second argument. The value of isless(x,y)
is always equal to (x) < (y); however, unlike (x) < (y),
isless(x,y) does not raise the invalid exception when x and
y are unordered.
Returns
[#3] The isless macro returns the value of (x) < (y).
7.12.14.1 Library 7.12.14.3
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7.12.14.4 The islessequal macro
Synopsis
[#1]
#include <math.h>
int islessequal(real-floating x, real-floating y);
Description
[#2] The islessequal macro determines whether its first
argument is less than or equal to its second argument. The
value of islessequal(x,y) is always equal to (x) <= (y);
however, unlike (x) <= (y), islessequal(x,y) does not raise
the invalid exception when x and y are unordered.
Returns
[#3] The islessequal macro returns the value of (x) <= (y).
7.12.14.5 The islessgreater macro
Synopsis
[#1]
#include <math.h>
int islessgreater(real-floating x, real-floating y);
Description
[#2] The islessgreater macro determines whether its first
argument is less than or greater than its second argument.
The islessgreater(x,y) macro is similar to (x) < (y) ||
(x) > (y); however, islessgreater(x,y) does not raise the
invalid exception when x and y are unordered (nor does it
evaluate x and y twice).
Returns
[#3] The islessgreater macro returns the value of (x) < (y)
|| (x) > (y).
7.12.14.3 Library 7.12.14.5
WG14/N843 Committee Draft -- August 3, 1998 271
7.12.14.6 The isunordered macro
Synopsis
[#1]
#include <math.h>
int isunordered(real-floating x, real-floating y);
Description
[#2] The isunordered macro determines whether its arguments
are unordered.
Returns
[#3] The isunordered macro returns 1 if its arguments are
unordered and 0 otherwise.
7.12.14.5 Library 7.12.14.6
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7.13 Nonlocal jumps <setjmp.h>
[#1] The header <setjmp.h> defines the macro setjmp, and
declares one function and one type, for bypassing the normal
function call and return discipline.194)
[#2] The type declared is
jmp_buf
which is an array type suitable for holding the information
needed to restore a calling environment.
[#3] It is unspecified whether setjmp is a macro or an
identifier declared with external linkage. If a macro
definition is suppressed in order to access an actual
function, or a program defines an external identifier with
the name setjmp, the behavior is undefined.
7.13.1 Save calling environment
7.13.1.1 The setjmp macro
Synopsis
[#1]
#include <setjmp.h>
int setjmp(jmp_buf env);
Description
[#2] The setjmp macro saves its calling environment in its
jmp_buf argument for later use by the longjmp function.
Returns
[#3] If the return is from a direct invocation, the setjmp
macro returns the value zero. If the return is from a call
to the longjmp function, the setjmp macro returns a nonzero
value. |
Environmental limits |
[#4] An invocation of the setjmp macro shall appear only in
one of the following contexts:
-- the entire controlling expression of a selection or
iteration statement;
____________________
194These functions are useful for dealing with unusual
conditions encountered in a low-level function of a
program.
7.13 Library 7.13.1.1
WG14/N843 Committee Draft -- August 3, 1998 273
-- one operand of a relational or equality operator with
the other operand an integer constant expression, with
the resulting expression being the entire controlling
expression of a selection or iteration statement;
-- the operand of a unary ! operator with the resulting
expression being the entire controlling expression of a
selection or iteration statement; or
-- the entire expression of an expression statement
(possibly cast to void).
[#5] If the invocation appears in any other context, the
behavior is undefined.
7.13.2 Restore calling environment
7.13.2.1 The longjmp function
Synopsis
[#1]
#include <setjmp.h>
void longjmp(jmp_buf env, int val);
Description
[#2] The longjmp function restores the environment saved by
the most recent invocation of the setjmp macro in the same
invocation of the program with the corresponding jmp_buf
argument. If there has been no such invocation, or if the
function containing the invocation of the setjmp macro has
terminated execution195) in the interim, or if the |
invocation of the setjmp macro was within the scope of an |
identifier with variably modified type and execution has |
left that scope in the interim, the behavior is undefined.
[#3] All accessible objects have values as of the time
longjmp was called, except that the values of objects of
automatic storage duration that are local to the function
containing the invocation of the corresponding setjmp macro
that do not have volatile-qualified type and have been
changed between the setjmp invocation and longjmp call are
indeterminate.
Returns
____________________
195For example, by executing a return statement or because
another longjmp call has caused a transfer to a setjmp
invocation in a function earlier in the set of nested
calls.
7.13.1.1 Library 7.13.2.1
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[#4] After longjmp is completed, program execution continues
as if the corresponding invocation of the setjmp macro had
just returned the value specified by val. The longjmp
function cannot cause the setjmp macro to return the value
0; if val is 0, the setjmp macro returns the value 1.
[#5] EXAMPLE The longjmp function that returns control back
to the point of the setjmp invocation might cause memory
associated with a variable length array object to be
squandered.
#include <setjmp.h>
jmp_buf buf;
void g(int n);
void h(int n);
int n = 6;
void f(void)
{
int x[n]; // OK, f is not terminated.
setjmp(buf);
g(n);
}
void g(int n)
{
int a[n]; // a may remain allocated.
h(n);
}
void h(int n)
{
int b[n]; // b may remain allocated.
longjmp(buf,2); // might cause memory loss.
}
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7.14 Signal handling <signal.h>
[#1] The header <signal.h> declares a type and two functions
and defines several macros, for handling various signals
(conditions that may be reported during program execution).
[#2] The type defined is
sig_atomic_t
which is the (possibly volatile-qualified) integer type of
an object that can be accessed as an atomic entity, even in
the presence of asynchronous interrupts.
[#3] The macros defined are
SIG_DFL
SIG_ERR
SIG_IGN
which expand to constant expressions with distinct values
that have type compatible with the second argument to, and
the return value of, the signal function, and whose values
compare unequal to the address of any declarable function;
and the following, which expand to positive integer constant
expressions with type int and distinct values that are the
signal numbers, each corresponding to the specified
condition:
SIGABRT abnormal termination, such as is initiated
by the abort function
SIGFPE an erroneous arithmetic operation, such as
zero divide or an operation resulting in
overflow
SIGILL detection of an invalid function image, such
as an invalid instruction
SIGINT receipt of an interactive attention signal
SIGSEGV an invalid access to storage
SIGTERM a termination request sent to the program
[#4] An implementation need not generate any of these
signals, except as a result of explicit calls to the raise
function. Additional signals and pointers to undeclarable
functions, with macro definitions beginning, respectively,
with the letters SIG and an uppercase letter or with SIG_
and an uppercase letter,196) may also be specified by the
implementation. The complete set of signals, their
semantics, and their default handling is implementation-
defined; all signal numbers shall be positive.
7.14 Library 7.14
276 Committee Draft -- August 3, 1998 WG14/N843
7.14.1 Specify signal handling
7.14.1.1 The signal function
Synopsis
[#1]
#include <signal.h>
void (*signal(int sig, void (*func)(int)))(int);
Description
[#2] The signal function chooses one of three ways in which
receipt of the signal number sig is to be subsequently
handled. If the value of func is SIG_DFL, default handling
for that signal will occur. If the value of func is
SIG_IGN, the signal will be ignored. Otherwise, func shall
point to a function to be called when that signal occurs.
An invocation of such a function because of a signal, or
(recursively) of any further functions called by that
invocation (other than functions in the standard library),
is called a signal handler.
[#3] When a signal occurs and func points to a function, it
is implementation-defined whether the equivalent of
signal(sig, SIG_DFL); is executed or the implementation
prevents some implementation-defined set of signals (at
least including sig) from occurring until the current signal
handling has completed; in the case of SIGILL, the
implementation may alternatively define that no action is
taken. Then the equivalent of (*func)(sig); is executed.
If and when the function returns, if the value of sig is
SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
value corresponding to a computational exception, the
behavior is undefined; otherwise the program will resume
execution at the point it was interrupted.
[#4] If the signal occurs as the result of calling the abort
or raise function, the signal handler shall not call the
raise function.
[#5] If the signal occurs other than as the result of
calling the abort or raise function, the behavior is
undefined if the signal handler refers to any object with
static storage duration other than by assigning a value to
an object declared as volatile sig_atomic_t, or the signal
____________________
196See ``future library directions'' (7.26.9). The names of
the signal numbers reflect the following terms
(respectively): abort, floating-point exception, illegal
instruction, interrupt, segmentation violation, and
termination.
7.14 Library 7.14.1.1
WG14/N843 Committee Draft -- August 3, 1998 277
handler calls any function in the standard library other
than the abort function or the signal function with the
first argument equal to the signal number corresponding to
the signal that caused the invocation of the handler.
Furthermore, if such a call to the signal function results
in a SIG_ERR return, the value of errno is
indeterminate.197)
[#6] At program startup, the equivalent of
signal(sig, SIG_IGN);
may be executed for some signals selected in an
implementation-defined manner; the equivalent of
signal(sig, SIG_DFL);
is executed for all other signals defined by the
implementation.
[#7] The implementation shall behave as if no library
function calls the signal function.
Returns
[#8] If the request can be honored, the signal function
returns the value of func for the most recent successful
call to signal for the specified signal sig. Otherwise, a
value of SIG_ERR is returned and a positive value is stored
in errno.
Forward references: the abort function (7.20.4.1), the exit
function (7.20.4.3).
7.14.2 Send signal
____________________
197If any signal is generated by an asynchronous signal
handler, the behavior is undefined.
7.14.1.1 Library 7.14.2
278 Committee Draft -- August 3, 1998 WG14/N843
7.14.2.1 The raise function
Synopsis
[#1]
#include <signal.h>
int raise(int sig);
Description
[#2] The raise function carries out the actions described in
7.14.1.1 for the signal sig. If a signal handler is called,
the raise function shall not return until after the signal
handler does.
Returns
[#3] The raise function returns zero if successful, nonzero
if unsuccessful.
7.14.2 Library 7.14.2.1
WG14/N843 Committee Draft -- August 3, 1998 279
7.15 Variable arguments <stdarg.h>
[#1] The header <stdarg.h> declares a type and defines four
macros, for advancing through a list of arguments whose
number and types are not known to the called function when
it is translated.
[#2] A function may be called with a variable number of
arguments of varying types. As described in 6.9.1, its
parameter list contains one or more parameters. The
rightmost parameter plays a special role in the access
mechanism, and will be designated parmN in this description.
[#3] The type declared is
va_list
which is an object type suitable for holding information
needed by the macros va_start, va_arg, va_end, and va_copy.
If access to the varying arguments is desired, the called
function shall declare an object (referred to as ap in this
subclause) having type va_list. The object ap may be passed
as an argument to another function; if that function invokes
the va_arg macro with parameter ap, the value of ap in the
calling function is indeterminate and shall be passed to the
va_end macro prior to any further reference to ap.198)
7.15.1 Variable argument list access macros
[#1] The va_start, va_arg, and va_copy macros described in
this subclause shall be implemented as macros, not
functions. It is unspecified whether va_end is a macro or
an identifier declared with external linkage. If a macro
definition is suppressed in order to access an actual
function, or a program defines an external identifier with
the name va_end, the behavior is undefined. Each invocation
of the va_start or va_copy macros shall be matched by a
corresponding invocation of the va_end macro in the function
accepting a varying number of arguments.
____________________
198It is permitted to create a pointer to a va_list and pass
that pointer to another function, in which case the
original function may make further use of the original
list after the other function returns.
7.15 Library 7.15.1
280 Committee Draft -- August 3, 1998 WG14/N843
7.15.1.1 The va_arg macro
Synopsis
[#1]
#include <stdarg.h>
type va_arg(va_list ap, type);
Description
[#2] The va_arg macro expands to an expression that has the |
specified type and the value of the next argument in the
call. The parameter ap shall be the same as the va_list ap
initialized by va_start. Each invocation of va_arg modifies
ap so that the values of successive arguments are returned
in turn. The parameter type shall be a type name specified |
such that the type of a pointer to an object that has the
specified type can be obtained simply by postfixing a * to
type. If there is no actual next argument, or if type is
not compatible with the type of the actual next argument (as
promoted according to the default argument promotions), the |
behavior is undefined, except for the following cases: |
-- one type is a signed integer type, the other type is |
the corresponding unsigned integer type, and the value |
is representable in both types; |
-- one type is pointer to void and the other is a pointer |
to a character type. |
Returns
[#3] The first invocation of the va_arg macro after that of
the va_start macro returns the value of the argument after
that specified by parmN. Successive invocations return the
values of the remaining arguments in succession.
7.15.1.2 The va_copy macro
Synopsis
[#1]
#include <stdarg.h>
void va_copy(va_list dest, va_list src);
Description
[#2] The va_copy macro makes the va_list dest be a copy of
the va_list src, as if the va_start macro had been applied
to it followed by the same sequence of uses of the va_arg
macro as had previously been used to reach the present state
of src.
7.15.1 Library 7.15.1.2
WG14/N843 Committee Draft -- August 3, 1998 281
Returns
[#3] The va_copy macro returns no value.
7.15.1.3 The va_end macro
Synopsis
[#1]
#include <stdarg.h>
void va_end(va_list ap);
Description
[#2] The va_end macro facilitates a normal return from the
function whose variable argument list was referred to by the
expansion of va_start that initialized the va_list ap. The
va_end macro may modify ap so that it is no longer usable
(without an intervening invocation of va_start). If there
is no corresponding invocation of the va_start macro, or if
the va_end macro is not invoked before the return, the
behavior is undefined.
Returns
[#3] The va_end macro returns no value.
7.15.1.4 The va_start macro
Synopsis
[#1]
#include <stdarg.h>
void va_start(va_list ap, parmN);
Description
[#2] The va_start macro shall be invoked before any access
to the unnamed arguments.
[#3] The va_start macro initializes ap for subsequent use by
va_arg and va_end. va_start shall not be invoked again for
the same ap without an intervening invocation of va_end for
the same ap.
[#4] The parameter parmN is the identifier of the rightmost
parameter in the variable parameter list in the function
definition (the one just before the , ...). If the
parameter parmN is declared with the register storage class,
with a function or array type, or with a type that is not
compatible with the type that results after application of
the default argument promotions, the behavior is undefined.
7.15.1.2 Library 7.15.1.4
282 Committee Draft -- August 3, 1998 WG14/N843
Returns
[#5] The va_start macro returns no value.
[#6] EXAMPLE The function f1 gathers into an array a list
of arguments that are pointers to strings (but not more than
MAXARGS arguments), then passes the array as a single
argument to function f2. The number of pointers is
specified by the first argument to f1.
#include <stdarg.h>
#define MAXARGS 31
void f1(int n_ptrs, ...)
{
va_list ap;
char *array[MAXARGS];
int ptr_no = 0;
if (n_ptrs > MAXARGS)
n_ptrs = MAXARGS;
va_start(ap, n_ptrs);
while (ptr_no < n_ptrs)
array[ptr_no++] = va_arg(ap, char *);
va_end(ap);
f2(n_ptrs, array);
}
Each call to f1 shall have visible the definition of the
function or a declaration such as
void f1(int, ...);
[#7] The function f3 is similar, but saves the status of the
variable argument list after the indicated number of
arguments; after f2 has been called once with the whole
list, the trailing part of the list is gathered again and
passed to function f4.
7.15.1.4 Library 7.15.1.4
WG14/N843 Committee Draft -- August 3, 1998 283
#include <stdarg.h>
#define MAXARGS 31
void f3(int n_ptrs, int f4_after, ...)
{
va_list ap, ap_save;
char *array[MAXARGS];
int ptr_no = 0;
if (n_ptrs > MAXARGS)
n_ptrs = MAXARGS;
va_start(ap, n_ptrs);
while (ptr_no < n_ptrs) {
array[ptr_no++] = va_arg(ap, char *);
if (ptr_no == f4_after)
va_copy(ap_save, ap);
}
va_end(ap);
f2(n_ptrs, array);
// Now process the saved copy.
n_ptrs -= f4_after;
ptr_no = 0;
while (ptr_no < n_ptrs)
array[ptr_no++] = va_arg(ap_save, char *);
va_end(ap_save);
f4(n_ptrs, array);
}
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7.16 Boolean type and values <stdbool.h>
[#1] The header <stdbool.h> defines four macros. |
[#2] The macro |
bool
expands to _Bool. |
[#3] The remaining three macros are suitable for use in #if |
preprocessing directives. They are
true
which expands to the decimal constant 1,
false
which expands to the decimal constant 0, and
__bool_true_false_are_defined
which expands to the decimal constant 1. |
[#4] Notwithstanding the provisions of 7.1.3, a program is |
permitted to undefine and perhaps then redefine the macros |
bool, true, and false.199)
____________________
199See ``future library directions'' (7.26.7).
7.16 Library 7.16
WG14/N843 Committee Draft -- August 3, 1998 285
7.17 Common definitions <stddef.h>
[#1] The following types and macros are defined in the
standard header <stddef.h>. Some are also defined in other
headers, as noted in their respective subclauses.
[#2] The types are
ptrdiff_t
which is the signed integer type of the result of
subtracting two pointers;
size_t
which is the unsigned integer type of the result of the
sizeof operator; and
wchar_t
which is an integer type whose range of values can represent
distinct codes for all members of the largest extended
character set specified among the supported locales; the
null character shall have the code value zero and each
member of the basic character set defined in 5.2.1 shall
have a code value equal to its value when used as the lone
character in an integer character constant.
[#3] The macros are
NULL
which expands to an implementation-defined null pointer
constant; and
offsetof(type, member-designator)
which expands to an integer constant expression that has
type size_t, the value of which is the offset in bytes, to
the structure member (designated by member-designator), from
the beginning of its structure (designated by type). The |
type and member designator shall be such that given
static type t;
then the expression &(t.member-designator) evaluates to an
address constant. (If the specified member is a bit-field,
the behavior is undefined.)
Forward references: localization (7.11).
7.17 Library 7.17
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7.18 Integer types <stdint.h>
[#1] The header <stdint.h> declares sets of integer types
having specified widths, and defines corresponding sets of
macros.200) It also defines macros that specify limits of
integer types corresponding to types defined in other
standard headers.
[#2] Types are defined in the following categories:
-- integer types having certain exact widths;
-- integer types having at least certain specified widths;
-- fastest integer types having at least certain specified
widths;
-- integer types wide enough to hold pointers to objects;
-- integer types having greatest width.
(Some of these types may denote the same type.) |
[#3] Corresponding macros specify limits of the declared
types and construct suitable constants.
[#4] For each type described herein that can be declared as
a type existing in the implementation,201) <stdint.h> shall
declare that type, and it shall define the associated
macros. Conversely, for each type described herein that
cannot be declared as a type existing in the implementation,
<stdint.h> shall not define that type, nor shall it define
the associated macros.
7.18.1 Integer types
[#1] When type names differing only in the absence or
presence of the initial u are defined, they shall denote
corresponding signed and unsigned types as described in
6.2.5.
7.18.1.1 Exact-width integer types
[#1] Each of the following types designates an integer type
that has exactly the specified width. These type names have
the general form of intn_t or uintn_t where n is the
required width. For example, uint8_t denotes an unsigned
integer type that has a width of exactly 8 bits.
____________________
200See ``future library directions'' (7.26.8).
201Some of these types may denote implementation-defined
extended integer types.
7.18 Library 7.18.1.1
WG14/N843 Committee Draft -- August 3, 1998 287
[#2] The following designate exact-width signed integer
types:
int8_t int16_t int32_t int64_t
The following designate exact-width unsigned integer types:
uint8_t uint16_t uint32_t uint64_t
(These types need not exist in an implementation.)
7.18.1.2 Minimum-width integer types
[#1] Each of the following types designates an integer type
that has at least the specified width, such that no integer
type of lesser size has at least the specified width. These
type names have the general form of int_leastn_t or
uint_leastn_t where n is the minimum required width. For
example, int_least32_t denotes a signed integer type that
has a width of at least 32 bits.
[#2] The following designate minimum-width signed integer
types:
int_least8_t int_least32_t
int_least16_t int_least64_t
The following designate minimum-width unsigned integer
types:
uint_least8_t uint_least32_t
uint_least16_t uint_least64_t
(These types exist in all implementations.)
7.18.1.3 Fastest minimum-width integer types
[#1] Each of the following types designates an integer type
that is usually fastest202) to operate with among all
integer types that have at least the specified width. These
type names have the general form of int_fastn_t or
uint_fastn_t where n is the minimum required width. For
example, int_fast16_t denotes the fastest signed integer
type that has a width of at least 16 bits.
[#2] The following designate fastest minimum-width signed
integer types:
____________________
202The designated type is not guaranteed to be fastest for
all purposes; if the implementation has no clear grounds
for choosing one type over another, it will simply pick
some integer type satisfying the signedness and width
requirements.
7.18.1.1 Library 7.18.1.3
288 Committee Draft -- August 3, 1998 WG14/N843
int_fast8_t int_fast32_t
int_fast16_t int_fast64_t
The following designate fastest minimum-width unsigned
integer types:
uint_fast8_t uint_fast32_t
uint_fast16_t uint_fast64_t
(These types exist in all implementations.)
7.18.1.4 Integer types capable of holding object pointers
[#1] The following type designates a signed integer type
with the property that any valid pointer to void can be
converted to this type, then converted back to pointer to
void, and the result will compare equal to the original
pointer:
intptr_t
The following type designates an unsigned integer type with
the property that any valid pointer to void can be converted
to this type, then converted back to pointer to void, and
the result will compare equal to the original pointer:
uintptr_t
(These types need not exist in an implementation.)
7.18.1.5 Greatest-width integer types
[#1] The following type designates a signed integer type
capable of representing any value of any signed integer
type:
intmax_t
The following type designates an unsigned integer type
capable of representing any value of any unsigned integer
type:
uintmax_t
(These types exist in all implementations.)
7.18.1.3 Library 7.18.1.5
WG14/N843 Committee Draft -- August 3, 1998 289
7.18.2 Limits of specified-width integer types
[#1] The following object-like macros203) specify the
minimum and maximum limits of the types declared in
<stdint.h>. Each macro name corresponds to a similar type
name in 7.18.1.
[#2] Each instance of any defined macro shall be replaced by
a constant expression suitable for use in #if preprocessing
directives, and this expression shall have the same type as
would an expression that is an object of the corresponding
type converted according to the integer promotions. Its
implementation-defined value shall be equal to or greater in
magnitude (absolute value) than the corresponding value
given below, with the same sign.
7.18.2.1 Limits of exact-width integer types
-- minimum values of exact-width signed integer types
INT8_MIN -127
INT16_MIN -32767
INT32_MIN -2147483647
INT64_MIN -9223372036854775807
(The value shall be either that given or exactly 1
less.)
-- maximum values of exact-width signed integer types
INT8_MAX +127
INT16_MAX +32767
INT32_MAX +2147483647
INT64_MAX +9223372036854775807
(The value shall be exactly that given.)
-- maximum values of exact-width unsigned integer types
UINT8_MAX 255
UINT16_MAX 65535
UINT32_MAX 4294967295
UINT64_MAX 18446744073709551615
(The value shall be exactly that given.)
____________________
203C++ implementations should define these macros only when
__STDC_LIMIT_MACROS is defined before <stdint.h> is
included.
7.18.2 Library 7.18.2.1
290 Committee Draft -- August 3, 1998 WG14/N843
7.18.2.2 Limits of minimum-width integer types
-- minimum values of minimum-width signed integer types
INT_LEAST8_MIN -127
INT_LEAST16_MIN -32767
INT_LEAST32_MIN -2147483647
INT_LEAST64_MIN -9223372036854775807
-- maximum values of minimum-width signed integer types
INT_LEAST8_MAX +127
INT_LEAST16_MAX +32767
INT_LEAST32_MAX +2147483647
INT_LEAST64_MAX +9223372036854775807
-- maximum values of minimum-width unsigned integer types
UINT_LEAST8_MAX 255
UINT_LEAST16_MAX 65535
UINT_LEAST32_MAX 4294967295
UINT_LEAST64_MAX 18446744073709551615
7.18.2.3 Limits of fastest minimum-width integer types
-- minimum values of fastest minimum-width signed integer
types
INT_FAST8_MIN -127
INT_FAST16_MIN -32767
INT_FAST32_MIN -2147483647
INT_FAST64_MIN -9223372036854775807
-- maximum values of fastest minimum-width signed integer
types
INT_FAST8_MAX +127
INT_FAST16_MAX +32767
INT_FAST32_MAX +2147483647
INT_FAST64_MAX +9223372036854775807
-- maximum values of fastest minimum-width unsigned
integer types
UINT_FAST8_MAX 255
UINT_FAST16_MAX 65535
UINT_FAST32_MAX 4294967295
UINT_FAST64_MAX 18446744073709551615
7.18.2.2 Library 7.18.2.3
WG14/N843 Committee Draft -- August 3, 1998 291
7.18.2.4 Limits of integer types capable of holding object
pointers
-- minimum value of pointer-holding signed integer type
INTPTR_MIN -32767
-- maximum value of pointer-holding signed integer type
INTPTR_MAX +32767
-- maximum value of pointer-holding unsigned integer type
UINTPTR_MAX 65535
7.18.2.5 Limits of greatest-width integer types
-- minimum value of greatest-width signed integer type
INTMAX_MIN -9223372036854775807
-- maximum value of greatest-width signed integer type
INTMAX_MAX +9223372036854775807
-- maximum value of greatest-width unsigned integer type
UINTMAX_MAX 18446744073709551615
7.18.3 Limits of other integer types
[#1] The following object-like macros204) specify the
minimum and maximum limits of integer types corresponding to
types defined in other standard headers.
[#2] Each instance of these macros shall be replaced by a
constant expression suitable for use in #if preprocessing
directives, and this expression shall have the same type as
would an expression that is an object of the corresponding
type converted according to the integer promotions. Its
implementation-defined value shall be equal to or greater in
magnitude (absolute value) than the corresponding value
given below, with the same sign.
-- limits of ptrdiff_t
PTRDIFF_MIN -65535
PTRDIFF_MAX +65535
____________________
204C++ implementations should define these macros only when
__STDC_LIMIT_MACROS is defined before <stdint.h> is
included.
7.18.2.4 Library 7.18.3
292 Committee Draft -- August 3, 1998 WG14/N843
-- limits of sig_atomic_t
SIG_ATOMIC_MIN see below
SIG_ATOMIC_MAX see below
-- limit of size_t
SIZE_MAX 65535
-- limits of wchar_t
WCHAR_MIN see below
WCHAR_MAX see below
-- limits of wint_t
WINT_MIN see below
WINT_MAX see below
[#3] If sig_atomic_t (see 7.14) is defined as a signed
integer type, the value of SIG_ATOMIC_MIN shall be no
greater than -127 and the value of SIG_ATOMIC_MAX shall be
no less than 127; otherwise, sig_atomic_t is defined as an
unsigned integer type, and the value of SIG_ATOMIC_MIN shall
be 0 and the value of SIG_ATOMIC_MAX shall be no less than
255.
[#4] If wchar_t is defined as a signed integer type, the
value of WCHAR_MIN shall be no greater than -127 and the
value of WCHAR_MAX shall be no less than 127; otherwise,
wchar_t is defined as an unsigned integer type, and the
value of WCHAR_MIN shall be 0 and the value of WCHAR_MAX
shall be no less than 255.
[#5] If wint_t (see 7.25) is defined as a signed integer
type, the value of WINT_MIN shall be no greater than -32767
and the value of WINT_MAX shall be no less than 32767;
otherwise, wint_t is defined as an unsigned integer type,
and the value of WINT_MIN shall be 0 and the value of
WINT_MAX shall be no less than 65535.
7.18.4 Macros for integer constants
[#1] The following function-like macros205) expand to
integer constants suitable for initializing objects that
have integer types corresponding to types defined in
<stdint.h>. Each macro name corresponds to a similar type
name in 7.18.1.2 or 7.18.1.5.
____________________
205C++ implementations should define these macros only when
__STDC_CONSTANT_MACROS is defined before <stdint.h> is
included.
7.18.3 Library 7.18.4
WG14/N843 Committee Draft -- August 3, 1998 293
[#2] The argument in any instance of these macros shall be a
decimal, octal, or hexadecimal constant (as defined in
6.4.4.1) with a value that does not exceed the limits for
the corresponding type.
7.18.4.1 Macros for minimum-width integer constants
[#1] Each of the following macros expands to an integer
constant having the value specified by its argument and a
type with at least the specified width. These macro names
have the general form of INTn_C or UINTn_C where n is the
minimum required width. For example, UINT64_C(0x123) might
expand to the integer constant 0x123ULL.
[#2] The following expand to integer constants that have
signed integer types:
INT8_C(value) INT32_C(value)
INT16_C(value) INT64_C(value)
The following expand to integer constants that have unsigned
integer types:
UINT8_C(value) UINT32_C(value)
UINT16_C(value) UINT64_C(value)
7.18.4.2 Macros for greatest-width integer constants
[#1] The following macro expands to an integer constant
having the value specified by its argument and the type
intmax_t:
INTMAX_C(value)
The following macro expands to an integer constant having
the value specified by its argument and the type uintmax_t:
UINTMAX_C(value)
7.18.4 Library 7.18.4.2
294 Committee Draft -- August 3, 1998 WG14/N843
7.19 Input/output <stdio.h>
7.19.1 Introduction
[#1] The header <stdio.h> declares three types, several
macros, and many functions for performing input and output.
[#2] The types declared are size_t (described in 7.17);
FILE
which is an object type capable of recording all the
information needed to control a stream, including its file
position indicator, a pointer to its associated buffer (if
any), an error indicator that records whether a read/write
error has occurred, and an end-of-file indicator that
records whether the end of the file has been reached; and
fpos_t
which is an object type other than an array type capable of
recording all the information needed to specify uniquely
every position within a file.
[#3] The macros are NULL (described in 7.17);
_IOFBF
_IOLBF
_IONBF
which expand to integer constant expressions with distinct
values, suitable for use as the third argument to the
setvbuf function;
BUFSIZ
which expands to an integer constant expression, which is
the size of the buffer used by the setbuf function;
EOF
which expands to an integer constant expression, with type
int and a negative value, that is returned by several
functions to indicate end-of-file, that is, no more input
from a stream;
FOPEN_MAX
which expands to an integer constant expression that is the
minimum number of files that the implementation guarantees
can be open simultaneously;
FILENAME_MAX
7.19 Library 7.19.1
WG14/N843 Committee Draft -- August 3, 1998 295
which expands to an integer constant expression that is the
size needed for an array of char large enough to hold the
longest file name string that the implementation guarantees
can be opened;206)
L_tmpnam
which expands to an integer constant expression that is the
size needed for an array of char large enough to hold a
temporary file name string generated by the tmpnam function;
SEEK_CUR
SEEK_END
SEEK_SET
which expand to integer constant expressions with distinct
values, suitable for use as the third argument to the fseek
function;
TMP_MAX
which expands to an integer constant expression that is the
minimum number of unique file names that can be generated by |
the tmpnam function;
stderr
stdin
stdout
which are expressions of type ``pointer to FILE'' that point
to the FILE objects associated, respectively, with the
standard error, input, and output streams.
[#4] The header <wchar.h> declares a number of functions
useful for wide-character input and output. The wide-
character input/output functions described in that subclause
provide operations analogous to most of those described
here, except that the fundamental units internal to the
program are wide characters. The external representation
(in the file) is a sequence of ``generalized'' multibyte
characters, as described further in 7.19.3.
[#5] The input/output functions are given the following
collective terms:
____________________
206If the implementation imposes no practical limit on the
length of file name strings, the value of FILENAME_MAX
should instead be the recommended size of an array
intended to hold a file name string. Of course, file
name string contents are subject to other system-specific
constraints; therefore all possible strings of length
FILENAME_MAX cannot be expected to be opened
successfully.
7.19.1 Library 7.19.1
296 Committee Draft -- August 3, 1998 WG14/N843
-- The wide-character input functions
-- those functions described in 7.24 that perform |
input into wide characters and wide strings: fgetwc,
fgetws, getwc, getwchar, fwscanf, wscanf, vfwscanf, and
vwscanf.
-- The wide-character output functions
-- those functions described in 7.24 that perform |
output from wide characters and wide strings: fputwc,
fputws, putwc, putwchar, fwprintf, wprintf, vfwprintf,
and vwprintf.
-- The wide-character input/output functions
-- the union of the ungetwc function, the wide-
character input functions, and the wide-character
output functions.
-- The byte input/output functions |
-- those functions described in this subclause that
perform input/output: fgetc, fgets, fprintf, fputc,
fputs, fread, fscanf, fwrite, getc, getchar, gets,
printf, putc, putchar, puts, scanf, ungetc, vfprintf,
vfscanf, vprintf, and vscanf.
Forward references: files (7.19.3), the fseek function
(7.19.9.2), streams (7.19.2), the tmpnam function
(7.19.4.4), <wchar.h> (7.24).
7.19.2 Streams
[#1] Input and output, whether to or from physical devices
such as terminals and tape drives, or whether to or from
files supported on structured storage devices, are mapped
into logical data streams, whose properties are more uniform
than their various inputs and outputs. Two forms of mapping
are supported, for text streams and for binary streams.207)
[#2] A text stream is an ordered sequence of characters
composed into lines, each line consisting of zero or more
characters plus a terminating new-line character. Whether
the last line requires a terminating new-line character is
implementation-defined. Characters may have to be added,
altered, or deleted on input and output to conform to
differing conventions for representing text in the host
environment. Thus, there need not be a one-to-one
correspondence between the characters in a stream and those
in the external representation. Data read in from a text
stream will necessarily compare equal to the data that were
____________________
207An implementation need not distinguish between text
streams and binary streams. In such an implementation,
there need be no new-line characters in a text stream nor
any limit to the length of a line.
7.19.1 Library 7.19.2
WG14/N843 Committee Draft -- August 3, 1998 297
earlier written out to that stream only if: the data consist
only of printable characters and the control characters
horizontal tab and new-line; no new-line character is
immediately preceded by space characters; and the last
character is a new-line character. Whether space characters
that are written out immediately before a new-line character
appear when read in is implementation-defined.
[#3] A binary stream is an ordered sequence of characters
that can transparently record internal data. Data read in
from a binary stream shall compare equal to the data that
were earlier written out to that stream, under the same
implementation. Such a stream may, however, have an
implementation-defined number of null characters appended to
the end of the stream.
[#4] Each stream has an orientation. After a stream is
associated with an external file, but before any operations
are performed on it, the stream is without orientation.
Once a wide-character input/output function has been applied
to a stream without orientation, the stream becomes a wide-
oriented stream. Similarly, once a byte input/output
function has been applied to a stream without orientation,
the stream becomes a byte-oriented stream. Only a call to
the freopen function or the fwide function can otherwise
alter the orientation of a stream. (A successful call to
freopen removes any orientation.)208)
[#5] Byte input/output functions shall not be applied to a
wide-oriented stream and wide-character input/output
functions shall not be applied to a byte-oriented stream.
The remaining stream operations do not affect, and are not
affected by, a stream's orientation, except for the
following additional restrictions:
-- Binary wide-oriented streams have the file-positioning
restrictions ascribed to both text and binary streams.
-- For wide-oriented streams, after a successful call to a
file-positioning function that leaves the file position
indicator prior to the end-of-file, a wide-character
output function can overwrite a partial multibyte
character; any file contents beyond the byte(s) written
are henceforth indeterminate.
[#6] Each wide-oriented stream has an associated mbstate_t
object that stores the current parse state of the stream. A
successful call to fgetpos stores a representation of the
value of this mbstate_t object as part of the value of the
fpos_t object. A later successful call to fsetpos using the
____________________
208The three predefined streams stdin, stdout, and stderr
are unoriented at program startup.
7.19.2 Library 7.19.2
298 Committee Draft -- August 3, 1998 WG14/N843
same stored fpos_t value restores the value of the
associated mbstate_t object as well as the position within
the controlled stream.
Environmental limits
[#7] An implementation shall support text files with lines
containing at least 254 characters, including the
terminating new-line character. The value of the macro
BUFSIZ shall be at least 256.
Forward references: the freopen function (7.19.5.4), the
fwide function (7.24.3.5), mbstate_t (7.25.1), the fgetpos
function (7.19.9.1), the fsetpos function (7.19.9.3).
7.19.3 Files
[#1] A stream is associated with an external file (which may
be a physical device) by opening a file, which may involve
creating a new file. Creating an existing file causes its
former contents to be discarded, if necessary. If a file
can support positioning requests (such as a disk file, as
opposed to a terminal), then a file position indicator
associated with the stream is positioned at the start
(character number zero) of the file, unless the file is
opened with append mode in which case it is implementation-
defined whether the file position indicator is initially
positioned at the beginning or the end of the file. The
file position indicator is maintained by subsequent reads,
writes, and positioning requests, to facilitate an orderly
progression through the file.
[#2] Binary files are not truncated, except as defined in
7.19.5.3. Whether a write on a text stream causes the
associated file to be truncated beyond that point is
implementation-defined.
[#3] When a stream is unbuffered, characters are intended to
appear from the source or at the destination as soon as
possible. Otherwise characters may be accumulated and
transmitted to or from the host environment as a block.
When a stream is fully buffered, characters are intended to
be transmitted to or from the host environment as a block
when a buffer is filled. When a stream is line buffered,
characters are intended to be transmitted to or from the
host environment as a block when a new-line character is
encountered. Furthermore, characters are intended to be
transmitted as a block to the host environment when a buffer
is filled, when input is requested on an unbuffered stream,
or when input is requested on a line buffered stream that
requires the transmission of characters from the host
environment. Support for these characteristics is
implementation-defined, and may be affected via the setbuf
and setvbuf functions.
7.19.2 Library 7.19.3
WG14/N843 Committee Draft -- August 3, 1998 299
[#4] A file may be disassociated from a controlling stream
by closing the file. Output streams are flushed (any
unwritten buffer contents are transmitted to the host
environment) before the stream is disassociated from the
file. The value of a pointer to a FILE object is
indeterminate after the associated file is closed (including
the standard text streams). Whether a file of zero length
(on which no characters have been written by an output
stream) actually exists is implementation-defined.
[#5] The file may be subsequently reopened, by the same or
another program execution, and its contents reclaimed or
modified (if it can be repositioned at its start). If the
main function returns to its original caller, or if the exit
function is called, all open files are closed (hence all
output streams are flushed) before program termination.
Other paths to program termination, such as calling the
abort function, need not close all files properly.
[#6] The address of the FILE object used to control a stream
may be significant; a copy of a FILE object need not serve
in place of the original.
[#7] At program startup, three text streams are predefined
and need not be opened explicitly -- standard input (for
reading conventional input), standard output (for writing
conventional output), and standard error (for writing
diagnostic output). As initially opened, the standard error |
stream is not fully buffered; the standard input and
standard output streams are fully buffered if and only if
the stream can be determined not to refer to an interactive
device.
[#8] Functions that open additional (nontemporary) files
require a file name, which is a string. The rules for
composing valid file names are implementation-defined.
Whether the same file can be simultaneously open multiple
times is also implementation-defined.
[#9] Although both text and binary wide-oriented streams are
conceptually sequences of wide characters, the external file
associated with a wide-oriented stream is a sequence of
multibyte characters, generalized as follows:
-- Multibyte encodings within files may contain embedded
null bytes (unlike multibyte encodings valid for use
internal to the program).
-- A file need not begin nor end in the initial shift
state.209)
[#10] Moreover, the encodings used for multibyte characters
may differ among files. Both the nature and choice of such
encodings are implementation-defined.
7.19.3 Library 7.19.3
300 Committee Draft -- August 3, 1998 WG14/N843
[#11] The wide-character input functions read multibyte
characters from the stream and convert them to wide
characters as if they were read by successive calls to the
fgetwc function. Each conversion occurs as if by a call to
the mbrtowc function, with the conversion state described by
the stream's own mbstate_t object. The byte input functions
read characters from the stream as if by successive calls to
the fgetc function.
[#12] The wide-character output functions convert wide
characters to multibyte characters and write them to the
stream as if they were written by successive calls to the
fputwc function. Each conversion occurs as if by a call to
the wcrtomb function, with the conversion state described by
the stream's own mbstate_t object. The byte output
functions write characters to the stream as if by successive
calls to the fputc function.
[#13] In some cases, some of the byte input/output functions |
also perform conversions between multibyte characters and |
wide characters. These conversions also occur as if by |
calls to the mbrtowc and wcrtomb functions. |
[#14] An encoding error occurs if the character sequence
presented to the underlying mbrtowc function does not form a
valid (generalized) multibyte character, or if the code
value passed to the underlying wcrtomb does not correspond
to a valid (generalized) multibyte character. The wide-
character input/output functions and the byte input/output
functions store the value of the macro EILSEQ in errno if
and only if an encoding error occurs.
Environmental limits
[#15] The value of FOPEN_MAX shall be at least eight,
including the three standard text streams.
Forward references: the exit function (7.20.4.3), the fgetc
function (7.19.7.1), the fopen function (7.19.5.3), the
fputc function (7.19.7.3), the setbuf function (7.19.5.5),
the setvbuf function (7.19.5.6), the fgetwc function
(7.24.3.1), the fputwc function (7.24.3.3), conversion state
(7.24.6), the mbrtowc function (7.24.6.3.2), the wcrtomb
function (7.24.6.3.3).
____________________
209Setting the file position indicator to end-of-file, as
with fseek(file, 0, SEEK_END), has undefined behavior for
a binary stream (because of possible trailing null
characters) or for any stream with state-dependent
encoding that does not assuredly end in the initial shift
state.
7.19.3 Library 7.19.3
WG14/N843 Committee Draft -- August 3, 1998 301
7.19.4 Operations on files
7.19.4.1 The remove function
Synopsis
[#1]
#include <stdio.h>
int remove(const char *filename);
Description
[#2] The remove function causes the file whose name is the
string pointed to by filename to be no longer accessible by
that name. A subsequent attempt to open that file using
that name will fail, unless it is created anew. If the file
is open, the behavior of the remove function is
implementation-defined.
Returns
[#3] The remove function returns zero if the operation
succeeds, nonzero if it fails.
7.19.4.2 The rename function
Synopsis
[#1]
#include <stdio.h>
int rename(const char *old, const char *new);
Description
[#2] The rename function causes the file whose name is the
string pointed to by old to be henceforth known by the name
given by the string pointed to by new. The file named old
is no longer accessible by that name. If a file named by
the string pointed to by new exists prior to the call to the
rename function, the behavior is implementation-defined.
Returns
[#3] The rename function returns zero if the operation
succeeds, nonzero if it fails,210) in which case if the file
existed previously it is still known by its original name.
____________________
210Among the reasons the implementation may cause the rename
function to fail are that the file is open or that it is
necessary to copy its contents to effectuate its
renaming.
7.19.4 Library 7.19.4.2
302 Committee Draft -- August 3, 1998 WG14/N843
7.19.4.3 The tmpfile function
Synopsis
[#1]
#include <stdio.h>
FILE *tmpfile(void);
Description
[#2] The tmpfile function creates a temporary binary file
that will automatically be removed when it is closed or at
program termination. If the program terminates abnormally,
whether an open temporary file is removed is implementation-
defined. The file is opened for update with "wb+" mode.
Returns
[#3] The tmpfile function returns a pointer to the stream of
the file that it created. If the file cannot be created,
the tmpfile function returns a null pointer.
Forward references: the fopen function (7.19.5.3).
7.19.4.4 The tmpnam function
Synopsis
[#1]
#include <stdio.h>
char *tmpnam(char *s);
Description
[#2] The tmpnam function generates a string that is a valid
file name and that is not the same as the name of an
existing file.211)
[#3] The tmpnam function generates a different string each
time it is called, up to TMP_MAX times. If it is called
more than TMP_MAX times, the behavior is implementation-
defined.
[#4] The implementation shall behave as if no library
____________________
211Files created using strings generated by the tmpnam
function are temporary only in the sense that their names
should not collide with those generated by conventional
naming rules for the implementation. It is still
necessary to use the remove function to remove such files
when their use is ended, and before program termination.
7.19.4.2 Library 7.19.4.4
WG14/N843 Committee Draft -- August 3, 1998 303
function calls the tmpnam function.
Returns
[#5] If the argument is a null pointer, the tmpnam function
leaves its result in an internal static object and returns a
pointer to that object. Subsequent calls to the tmpnam
function may modify the same object. If the argument is not
a null pointer, it is assumed to point to an array of at
least L_tmpnam chars; the tmpnam function writes its result
in that array and returns the argument as its value.
Environmental limits
[#6] The value of the macro TMP_MAX shall be at least 25.
7.19.5 File access functions
7.19.5.1 The fclose function
Synopsis
[#1]
#include <stdio.h>
int fclose(FILE *stream);
Description
[#2] The fclose function causes the stream pointed to by
stream to be flushed and the associated file to be closed.
Any unwritten buffered data for the stream are delivered to
the host environment to be written to the file; any unread
buffered data are discarded. The stream is disassociated
from the file. If the associated buffer was automatically
allocated, it is deallocated.
Returns
[#3] The fclose function returns zero if the stream was
successfully closed, or EOF if any errors were detected.
7.19.4.4 Library 7.19.5.1
304 Committee Draft -- August 3, 1998 WG14/N843
7.19.5.2 The fflush function
Synopsis
[#1]
#include <stdio.h>
int fflush(FILE *stream);
Description
[#2] If stream points to an output stream or an update
stream in which the most recent operation was not input, the
fflush function causes any unwritten data for that stream to
be delivered to the host environment to be written to the
file; otherwise, the behavior is undefined.
[#3] If stream is a null pointer, the fflush function
performs this flushing action on all streams for which the
behavior is defined above.
Returns
[#4] The fflush function sets the error indicator for the
stream and returns EOF if a write error occurs, otherwise it
returns zero.
Forward references: the fopen function (7.19.5.3). |
7.19.5.3 The fopen function
Synopsis
[#1]
#include <stdio.h>
FILE *fopen(const char * filename,
const char * mode);
Description
[#2] The fopen function opens the file whose name is the
string pointed to by filename, and associates a stream with
it.
[#3] The argument mode points to a string. If the string is
one of the following, the file is open in the indicated
mode. Otherwise, the behavior is undefined.212)
WG14/N843 Committee Draft -- August 3, 1998 305
r open text file for reading
w truncate to zero length or create text file for writing
a append; open or create text file for writing at end-of-file
rb open binary file for reading
wb truncate to zero length or create binary file for writing
ab append; open or create binary file for writing at end-of-file
r+ open text file for update (reading and writing)
w+ truncate to zero length or create text file for update
a+ append; open or create text file for update, writing at end-of-file
r+b or rb+ open binary file for update (reading and writing)
w+b or wb+ truncate to zero length or create binary file for update
a+b or ab+ append; open or create binary file for update, writing at end-of-file
[#4] Opening a file with read mode ('r' as the first
character in the mode argument) fails if the file does not
exist or cannot be read.
[#5] Opening a file with append mode ('a' as the first
character in the mode argument) causes all subsequent writes
to the file to be forced to the then current end-of-file,
regardless of intervening calls to the fseek function. In
some implementations, opening a binary file with append mode
('b' as the second or third character in the above list of
mode argument values) may initially position the file
position indicator for the stream beyond the last data
written, because of null character padding.
[#6] When a file is opened with update mode ('+' as the
second or third character in the above list of mode argument
values), both input and output may be performed on the
associated stream. However, output shall not be directly
followed by input without an intervening call to the fflush
function or to a file positioning function (fseek, fsetpos,
or rewind), and input shall not be directly followed by
output without an intervening call to a file positioning
function, unless the input operation encounters end-of-file.
Opening (or creating) a text file with update mode may
instead open (or create) a binary stream in some
implementations.
[#7] When opened, a stream is fully buffered if and only if
it can be determined not to refer to an interactive device.
The error and end-of-file indicators for the stream are
cleared.
Returns
____________________
212If the string begins with one of the above sequences, the
implementation might choose to ignore the remaining
characters, or it might use them to select different
kinds of a file (some of which might not conform to the
properties in 7.19.2).
7.19.5.3 Library 7.19.5.3
306 Committee Draft -- August 3, 1998 WG14/N843
[#8] The fopen function returns a pointer to the object
controlling the stream. If the open operation fails, fopen
returns a null pointer.
Forward references: file positioning functions (7.19.9).
7.19.5.4 The freopen function
Synopsis
[#1]
#include <stdio.h>
FILE *freopen(const char * filename,
const char * mode,
FILE * restrict stream);
Description
[#2] The freopen function opens the file whose name is the
string pointed to by filename and associates the stream
pointed to by stream with it. The mode argument is used
just as in the fopen function.213)
[#3] If filename is a null pointer, the freopen function |
attempts to change the mode of the stream to that specified |
by mode, as if the name of the file currently associated |
with the stream had been used. It is implementation-defined |
which changes of mode are permitted (if any), and under what |
circumstances. |
[#4] The freopen function first attempts to close any file
that is associated with the specified stream. Failure to |
close the file is ignored. The error and end-of-file
indicators for the stream are cleared.
Returns
[#5] The freopen function returns a null pointer if the open
operation fails. Otherwise, freopen returns the value of
stream.
____________________
213The primary use of the freopen function is to change the
file associated with a standard text stream (stderr,
stdin, or stdout), as those identifiers need not be
modifiable lvalues to which the value returned by the
fopen function may be assigned.
7.19.5.3 Library 7.19.5.4
WG14/N843 Committee Draft -- August 3, 1998 307
7.19.5.5 The setbuf function
Synopsis
[#1]
#include <stdio.h>
void setbuf(FILE * restrict stream,
char * restrict buf);
Description
[#2] Except that it returns no value, the setbuf function is
equivalent to the setvbuf function invoked with the values
_IOFBF for mode and BUFSIZ for size, or (if buf is a null
pointer), with the value _IONBF for mode.
Returns
[#3] The setbuf function returns no value.
Forward references: the setvbuf function (7.19.5.6).
7.19.5.6 The setvbuf function
Synopsis
[#1]
#include <stdio.h>
int setvbuf(FILE * restrict stream,
char * restrict buf,
int mode, size_t size);
Description
[#2] The setvbuf function may be used only after the stream
pointed to by stream has been associated with an open file
and before any other operation (other than an unsuccessful
call to setvbuf) is performed on the stream. The argument
mode determines how stream will be buffered, as follows:
_IOFBF causes input/output to be fully buffered; _IOLBF
causes input/output to be line buffered; _IONBF causes
input/output to be unbuffered. If buf is not a null
pointer, the array it points to may be used instead of a
buffer allocated by the setvbuf function214) and the
argument size specifies the size of the array; otherwise,
size may determine the size of a buffer allocated by the
____________________
214The buffer has to have a lifetime at least as great as
the open stream, so the stream should be closed before a
buffer that has automatic storage duration is deallocated
upon block exit.
7.19.5.4 Library 7.19.5.6
308 Committee Draft -- August 3, 1998 WG14/N843
setvbuf function. The contents of the array at any time are
indeterminate.
Returns
[#3] The setvbuf function returns zero on success, or
nonzero if an invalid value is given for mode or if the
request cannot be honored.
7.19.6 Formatted input/output functions
[#1] The formatted input/output functions215) shall behave
as if there is a sequence point after the actions associated
with each specifier.
7.19.6.1 The fprintf function
Synopsis
[#1]
#include <stdio.h>
int fprintf(FILE * restrict stream,
const char * restrict format, ...);
Description
[#2] The fprintf function writes output to the stream
pointed to by stream, under control of the string pointed to
by format that specifies how subsequent arguments are
converted for output. If there are insufficient arguments
for the format, the behavior is undefined. If the format is
exhausted while arguments remain, the excess arguments are
evaluated (as always) but are otherwise ignored. The
fprintf function returns when the end of the format string
is encountered.
[#3] The format shall be a multibyte character sequence,
beginning and ending in its initial shift state. The format
is composed of zero or more directives: ordinary multibyte
characters (not %), which are copied unchanged to the output
stream; and conversion specifications, each of which results
in fetching zero or more subsequent arguments, converting
them, if applicable, according to the corresponding
conversion specifier, and then writing the result to the
output stream.
[#4] Each conversion specification is introduced by the
character %. After the %, the following appear in sequence:
____________________
215The printf functions perform writes to memory for the %n
specifier.
7.19.5.6 Library 7.19.6.1
WG14/N843 Committee Draft -- August 3, 1998 309
-- Zero or more flags (in any order) that modify the
meaning of the conversion specification.
-- An optional minimum field width. If the converted value
has fewer characters than the field width, it is padded
with spaces (by default) on the left (or right, if the
left adjustment flag, described later, has been given)
to the field width. The field width takes the form of
an asterisk * (described later) or a decimal
integer.216)
-- An optional precision that gives the minimum number of
digits to appear for the d, i, o, u, x, and X
conversions, the number of digits to appear after the
decimal-point character for a, A, e, E, f, and F
conversions, the maximum number of significant digits
for the g and G conversions, or the maximum number of
characters to be written from a string in s
conversions. The precision takes the form of a period
(.) followed either by an asterisk * (described later)
or by an optional decimal integer; if only the period
is specified, the precision is taken as zero. If a
precision appears with any other conversion specifier,
the behavior is undefined.
-- An optional length modifier that specifies the size of
the argument.
-- A conversion specifier character that specifies the
type of conversion to be applied.
[#5] As noted above, a field width, or precision, or both,
may be indicated by an asterisk. In this case, an int
argument supplies the field width or precision. The
arguments specifying field width, or precision, or both,
shall appear (in that order) before the argument (if any) to
be converted. A negative field width argument is taken as a
- flag followed by a positive field width. A negative
precision argument is taken as if the precision were
omitted.
[#6] The flag characters and their meanings are:
- The result of the conversion is left-justified within
the field. (It is right-justified if this flag is not
specified.)
+ The result of a signed conversion always begins with a
plus or minus sign. (It begins with a sign only when
a negative value is converted if this flag is not
____________________
216Note that 0 is taken as a flag, not as the beginning of a
field width.
7.19.6.1 Library 7.19.6.1
310 Committee Draft -- August 3, 1998 WG14/N843
specified.)217)
space If the first character of a signed conversion is not a
sign, or if a signed conversion results in no
characters, a space is prefixed to the result. If the
space and + flags both appear, the space flag is
ignored.
# The result is converted to an ``alternative form''. |
For o conversion, it increases the precision, if and
only if necessary, to force the first digit of the
result to be a zero (if the value and precision are
both 0, a single 0 is printed). For x (or X)
conversion, a nonzero result has 0x (or 0X) prefixed
to it. For a, A, e, E, f, F, g, and G conversions,
the result always contains a decimal-point character,
even if no digits follow it. (Normally, a decimal-
point character appears in the result of these
conversions only if a digit follows it.) For g and G
conversions, trailing zeros are not removed from the
result. For other conversions, the behavior is
undefined.
0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G
conversions, leading zeros (following any indication
of sign or base) are used to pad to the field width;
no space padding is performed. If the 0 and - flags
both appear, the 0 flag is ignored. For d, i, o, u,
x, and X conversions, if a precision is specified, the
0 flag is ignored. For other conversions, the
behavior is undefined.
[#7] The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a signed char
or unsigned char argument (the argument will
have been promoted according to the integer |
promotions, but its value shall be converted to
signed char or unsigned char before printing);
or that a following n conversion specifier
applies to a pointer to a signed char argument.
h Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a short int or
unsigned short int argument (the argument will
have been promoted according to the integer
promotions, but its value shall be converted to |
short int or unsigned short int before
____________________
217The results of all floating conversions of a negative
zero, and of negative values that round to zero, include
a minus sign.
7.19.6.1 Library 7.19.6.1
WG14/N843 Committee Draft -- August 3, 1998 311
printing); or that a following n conversion
specifier applies to a pointer to a short int
argument.
l (ell) Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a long int or
unsigned long int argument; that a following n
conversion specifier applies to a pointer to a
long int argument; that a following c
conversion specifier applies to a wint_t
argument; that a following s conversion
specifier applies to a pointer to a wchar_t
argument; or has no effect on a following a, A,
e, E, f, F, g, or G conversion specifier.
ll (ell-ell) Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a long long int
or unsigned long long int argument; or that a
following n conversion specifier applies to a
pointer to a long long int argument. |
j Specifies that a following d, i, o, u, x, or X |
conversion specifier applies to an intmax_t or |
uintmax_t argument; or that a following n |
conversion specifier applies to a pointer to an |
intmax_t argument. |
z Specifies that a following d, i, o, u, x, or X |
conversion specifier applies to a size_t or the |
corresponding signed integer type argument; or |
that a following n conversion specifier applies |
to a pointer to a signed integer type |
corresponding to size_t argument. |
t Specifies that a following d, i, o, u, x, or X |
conversion specifier applies to a ptrdiff_t or |
the corresponding unsigned integer type |
argument; or that a following n conversion |
specifier applies to a pointer to a ptrdiff_t |
argument.
L Specifies that a following a, A, e, E, f, F, g,
or G conversion specifier applies to a long
double argument.
If a length modifier appears with any conversion specifier |
other than as specified above, the behavior is undefined.
[#8] The conversion specifiers and their meanings are:
d,i The int argument is converted to signed decimal in
the style [-]dddd. The precision specifies the
minimum number of digits to appear; if the value
being converted can be represented in fewer digits,
7.19.6.1 Library 7.19.6.1
312 Committee Draft -- August 3, 1998 WG14/N843
it is expanded with leading zeros. The default
precision is 1. The result of converting a zero
value with a precision of zero is no characters.
o,u,x,X The unsigned int argument is converted to unsigned
octal (o), unsigned decimal (u), or unsigned
hexadecimal notation (x or X) in the style dddd; the
letters abcdef are used for x conversion and the
letters ABCDEF for X conversion. The precision
specifies the minimum number of digits to appear; if
the value being converted can be represented in
fewer digits, it is expanded with leading zeros.
The default precision is 1. The result of
converting a zero value with a precision of zero is
no characters.
f,F A double argument representing a (finite) floating- |
point number is converted to decimal notation in the
style [-]ddd.ddd, where the number of digits after
the decimal-point character is equal to the
precision specification. If the precision is
missing, it is taken as 6; if the precision is zero
and the # flag is not specified, no decimal-point
character appears. If a decimal-point character
appears, at least one digit appears before it. The
value is rounded to the appropriate number of
digits.
A double argument representing an infinity is
converted in one of the styles [-]inf or [-]infinity
-- which style is implementation-defined. A
double argument representing a NaN is converted in
one of the styles [-]nan or [-]nan(n-char-sequence)
-- which style, and the meaning of any n-char-
sequence, is implementation-defined. The F
conversion specifier produces INF, INFINITY, or NAN
instead of inf, infinity, or nan, respectively.218)
e,E A double argument representing a (finite) floating- |
point number is converted in the style [-]d.ddde±dd,
where there is one digit (which is nonzero if the
argument is nonzero) before the decimal-point
character and the number of digits after it is equal
to the precision; if the precision is missing, it is
taken as 6; if the precision is zero and the # flag
is not specified, no decimal-point character
appears. The value is rounded to the appropriate
number of digits. The E conversion specifier
produces a number with E instead of e introducing
____________________
218When applied to infinite and NaN values, the -, +, and
space flag characters have their usual meaning; the # and
0 flag characters have no effect.
7.19.6.1 Library 7.19.6.1
WG14/N843 Committee Draft -- August 3, 1998 313
the exponent. The exponent always contains at least
two digits, and only as many more digits as
necessary to represent the exponent. If the value
is zero, the exponent is zero.
A double argument representing an infinity or NaN is
converted in the style of an f or F conversion
specifier.
g,G A double argument representing a (finite) floating- |
point number is converted in style f or e (or in
style F or E in the case of a G conversion
specifier), with the precision specifying the number
of significant digits. If the precision is zero, it
is taken as 1. The style used depends on the value
converted; style e (or E) is used only if the
exponent resulting from such a conversion is less
than -4 or greater than or equal to the precision. |
Trailing zeros are removed from the fractional |
portion of the result unless the # flag is |
specified; a decimal-point character appears only if
it is followed by a digit.
A double argument representing an infinity or NaN is
converted in the style of an f or F conversion
specifier.
a,A A double argument representing a (finite) floating- |
point number is converted in the style
[-]0xh.hhhhp±d, where there is one hexadecimal digit
(which is nonzero if the argument is a normalized
floating-point number and is otherwise unspecified) |
before the decimal-point character219) and the *
number of hexadecimal digits after it is equal to
the precision; if the precision is missing and
FLT_RADIX is a power of 2, then the precision is
sufficient for an exact representation of the value;
if the precision is missing and FLT_RADIX is not a
power of 2, then the precision is sufficient to
distinguish220) values of type double, except that
trailing zeros may be omitted; if the precision is
zero and the # flag is not specified, no decimal-
____________________
219Binary implementations can choose the hexadecimal digit
to the left of the decimal-point character so that
subsequent digits align to nibble (4-bit) boundaries.
220The precision p is sufficient to distinguish values of
the source type if 16p-1>bn where b is FLT_RADIX and n is
the number of base-b digits in the significand of the
source type. A smaller p might suffice depending on the
implementation's scheme for determining the digit to the
left of the decimal-point character.
7.19.6.1 Library 7.19.6.1
314 Committee Draft -- August 3, 1998 WG14/N843
point character appears. The letters abcdef are
used for a conversion and the letters ABCDEF for A
conversion. The A conversion specifier produces a
number with X and P instead of x and p. The
exponent always contains at least one digit, and
only as many more digits as necessary to represent
the decimal exponent of 2. If the value is zero,
the exponent is zero.
A double argument representing an infinity or NaN is
converted in the style of an f or F conversion
specifier.
c If no l length modifier is present, the int argument
is converted to an unsigned char, and the resulting
character is written.
If an l length modifier is present, the wint_t
argument is converted as if by an ls conversion
specification with no precision and an argument that
points to the initial element of a two-element array
of wchar_t, the first element containing the wint_t
argument to the lc conversion specification and the
second a null wide character.
s If no l length modifier is present, the argument
shall be a pointer to the initial element of an
array of character type.221) Characters from the
array are written up to (but not including) the
terminating null character. If the precision is
specified, no more than that many characters are
written. If the precision is not specified or is
greater than the size of the array, the array shall
contain a null character.
If an l length modifier is present, the argument
shall be a pointer to the initial element of an
array of wchar_t type. Wide characters from the
array are converted to multibyte characters (each as
if by a call to the wcrtomb function, with the
conversion state described by an mbstate_t object
initialized to zero before the first wide character
is converted) up to and including a terminating null
wide character. The resulting multibyte characters
are written up to (but not including) the
terminating null character (byte). If no precision
is specified, the array shall contain a null wide
character. If a precision is specified, no more
than that many characters (bytes) are written
(including shift sequences, if any), and the array
shall contain a null wide character if, to equal the
____________________
221No special provisions are made for multibyte characters.
7.19.6.1 Library 7.19.6.1
WG14/N843 Committee Draft -- August 3, 1998 315
multibyte character sequence length given by the
precision, the function would need to access a wide
character one past the end of the array. In no case
is a partial multibyte character written.222)
p The argument shall be a pointer to void. The value
of the pointer is converted to a sequence of
printable characters, in an implementation-defined
manner.
n The argument shall be a pointer to signed integer
into which is written the number of characters
written to the output stream so far by this call to
fprintf. No argument is converted, but one is
consumed. If the conversion specification includes |
any flags, a field width, or a precision, the
behavior is undefined.
% A % character is written. No argument is converted.
The complete conversion specification shall be %%.
[#9] If a conversion specification is invalid, the behavior
is undefined.223) If any argument is not the correct type |
for the corresponding coversion specification, the behavior
is undefined.
[#10] In no case does a nonexistent or small field width
cause truncation of a field; if the result of a conversion
is wider than the field width, the field is expanded to
contain the conversion result.
[#11] For a and A conversions, if FLT_RADIX is a power of 2,
the value is correctly rounded to a hexadecimal floating
number with the given precision.
Recommended practice
[#12] If FLT_RADIX is not a power of 2, the result should be
one of the two adjacent numbers in hexadecimal floating
style with the given precision, with the extra stipulation
that the error should have a correct sign for the current
rounding direction.
[#13] For e, E, f, F, g, and G conversions, if the number of
significant decimal digits is at most DECIMAL_DIG, then the
result should be correctly rounded.224) If the number of
significant decimal digits is more than DECIMAL_DIG but the
source value is exactly representable with DECIMAL_DIG
____________________
222Redundant shift sequences may result if multibyte
characters have a state-dependent encoding.
223See ``future library directions'' (7.26.9).
7.19.6.1 Library 7.19.6.1
316 Committee Draft -- August 3, 1998 WG14/N843
digits, then the result should be an exact representation
with trailing zeros. Otherwise, the source value is bounded
by two adjacent decimal strings L < U, both having
DECIMAL_DIG significant digits; the value of the resultant
decimal string D should satisfy L <= D <= U, with the extra
stipulation that the error should have a correct sign for
the current rounding direction.
Returns
[#14] The fprintf function returns the number of characters
transmitted, or a negative value if an output or encoding |
error occurred.
Environmental limits
[#15] The number of characters that can be produced by any |
single conversion shall be at least 4095. |
[#16] EXAMPLE 1 To print a date and time in the form
``Sunday, July 3, 10:02'' followed by pi to five decimal
places:
#include <math.h>
#include <stdio.h>
/* ... */
char *weekday, *month; // pointers to strings
int day, hour, min;
fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
|
[#17] EXAMPLE 2 In this example, multibyte characters do not
have a state-dependent encoding, and the multibyte members
of the extended character set each consist of two bytes, the
first of which is denoted here by a [] and the second by an
uppercase letter.
[#18] Given the following wide string with length seven,
static wchar_t wstr[] = L"[]X[]Yabc[]Z[]W";
the seven calls
____________________
224For binary-to-decimal conversion, the result format's
values are the numbers representable with the given
format specifier. The number of significant digits is
determined by the format specifier, and in the case of
fixed-point conversion by the source value as well.
7.19.6.1 Library 7.19.6.1
WG14/N843 Committee Draft -- August 3, 1998 317
fprintf(stdout, "|1234567890123|\n"); |
fprintf(stdout, "|%13ls|\n", wstr); |
fprintf(stdout, "|%-13.9ls|\n", wstr); |
fprintf(stdout, "|%13.10ls|\n", wstr); |
fprintf(stdout, "|%13.11ls|\n", wstr); |
fprintf(stdout, "|%13.15ls|\n", &wstr[2]); |
fprintf(stdout, "|%13lc|\n", wstr[5]); |
will print the following seven lines:
|1234567890123|
| []X[]Yabc[]Z[]W|
|[]X[]Yabc[]Z |
| []X[]Yabc[]Z|
| []X[]Yabc[]Z[]W|
| abc[]Z[]W|
| []Z|
Forward references: conversion state (7.24.6), the wcrtomb
function (7.24.6.3.3).
7.19.6.2 The fscanf function
Synopsis
[#1]
#include <stdio.h>
int fscanf(FILE * restrict stream,
const char * restrict format, ...);
Description
[#2] The fscanf function reads input from the stream pointed
to by stream, under control of the string pointed to by
format that specifies the admissible input sequences and how
they are to be converted for assignment, using subsequent
arguments as pointers to the objects to receive the
converted input. If there are insufficient arguments for
the format, the behavior is undefined. If the format is
exhausted while arguments remain, the excess arguments are
evaluated (as always) but are otherwise ignored.
[#3] The format shall be a multibyte character sequence,
beginning and ending in its initial shift state. The format
is composed of zero or more directives: one or more white- |
space characters, an ordinary multibyte character (neither % |
nor a white-space character), or a conversion specification.
Each conversion specification is introduced by the character
%. After the %, the following appear in sequence:
7.19.6.1 Library 7.19.6.2
318 Committee Draft -- August 3, 1998 WG14/N843
-- An optional assignment-suppressing character *.
-- An optional nonzero decimal integer that specifies the
maximum field width (in characters).
-- An optional length modifier that specifies the size of
the receiving object.
-- A conversion specifier character that specifies the
type of conversion to be applied.
[#4] The fscanf function executes each directive of the
format in turn. If a directive fails, as detailed below,
the function returns. Failures are described as input
failures (due to the occurrence of an encoding error or the
unavailability of input characters), or matching failures
(due to inappropriate input).
[#5] A directive composed of white-space character(s) is
executed by reading input up to the first non-white-space
character (which remains unread), or until no more
characters can be read.
[#6] A directive that is an ordinary multibyte character is
executed by reading the next characters of the stream. If
any of those characters differ from the ones composing the
directive, the directive fails and the differing and
subsequent characters remain unread.
[#7] A directive that is a conversion specification defines
a set of matching input sequences, as described below for
each specifier. A conversion specification is executed in
the following steps:
[#8] Input white-space characters (as specified by the
isspace function) are skipped, unless the specification
includes a [, c, or n specifier.225)
[#9] An input item is read from the stream, unless the
specification includes an n specifier. An input item is
defined as the longest sequence of input characters which
does not exceed any specified field width and which is, or
is a prefix of, a matching input sequence. The first
character, if any, after the input item remains unread. If
the length of the input item is zero, the execution of the
directive fails; this condition is a matching failure unless
end-of-file, an encoding error, or a read error prevented
input from the stream, in which case it is an input failure.
[#10] Except in the case of a % specifier, the input item
____________________
225These white-space characters are not counted against a
specified field width.
7.19.6.2 Library 7.19.6.2
WG14/N843 Committee Draft -- August 3, 1998 319
(or, in the case of a %n directive, the count of input
characters) is converted to a type appropriate to the
conversion specifier. If the input item is not a matching
sequence, the execution of the directive fails: this
condition is a matching failure. Unless assignment
suppression was indicated by a *, the result of the
conversion is placed in the object pointed to by the first
argument following the format argument that has not already
received a conversion result. If this object does not have
an appropriate type, or if the result of the conversion
cannot be represented in the object, the behavior is
undefined.
[#11] The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
with type pointer to signed char or unsigned
char.
h Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
with type pointer to short int or unsigned
short int.
l (ell) Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
with type pointer to long int or unsigned long
int; that a following a, A, e, E, f, F, g, or G
conversion specifier applies to an argument
with type pointer to double; or that a
following c, s, or [ conversion specifier
applies to an argument with type pointer to
wchar_t.
ll (ell-ell) Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
with type pointer to long long int or unsigned
long long int. |
j Specifies that a following d, i, o, u, x, X, or |
n conversion specifier applies to an argument |
with type pointer to intmax_t or uintmax_t. |
z Specifies that a following d, i, o, u, x, X, or |
n conversion specifier applies to an argument |
with type pointer to size_t or the |
corresponding signed integer type. |
t Specifies that a following d, i, o, u, x, X, or |
n conversion specifier applies to an argument |
with type pointer to ptrdiff_t or the |
corresponding unsigned integer type.
7.19.6.2 Library 7.19.6.2
320 Committee Draft -- August 3, 1998 WG14/N843
L Specifies that a following a, A, e, E, f, F, g,
or G conversion specifier applies to an
argument with type pointer to long double.
If a length modifier appears with any conversion specifier |
other than as specified above, the behavior is undefined.
[#12] The conversion specifiers and their meanings are:
d Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the strtol function with the value 10
for the base argument. The corresponding argument
shall be a pointer to signed integer.
i Matches an optionally signed integer, whose format
is the same as expected for the subject sequence of
the strtol function with the value 0 for the base
argument. The corresponding argument shall be a
pointer to signed integer.
o Matches an optionally signed octal integer, whose
format is the same as expected for the subject
sequence of the strtoul function with the value 8
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
u Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the strtoul function with the value 10
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
x Matches an optionally signed hexadecimal integer,
whose format is the same as expected for the subject
sequence of the strtoul function with the value 16
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
a,e,f,g Matches an optionally signed floating-point number, |
infinity, or NaN, whose format is the same as
expected for the subject sequence of the strtod
function. The corresponding argument shall be a
pointer to floating.
c Matches a sequence of characters of exactly the
number specified by the field width (1 if no field
width is present in the directive).226)
If no l length modifier is present, the
corresponding argument shall be a pointer to the
initial element of a character array large enough to
accept the sequence. No null character is added.
7.19.6.2 Library 7.19.6.2
WG14/N843 Committee Draft -- August 3, 1998 321
If an l length modifier is present, the input shall
be a sequence of multibyte characters that begins in
the initial shift state. Each multibyte character
in the sequence is converted to a wide character as
if by a call to the mbrtowc function, with the
conversion state described by an mbstate_t object
initialized to zero before the first multibyte
character is converted. The corresponding argument
shall be a pointer to the initial element of an
array of wchar_t large enough to accept the
resulting sequence of wide characters. No null wide
character is added.
s Matches a sequence of non-white-space
characters.226)
If no l length modifier is present, the
corresponding argument shall be a pointer to the
initial element of a character array large enough to
accept the sequence and a terminating null
character, which will be added automatically.
If an l length modifier is present, the input shall
be a sequence of multibyte characters that begins in
the initial shift state. Each multibyte character
is converted to a wide character as if by a call to
the mbrtowc function, with the conversion state
described by an mbstate_t object initialized to zero
before the first multibyte character is converted.
The corresponding argument shall be a pointer to the
initial element of an array of wchar_t large enough
to accept the sequence and the terminating null wide
character, which will be added automatically.
[ Matches a nonempty sequence of characters from a set
of expected characters (the scanset).226)
If no l length modifier is present, the
corresponding argument shall be a pointer to the
initial element of a character array large enough to
accept the sequence and a terminating null
character, which will be added automatically.
If an l length modifier is present, the input shall
be a sequence of multibyte characters that begins in
____________________
226No special provisions are made for multibyte characters
in the matching rules used by the c, s, and [ conversion
specifiers
-- the extent of the input field is still determined on
a byte-by-byte basis. The resulting field is
nevertheless a sequence of multibyte characters that
begins in the initial shift state.
7.19.6.2 Library 7.19.6.2
322 Committee Draft -- August 3, 1998 WG14/N843
the initial shift state. Each multibyte character
is converted to a wide character as if by a call to
the mbrtowc function, with the conversion state
described by an mbstate_t object initialized to zero
before the first multibyte character is converted.
The corresponding argument shall be a pointer to the
initial element of an array of wchar_t large enough
to accept the sequence and the terminating null wide
character, which will be added automatically.
The conversion specifier includes all subsequent
characters in the format string, up to and including
the matching right bracket (]). The characters
between the brackets (the scanlist) compose the
scanset, unless the character after the left bracket
is a circumflex (^), in which case the scanset
contains all characters that do not appear in the
scanlist between the circumflex and the right
bracket. If the conversion specifier begins with []
or [^], the right bracket character is in the
scanlist and the next following right bracket |
character is the matching right bracket that ends
the specification; otherwise the first following |
right bracket character is the one that ends the
specification. If a - character is in the scanlist
and is not the first, nor the second where the first
character is a ^, nor the last character, the
behavior is implementation-defined.
p Matches an implementation-defined set of sequences,
which should be the same as the set of sequences
that may be produced by the %p conversion of the
fprintf function. The corresponding argument shall
be a pointer to a pointer to void. The
interpretation of the input item is implementation-
defined. If the input item is a value converted
earlier during the same program execution, the
pointer that results shall compare equal to that
value; otherwise the behavior of the %p conversion
is undefined.
n No input is consumed. The corresponding argument
shall be a pointer to signed integer into which is
to be written the number of characters read from the
input stream so far by this call to the fscanf
function. Execution of a %n directive does not
increment the assignment count returned at the
completion of execution of the fscanf function. No
argument is converted, but one is consumed. If the |
conversion specification includes an assignment- |
suppressing character or a field width, the behavior
is undefined.
7.19.6.2 Library 7.19.6.2
WG14/N843 Committee Draft -- August 3, 1998 323
% Matches a single % character; no conversion or |
assignment occurs. The complete conversion
specification shall be %%.
[#13] If a conversion specification is invalid, the behavior
is undefined.227)
[#14] The conversion specifiers A, E, F, G, and X are also
valid and behave the same as, respectively, a, e, f, g, and
x.
[#15] If end-of-file is encountered during input, conversion
is terminated. If end-of-file occurs before any characters
matching the current directive have been read (other than
leading white space, where permitted), execution of the
current directive terminates with an input failure;
otherwise, unless execution of the current directive is
terminated with a matching failure, execution of the
following directive (other than %n, if any) is terminated
with an input failure.
[#16] Trailing white space (including new-line characters)
is left unread unless matched by a directive. The success
of literal matches and suppressed assignments is not
directly determinable other than via the %n directive.
[#17] If conversion terminates on a conflicting input
character, the offending input character is left unread in
the input stream.228)
Returns
[#18] The fscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the function returns the number of input items
assigned, which can be fewer than provided for, or even
zero, in the event of an early matching failure.
[#19] EXAMPLE 1 The call:
#include <stdio.h>
/* ... */
int n, i; float x; char name[50];
n = fscanf(stdin, "%d%f%s", &i, &x, name);
with the input line:
____________________
227See ``future library directions'' (7.26.9).
228fscanf pushes back at most one input character onto the
input stream. Therefore, some sequences that are
acceptable to strtod, strtol, etc., are unacceptable to
fscanf.
7.19.6.2 Library 7.19.6.2
324 Committee Draft -- August 3, 1998 WG14/N843
25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the
value 5.432, and to name the sequence thompson\0.
[#20] EXAMPLE 2 The call:
#include <stdio.h>
/* ... */
int i; float x; char name[50];
fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
with input:
56789 0123 56a72
will assign to i the value 56 and to x the value 789.0, will
skip 0123, and will assign to name the sequence 56\0. The
next character read from the input stream will be a.
[#21] EXAMPLE 3 To accept repeatedly from stdin a quantity,
a unit of measure, and an item name:
#include <stdio.h>
/* ... */
int count; float quant; char units[21], item[21];
do { |
count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);|
fscanf(stdin,"%*[^\n]");
} while (!feof(stdin) && !ferror(stdin)); |
[#22] If the stdin stream contains the following lines:
2 quarts of oil
-12.8degrees Celsius
lots of luck
10.0LBS of
dirt
100ergs of energy
the execution of the above example will be analogous to the
following assignments:
7.19.6.2 Library 7.19.6.2
WG14/N843 Committee Draft -- August 3, 1998 325
quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");
count = 3;
quant = -12.8; strcpy(units, "degrees");
count = 2; // "C" fails to match "o"
count = 0; // "l" fails to match "%f"
quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
count = 3;
count = 0; // "100e" fails to match "%f"
count = EOF;
[#23] EXAMPLE 4 In:
#include <stdio.h>
/* ... */
int d1, d2, n1, n2, i;
i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
the value 123 is assigned to d1 and the value 3 to n1.
Because %n can never get an input failure the value of 3 is
also assigned to n2. The value of d2 is not affected. The
value 1 is assigned to i.
|
[#24] EXAMPLE 5 In these examples, multibyte characters do
have a state-dependent encoding, and multibyte members of
the extended character set consist of two bytes, the first
of which is denoted here by a [] and the second by an
uppercase letter, but are only recognized as such when in
the alternate shift state. The shift sequences are denoted
by and , in which the first causes entry into the alternate
shift state. |
[#25] After the call:
#include <stdio.h>
/* ... */
char str[50];
fscanf(stdin, "a%s", str);
with the input line:
a[]X[]Y bc
str will contain []X[]Y\0 assuming that none of the bytes of |
the shift sequences (or of the multibyte characters, in the
more general case) appears to be a single-byte white-space
character. |
[#26] In contrast, after the call:
7.19.6.2 Library 7.19.6.2
326 Committee Draft -- August 3, 1998 WG14/N843
#include <stdio.h>
#include <stddef.h>
/* ... */
wchar_t wstr[50];
fscanf(stdin, "a%ls", wstr);
with the same input line, wstr will contain the two wide
characters that correspond to []X and []Y and a terminating
null wide character. |
[#27] However, the call:
#include <stdio.h>
#include <stddef.h>
/* ... */
wchar_t wstr[50];
fscanf(stdin, "a[]X%ls", wstr);
with the same input line will return zero due to a matching
failure against the sequence in the format string. |
[#28] Assuming that the first byte of the multibyte
character []X is the same as the first byte of the multibyte
character []Y, after the call:
#include <stdio.h>
#include <stddef.h>
/* ... */
wchar_t wstr[50];
fscanf(stdin, "a[]Y%ls", wstr);
with the same input line, zero will again be returned, but
stdin will be left with a partially consumed multibyte
character. |
Forward references: the strtod, strtof, and strtold
functions (7.20.1.3), the strtol, strtoll, strtoul, and |
strtoull functions (7.20.1.4), conversion state (7.24.6),
the wcrtomb function (7.24.6.3.3).
7.19.6.2 Library 7.19.6.2
WG14/N843 Committee Draft -- August 3, 1998 327
7.19.6.3 The printf function
Synopsis
[#1]
#include <stdio.h>
int printf(const char * restrict format, ...);
Description
[#2] The printf function is equivalent to fprintf with the
argument stdout interposed before the arguments to printf.
Returns
[#3] The printf function returns the number of characters
transmitted, or a negative value if an output or encoding |
error occurred.
7.19.6.4 The scanf function
Synopsis
[#1]
#include <stdio.h>
int scanf(const char * restrict format, ...);
Description
[#2] The scanf function is equivalent to fscanf with the
argument stdin interposed before the arguments to scanf.
Returns
[#3] The scanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the scanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.19.6.2 Library 7.19.6.4
328 Committee Draft -- August 3, 1998 WG14/N843
7.19.6.5 The snprintf function
Synopsis
[#1]
#include <stdio.h>
int snprintf(char * restrict s, size_t n,
const char * restrict format, ...);
Description
[#2] The snprintf function is equivalent to fprintf, except |
that the output is written into an array (specified by |
argument s) rather than to a stream. If n is zero, nothing
is written, and s may be a null pointer. Otherwise, output
characters beyond the n-1st are discarded rather than being
written to the array, and a null character is written at the
end of the characters actually written into the array. If
copying takes place between objects that overlap, the
behavior is undefined.
Returns
[#3] The snprintf function returns the number of characters
that would have been written had n been sufficiently large,
not counting the terminating null character, or a negative |
value if an encoding error occurred. Thus, the null-
terminated output has been completely written if and only if
the returned value is nonnegative and less than n. |
7.19.6.6 The sprintf function
Synopsis
[#1]
#include <stdio.h>
int sprintf(char * restrict s,
const char * restrict format, ...);
Description
[#2] The sprintf function is equivalent to fprintf, except |
that the output is written into an array (specified by the |
argument s) rather than to a stream. A null character is
written at the end of the characters written; it is not |
counted as part of the returned value. If copying takes
place between objects that overlap, the behavior is
undefined.
Returns
[#3] The sprintf function returns the number of characters
7.19.6.4 Library 7.19.6.6
WG14/N843 Committee Draft -- August 3, 1998 329
written in the array, not counting the terminating null |
character, or a negative value if an encoding error |
occurred.
7.19.6.7 The sscanf function
Synopsis
[#1]
#include <stdio.h>
int sscanf(const char * restrict s,
const char * restrict format, ...);
Description
[#2] The sscanf function is equivalent to fscanf, except |
that input is obtained from a string (specified by the |
argument s) rather than from a stream. Reaching the end of
the string is equivalent to encountering end-of-file for the
fscanf function. If copying takes place between objects
that overlap, the behavior is undefined.
Returns
[#3] The sscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the sscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.19.6.8 The vfprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vfprintf(FILE * restrict stream,
const char * restrict format,
va_list arg);
Description
[#2] The vfprintf function is equivalent to fprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfprintf function does not
invoke the va_end macro.229)
Returns
[#3] The vfprintf function returns the number of characters
transmitted, or a negative value if an output or encoding |
error occurred.
[#4] EXAMPLE The following shows the use of the vfprintf
function in a general error-reporting routine.
330 Committee Draft -- August 3, 1998 WG14/N843
#include <stdarg.h>
#include <stdio.h>
void error(char *function_name, char *format, ...)
{
va_list args;
va_start(args, format);
// print out name of function causing error
fprintf(stderr, "ERROR in %s: ", function_name);
// print out remainder of message
vfprintf(stderr, format, args);
va_end(args);
}
7.19.6.9 The vfscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vfscanf(FILE * restrict stream,
const char * restrict format,
va_list arg);
Description
[#2] The vfscanf function is equivalent to fscanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfscanf function does not |
invoke the va_end macro.229)
Returns
[#3] The vfscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vfscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
____________________
229As the functions vfprintf, vfscanf, vprintf, vscanf,
vsnprintf, vsprintf, and vsscanf invoke the va_arg macro,
the value of arg after the return is indeterminate.
7.19.6.8 Library 7.19.6.9
WG14/N843 Committee Draft -- August 3, 1998 331
7.19.6.10 The vprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vprintf(const char * restrict format,
va_list arg);
Description
[#2] The vprintf function is equivalent to printf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vprintf function does not
invoke the va_end macro.229)
Returns
[#3] The vprintf function returns the number of characters
transmitted, or a negative value if an output or encoding |
error occurred.
7.19.6.11 The vscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vscanf(const char * restrict format,
va_list arg);
Description
[#2] The vscanf function is equivalent to scanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vscanf function does not |
invoke the va_end macro.229)
Returns
[#3] The vscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.19.6.9 Library 7.19.6.11
332 Committee Draft -- August 3, 1998 WG14/N843
7.19.6.12 The vsnprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vsprintf(char * restrict s, size_t n,
const char * restrict format,
va_list arg);
Description
[#2] The vsnprintf function is equivalent to snprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vsnprintf function does not
invoke the va_end macro.229) If copying takes place between
objects that overlap, the behavior is undefined.
Returns
[#3] The vsnprintf function returns the number of characters
that would have been written had n been sufficiently large,
not counting the terminating null character, or a negative |
value if an encoding error occurred. Thus, the null-
terminated output has been completely written if and only if
the returned value is nonnegative and less than n. |
7.19.6.13 The vsprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vsprintf(char * restrict s,
const char * restrict format,
va_list arg);
Description
[#2] The vsprintf function is equivalent to sprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vsprintf function does not
invoke the va_end macro.229) If copying takes place between
objects that overlap, the behavior is undefined.
Returns
[#3] The vsprintf function returns the number of characters
7.19.6.11 Library 7.19.6.13
WG14/N843 Committee Draft -- August 3, 1998 333
written in the array, not counting the terminating null |
character, or a negative value if an encoding error |
occurred.
7.19.6.14 The vsscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
int vsscanf(const char * restrict s,
const char * restrict format,
va_list arg);
Description
[#2] The vsscanf function is equivalent to sscanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vsscanf function does not |
invoke the va_end macro.229)
Returns
[#3] The vsscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.19.7 Character input/output functions
7.19.7.1 The fgetc function
Synopsis
[#1]
#include <stdio.h>
int fgetc(FILE *stream);
Description
[#2] If a next character is present from the input stream
pointed to by stream, the fgetc function obtains that
character as an unsigned char converted to an int and
advances the associated file position indicator for the
stream (if defined).
Returns
[#3] The fgetc function returns the next character from the
7.19.6.13 Library 7.19.7.1
334 Committee Draft -- August 3, 1998 WG14/N843
input stream pointed to by stream. If the stream is at end-
of-file, the end-of-file indicator for the stream is set and
fgetc returns EOF. If a read error occurs, the error
indicator for the stream is set and fgetc returns EOF.230)
7.19.7.2 The fgets function
Synopsis
[#1]
#include <stdio.h>
char *fgets(char * restrict s, int n,
FILE * restrict stream);
Description
[#2] The fgets function reads at most one less than the
number of characters specified by n from the stream pointed
to by stream into the array pointed to by s. No additional
characters are read after a new-line character (which is
retained) or after end-of-file. A null character is written
immediately after the last character read into the array.
Returns
[#3] The fgets function returns s if successful. If end-of-
file is encountered and no characters have been read into
the array, the contents of the array remain unchanged and a
null pointer is returned. If a read error occurs during the
operation, the array contents are indeterminate and a null
pointer is returned.
7.19.7.3 The fputc function
Synopsis
[#1]
#include <stdio.h>
int fputc(int c, FILE *stream);
Description
[#2] The fputc function writes the character specified by c
(converted to an unsigned char) to the output stream pointed
to by stream, at the position indicated by the associated
file position indicator for the stream (if defined), and
advances the indicator appropriately. If the file cannot
support positioning requests, or if the stream was opened
____________________
230An end-of-file and a read error can be distinguished by
use of the feof and ferror functions.
7.19.7.1 Library 7.19.7.3
WG14/N843 Committee Draft -- August 3, 1998 335
with append mode, the character is appended to the output
stream.
Returns
[#3] The fputc function returns the character written. If a
write error occurs, the error indicator for the stream is
set and fputc returns EOF.
7.19.7.4 The fputs function
Synopsis
[#1]
#include <stdio.h>
int fputs(const char * restrict s,
FILE * restrict stream);
Description
[#2] The fputs function writes the string pointed to by s to
the stream pointed to by stream. The terminating null
character is not written.
Returns
[#3] The fputs function returns EOF if a write error occurs;
otherwise it returns a nonnegative value.
7.19.7.5 The getc function
Synopsis
[#1]
#include <stdio.h>
int getc(FILE *stream);
Description
[#2] The getc function is equivalent to fgetc, except that
if it is implemented as a macro, it may evaluate stream more
than once, so the argument should never be an expression
with side effects.
Returns
[#3] The getc function returns the next character from the
input stream pointed to by stream. If the stream is at end-
of-file, the end-of-file indicator for the stream is set and
getc returns EOF. If a read error occurs, the error
indicator for the stream is set and getc returns EOF.
7.19.7.3 Library 7.19.7.5
336 Committee Draft -- August 3, 1998 WG14/N843
7.19.7.6 The getchar function
Synopsis
[#1]
#include <stdio.h>
int getchar(void);
Description
[#2] The getchar function is equivalent to getc with the
argument stdin.
Returns
[#3] The getchar function returns the next character from
the input stream pointed to by stdin. If the stream is at
end-of-file, the end-of-file indicator for the stream is set
and getchar returns EOF. If a read error occurs, the error
indicator for the stream is set and getchar returns EOF.
7.19.7.7 The gets function
Synopsis
[#1]
#include <stdio.h>
char *gets(char *s);
Description
[#2] The gets function reads characters from the input
stream pointed to by stdin, into the array pointed to by s,
until end-of-file is encountered or a new-line character is
read. Any new-line character is discarded, and a null
character is written immediately after the last character
read into the array.
Returns
[#3] The gets function returns s if successful. If end-of-
file is encountered and no characters have been read into
the array, the contents of the array remain unchanged and a
null pointer is returned. If a read error occurs during the
operation, the array contents are indeterminate and a null
pointer is returned.
7.19.7.5 Library 7.19.7.7
WG14/N843 Committee Draft -- August 3, 1998 337
7.19.7.8 The putc function
Synopsis
[#1]
#include <stdio.h>
int putc(int c, FILE *stream);
Description
[#2] The putc function is equivalent to fputc, except that
if it is implemented as a macro, it may evaluate stream more
than once, so that argument should never be an expression |
with side effects.
Returns
[#3] The putc function returns the character written. If a
write error occurs, the error indicator for the stream is
set and putc returns EOF.
7.19.7.9 The putchar function
Synopsis
[#1]
#include <stdio.h>
int putchar(int c);
Description
[#2] The putchar function is equivalent to putc with the
second argument stdout.
Returns
[#3] The putchar function returns the character written. If
a write error occurs, the error indicator for the stream is
set and putchar returns EOF.
7.19.7.7 Library 7.19.7.9
338 Committee Draft -- August 3, 1998 WG14/N843
7.19.7.10 The puts function
Synopsis
[#1]
#include <stdio.h>
int puts(const char *s);
Description
[#2] The puts function writes the string pointed to by s to
the stream pointed to by stdout, and appends a new-line
character to the output. The terminating null character is
not written.
Returns
[#3] The puts function returns EOF if a write error occurs;
otherwise it returns a nonnegative value.
7.19.7.11 The ungetc function
Synopsis
[#1]
#include <stdio.h>
int ungetc(int c, FILE *stream);
Description
[#2] The ungetc function pushes the character specified by c
(converted to an unsigned char) back onto the input stream
pointed to by stream. Pushed-back characters will be |
returned by subsequent reads on that stream in the reverse
order of their pushing. A successful intervening call (with
the stream pointed to by stream) to a file positioning
function (fseek, fsetpos, or rewind) discards any pushed-
back characters for the stream. The external storage
corresponding to the stream is unchanged.
[#3] One character of pushback is guaranteed. If the ungetc
function is called too many times on the same stream without
an intervening read or file positioning operation on that
stream, the operation may fail.
[#4] If the value of c equals that of the macro EOF, the
operation fails and the input stream is unchanged.
[#5] A successful call to the ungetc function clears the
end-of-file indicator for the stream. The value of the file
position indicator for the stream after reading or
discarding all pushed-back characters shall be the same as
7.19.7.9 Library 7.19.7.11
WG14/N843 Committee Draft -- August 3, 1998 339
it was before the characters were pushed back. For a text
stream, the value of its file position indicator after a
successful call to the ungetc function is unspecified until
all pushed-back characters are read or discarded. For a
binary stream, its file position indicator is decremented by
each successful call to the ungetc function; if its value
was zero before a call, it is indeterminate after the
call.231)
Returns
[#6] The ungetc function returns the character pushed back
after conversion, or EOF if the operation fails.
Forward references: file positioning functions (7.19.9).
7.19.8 Direct input/output functions
7.19.8.1 The fread function
Synopsis
[#1]
#include <stdio.h>
size_t fread(void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
Description
[#2] The fread function reads, into the array pointed to by
ptr, up to nmemb elements whose size is specified by size,
from the stream pointed to by stream. The file position
indicator for the stream (if defined) is advanced by the
number of characters successfully read. If an error occurs,
the resulting value of the file position indicator for the
stream is indeterminate. If a partial element is read, its
value is indeterminate.
Returns
[#3] The fread function returns the number of elements
successfully read, which may be less than nmemb if a read
error or end-of-file is encountered. If size or nmemb is
zero, fread returns zero and the contents of the array and
the state of the stream remain unchanged.
____________________
231See ``future library directions'' (7.26.9).
7.19.7.11 Library 7.19.8.1
340 Committee Draft -- August 3, 1998 WG14/N843
7.19.8.2 The fwrite function
Synopsis
[#1]
#include <stdio.h>
size_t fwrite(const void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
Description
[#2] The fwrite function writes, from the array pointed to
by ptr, up to nmemb elements whose size is specified by
size, to the stream pointed to by stream. The file position
indicator for the stream (if defined) is advanced by the
number of characters successfully written. If an error
occurs, the resulting value of the file position indicator
for the stream is indeterminate.
Returns
[#3] The fwrite function returns the number of elements
successfully written, which will be less than nmemb only if
a write error is encountered.
7.19.9 File positioning functions
7.19.9.1 The fgetpos function
Synopsis
[#1]
#include <stdio.h>
int fgetpos(FILE * restrict stream,
fpos_t * restrict pos);
Description
[#2] The fgetpos function stores the current values of the |
parse state (if any) and file position indicator for the
stream pointed to by stream in the object pointed to by pos. |
The values stored contain unspecified information usable by
the fsetpos function for repositioning the stream to its
position at the time of the call to the fgetpos function.
Returns
[#3] If successful, the fgetpos function returns zero; on
failure, the fgetpos function returns nonzero and stores an
implementation-defined positive value in errno.
7.19.8.1 Library 7.19.9.1
WG14/N843 Committee Draft -- August 3, 1998 341
Forward references: the fsetpos function (7.19.9.3).
7.19.9.2 The fseek function
Synopsis
[#1]
#include <stdio.h>
int fseek(FILE *stream, long int offset, int whence);
Description
[#2] The fseek function sets the file position indicator for
the stream pointed to by stream. If a read or write error
occurs, the error indicator for the stream is set and fseek
fails.
[#3] For a binary stream, the new position, measured in
characters from the beginning of the file, is obtained by
adding offset to the position specified by whence. The
specified position is the beginning of the file if whence is
SEEK_SET, the current value of the file position indicator
if SEEK_CUR, or end-of-file if SEEK_END. A binary stream
need not meaningfully support fseek calls with a whence
value of SEEK_END.
[#4] For a text stream, either offset shall be zero, or
offset shall be a value returned by an earlier successful
call to the ftell function on a stream associated with the
same file and whence shall be SEEK_SET.
[#5] After determining the new position, a successful call
to the fseek function undoes any effects of the ungetc
function on the stream, clears the end-of-file indicator for
the stream, and then establishes the new position. After a
successful fseek call, the next operation on an update
stream may be either input or output.
Returns
[#6] The fseek function returns nonzero only for a request
that cannot be satisfied.
Forward references: the ftell function (7.19.9.4).
7.19.9.1 Library 7.19.9.2
342 Committee Draft -- August 3, 1998 WG14/N843
7.19.9.3 The fsetpos function
Synopsis
[#1]
#include <stdio.h>
int fsetpos(FILE *stream, const fpos_t *pos);
Description
[#2] The fsetpos function sets the mbstate_t object (if any) |
and file position indicator for the stream pointed to by
stream according to the value of the object pointed to by
pos, which shall be a value obtained from an earlier
successful call to the fgetpos function on a stream
associated with the same file. If a read or write error
occurs, the error indicator for the stream is set and
fsetpos fails.
[#3] A successful call to the fsetpos function undoes any
effects of the ungetc function on the stream, clears the
end-of-file indicator for the stream, and then establishes |
the new parse state and position. After a successful
fsetpos call, the next operation on an update stream may be
either input or output.
Returns
[#4] If successful, the fsetpos function returns zero; on
failure, the fsetpos function returns nonzero and stores an
implementation-defined positive value in errno.
7.19.9.4 The ftell function
Synopsis
[#1]
#include <stdio.h>
long int ftell(FILE *stream);
Description
[#2] The ftell function obtains the current value of the
file position indicator for the stream pointed to by stream.
For a binary stream, the value is the number of characters
from the beginning of the file. For a text stream, its file
position indicator contains unspecified information, usable
by the fseek function for returning the file position
indicator for the stream to its position at the time of the
ftell call; the difference between two such return values is
not necessarily a meaningful measure of the number of
characters written or read.
7.19.9.2 Library 7.19.9.4
WG14/N843 Committee Draft -- August 3, 1998 343
Returns
[#3] If successful, the ftell function returns the current
value of the file position indicator for the stream. On
failure, the ftell function returns -1L and stores an
implementation-defined positive value in errno.
7.19.9.5 The rewind function
Synopsis
[#1]
#include <stdio.h>
void rewind(FILE *stream);
Description
[#2] The rewind function sets the file position indicator
for the stream pointed to by stream to the beginning of the
file. It is equivalent to
(void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also
cleared.
Returns
[#3] The rewind function returns no value.
7.19.10 Error-handling functions
7.19.10.1 The clearerr function
Synopsis
[#1]
#include <stdio.h>
void clearerr(FILE *stream);
Description
[#2] The clearerr function clears the end-of-file and error
indicators for the stream pointed to by stream.
Returns
[#3] The clearerr function returns no value.
7.19.9.4 Library 7.19.10.1
344 Committee Draft -- August 3, 1998 WG14/N843
7.19.10.2 The feof function
Synopsis
[#1]
#include <stdio.h>
int feof(FILE *stream);
Description
[#2] The feof function tests the end-of-file indicator for
the stream pointed to by stream.
Returns
[#3] The feof function returns nonzero if and only if the
end-of-file indicator is set for stream.
7.19.10.3 The ferror function
Synopsis
[#1]
#include <stdio.h>
int ferror(FILE *stream);
Description
[#2] The ferror function tests the error indicator for the
stream pointed to by stream.
Returns
[#3] The ferror function returns nonzero if and only if the
error indicator is set for stream.
7.19.10.4 The perror function
Synopsis
[#1]
#include <stdio.h>
void perror(const char *s);
Description
[#2] The perror function maps the error number in the
integer expression errno to an error message. It writes a
sequence of characters to the standard error stream thus:
first (if s is not a null pointer and the character pointed
to by s is not the null character), the string pointed to by
7.19.10.1 Library 7.19.10.4
WG14/N843 Committee Draft -- August 3, 1998 345
s followed by a colon (:) and a space; then an appropriate
error message string followed by a new-line character. The
contents of the error message strings are the same as those
returned by the strerror function with argument errno.
Returns
[#3] The perror function returns no value.
Forward references: the strerror function (7.21.6.2).
7.19.10.4 Library 7.19.10.4
346 Committee Draft -- August 3, 1998 WG14/N843
7.20 General utilities <stdlib.h>
[#1] The header <stdlib.h> declares five types and several
functions of general utility, and defines several
macros.232)
[#2] The types declared are size_t and wchar_t (both
described in 7.17),
div_t
which is a structure type that is the type of the value
returned by the div function,
ldiv_t
which is a structure type that is the type of the value
returned by the ldiv function, and
lldiv_t
which is a structure type that is the type of the value
returned by the lldiv function.
[#3] The macros defined are NULL (described in 7.17);
EXIT_FAILURE
and
EXIT_SUCCESS
which expand to integer expressions that may be used as the
argument to the exit function to return unsuccessful or
successful termination status, respectively, to the host
environment;
RAND_MAX
which expands to an integer constant expression, the value
of which is the maximum value returned by the rand function;
and
MB_CUR_MAX
which expands to a positive integer expression whose value
is the maximum number of bytes in a multibyte character for
the extended character set specified by the current locale
(category LC_CTYPE), and whose value is never greater than
MB_LEN_MAX.
____________________
232See ``future library directions'' (7.26.10).
7.20 Library 7.20
WG14/N843 Committee Draft -- August 3, 1998 347
7.20.1 String conversion functions
[#1] The functions atof, atoi, atol, and atoll need not
affect the value of the integer expression errno on an
error. If the value of the result cannot be represented,
the behavior is undefined.
7.20.1.1 The atof function
Synopsis
[#1]
#include <stdlib.h>
double atof(const char *nptr);
Description
[#2] The atof function converts the initial portion of the
string pointed to by nptr to double representation. Except
for the behavior on error, it is equivalent to
strtod(nptr, (char **)NULL)
Returns
[#3] The atof function returns the converted value.
Forward references: the strtod, strtof, and strtold
functions (7.20.1.3). |
7.20.1.2 The atoi, atol, and atoll functions |
Synopsis
[#1]
#include <stdlib.h>
int atoi(const char *nptr);
long int atol(const char *nptr); |
long long int atoll(const char *nptr); |
Description
[#2] The atoi, atol, and atoll functions convert the initial |
portion of the string pointed to by nptr to int, long int, |
and long long int representation, respectively. Except for
the behavior on error, they are equivalent to |
atoi: (int)strtol(nptr, (char **)NULL, 10) |
atol: strtol(nptr, (char **)NULL, 10) |
atoll: strtoll(nptr, (char **)NULL, 10) |
7.20.1 Library 7.20.1.2
348 Committee Draft -- August 3, 1998 WG14/N843
Returns
[#3] The atoi, atol, and atoll functions return the |
converted value.
Forward references: the strtol, strtoll, strtoul, and |
strtoull functions (7.20.1.4). *
7.20.1.3 The strtod, strtof, and strtold functions
Synopsis
[#1]
#include <stdlib.h>
double strtod(const char * restrict nptr,
char ** restrict endptr);
float strtof(const char * restrict nptr,
char ** restrict endptr);
long double strtold(const char * restrict nptr,
char ** restrict endptr);
Description
[#2] The strtod, strtof, and strtold functions convert the
initial portion of the string pointed to by nptr to double, |
float, and long double representation, respectively. First,
they decompose the input string into three parts: an
initial, possibly empty, sequence of white-space characters
(as specified by the isspace function), a subject sequence |
resembling a floating-point constant or representing an |
infinity or NaN; and a final string of one or more
unrecognized characters, including the terminating null
character of the input string. Then, they attempt to
convert the subject sequence to a floating-point number, and
return the result.
[#3] The expected form of the subject sequence is an
optional plus or minus sign, then one of the following:
-- a nonempty sequence of decimal digits optionally
containing a decimal-point character, then an optional
exponent part as defined in 6.4.4.2;
-- a 0x or 0X, then a nonempty sequence of hexadecimal
digits optionally containing a decimal-point character,
then an optional binary-exponent part as defined in
6.4.4.2, where either the decimal-point character or
the binary-exponent part is present;
-- one of INF or INFINITY, ignoring case
-- one of NAN or NAN(n-char-sequence-opt), ignoring case
in the NAN part, where:
7.20.1.2 Library 7.20.1.3
WG14/N843 Committee Draft -- August 3, 1998 349
n-char-sequence:
digit
nondigit
n-char-sequence digit
n-char-sequence nondigit
The subject sequence is defined as the longest initial *
subsequence of the input string, starting with the first
non-white-space character, that is of the expected form.
The subject sequence contains no characters if the input
string is not of the expected form.
[#4] If the subject sequence has the expected form for a
floating-point number, the sequence of characters starting
with the first digit or the decimal-point character
(whichever occurs first) is interpreted as a floating
constant according to the rules of 6.4.4.2, except that the
decimal-point character is used in place of a period, and
that if neither an exponent part, a binary-exponent part,
nor a decimal-point character appears, a decimal point is
assumed to follow the last digit in the string. A character
sequence INF or INFINITY is interpreted as an infinity, if
representable in the return type, else like a floating
constant that is too large for the range of the return type.
A character sequence NAN or NAN(n-char-sequence-opt), is
interpreted as a quiet NaN, if supported in the return type,
else like a subject sequence part that does not have the
expected form; the meaning of the n-char sequences is
implementation-defined.233) If the subject sequence begins
with a minus sign, the value resulting from the conversion
is negated.234) A pointer to the final string is stored in
the object pointed to by endptr, provided that endptr is not
a null pointer.
[#5] If the subject sequence has the hexadecimal form and |
FLT_RADIX is a power of 2, then the value resulting from the |
conversion is correctly rounded. |
[#6] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer. *
____________________
233An implementation may use the n-char-sequence to
determine extra information to be represented in the
NaN's significand.
234The functions honor the sign of zero if floating-point |
arithmetic supports signed zeros.
7.20.1.3 Library 7.20.1.3
350 Committee Draft -- August 3, 1998 WG14/N843
Recommended practice
[#8] If the subject sequence has the hexadecimal form and
FLT_RADIX is not a power of 2, then the result should be one
of the two numbers in the appropriate internal format that
are adjacent to the hexadecimal floating source value, with
the extra stipulation that the error should have a correct
sign for the current rounding direction.
[#9] If the subject sequence has the decimal form and at
most DECIMAL_DIG (defined in <float.h>) significant digits, |
then the value resulting from the conversion should be
correctly rounded. If the subject sequence D has the
decimal form and more than DECIMAL_DIG significant digits,
consider the two bounding, adjacent decimal strings L and U,
both having DECIMAL_DIG significant digits, such that the
values of L, D, and U satisfy L <= D <= U. The result of
conversion should be one of the (equal or adjacent) values
that would be obtained by correctly rounding L and U
according to the current rounding direction, with the extra
stipulation that the error with respect to D should have a
correct sign for the current rounding direction.235)
Returns
[#10] The functions return the converted value, if any. If
no conversion could be performed, zero is returned. If the
correct value is outside the range of representable values,
plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned
(according to the return type and sign of the value), and
the value of the macro ERANGE is stored in errno. If the
result underflows (7.12.1), the functions return a value
whose magnitude is no greater than the smallest normalized
positive number in the return type; whether errno acquires
the value ERANGE is implementation-defined. |
7.20.1.4 The strtol, strtoll, strtoul, and strtoull |
functions |
Synopsis
[#1]
____________________
235DECIMAL_DIG, defined in <float.h>, should be sufficiently |
large that L and U will usually round to the same
internal floating value, but if not will round to
adjacent values.
7.20.1.3 Library 7.20.1.4
WG14/N843 Committee Draft -- August 3, 1998 351
#include <stdlib.h>
long int strtol( |
const char * restrict nptr, |
char ** restrict endptr, |
int base); |
long long int strtoll( |
const char * restrict nptr, |
char ** restrict endptr, |
int base); |
unsigned long int strtoul( |
const char * restrict nptr, |
char ** restrict endptr, |
int base); |
unsigned long long int strtoull( |
const char * restrict nptr, |
char ** restrict endptr, |
int base); |
Description
[#2] The strtol, strtoll, strtoul, and strtoull functions |
convert the initial portion of the string pointed to by nptr
to long int, long long int, unsigned long int, and unsigned |
long long int representation, respectively. First, they |
decompose the input string into three parts: an initial,
possibly empty, sequence of white-space characters (as
specified by the isspace function), a subject sequence
resembling an integer represented in some radix determined
by the value of base, and a final string of one or more
unrecognized characters, including the terminating null
character of the input string. Then, they attempt to |
convert the subject sequence to an integer, and return the |
result.
[#3] If the value of base is zero, the expected form of the
subject sequence is that of an integer constant as described
in 6.4.4.1, optionally preceded by a plus or minus sign, but
not including an integer suffix. If the value of base is |
between 2 and 36 (inclusive), the expected form of the
subject sequence is a sequence of letters and digits
representing an integer with the radix specified by base,
optionally preceded by a plus or minus sign, but not
including an integer suffix. The letters from a (or A)
through z (or Z) are ascribed the values 10 through 35; only |
letters and digits whose ascribed values are less than that |
of base are permitted. If the value of base is 16, the
characters 0x or 0X may optionally precede the sequence of
letters and digits, following the sign if present.
[#4] The subject sequence is defined as the longest initial
subsequence of the input string, starting with the first
non-white-space character, that is of the expected form.
The subject sequence contains no characters if the input
string is empty or consists entirely of white space, or if
7.20.1.4 Library 7.20.1.4
352 Committee Draft -- August 3, 1998 WG14/N843
the first non-white-space character is other than a sign or
a permissible letter or digit.
[#5] If the subject sequence has the expected form and the
value of base is zero, the sequence of characters starting
with the first digit is interpreted as an integer constant |
according to the rules of 6.4.4.1. If the subject sequence
has the expected form and the value of base is between 2 and
36, it is used as the base for conversion, ascribing to each
letter its value as given above. If the subject sequence
begins with a minus sign, the value resulting from the |
conversion is negated (in the return type). A pointer to
the final string is stored in the object pointed to by
endptr, provided that endptr is not a null pointer.
[#6] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
Returns
[#8] The strtol, strtoll, strtoul, and strtoull functions |
return the converted value, if any. If no conversion could
be performed, zero is returned. If the correct value is
outside the range of representable values, LONG_MIN, |
LONG_MAX, LLONG_MIN, LLONG_MAX, ULONG_MAX, or ULLONG_MAX is |
returned (according to the return type and sign of the |
value, if any), and the value of the macro ERANGE is stored
in errno. *
7.20.2 Pseudo-random sequence generation functions
7.20.2.1 The rand function
Synopsis
[#1]
#include <stdlib.h>
int rand(void);
Description
[#2] The rand function computes a sequence of pseudo-random
integers in the range 0 to RAND_MAX.
[#3] The implementation shall behave as if no library
function calls the rand function.
7.20.1.4 Library 7.20.2.1
WG14/N843 Committee Draft -- August 3, 1998 353
Returns
[#4] The rand function returns a pseudo-random integer.
Environmental limits
[#5] The value of the RAND_MAX macro shall be at least
32767.
7.20.2.2 The srand function
Synopsis
[#1]
#include <stdlib.h>
void srand(unsigned int seed);
Description
[#2] The srand function uses the argument as a seed for a
new sequence of pseudo-random numbers to be returned by
subsequent calls to rand. If srand is then called with the
same seed value, the sequence of pseudo-random numbers shall
be repeated. If rand is called before any calls to srand
have been made, the same sequence shall be generated as when
srand is first called with a seed value of 1.
[#3] The implementation shall behave as if no library
function calls the srand function.
Returns
[#4] The srand function returns no value.
[#5] EXAMPLE The following functions define a portable
implementation of rand and srand.
static unsigned long int next = 1;
int rand(void) // RAND_MAX assumed to be 32767
{
next = next * 1103515245 + 12345;
return (unsigned int)(next/65536) % 32768;
}
void srand(unsigned int seed)
{
next = seed;
}
7.20.2.1 Library 7.20.2.2
354 Committee Draft -- August 3, 1998 WG14/N843
7.20.3 Memory management functions
[#1] The order and contiguity of storage allocated by
successive calls to the calloc, malloc, and realloc
functions is unspecified. The pointer returned if the
allocation succeeds is suitably aligned so that it may be
assigned to a pointer to any type of object and then used to
access such an object or an array of such objects in the
space allocated (until the space is explicitly freed or
reallocated). Each such allocation shall yield a pointer to
an object disjoint from any other object. The pointer
returned points to the start (lowest byte address) of the
allocated space. If the space cannot be allocated, a null
pointer is returned. If the size of the space requested is
zero, the behavior is implementation-defined: either a null
pointer is returned, or the behavior is as if the size were
some nonzero value, except that the returned pointer shall
not be used to access an object. The value of a pointer
that refers to freed space is indeterminate.
7.20.3.1 The calloc function
Synopsis
[#1]
#include <stdlib.h>
void *calloc(size_t nmemb, size_t size);
Description
[#2] The calloc function allocates space for an array of
nmemb objects, each of whose size is size. The space is
initialized to all bits zero.236)
Returns
[#3] The calloc function returns either a null pointer or a
pointer to the allocated space.
____________________
236Note that this need not be the same as the representation
of floating-point zero or a null pointer constant.
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7.20.3.2 The free function
Synopsis
[#1]
#include <stdlib.h>
void free(void *ptr);
Description
[#2] The free function causes the space pointed to by ptr to
be deallocated, that is, made available for further
allocation. If ptr is a null pointer, no action occurs.
Otherwise, if the argument does not match a pointer earlier
returned by the calloc, malloc, or realloc function, or if
the space has been deallocated by a call to free or realloc,
the behavior is undefined.
Returns
[#3] The free function returns no value.
7.20.3.3 The malloc function
Synopsis
[#1]
#include <stdlib.h>
void *malloc(size_t size);
Description
[#2] The malloc function allocates space for an object whose
size is specified by size and whose value is indeterminate.
Returns
[#3] The malloc function returns either a null pointer or a
pointer to the allocated space.
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7.20.3.4 The realloc function
Synopsis
[#1]
#include <stdlib.h>
void *realloc(void *ptr, size_t size);
Description
[#2] The realloc function changes the size of the object
pointed to by ptr to the size specified by size. The
contents of the object shall be unchanged up to the lesser
of the new and old sizes. If the new size is larger, the
value of the newly allocated portion of the object is
indeterminate. If ptr is a null pointer, the realloc
function behaves like the malloc function for the specified
size. Otherwise, if ptr does not match a pointer earlier
returned by the calloc, malloc, or realloc function, or if
the space has been deallocated by a call to the free or
realloc function, the behavior is undefined. If the space
cannot be allocated, the object pointed to by ptr is
unchanged. If the realloc function returns a null pointer |
when size is zero and ptr is not a null pointer, the object |
it pointed to has been freed.
Returns
[#3] The realloc function returns either a null pointer or a
pointer to the possibly moved allocated space. If the
object has moved, ptr is a pointer that refers to freed
space.
7.20.4 Communication with the environment
7.20.4.1 The abort function
Synopsis
[#1]
#include <stdlib.h>
void abort(void);
Description
[#2] The abort function causes abnormal program termination
to occur, unless the signal SIGABRT is being caught and the
signal handler does not return. Whether open output streams
are flushed or open streams closed or temporary files
removed is implementation-defined. An implementation-
defined form of the status unsuccessful termination is
returned to the host environment by means of the function
7.20.3.3 Library 7.20.4.1
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call raise(SIGABRT).
Returns
[#3] The abort function does not return to its caller. |
7.20.4.2 The atexit function
Synopsis
[#1]
#include <stdlib.h>
int atexit(void (*func)(void));
Description
[#2] The atexit function registers the function pointed to
by func, to be called without arguments at normal program
termination. |
Environmental limits |
[#3] The implementation shall support the registration of at
least 32 functions.
Returns
[#4] The atexit function returns zero if the registration
succeeds, nonzero if it fails.
Forward references: the exit function (7.20.4.3).
7.20.4.3 The exit function
Synopsis
[#1]
#include <stdlib.h>
void exit(int status);
Description
[#2] The exit function causes normal program termination to
occur. If more than one call to the exit function is
executed by a program, the behavior is undefined.
[#3] First, all functions registered by the atexit function
are called, in the reverse order of their registration.237)
____________________
237Each function is called as many times as it was
registered.
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[#4] Next, all open streams with unwritten buffered data are
flushed, all open streams are closed, and all files created
by the tmpfile function are removed.
[#5] Finally, control is returned to the host environment.
If the value of status is zero or EXIT_SUCCESS, an
implementation-defined form of the status successful
termination is returned. If the value of status is
EXIT_FAILURE, an implementation-defined form of the status
unsuccessful termination is returned. Otherwise the status
returned is implementation-defined.
Returns
[#6] The exit function cannot return to its caller.
7.20.4.4 The getenv function
Synopsis
[#1]
#include <stdlib.h>
char *getenv(const char *name);
Description
[#2] The getenv function searches an environment list,
provided by the host environment, for a string that matches
the string pointed to by name. The set of environment names
and the method for altering the environment list are
implementation-defined.
[#3] The implementation shall behave as if no library
function calls the getenv function.
Returns
[#4] The getenv function returns a pointer to a string
associated with the matched list member. The string pointed
to shall not be modified by the program, but may be
overwritten by a subsequent call to the getenv function. If
the specified name cannot be found, a null pointer is
returned.
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7.20.4.5 The system function
Synopsis
[#1]
#include <stdlib.h>
int system(const char *string);
Description
[#2] If string is a null pointer, the system function
determines whether the host environment has a command
processor. If string is not a null pointer, the system
function passes the string pointed to by string to that
command processor to be executed in a manner which the
implementation shall document; this might then cause the
program calling system to behave in a non-conforming manner
or to terminate.
Returns
[#3] If the argument is a null pointer, the system function
returns nonzero only if a command processor is available.
If the argument is not a null pointer, and the system
function does return, it returns an implementation-defined
value.
7.20.5 Searching and sorting utilities
[#1] These utilities make use of a comparison function.
[#2] The implementation shall ensure that the second
argument of the comparison function (when called from
bsearch), or both arguments (when called from qsort), are
pointers to elements of the array.238) The first argument
when called from bsearch shall equal key.
[#3] The comparison function shall not alter the contents of
the array. The implementation may reorder elements of the
array between calls to the comparison function, but shall
not alter the contents of any individual element.
[#4] When the same objects (consisting of size bytes, |
irrespective of their current positions in the array) are
passed more than once to the comparison function, the
results shall be consistent with one another. That is, for
____________________
238That is, if the value passed is p, then the following
expressions are always non-zero:
((char *)p - (char *)base) % size == 0 |
(char *)p >= (char *)base
(char *)p < (char *)base + nmemb * size
7.20.4.4 Library 7.20.5
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qsort they shall define a total ordering on the array, and
for bsearch the same object shall always compare the same
way with the key.
[#5] A sequence point occurs immediately before and
immediately after each call to the comparison function, and
also between any call to the comparison function and any
movement of the objects passed as arguments to that call.
7.20.5.1 The bsearch function
Synopsis
[#1]
#include <stdlib.h>
void *bsearch(const void *key, const void *base,
size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
Description
[#2] The bsearch function searches an array of nmemb
objects, the initial element of which is pointed to by base,
for an element that matches the object pointed to by key.
The size of each element of the array is specified by size.
[#3] The comparison function pointed to by compar is called
with two arguments that point to the key object and to an
array element, in that order. The function shall return an
integer less than, equal to, or greater than zero if the key
object is considered, respectively, to be less than, to
match, or to be greater than the array element. The array
shall consist of: all the elements that compare less than,
all the elements that compare equal to, and all the elements
that compare greater than the key object, in that order.239)
Returns
[#4] The bsearch function returns a pointer to a matching
element of the array, or a null pointer if no match is
found. If two elements compare as equal, which element is
matched is unspecified.
____________________
239In practice, the entire array is sorted according to the
comparison function.
7.20.5 Library 7.20.5.1
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7.20.5.2 The qsort function
Synopsis
[#1]
#include <stdlib.h>
void qsort(void *base, size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
Description
[#2] The qsort function sorts an array of nmemb objects, the
initial element of which is pointed to by base. The size of
each object is specified by size.
[#3] The contents of the array are sorted into ascending
order according to a comparison function pointed to by
compar, which is called with two arguments that point to the
objects being compared. The function shall return an
integer less than, equal to, or greater than zero if the
first argument is considered to be respectively less than,
equal to, or greater than the second.
[#4] If two elements compare as equal, their order in the |
resulting sorted array is unspecified.
Returns
[#5] The qsort function returns no value.
7.20.6 Integer arithmetic functions
7.20.6.1 The abs, labs and llabs functions |
Synopsis
[#1]
#include <stdlib.h>
int abs(int j);
long int labs(long int j); |
long long int llabs(long long int j); |
Description
[#2] The abs, labs, and llabs functions compute the absolute |
value of an integer j. If the result cannot be represented,
the behavior is undefined.240)
____________________
240The absolute value of the most negative number cannot be
represented in two's complement.
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Returns
[#3] The abs, labs, and llabs, functions return the absolute |
value. |
7.20.6.2 The div, ldiv, and lldiv functions |
Synopsis
[#1]
#include <stdlib.h>
div_t div(int numer, int denom);
ldiv_t div(long int numer, long int denom); |
lldiv_t div(long long int numer, long long int denom);|
Description
[#2] The div, ldiv, and lldiv, functions compute numer / |
denom and numer % denom in a single operation.
Returns
[#3] The div, ldiv, and lldiv functions return a structure |
of type div_t, ldiv_t, and lldiv_t, respectively, comprising |
both the quotient and the remainder. The structures shall |
contain (in either order) the members quot (the quotient) |
and rem (the remainder), each of which have the same type as |
the arguments numer and denom. If either part of the result |
cannot be represented, the behavior is undefined.
7.20.7 Multibyte character functions
[#1] The behavior of the multibyte character functions is
affected by the LC_CTYPE category of the current locale.
For a state-dependent encoding, each function is placed into
its initial state by a call for which its character pointer
argument, s, is a null pointer. Subsequent calls with s as
other than a null pointer cause the internal state of the
function to be altered as necessary. A call with s as a
null pointer causes these functions to return a nonzero
value if encodings have state dependency, and zero
otherwise.241) Changing the LC_CTYPE category causes the
shift state of these functions to be indeterminate.
____________________
241If the locale employs special bytes to change the shift
state, these bytes do not produce separate wide character
codes, but are grouped with an adjacent multibyte
character.
7.20.6.1 Library 7.20.7
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7.20.7.1 The mblen function
[#1]
#include <stdlib.h>
int mblen(const char *s, size_t n);
Description
[#2] If s is not a null pointer, the mblen function
determines the number of bytes contained in the multibyte
character pointed to by s. Except that the shift state of
the mbtowc function is not affected, it is equivalent to
mbtowc((wchar_t *)0, s, n);
[#3] The implementation shall behave as if no library
function calls the mblen function.
Returns
[#4] If s is a null pointer, the mblen function returns a
nonzero or zero value, if multibyte character encodings,
respectively, do or do not have state-dependent encodings.
If s is not a null pointer, the mblen function either
returns 0 (if s points to the null character), or returns
the number of bytes that are contained in the multibyte
character (if the next n or fewer bytes form a valid
multibyte character), or returns -1 (if they do not form a
valid multibyte character).
Forward references: the mbtowc function (7.20.7.2).
7.20.7.2 The mbtowc function
Synopsis
[#1]
#include <stdlib.h>
int mbtowc(wchar_t * restrict pwc,
const char * restrict s,
size_t n);
Description
[#2] If s is not a null pointer, the mbtowc function
determines the number of bytes that are contained in the
multibyte character pointed to by s. It then determines the
code for the value of type wchar_t that corresponds to that
multibyte character. (The value of the code corresponding
to the null character is zero.) If the multibyte character
is valid and pwc is not a null pointer, the mbtowc function
stores the code in the object pointed to by pwc. At most n
7.20.7 Library 7.20.7.2
364 Committee Draft -- August 3, 1998 WG14/N843
bytes of the array pointed to by s will be examined.
[#3] The implementation shall behave as if no library
function calls the mbtowc function.
Returns
If s is a null pointer, the mbtowc function returns a
nonzero or zero value, if multibyte character encodings,
respectively, do or do not have state-dependent encodings.
If s is not a null pointer, the mbtowc function either
returns 0 (if s points to the null character), or returns
the number of bytes that are contained in the converted
multibyte character (if the next n or fewer bytes form a
valid multibyte character), or returns -1 (if they do not
form a valid multibyte character).
[#4] In no case will the value returned be greater than n or
the value of the MB_CUR_MAX macro.
7.20.7.3 The wctomb function
Synopsis
[#1]
#include <stdlib.h>
int wctomb(char *s, wchar_t wchar);
Description
[#2] The wctomb function determines the number of bytes
needed to represent the multibyte character corresponding to
the code whose value is wchar (including any change in shift
state). It stores the multibyte character representation in
the array object pointed to by s (if s is not a null
pointer). At most MB_CUR_MAX characters are stored. If the
value of wchar is zero, the wctomb function is left in the
initial shift state.
[#3] The implementation shall behave as if no library
function calls the wctomb function.
Returns
[#4] If s is a null pointer, the wctomb function returns a
nonzero or zero value, if multibyte character encodings,
respectively, do or do not have state-dependent encodings.
If s is not a null pointer, the wctomb function returns -1
if the value of wchar does not correspond to a valid
multibyte character, or returns the number of bytes that are
contained in the multibyte character corresponding to the
value of wchar.
7.20.7.2 Library 7.20.7.3
WG14/N843 Committee Draft -- August 3, 1998 365
[#5] In no case will the value returned be greater than the
value of the MB_CUR_MAX macro.
7.20.8 Multibyte string functions
[#1] The behavior of the multibyte string functions is
affected by the LC_CTYPE category of the current locale.
7.20.8.1 The mbstowcs function
Synopsis
[#1]
#include <stdlib.h>
size_t mbstowcs(wchar_t * restrict pwcs,
const char * restrict s,
size_t n);
Description
[#2] The mbstowcs function converts a sequence of multibyte
characters that begins in the initial shift state from the
array pointed to by s into a sequence of corresponding codes
and stores not more than n codes into the array pointed to
by pwcs. No multibyte characters that follow a null
character (which is converted into a code with value zero)
will be examined or converted. Each multibyte character is
converted as if by a call to the mbtowc function, except
that the shift state of the mbtowc function is not affected.
[#3] No more than n elements will be modified in the array
pointed to by pwcs. If copying takes place between objects
that overlap, the behavior is undefined.
Returns
[#4] If an invalid multibyte character is encountered, the
mbstowcs function returns (size_t)-1. Otherwise, the
mbstowcs function returns the number of array elements
modified, not including a terminating zero code, if any.242)
____________________
242The array will not be null- or zero-terminated if the
value returned is n.
7.20.7.3 Library 7.20.8.1
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7.20.8.2 The wcstombs function
Synopsis
[#1]
#include <stdlib.h>
size_t wcstombs(char * restrict s,
const wchar_t * restrict pwcs,
size_t n);
Description
[#2] The wcstombs function converts a sequence of codes that
correspond to multibyte characters from the array pointed to
by pwcs into a sequence of multibyte characters that begins
in the initial shift state and stores these multibyte
characters into the array pointed to by s, stopping if a
multibyte character would exceed the limit of n total bytes
or if a null character is stored. Each code is converted as
if by a call to the wctomb function, except that the shift
state of the wctomb function is not affected.
[#3] No more than n bytes will be modified in the array
pointed to by s. If copying takes place between objects
that overlap, the behavior is undefined.
Returns
[#4] If a code is encountered that does not correspond to a
valid multibyte character, the wcstombs function returns
(size_t)-1. Otherwise, the wcstombs function returns the
number of bytes modified, not including a terminating null
character, if any.242)
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7.21 String handling <string.h>
7.21.1 String function conventions
[#1] The header <string.h> declares one type and several
functions, and defines one macro useful for manipulating
arrays of character type and other objects treated as arrays
of character type.243) The type is size_t and the macro is
NULL (both described in 7.17). Various methods are used for
determining the lengths of the arrays, but in all cases a
char * or void * argument points to the initial (lowest
addressed) character of the array. If an array is accessed
beyond the end of an object, the behavior is undefined.
[#2] Where an argument declared as size_t n specifies the
length of the array for a function, n can have the value
zero on a call to that function. Unless explicitly stated
otherwise in the description of a particular function in
this subclause, pointer arguments on such a call shall still
have valid values, as described in 7.1.4. On such a call, a
function that locates a character finds no occurrence, a
function that compares two character sequences returns zero,
and a function that copies characters copies zero
characters.
7.21.2 Copying functions
7.21.2.1 The memcpy function
Synopsis
[#1]
#include <string.h>
void *memcpy(void * restrict s1,
const void * restrict s2,
size_t n);
Description
[#2] The memcpy function copies n characters from the object
pointed to by s2 into the object pointed to by s1. If
copying takes place between objects that overlap, the
behavior is undefined.
Returns
[#3] The memcpy function returns the value of s1.
____________________
243See ``future library directions'' (7.26.11).
7.21 Library 7.21.2.1
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7.21.2.2 The memmove function
Synopsis
[#1]
#include <string.h>
void *memmove(void *s1, const void *s2, size_t n);
Description
[#2] The memmove function copies n characters from the
object pointed to by s2 into the object pointed to by s1.
Copying takes place as if the n characters from the object
pointed to by s2 are first copied into a temporary array of
n characters that does not overlap the objects pointed to by
s1 and s2, and then the n characters from the temporary
array are copied into the object pointed to by s1.
Returns
[#3] The memmove function returns the value of s1.
7.21.2.3 The strcpy function
Synopsis
[#1]
#include <string.h>
char *strcpy(char * restrict s1,
const char * restrict s2);
Description
[#2] The strcpy function copies the string pointed to by s2
(including the terminating null character) into the array
pointed to by s1. If copying takes place between objects
that overlap, the behavior is undefined.
Returns
[#3] The strcpy function returns the value of s1.
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7.21.2.4 The strncpy function
Synopsis
[#1]
#include <string.h>
char *strncpy(char * restrict s1,
const char * restrict s2,
size_t n);
Description
[#2] The strncpy function copies not more than n characters
(characters that follow a null character are not copied)
from the array pointed to by s2 to the array pointed to by
s1.244) If copying takes place between objects that
overlap, the behavior is undefined.
[#3] If the array pointed to by s2 is a string that is
shorter than n characters, null characters are appended to
the copy in the array pointed to by s1, until n characters
in all have been written.
Returns
[#4] The strncpy function returns the value of s1.
7.21.3 Concatenation functions
7.21.3.1 The strcat function
Synopsis
[#1]
#include <string.h>
char *strcat(char * restrict s1,
const char * restrict s2);
Description
[#2] The strcat function appends a copy of the string
pointed to by s2 (including the terminating null character)
to the end of the string pointed to by s1. The initial
character of s2 overwrites the null character at the end of
s1. If copying takes place between objects that overlap,
the behavior is undefined.
____________________
244Thus, if there is no null character in the first n
characters of the array pointed to by s2, the result will
not be null-terminated.
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Returns
[#3] The strcat function returns the value of s1.
7.21.3.2 The strncat function
Synopsis
[#1]
#include <string.h>
char *strncat(char * restrict s1,
const char * restrict s2,
size_t n);
Description
[#2] The strncat function appends not more than n characters
(a null character and characters that follow it are not
appended) from the array pointed to by s2 to the end of the
string pointed to by s1. The initial character of s2
overwrites the null character at the end of s1. A
terminating null character is always appended to the
result.245) If copying takes place between objects that
overlap, the behavior is undefined.
Returns
[#3] The strncat function returns the value of s1.
Forward references: the strlen function (7.21.6.3).
7.21.4 Comparison functions
[#1] The sign of a nonzero value returned by the comparison
functions memcmp, strcmp, and strncmp is determined by the
sign of the difference between the values of the first pair
of characters (both interpreted as unsigned char) that
differ in the objects being compared.
____________________
245Thus, the maximum number of characters that can end up in
the array pointed to by s1 is strlen(s1)+n+1.
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7.21.4.1 The memcmp function
Synopsis
[#1]
#include <string.h>
int memcmp(const void *s1, const void *s2, size_t n);
Description
[#2] The memcmp function compares the first n characters of
the object pointed to by s1 to the first n characters of the
object pointed to by s2.246)
Returns
[#3] The memcmp function returns an integer greater than,
equal to, or less than zero, accordingly as the object
pointed to by s1 is greater than, equal to, or less than the
object pointed to by s2.
7.21.4.2 The strcmp function
Synopsis
[#1]
#include <string.h>
int strcmp(const char *s1, const char *s2);
Description
[#2] The strcmp function compares the string pointed to by
s1 to the string pointed to by s2.
Returns
[#3] The strcmp function returns an integer greater than,
equal to, or less than zero, accordingly as the string
pointed to by s1 is greater than, equal to, or less than the
string pointed to by s2.
____________________
246The contents of ``holes'' used as padding for purposes of
alignment within structure objects are indeterminate.
Strings shorter than their allocated space and unions may
also cause problems in comparison.
7.21.4 Library 7.21.4.2
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7.21.4.3 The strcoll function
Synopsis
[#1]
#include <string.h>
int strcoll(const char *s1, const char *s2);
Description
The strcoll function compares the string pointed to by s1 to
the string pointed to by s2, both interpreted as appropriate
to the LC_COLLATE category of the current locale.
Returns
[#2] The strcoll function returns an integer greater than,
equal to, or less than zero, accordingly as the string
pointed to by s1 is greater than, equal to, or less than the
string pointed to by s2 when both are interpreted as
appropriate to the current locale.
7.21.4.4 The strncmp function
Synopsis
[#1]
#include <string.h>
int strncmp(const char *s1, const char *s2, size_t n);
Description
[#2] The strncmp function compares not more than n
characters (characters that follow a null character are not
compared) from the array pointed to by s1 to the array
pointed to by s2.
Returns
[#3] The strncmp function returns an integer greater than,
equal to, or less than zero, accordingly as the possibly
null-terminated array pointed to by s1 is greater than,
equal to, or less than the possibly null-terminated array
pointed to by s2.
7.21.4.2 Library 7.21.4.4
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7.21.4.5 The strxfrm function
Synopsis
[#1]
#include <string.h>
size_t strxfrm(char * restrict s1,
const char * restrict s2,
size_t n);
Description
[#2] The strxfrm function transforms the string pointed to
by s2 and places the resulting string into the array pointed
to by s1. The transformation is such that if the strcmp
function is applied to two transformed strings, it returns a
value greater than, equal to, or less than zero,
corresponding to the result of the strcoll function applied
to the same two original strings. No more than n characters
are placed into the resulting array pointed to by s1,
including the terminating null character. If n is zero, s1
is permitted to be a null pointer. If copying takes place
between objects that overlap, the behavior is undefined.
Returns
[#3] The strxfrm function returns the length of the
transformed string (not including the terminating null
character). If the value returned is n or more, the
contents of the array pointed to by s1 are indeterminate.
[#4] EXAMPLE The value of the following expression is the
size of the array needed to hold the transformation of the
string pointed to by s.
1 + strxfrm(NULL, s, 0)
7.21.5 Search functions
7.21.4.4 Library 7.21.5
374 Committee Draft -- August 3, 1998 WG14/N843
7.21.5.1 The memchr function
Synopsis
[#1]
#include <string.h>
void *memchr(const void *s, int c, size_t n);
Description
[#2] The memchr function locates the first occurrence of c
(converted to an unsigned char) in the initial n characters
(each interpreted as unsigned char) of the object pointed to
by s.
Returns
[#3] The memchr function returns a pointer to the located
character, or a null pointer if the character does not occur
in the object.
7.21.5.2 The strchr function
Synopsis
[#1]
#include <string.h>
char *strchr(const char *s, int c);
Description
[#2] The strchr function locates the first occurrence of c
(converted to a char) in the string pointed to by s. The
terminating null character is considered to be part of the
string.
Returns
[#3] The strchr function returns a pointer to the located
character, or a null pointer if the character does not occur
in the string.
7.21.5 Library 7.21.5.2
WG14/N843 Committee Draft -- August 3, 1998 375
7.21.5.3 The strcspn function
Synopsis
[#1]
#include <string.h>
size_t strcspn(const char *s1, const char *s2);
Description
[#2] The strcspn function computes the length of the maximum
initial segment of the string pointed to by s1 which
consists entirely of characters not from the string pointed
to by s2.
Returns
[#3] The strcspn function returns the length of the segment.
7.21.5.4 The strpbrk function
Synopsis
[#1]
#include <string.h>
char *strpbrk(const char *s1, const char *s2);
Description
[#2] The strpbrk function locates the first occurrence in
the string pointed to by s1 of any character from the string
pointed to by s2.
Returns
[#3] The strpbrk function returns a pointer to the
character, or a null pointer if no character from s2 occurs
in s1.
7.21.5.2 Library 7.21.5.4
376 Committee Draft -- August 3, 1998 WG14/N843
7.21.5.5 The strrchr function
Synopsis
[#1]
#include <string.h>
char *strrchr(const char *s, int c);
Description
[#2] The strrchr function locates the last occurrence of c
(converted to a char) in the string pointed to by s. The
terminating null character is considered to be part of the
string.
Returns
[#3] The strrchr function returns a pointer to the
character, or a null pointer if c does not occur in the
string.
7.21.5.6 The strspn function
Synopsis
[#1]
#include <string.h>
size_t strspn(const char *s1, const char *s2);
Description
[#2] The strspn function computes the length of the maximum
initial segment of the string pointed to by s1 which
consists entirely of characters from the string pointed to
by s2.
Returns
[#3] The strspn function returns the length of the segment.
7.21.5.4 Library 7.21.5.6
WG14/N843 Committee Draft -- August 3, 1998 377
7.21.5.7 The strstr function
Synopsis
[#1]
#include <string.h>
char *strstr(const char *s1, const char *s2);
Description
[#2] The strstr function locates the first occurrence in the
string pointed to by s1 of the sequence of characters
(excluding the terminating null character) in the string
pointed to by s2. |
Returns
[#3] The strstr function returns a pointer to the located
string, or a null pointer if the string is not found. If s2
points to a string with zero length, the function returns
s1.
7.21.5.8 The strtok function
Synopsis
[#1]
#include <string.h>
char *strtok(char * restrict s1,
const char * restrict s2);
Description
[#2] A sequence of calls to the strtok function breaks the
string pointed to by s1 into a sequence of tokens, each of
which is delimited by a character from the string pointed to
by s2. The first call in the sequence has a non-null first |
argument; subsequent calls in the sequence have a null first |
argument. The separator string pointed to by s2 may be
different from call to call.
[#3] The first call in the sequence searches the string
pointed to by s1 for the first character that is not
contained in the current separator string pointed to by s2.
If no such character is found, then there are no tokens in
the string pointed to by s1 and the strtok function returns
a null pointer. If such a character is found, it is the
start of the first token.
[#4] The strtok function then searches from there for a
character that is contained in the current separator string.
If no such character is found, the current token extends to
7.21.5.6 Library 7.21.5.8
378 Committee Draft -- August 3, 1998 WG14/N843
the end of the string pointed to by s1, and subsequent
searches for a token will return a null pointer. If such a
character is found, it is overwritten by a null character,
which terminates the current token. The strtok function
saves a pointer to the following character, from which the
next search for a token will start.
[#5] Each subsequent call, with a null pointer as the value
of the first argument, starts searching from the saved
pointer and behaves as described above.
[#6] The implementation shall behave as if no library
function calls the strtok function.
Returns
[#7] The strtok function returns a pointer to the first
character of a token, or a null pointer if there is no
token.
[#8] EXAMPLE 1
#include <string.h>
static char str[] = "?a???b,,,#c";
char *t;
t = strtok(str, "?"); // t points to the token "a"
t = strtok(NULL, ","); // t points to the token "??b"
t = strtok(NULL, "#,"); // t points to the token "c"
t = strtok(NULL, "?"); // t is a null pointer
7.21.6 Miscellaneous functions
7.21.6.1 The memset function
Synopsis
[#1]
#include <string.h>
void *memset(void *s, int c, size_t n);
Description
[#2] The memset function copies the value of c (converted to
an unsigned char) into each of the first n characters of the
object pointed to by s.
Returns
[#3] The memset function returns the value of s.
7.21.5.8 Library 7.21.6.1
WG14/N843 Committee Draft -- August 3, 1998 379
7.21.6.2 The strerror function
Synopsis
[#1]
#include <string.h>
char *strerror(int errnum);
Description
[#2] The strerror function maps the number in errnum to a
message string. Typically, the values for errnum come from
errno, but strerror shall map any value of type int to a
message.
[#3] The implementation shall behave as if no library
function calls the strerror function.
Returns
[#4] The strerror function returns a pointer to the string,
the contents of which are locale-specific. The array
pointed to shall not be modified by the program, but may be
overwritten by a subsequent call to the strerror function.
7.21.6.3 The strlen function
Synopsis
[#1]
#include <string.h>
size_t strlen(const char *s);
Description
[#2] The strlen function computes the length of the string
pointed to by s.
Returns
[#3] The strlen function returns the number of characters
that precede the terminating null character.
7.21.6.1 Library 7.21.6.3
380 Committee Draft -- August 3, 1998 WG14/N843
7.22 Type-generic math <tgmath.h>
[#1] The header <tgmath.h> includes the headers <math.h> and
<complex.h> and defines several type-generic macros.
7.22.1 Type-generic macros
[#1] Of the <math.h> and <complex.h> functions without an f
(float) or l (long double) suffix, several have one or more
parameters whose corresponding real type is double. For
each such function, except modf, there is a corresponding
type-generic macro.247) The parameters whose corresponding
real type is double in the function synopsis are generic
parameters. Use of the macro invokes a function whose
corresponding real type and type domain are determined by |
the arguments for the generic parameters.248)
[#2] Use of the macro invokes a function whose generic
parameters have the corresponding real type determined as
follows:
-- First, if any argument for generic parameters has type
long double, the type determined is long double.
-- Otherwise, if any argument for generic parameters has
type double or is of integer type, the type determined
is double.
-- Otherwise, the type determined is float.
[#3] For each unsuffixed function in <math.h> for which
there is a function in <complex.h> with the same name except
for a c prefix, the corresponding type-generic macro (for
both functions) has the same name as the function in
<math.h>. The corresponding type-generic macro for fabs and
cabs is fabs.
____________________
247Like other function-like macros in Standard libraries,
each type-generic macro can be suppressed to make
available the corresponding ordinary function.
248If the type of the argument is incompatible with the type
of the parameter for the selected function, the behavior
is undefined.
7.22 Library 7.22.1
WG14/N843 Committee Draft -- August 3, 1998 381
<math.h> <complex.h> type-generic
function function macro
------------- ------------- -------------
acos cacos acos
asin casin asin
atan catan atan
acosh cacosh acosh
asinh casinh asinh
atanh catanh atanh
cos ccos cos
sin csin sin
tan ctan tan
cosh ccosh cosh
sinh csinh sinh
tanh ctanh tanh
exp cexp exp
log clog log
pow cpow pow
sqrt csqrt sqrt
fabs cabs fabs
If at least one argument for a generic parameter is complex,
then use of the macro invokes a complex function; otherwise,
use of the macro invokes a real function.
[#4] For each unsuffixed function in <math.h> without a c-
prefixed counterpart in <complex.h>, the corresponding type-
generic macro has the same name as the function. These
type-generic macros are:
atan2 fma llround remainder
cbrt fmax log10 remquo
ceil fmin log1p rint
copysign fmod log2 round
erf frexp logb scalbn
erfc hypot *lrint scalbln
exp2 ilogb lround tgamma |
expm1 ldexp nearbyint trunc
fdim lgamma nextafter
floor llrint nextafterx
If all arguments for generic parameters are real, then use
of the macro invokes a real function; otherwise, use of the
macro results in undefined behavior.
[#5] For each unsuffixed function in <complex.h> that is not
a c-prefixed counterpart to a function in <math.h>, the
corresponding type-generic macro has the same name as the
function. These type-generic macros are:
carg conj creal
cimag cproj
Use of the macro with any real or complex argument invokes a
7.22.1 Library 7.22.1
382 Committee Draft -- August 3, 1998 WG14/N843
complex function.
[#6] EXAMPLE With the declarations
#include <tgmath.h>
int n;
float f;
double d;
long double ld;
float complex fc;
double complex dc;
long double complex ldc;
functions invoked by use of type-generic macros are shown in
the following table:
macro use invokes
-------------------------------- --------------------------------
exp(n) exp(n), the function
acosh(f) acoshf(f)
sin(d) sin(d), the function
atan(ld) atanl(ld)
log(fc) clogf(fc)
sqrt(dc) csqrt(dc)
pow(ldc, f) cpowl(ldc, f)
remainder(n, n) remainder(n, n), the function
nextafter(d, f) nextafter(d, f), the function
nextafterx(f, ld) nextafterxf(f, ld)
copysign(n, ld) copysignl(n, ld)
ceil(fc) undefined behavior
rint(dc) undefined behavior
fmax(ldc, ld) undefined behavior
carg(n) carg(n), the function
cproj(f) cprojf(f)
creal(d) creal(d), the function
cimag(ld) cimagl(ld)
cabs(fc) cabsf(fc)
carg(dc) carg(dc), the function
cproj(ldc) cprojl(ldc)
7.22.1 Library 7.22.1
WG14/N843 Committee Draft -- August 3, 1998 383
7.23 Date and time <time.h>
7.23.1 Components of time
[#1] The header <time.h> defines four macros, and declares
several types and functions for manipulating time. Many
functions deal with a calendar time that represents the
current date (according to the Gregorian calendar) and time.
Some functions deal with local time, which is the calendar
time expressed for some specific time zone, and with
Daylight Saving Time, which is a temporary change in the
algorithm for determining local time. The local time zone
and Daylight Saving Time are implementation-defined.
[#2] The macros defined are NULL (described in 7.17);
CLOCKS_PER_SEC
which expands to a constant expression with the type clock_t
described below, and which is the number per second of the
value returned by the clock function;
_NO_LEAP_SECONDS
which expands to an integral constant expression of type int |
with a value outside the range [-3600, +3600] (described in |
7.23.2.4). and
_LOCALTIME |
which expands to an integral constant expression of type int |
with a value outside the range [-14400, +14400] (described
in 7.23.2.4).
[#3] The types declared are size_t (described in 7.17);
clock_t
and
time_t
which are arithmetic types capable of representing times;
and
struct tm
and
struct tmx
which hold the components of a calendar time, called the
broken-down time.
7.23 Library 7.23.1
384 Committee Draft -- August 3, 1998 WG14/N843
[#4] The tm structure shall contain at least the following
members, in any order. The semantics of the members and
their normal ranges are expressed in the comments.249)
int tm_sec; // seconds after the minute -- [0, 60]
int tm_min; // minutes after the hour -- [0, 59]
int tm_hour; // hours since midnight -- [0, 23]
int tm_mday; // day of the month -- [1, 31]
int tm_mon; // months since January -- [0, 11]
int tm_year; // years since 1900
int tm_wday; // days since Sunday -- [0, 6]
int tm_yday; // days since January 1 -- [0, 365]
int tm_isdst; // Daylight Saving Time flag
The value of tm_isdst is positive if Daylight Saving Time is
in effect, zero if Daylight Saving Time is not in effect,
and negative if the information is not available.
[#5] The tmx structure shall contain all the members of
struct tm in a manner such that all these members are part
of a common initial subsequence. In addition, it contains
the members:
int tm_version; // version number
int tm_zone; // time zone offset in minutes
// from UTC [-1439, +1439]
int tm_leapsecs; // number of leap seconds applied
void *tm_ext; // extension block
size_t tm_extlen; // size of the extension block
The meaning of tm_isdst is also different: it is the
positive number of minutes of offset if Daylight Saving Time
is in effect, zero if Daylight Saving Time is not in effect,
and -1 if the information is not available. A positive
value for tm_zone indicates a time that is ahead of
Coordinated Universal Time (UTC). The implementation or a
future version of this International Standard may include
further members in a separate object. If so, the tm_ext
member shall point to this object and the tm_extlen object
shall be its size. Otherwise, the tm_ext member shall be a
null pointer and the value of the tm_extlen object is
unspecified.
____________________
249The range [0, 60] for tm_sec allows for a positive leap
second.
7.23.1 Library 7.23.1
WG14/N843 Committee Draft -- August 3, 1998 385
7.23.2 Time manipulation functions
7.23.2.1 The clock function
Synopsis
[#1]
#include <time.h>
clock_t clock(void);
Description
[#2] The clock function determines the processor time used.
Returns
[#3] The clock function returns the implementation's best
approximation to the processor time used by the program
since the beginning of an implementation-defined era related
only to the program invocation. To determine the time in
seconds, the value returned by the clock function should be
divided by the value of the macro CLOCKS_PER_SEC. If the
processor time used is not available or its value cannot be
represented, the function returns the value (clock_t)-1.250)
7.23.2.2 The difftime function
Synopsis
[#1]
#include <time.h>
double difftime(time_t time1, time_t time0);
Description
[#2] The difftime function computes the difference between
two calendar times: time1 - time0.
Returns
[#3] The difftime function returns the difference expressed
in seconds as a double.
____________________
250In order to measure the time spent in a program, the
clock function should be called at the start of the
program and its return value subtracted from the value
returned by subsequent calls.
7.23.2 Library 7.23.2.2
386 Committee Draft -- August 3, 1998 WG14/N843
7.23.2.3 The mktime function
Synopsis
[#1]
#include <time.h>
time_t mktime(struct tm *timeptr);
Description
[#2] The mktime function converts the broken-down time,
expressed as local time, in the structure pointed to by
timeptr into a calendar time value with the same encoding as
that of the values returned by the time function. The
original values of the tm_wday and tm_yday components of the
structure are ignored, and the original values of the other
components are not restricted to the ranges indicated
above.251) On successful completion, the values of the
tm_wday and tm_yday components of the structure are set
appropriately, and the other components are set to represent
the specified calendar time, but with their values forced to
the ranges indicated above; the final value of tm_mday is
not set until tm_mon and tm_year are determined.
[#3] The normalization process shall be as described in
7.23.2.6.
[#4] If the call is successful, a second call to the mktime
function with the resulting struct tm value shall always
leave it unchanged and return the same value as the first
call. Furthermore, if the normalized time is exactly
representable as a time_t value, then the normalized broken-
down time and the broken-down time generated by converting
the result of the mktime function by a call to localtime
shall be identical.
Returns
[#5] The mktime function returns the specified calendar time
encoded as a value of type time_t. If the calendar time
cannot be represented, the function returns the value
(time_t)-1.
[#6] EXAMPLE What day of the week is July 4, 2001?
____________________
251Thus, a positive or zero value for tm_isdst causes the
mktime function to presume initially that Daylight Saving
Time, respectively, is or is not in effect for the
specified time. A negative value causes it to attempt to
determine whether Daylight Saving Time is in effect for
the specified time.
7.23.2.2 Library 7.23.2.3
WG14/N843 Committee Draft -- August 3, 1998 387
#include <stdio.h>
#include <time.h>
static const char *const wday[] = {
"Sunday", "Monday", "Tuesday", "Wednesday",
"Thursday", "Friday", "Saturday", "-unknown-"
};
struct tm time_str;
/* ... */
time_str.tm_year = 2001 - 1900;
time_str.tm_mon = 7 - 1;
time_str.tm_mday = 4;
time_str.tm_hour = 0;
time_str.tm_min = 0;
time_str.tm_sec = 1;
time_str.tm_isdst = -1;
if (mktime(&time_str) == (time_t)-1)
time_str.tm_wday = 7;
printf("%s\n", wday[time_str.tm_wday]);
7.23.2.4 The mkxtime function
Synopsis
[#1]
#include <time.h>
time_t mkxtime(struct tmx *timeptr);
Description
[#2] The mkxtime function has the same behavior and result
as the mktime function except that it takes into account the |
values of the additional members of struct tmx.
[#3] If the value of the tm_version member is not 1, the
behavior is undefined. If the implementation cannot
determine the relationship between local time and UTC, it
shall set the tm_zone member of the pointed-to structure to
_LOCALTIME. Otherwise, if the tm_zone member was
_LOCALTIME, it shall be set to the offset of local time from
UTC, including the effects of the value of the tm_isdst |
member; otherwise, the original value of the tm_isdst member
does not affect the result.
[#4] If the tm_leapsecs member is equal to _NO_LEAP_SECONDS,
then the implementation shall determine the number of leap
seconds that apply and set the member accordingly (or use 0
if it cannot determine it); otherwise, it shall use the
number of leap seconds given. The tm_leapsecs member shall
then be set to the number of leap seconds actually applied
to produce the value represented by the structure, or to
7.23.2.3 Library 7.23.2.4
388 Committee Draft -- August 3, 1998 WG14/N843
_NO_LEAP_SECONDS if it was not possible to determine it.
[#5] If the call is successful, a second call to the mkxtime
function with the resulting struct tmx value shall always
leave it unchanged and return the same value as the first
call. Furthermore, if the normalized time is exactly
representable as a time_t value, then the normalized broken-
down time and the broken-down time generated by converting
the result of the mkxtime function by a call to zonetime
(with zone set to the value of the tm_zone member) shall be
identical. |
Returns |
[#6] The mkxtime function returns the specified calendar |
time encoded as a value of type time_t. If the calendar |
time cannot be represented, the function returns the value |
(time_t)-1.
7.23.2.5 The time function
Synopsis
[#1]
#include <time.h>
time_t time(time_t *timer);
Description
[#2] The time function determines the current calendar time.
The encoding of the value is unspecified.
Returns
[#3] The time function returns the implementation's best
approximation to the current calendar time. The value
(time_t)-1 is returned if the calendar time is not
available. If timer is not a null pointer, the return value
is also assigned to the object it points to.
7.23.2.6 Normalization of broken-down times
[#1] A broken-down time is normalized by the mkxtime
function in the following manner. A broken-down time is
normalized by the mktime function in the same manner, but as
if the struct tm structure had been replaced by a struct tmx
structure containing the same values except:
tm_version is 1
tm_zone is _LOCALTIME
7.23.2.4 Library 7.23.2.6
WG14/N843 Committee Draft -- August 3, 1998 389
tm_leapsecs is _NO_LEAP_SECONDS
tm_isdst is -1, 0, or an implementation-defined
positive value according to whether the
original member is less than, equal to, or
greater than zero
[#2] If any of the following members is outside the
indicated range (where L is LONG_MAX/8), the behavior is
undefined:
tm_year [-L/366, +L/366]
tm_mon [-L/31, +L/31]
tm_mday [-L, +L]
tm_hour [-L/3600, +L/3600]
tm_min [-L/60, +L/60]
tm_sec [-L, +L]
tm_leapsecs [-L, +L] or _NO_LEAP_SECONDS
tm_zone [-L/60, +L/60]
tm_isdst [-L/60, +L/60] or _LOCALTIME
The tm_version member shall be 1.
[#3] Values S and D shall be determined as follows:
7.23.2.6 Library 7.23.2.6
390 Committee Draft -- August 3, 1998 WG14/N843
#define QUOT(a,b) ((a)>0 ? (a)/(b) : -(((b)-(a)-1)/(b)))
#define REM(a,b) ((a)-(b)*QUOT(a,b))
SS = tm_hour*3600 + tm_min*60 + tm_sec +
(tm_leapsecs == _NO_LEAP_SECONDS ? X1 :
tm_leapsecs) -
(tm_zone == _LOCALTIME ? X2 : tm_zone) * 60;
// X1 is the appropriate number of leap seconds, determined by
// the implementation, or 0 if it cannot be determined.
// X2 is the appropriate offset from local time to UTC,
// determined by the implementation, or
// (tm_isdst >= 0 ? tm_isdst : 0)
// if the offset cannot be determined
M = REM(tm_mon, 12);
Y = tm_year + 1900 + QUOT(tm_mon, 12);
Z = Y - (M < 2 ? 1 : 0);
D = Y*365 + (Z/400)*97 + (Z%400)/4 +
M[(int []){0,31,59,90,120,151,181,212,243,273,
304,335}] +
tm_mday + QUOT(SS, 86400);
S = REM(SS, 86400);
[#4] The normalized broken-down time shall produce the same
values of S and D (though possibly different values of M, Y,
and Z) as the original broken-down time.252)
7.23.3 Time conversion functions
[#1] Except for the strftime and strfxtime functions, these
functions each return a pointer to one of two types of
static objects: a broken-down time structure or an array of
char. Execution of any of the functions that return a
pointer to one of these object types may overwrite the
information in any object of the same type pointed to by the
value returned from any previous call to any of them. The
implementation shall behave as if no other library functions
call these functions.
____________________
252The effect of the above rules is to consistently use the
Gregorian calendar, regardless of which calendar was in
use in which year. In particular, the years 1100 and
-300 are not leap years, while the years 1200 and -400
are (these 4 years correspond to tm_year values of -800,
-2200, -700, and -2300 respectively, and the last of
these is 401 B.C.E.). In the normalized broken-down
time, tm_wday is equal to QUOT(D-2,7).
7.23.2.6 Library 7.23.3
WG14/N843 Committee Draft -- August 3, 1998 391
7.23.3.1 The asctime function
Synopsis
[#1]
#include <time.h>
char *asctime(const struct tm *timeptr);
Description
[#2] The asctime function converts the broken-down time in
the structure pointed to by timeptr into a string in the
form
Sun Sep 16 01:03:52 1973\n\0
using the equivalent of the following algorithm.
char *asctime(const struct tm *timeptr)
{
static const char wday_name[7][3] = {
"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
};
static const char mon_name[12][3] = {
"Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};
static char result[26];
sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
wday_name[timeptr->tm_wday],
mon_name[timeptr->tm_mon],
timeptr->tm_mday, timeptr->tm_hour,
timeptr->tm_min, timeptr->tm_sec,
1900 + timeptr->tm_year);
return result;
}
Returns
[#3] The asctime function returns a pointer to the string.
7.23.3 Library 7.23.3.1
392 Committee Draft -- August 3, 1998 WG14/N843
7.23.3.2 The ctime function
Synopsis
[#1]
#include <time.h>
char *ctime(const time_t *timer);
Description
[#2] The ctime function converts the calendar time pointed
to by timer to local time in the form of a string. It is
equivalent to
asctime(localtime(timer))
Returns
[#3] The ctime function returns the pointer returned by the
asctime function with that broken-down time as argument.
Forward references: the localtime function (7.23.3.4).
7.23.3.3 The gmtime function
Synopsis
[#1]
#include <time.h>
struct tm *gmtime(const time_t *timer);
Description
[#2] The gmtime function converts the calendar time pointed
to by timer into a broken-down time, expressed as UTC.
Returns
[#3] The gmtime function returns a pointer to the broken- |
down time, or a null pointer if the specified time cannot be |
converted to UTC.
7.23.3.1 Library 7.23.3.3
WG14/N843 Committee Draft -- August 3, 1998 393
7.23.3.4 The localtime function
Synopsis
[#1]
#include <time.h>
struct tm *localtime(const time_t *timer);
Description
[#2] The localtime function converts the calendar time
pointed to by timer into a broken-down time, expressed as
local time.
Returns
[#3] The localtime function returns a pointer to the broken- |
down time, or a null pointer if the specified time cannot be |
converted to local time.
7.23.3.5 The strftime function
Synopsis
[#1]
#include <time.h>
size_t strftime(char * restrict s,
size_t maxsize,
const char * restrict format,
const struct tm * restrict timeptr);
Description
[#2] The strftime function places characters into the array
pointed to by s as controlled by the string pointed to by
format. The format shall be a multibyte character sequence,
beginning and ending in its initial shift state. The format
string consists of zero or more conversion specifiers and
ordinary multibyte characters. A conversion specifier
consists of a % character, possibly followed by an E or O |
modifier character (described below), followed by a |
character that determines the behavior of the conversion
specifier. All ordinary multibyte characters (including the
terminating null character) are copied unchanged into the
array. If copying takes place between objects that overlap,
the behavior is undefined. No more than maxsize characters
are placed into the array. |
[#3] Each conversion specifier is replaced by appropriate
characters as described in the following list. The |
appropriate characters are determined using the LC_TIME
category of the current locale and by the values of zero or |
7.23.3.3 Library 7.23.3.5
394 Committee Draft -- August 3, 1998 WG14/N843
more members of the broken-down time structure pointed to by
timeptr, as specified in brackets in the description. If |
any of the specified values is outside the normal range, the
characters stored are unspecified.
%a is replaced by the locale's abbreviated weekday name.
[tm_wday]
%A is replaced by the locale's full weekday name.
[tm_wday]
%b is replaced by the locale's abbreviated month name.
[tm_mon]
%B is replaced by the locale's full month name. [tm_mon]
%c is replaced by the locale's appropriate date and time
representation. [all specified in 7.23.1] |
%C is replaced by the year divided by 100 and truncated |
to an integer, as a decimal number (00-99). [tm_year]
%d is replaced by the day of the month as a decimal
number (01-31). [tm_mday] |
%D is equivalent to ``%m/%d/%y''. [tm_mon, tm_mday, |
tm_year] |
%e is replaced by the day of the month as a decimal |
number (1-31); a single digit is preceded by a space. |
[tm_mday]
%F is equivalent to ``%Y-%m-%d'' (the ISO 8601 date
format). [tm_year, tm_mon, tm_mday]
%g is replaced by the last 2 digits of the week-based
year (see below) as a decimal number (00-99).
[tm_year, tm_wday, tm_yday]
%G is replaced by the week-based year (see below) as a
decimal number (e.g., 1997). [tm_year, tm_wday,
tm_yday] |
%h is equivalent to ``%b''. [tm_mon]
%H is replaced by the hour (24-hour clock) as a decimal
number (00-23). [tm_hour]
%I is replaced by the hour (12-hour clock) as a decimal
number (01-12). [tm_hour]
%j is replaced by the day of the year as a decimal number
(001-366). [tm_yday]
%m is replaced by the month as a decimal number (01-12).
[tm_mon]
%M is replaced by the minute as a decimal number (00-59).
[tm_min] |
%n is replaced by a new-line character.
%p is replaced by the locale's equivalent of the AM/PM
designations associated with a 12-hour clock.
[tm_hour] |
%r is replaced by the locale's 12-hour clock time. |
[tm_hour, tm_min, tm_sec] |
%R is equivalent to ``%H:%M''. [tm_hour, tm_min]
%S is replaced by the second as a decimal number (00-60).
[tm_sec] |
%t is replaced by a horizontal-tab character.
%T is equivalent to ``%H:%M:%S'' (the ISO 8601 time
format). [tm_hour, tm_min, tm_sec]
%u is replaced by the ISO 8601 weekday as a decimal |
7.23.3.5 Library 7.23.3.5
WG14/N843 Committee Draft -- August 3, 1998 395
number (1-7), where Monday is 1. [tm_wday] |
%U is replaced by the week number of the year (the first
Sunday as the first day of week 1) as a decimal number
(00-53). [tm_year, tm_wday, tm_yday]
%V is replaced by the ISO 8601 week number (see below) as
a decimal number (01-53). [tm_year, tm_wday, tm_yday]
%w is replaced by the weekday as a decimal number (0-6),
where Sunday is 0. [tm_wday]
%W is replaced by the week number of the year (the first
Monday as the first day of week 1) as a decimal number
(00-53). [tm_year, tm_wday, tm_yday]
%x is replaced by the locale's appropriate date
representation. [all specified in 7.23.1]
%X is replaced by the locale's appropriate time
representation. [all specified in 7.23.1]
%y is replaced by the last 2 digits of the year as a
decimal number (00-99). [tm_year]
%Y is replaced by the year as a decimal number (e.g., |
1997). [tm_year]
%z is replaced by the offset from UTC in the ISO 8601 |
format ``-0430'' (meaning 4 hours 30 minutes behind |
UTC, west of Greenwich), or by no characters if no |
time zone is determinable. [tm_isdst]
%Z is replaced by the locale's time zone name or |
abbreviation, or by no characters if no time zone is
determinable. [tm_isdst]
%% is replaced by %.
[#4] Some conversion specifiers can be modified by the |
inclusion of the E or O modifier characters to indicate an |
alternative format or specification. If the alternative |
format or specification does not exist for the current |
locale, the modifier is ignored. |
%Ec is replaced by the locale's alternative date and time |
representation. |
%EC is replaced by the name of the base year (period) in |
the locale's alternative representation. |
%Ex is replaced by the locale's alternative date |
representation. |
%EX is replaced by the locale's alternative time |
representation. |
%Ey is replaced by the offset from %EC (year only) in the |
locale's alternative representation. |
%EY is replaced by the locale's full alternative year |
representation. |
%Od is replaced by the day of the month, using the |
locale's alternative numeric symbols (filled as needed |
with leading zeros, or with leading spaces if there is |
no alternative symbol for zero). |
%Oe is replaced by the day of the month, using the |
locale's alternative numeric symbols (filled as needed |
with leading spaces). |
%OH is replaced by the hour (24-hour clock), using the |
locale's alternative numeric symbols. |
7.23.3.5 Library 7.23.3.5
396 Committee Draft -- August 3, 1998 WG14/N843
%OI is replaced by the hour (12-hour clock), using the |
locale's alternative numeric symbols. |
%Om is replaced by the month, using the locale's |
alternative numeric symbols. |
%OM is replaced by the minutes, using the locale's |
alternative numeric symbols. |
%OS is replaced by the seconds, using the locale's |
alternative numeric symbols. |
%Ou is replaced by the ISO 8601 weekday as a number in the |
locale's alternative representation, where Monday is |
1. |
%OU is replaced by the week number, using the locale's |
alternative numeric symbols. |
%OV is replaced by the ISO 8601 week number, using the |
locale's alternative numeric symbols. |
%Ow is replaced by the weekday as a number, using the |
locale's alternative numeric symbols. |
%Ou is replaced by the week number of the year, using the |
locale's alternative numeric symbols. |
%Oy is replaced by the last 2 digits of the year, using |
the locale's alternative numeric symbols. |
[#5] %g, %G, and %V give values according to the ISO 8601
week-based year. In this system, weeks begin on a Monday
and week 1 of the year is the week that includes January
4th, which is also the week that includes the first Thursday |
of the year, and is also the first week that contains at |
least four days in the year. If the first Monday of January
is the 2nd, 3rd, or 4th, the preceding days are part of the
last week of the preceding year; thus, for Saturday 2nd
January 1999, %G is replaced by 1998 and %V is replaced by
53. If December 29th, 30th, or 31st is a Monday, it and any
following days are part of week 1 of the following year.
Thus, for Tuesday 30th December 1997, %G is replaced by 1998
and %V is replaced by 1.
[#6] If a conversion specifier is not one of the above, the
behavior is undefined.
[#7] In the "C" locale, the E and O modifiers are ignored |
and the replacement strings for the following specifiers |
are:
%a the first three characters of %A.
%A one of ``Sunday'', ``Monday'', ... , ``Saturday''.
%b the first three characters of %B.
%B one of ``January'', ``February'', ... , ``December''.
%c equivalent to ``%A %B %d %T %Y''.
%p one of ``am'' or ``pm''. |
%r equivalent to ``%I:%M:%S %p''.
%x equivalent to ``%A %B %d %Y''.
%X equivalent to %T.
%Z implementation-defined.
7.23.3.5 Library 7.23.3.5
WG14/N843 Committee Draft -- August 3, 1998 397
Returns
[#8] If the total number of resulting characters including
the terminating null character is not more than maxsize, the
strftime function returns the number of characters placed
into the array pointed to by s not including the terminating
null character. Otherwise, zero is returned and the
contents of the array are indeterminate.
7.23.3.6 The strfxtime function
Synopsis
[#1]
#include <time.h>
size_t strfxtime(char * restrict s,
size_t maxsize,
const char * restrict format,
const struct tmx * restrict timeptr);
Description
[#2] The behavior and result of the strfxtime is identical
to that of the strftime function, except that the timeptr
parameter has a different type, and the %z and %Z conversion
specifiers depend on tm_zone in addition to tm_isdst.
7.23.3.7 The zonetime function
Synopsis
[#1]
#include <time.h>
struct tmx *zonetime(const time_t *timer, int zone);
Description
[#2] The zonetime function converts the calendar time
pointed to by timer into a broken-down time as represented
in the specified time zone. The tm_version member is set to
1. If the implementation cannot determine the relationship
between local time and UTC, it shall set the tm_zone member
to _LOCALTIME; otherwise, it shall set the tm_zone member to
the value of zone unless the latter is _LOCALTIME, in which
case it shall set it to the offset of local time from UTC.
The value shall include the effect of Daylight Saving Time,
if in effect. The tm_leapsecs member shall be set to the
number of leap seconds (the UTC-UT1 offset) applied in the
result253) if it can be determined, or to the value
_NO_LEAP_SECONDS if it cannot (and so none were applied).
Returns
[#3] The zonetime function returns a pointer to the broken- |
down time, or a null pointer if the specified time cannot be |
converted to the specified time zone.
398 Committee Draft -- August 3, 1998 WG14/N843
7.24 Extended multibyte and wide-character utilities
<wchar.h>
7.24.1 Introduction
[#1] The header <wchar.h> declares four data types, one tag,
four macros, and many functions.254)
[#2] The types declared are wchar_t and size_t (both
described in 7.17);
mbstate_t
which is an object type other than an array type that can
hold the conversion state information necessary to convert
between sequences of multibyte characters and wide
characters;
wint_t
described in 7.25.1; and
struct tm
and
struct tmx
which are declared as incomplete structure types, the
contents of which are described in 7.23.1.
[#3] The macros defined are NULL (described in 7.17);
WCHAR_MAX
which is the maximum value representable by an object of
type wchar_t;255)
WCHAR_MIN
which is the minimum value representable by an object of
type wchar_t; and
WEOF
____________________
253If the tm_sec member is set to 60, that leap second shall
not be included in the value of tm_leapsecs.
254See ``future library directions'' (7.26.12).
255The values WCHAR_MAX and WCHAR_MIN do not necessarily
correspond to members of the extended character set.
7.24 Library 7.24.1
WG14/N843 Committee Draft -- August 3, 1998 399
described in 7.25.1.
[#4] The functions declared are grouped as follows:
-- Functions that perform input and output of wide
characters, or multibyte characters, or both;
-- Functions that provide wide-string numeric conversion;
-- Functions that perform general wide-string
manipulation;
-- Functions for wide-string date and time conversion; and |
-- Functions that provide extended capabilities for
conversion between multibyte and wide-character
sequences.
[#5] Unless explicitly stated otherwise, if the execution of
a function described in this subclause causes copying to
take place between objects that overlap, the behavior is
undefined.
7.24.2 Formatted wide-character input/output functions
[#1] The formatted wide-character input/output
functions256) shall behave as if there is a sequence point
after the actions associated with each specifier.
7.24.2.1 The fwprintf function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fwprintf(FILE * restrict stream,
const wchar_t * restrict format, ...);
Description
[#2] The fwprintf function writes output to the stream
pointed to by stream, under control of the wide string
pointed to by format that specifies how subsequent arguments
are converted for output. If there are insufficient
arguments for the format, the behavior is undefined. If the
format is exhausted while arguments remain, the excess
arguments are evaluated (as always) but are otherwise
ignored. The fwprintf function returns when the end of the
____________________
256The fwprintf functions perform writes to memory for the
%n specifier.
7.24.1 Library 7.24.2.1
400 Committee Draft -- August 3, 1998 WG14/N843
format string is encountered.
[#3] The format is composed of zero or more directives:
ordinary wide characters (not %), which are copied unchanged
to the output stream; and conversion specifications, each of
which results in fetching zero or more subsequent arguments,
converting them, if applicable, according to the
corresponding conversion specifier, and then writing the
result to the output stream.
[#4] Each conversion specification is introduced by the wide
character %. After the %, the following appear in sequence:
-- Zero or more flags (in any order) that modify the
meaning of the conversion specification.
-- An optional minimum field width. If the converted value
has fewer wide characters than the field width, it is
padded with spaces (by default) on the left (or right,
if the left adjustment flag, described later, has been
given) to the field width. The field width takes the
form of an asterisk * (described later) or a decimal
integer.257)
-- An optional precision that gives the minimum number of
digits to appear for the d, i, o, u, x, and X
conversions, the number of digits to appear after the
decimal-point wide character for a, A, e, E, f, and F
conversions, the maximum number of significant digits
for the g and G conversions, or the maximum number of
wide characters to be written from a string in s
conversions. The precision takes the form of a period
(.) followed either by an asterisk * (described later)
or by an optional decimal integer; if only the period
is specified, the precision is taken as zero. If a
precision appears with any other conversion specifier,
the behavior is undefined.
-- An optional length modifier that specifies the size of
the argument.
-- A conversion specifier wide character that specifies
the type of conversion to be applied.
[#5] As noted above, a field width, or precision, or both,
may be indicated by an asterisk. In this case, an int
argument supplies the field width or precision. The
arguments specifying field width, or precision, or both,
shall appear (in that order) before the argument (if any) to
be converted. A negative field width argument is taken as a
____________________
257Note that 0 is taken as a flag, not as the beginning of a
field width.
7.24.2.1 Library 7.24.2.1
WG14/N843 Committee Draft -- August 3, 1998 401
- flag followed by a positive field width. A negative
precision argument is taken as if the precision were
omitted.
[#6] The flag wide characters and their meanings are:
- The result of the conversion is left-justified within
the field. (It is right-justified if this flag is not
specified.)
+ The result of a signed conversion always begins with a
plus or minus sign. (It begins with a sign only when
a negative value is converted if this flag is not
specified.)258)
space If the first wide character of a signed conversion is
not a sign, or if a signed conversion results in no
wide characters, a space is prefixed to the result.
If the space and + flags both appear, the space flag
is ignored.
# The result is converted to an ``alternative form''. |
For o conversion, it increases the precision, if and
only if necessary, to force the first digit of the
result to be a zero (if the value and precision are
both 0, a single 0 is printed). For x (or X)
conversion, a nonzero result has 0x (or 0X) prefixed
to it. For a, A, e, E, f, F, g, and G conversions,
the result always contains a decimal-point wide
character, even if no digits follow it. (Normally, a
decimal-point wide character appears in the result of
these conversions only if a digit follows it.) For g
and G conversions, trailing zeros are not removed from
the result. For other conversions, the behavior is
undefined.
0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G
conversions, leading zeros (following any indication
of sign or base) are used to pad to the field width;
no space padding is performed. If the 0 and - flags
both appear, the 0 flag is ignored. For d, i, o, u,
x, and X conversions, if a precision is specified, the
0 flag is ignored. For other conversions, the
behavior is undefined.
[#7] The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a signed char
____________________
258The results of all floating conversions of a negative
zero, and of negative values that round to zero, include
a minus sign.
7.24.2.1 Library 7.24.2.1
402 Committee Draft -- August 3, 1998 WG14/N843
or unsigned char argument (the argument will
have been promoted according to the integer |
promotions, but its value shall be converted to
signed char or unsigned char before printing);
or that a following n conversion specifier
applies to a pointer to a signed char argument.
h Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a short int or
unsigned short int argument (the argument will
have been promoted according to the integer
promotions, but its value shall be converted to |
short int or unsigned short int before
printing); or that a following n conversion
specifier applies to a pointer to a short int
argument.
l (ell) Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a long int or
unsigned long int argument; that a following n
conversion specifier applies to a pointer to a
long int argument; that a following c
conversion specifier applies to a wint_t
argument; that a following s conversion
specifier applies to a pointer to a wchar_t
argument; or has no effect on a following a, A,
e, E, f, F, g, or G conversion specifier.
ll (ell-ell) Specifies that a following d, i, o, u, x, or X
conversion specifier applies to a long long int
or unsigned long long int argument; or that a
following n conversion specifier applies to a
pointer to a long long int argument. |
j Specifies that a following d, i, o, u, x, or X |
conversion specifier applies to an intmax_t or |
uintmax_t argument; or that a following n |
conversion specifier applies to a pointer to an |
intmax_t argument. |
z Specifies that a following d, i, o, u, x, or X |
conversion specifier applies to a size_t or the |
corresponding signed integer type argument; or |
that a following n conversion specifier applies |
to a pointer to a signed integer type |
corresponding to size_t argument. |
t Specifies that a following d, i, o, u, x, or X |
conversion specifier applies to a ptrdiff_t or |
the corresponding unsigned integer type |
argument; or that a following n conversion |
specifier applies to a pointer to a ptrdiff_t |
argument.
7.24.2.1 Library 7.24.2.1
WG14/N843 Committee Draft -- August 3, 1998 403
L Specifies that a following a, A, e, E, f, F, g,
or G conversion specifier applies to a long
double argument.
If a length modifier appears with any conversion specifier |
other than as specified above, the behavior is undefined.
[#8] The conversion specifiers and their meanings are:
d,i The int argument is converted to signed decimal in
the style [-]dddd. The precision specifies the
minimum number of digits to appear; if the value
being converted can be represented in fewer digits,
it is expanded with leading zeros. The default
precision is 1. The result of converting a zero
value with a precision of zero is no wide
characters.
o,u,x,X The unsigned int argument is converted to unsigned
octal (o), unsigned decimal (u), or unsigned
hexadecimal notation (x or X) in the style dddd; the
letters abcdef are used for x conversion and the
letters ABCDEF for X conversion. The precision
specifies the minimum number of digits to appear; if
the value being converted can be represented in
fewer digits, it is expanded with leading zeros.
The default precision is 1. The result of
converting a zero value with a precision of zero is
no wide characters.
f,F A double argument representing a (finite) floating- |
point number is converted to decimal notation in the
style [-]ddd.ddd, where the number of digits after
the decimal-point wide character is equal to the
precision specification. If the precision is
missing, it is taken as 6; if the precision is zero
and the # flag is not specified, no decimal-point
wide character appears. If a decimal-point wide
character appears, at least one digit appears before
it. The value is rounded to the appropriate number
of digits.
A double argument representing an infinity is
converted in one of the styles [-]inf or [-]infinity
-- which style is implementation-defined. A
double argument representing a NaN is converted in
one of the styles [-]nan or [-]nan(n-wchar-sequence)
-- which style, and the meaning of any n-wchar-
sequence, is implementation-defined. The F
conversion specifier produces INF, INFINITY, or NAN
instead of inf, infinity, or nan, respectively.259)
e,E A double argument representing a (finite) floating- |
point number is converted in the style [-]d.ddde±dd,
7.24.2.1 Library 7.24.2.1
404 Committee Draft -- August 3, 1998 WG14/N843
where there is one digit (which is nonzero if the
argument is nonzero) before the decimal-point wide
character and the number of digits after it is equal
to the precision; if the precision is missing, it is
taken as 6; if the precision is zero and the # flag
is not specified, no decimal-point wide character
appears. The value is rounded to the appropriate
number of digits. The E conversion specifier
produces a number with E instead of e introducing
the exponent. The exponent always contains at least
two digits, and only as many more digits as
necessary to represent the exponent. If the value
is zero, the exponent is zero.
A double argument representing an infinity or NaN is
converted in the style of an f or F conversion
specifier.
g,G A double argument representing a (finite) floating- |
point number is converted in style f or e (or in
style F or E in the case of a G conversion
specifier), with the precision specifying the number
of significant digits. If the precision is zero, it
is taken as 1. The style used depends on the value
converted; style e (or E) is used only if the
exponent resulting from such a conversion is less
than -4 or greater than or equal to the precision. |
Trailing zeros are removed from the fractional |
portion of the result unless the # flag is |
specified; a decimal-point wide character appears
only if it is followed by a digit.
A double argument representing an infinity or NaN is
converted in the style of an f or F conversion
specifier.
a,A A double argument representing a (finite) floating- |
point number is converted in the style
[-]0xh.hhhhp±d, where there is one hexadecimal digit
(which is nonzero if the argument is a normalized
floating-point number and is otherwise unspecified) |
before the decimal-point wide character260) and the *
number of hexadecimal digits after it is equal to
the precision; if the precision is missing and
FLT_RADIX is a power of 2, then the precision is
____________________
259When applied to infinite and NaN values, the -, +, and
space flag wide characters have their usual meaning; the
# and 0 flag wide characters have no effect.
260Binary implementations can choose the hexadecimal digit
to the left of the decimal-point wide character so that
subsequent digits align to nibble (4-bit) boundaries.
7.24.2.1 Library 7.24.2.1
WG14/N843 Committee Draft -- August 3, 1998 405
sufficient for an exact representation of the value;
if the precision is missing and FLT_RADIX is not a
power of 2, then the precision is sufficient to
distinguish261) values of type double, except that
trailing zeros may be omitted; if the precision is
zero and the # flag is not specified, no decimal-
point wide character appears. The letters abcdef
are used for a conversion and the letters ABCDEF for
A conversion. The A conversion specifier produces a
number with X and P instead of x and p. The
exponent always contains at least one digit, and
only as many more digits as necessary to represent
the decimal exponent of 2. If the value is zero,
the exponent is zero.
A double argument representing an infinity or NaN is
converted in the style of an f or F conversion
specifier.
c If no l length modifier is present, the int argument
is converted to a wide character as if by calling
btowc and the resulting wide character is written.
If an l length modifier is present, the wint_t
argument is converted to wchar_t and written.
s If no l length modifier is present, the argument
shall be a pointer to the initial element of a |
character array containing a multibyte character |
sequence beginning in the initial shift state.
Characters from the array are converted as if by
repeated calls to the mbrtowc function, with the
conversion state described by an mbstate_t object
initialized to zero before the first multibyte
character is converted, and written up to (but not
including) the terminating null wide character. If
the precision is specified, no more than that many
wide characters are written. If the precision is
not specified or is greater than the size of the
converted array, the converted array shall contain a
null wide character.
If an l length modifier is present, the argument
shall be a pointer to the initial element of an
array of wchar_t type. Wide characters from the
array are written up to (but not including) a
____________________
261The precision p is sufficient to distinguish values of
the source type if 16p-1>bn where b is FLT_RADIX and n is
the number of base-b digits in the significand of the
source type. A smaller p might suffice depending on the
implementation's scheme for determining the digit to the
left of the decimal-point wide character.
7.24.2.1 Library 7.24.2.1
406 Committee Draft -- August 3, 1998 WG14/N843
terminating null wide character. If the precision
is specified, no more than that many wide characters
are written. If the precision is not specified or
is greater than the size of the array, the array
shall contain a null wide character.
p The argument shall be a pointer to void. The value
of the pointer is converted to a sequence of
printable wide characters, in an implementation-
defined manner.
n The argument shall be a pointer to signed integer
into which is written the number of wide characters
written to the output stream so far by this call to
fwprintf. No argument is converted, but one is
consumed. If the conversion specification includes |
any flags, a field width, or a precision, the
behavior is undefined.
% A % wide character is written. No argument is
converted. The complete conversion specification
shall be %%.
[#9] If a conversion specification is invalid, the behavior
is undefined.262) If any argument is not the correct type |
for the corresponding coversion specification, the behavior
is undefined.
[#10] In no case does a nonexistent or small field width
cause truncation of a field; if the result of a conversion
is wider than the field width, the field is expanded to
contain the conversion result.
[#11] For a and A conversions, if FLT_RADIX is a power of 2,
the value is correctly rounded to a hexadecimal floating
number with the given precision.
Recommended practice
[#12] If FLT_RADIX is not a power of 2, the result should be
one of the two adjacent numbers in hexadecimal floating
style with the given precision, with the extra stipulation
that the error should have a correct sign for the current
rounding direction.
[#13] For e, E, f, F, g, and G conversions, if the number of
significant decimal digits is at most DECIMAL_DIG, then the
result should be correctly rounded.263) If the number of
significant decimal digits is more than DECIMAL_DIG but the
source value is exactly representable with DECIMAL_DIG
digits, then the result should be an exact representation
____________________
262See ``future library directions'' (7.26.12).
7.24.2.1 Library 7.24.2.1
WG14/N843 Committee Draft -- August 3, 1998 407
with trailing zeros. Otherwise, the source value is bounded
by two adjacent decimal strings L < U, both having
DECIMAL_DIG significant digits; the value of the resultant
decimal string D should satisfy L <= D <= U, with the extra
stipulation that the error should have a correct sign for
the current rounding direction.
Returns
[#14] The fwprintf function returns the number of wide
characters transmitted, or a negative value if an output or |
encoding error occurred.
Environmental limits
[#15] The number of wide characters that can be produced by |
any single conversion shall be at least 4095.
[#16] EXAMPLE To print a date and time in the form
``Sunday, July 3, 10:02'' followed by pi to five decimal
places:
#include <math.h>
#include <stdio.h>
#include <wchar.h>
/* ... */
wchar_t *weekday, *month; // pointers to wide strings
int day, hour, min;
fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
Forward references: the btowc function (7.24.6.1.1), the
mbrtowc function (7.24.6.3.2).
____________________
263For binary-to-decimal conversion, the result format's
values are the numbers representable with the given
format specifier. The number of significant digits is
determined by the format specifier, and in the case of
fixed-point conversion by the source value as well.
7.24.2.1 Library 7.24.2.1
408 Committee Draft -- August 3, 1998 WG14/N843
7.24.2.2 The fwscanf function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fwscanf(FILE * restrict stream,
const wchar_t * restrict format, ...);
Description
[#2] The fwscanf function reads input from the stream
pointed to by stream, under control of the wide string
pointed to by format that specifies the admissible input
sequences and how they are to be converted for assignment,
using subsequent arguments as pointers to the objects to
receive the converted input. If there are insufficient
arguments for the format, the behavior is undefined. If the
format is exhausted while arguments remain, the excess
arguments are evaluated (as always) but are otherwise
ignored.
[#3] The format is composed of zero or more directives: one |
or more white-space wide characters, an ordinary wide
character (neither % nor a white-space wide character), or a |
conversion specification. Each conversion specification is
introduced by the wide character %. After the %, the
following appear in sequence:
-- An optional assignment-suppressing wide character *.
-- An optional nonzero decimal integer that specifies the
maximum field width (in wide characters).
-- An optional length modifier that specifies the size of
the receiving object.
-- A conversion specifier wide character that specifies
the type of conversion to be applied.
[#4] The fwscanf function executes each directive of the
format in turn. If a directive fails, as detailed below,
the function returns. Failures are described as input
failures (due to the occurrence of an encoding error or the
unavailability of input characters), or matching failures
(due to inappropriate input).
[#5] A directive composed of white-space wide character(s)
is executed by reading input up to the first non-white-space
wide character (which remains unread), or until no more wide
characters can be read.
7.24.2.1 Library 7.24.2.2
WG14/N843 Committee Draft -- August 3, 1998 409
[#6] A directive that is an ordinary wide character is
executed by reading the next wide character of the stream.
If that wide character differs from the directive, the
directive fails and the differing and subsequent wide
characters remain unread.
[#7] A directive that is a conversion specification defines
a set of matching input sequences, as described below for
each specifier. A conversion specification is executed in
the following steps:
[#8] Input white-space wide characters (as specified by the
iswspace function) are skipped, unless the specification
includes a [, c, or n specifier.264)
[#9] An input item is read from the stream, unless the
specification includes an n specifier. An input item is
defined as the longest sequence of input wide characters
which does not exceed any specified field width and which
is, or is a prefix of, a matching input sequence. The first
wide character, if any, after the input item remains unread.
If the length of the input item is zero, the execution of
the directive fails; this condition is a matching failure
unless end-of-file, an encoding error, or a read error
prevented input from the stream, in which case it is an
input failure.
[#10] Except in the case of a % specifier, the input item
(or, in the case of a %n directive, the count of input wide
characters) is converted to a type appropriate to the
conversion specifier. If the input item is not a matching
sequence, the execution of the directive fails: this
condition is a matching failure. Unless assignment
suppression was indicated by a *, the result of the
conversion is placed in the object pointed to by the first
argument following the format argument that has not already
received a conversion result. If this object does not have
an appropriate type, or if the result of the conversion
cannot be represented in the object, the behavior is
undefined.
[#11] The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
with type pointer to signed char or unsigned
char.
h Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
____________________
264These white-space wide characters are not counted against
a specified field width.
7.24.2.2 Library 7.24.2.2
410 Committee Draft -- August 3, 1998 WG14/N843
with type pointer to short int or unsigned
short int.
l (ell) Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
with type pointer to long int or unsigned long
int; that a following a, A, e, E, f, F, g, or G
conversion specifier applies to an argument
with type pointer to double; or that a
following c, s, or [ conversion specifier
applies to an argument with type pointer to
wchar_t.
ll (ell-ell) Specifies that a following d, i, o, u, x, X, or
n conversion specifier applies to an argument
with type pointer to long long int or unsigned
long long int. |
j Specifies that a following d, i, o, u, x, X, or |
n conversion specifier applies to an argument |
with type pointer to intmax_t or uintmax_t. |
z Specifies that a following d, i, o, u, x, X, or |
n conversion specifier applies to an argument |
with type pointer to size_t or the |
corresponding signed integer type. |
t Specifies that a following d, i, o, u, x, X, or |
n conversion specifier applies to an argument |
with type pointer to ptrdiff_t or the |
corresponding unsigned integer type.
L Specifies that a following a, A, e, E, f, F, g,
or G conversion specifier applies to an
argument with type pointer to long double.
If a length modifier appears with any conversion specifier |
other than as specified above, the behavior is undefined.
[#12] The conversion specifiers and their meanings are:
d Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the wcstol function with the value 10
for the base argument. The corresponding argument
shall be a pointer to signed integer.
i Matches an optionally signed integer, whose format
is the same as expected for the subject sequence of
the wcstol function with the value 0 for the base
argument. The corresponding argument shall be a
pointer to signed integer.
7.24.2.2 Library 7.24.2.2
WG14/N843 Committee Draft -- August 3, 1998 411
o Matches an optionally signed octal integer, whose
format is the same as expected for the subject
sequence of the wcstoul function with the value 8
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
u Matches an optionally signed decimal integer, whose
format is the same as expected for the subject
sequence of the wcstoul function with the value 10
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
x Matches an optionally signed hexadecimal integer,
whose format is the same as expected for the subject
sequence of the wcstoul function with the value 16
for the base argument. The corresponding argument
shall be a pointer to unsigned integer.
a,e,f,g Matches an optionally signed floating-point number, |
infinity, or NaN, whose format is the same as
expected for the subject sequence of the wcstod
function. The corresponding argument shall be a
pointer to floating.
c Matches a sequence of wide characters of exactly the
number specified by the field width (1 if no field
width is present in the directive).
If no l length modifier is present, characters from
the input field are converted as if by repeated
calls to the wcrtomb function, with the conversion
state described by an mbstate_t object initialized
to zero before the first wide character is
converted. The corresponding argument shall be a
pointer to the initial element of a character array
large enough to accept the sequence. No null
character is added.
If an l length modifier is present, the
corresponding argument shall be a pointer to the
initial element of an array of wchar_t large enough
to accept the sequence. No null wide character is
added.
s Matches a sequence of non-white-space wide
characters.
If no l length modifier is present, characters from
the input field are converted as if by repeated
calls to the wcrtomb function, with the conversion
state described by an mbstate_t object initialized
to zero before the first wide character is
converted. The corresponding argument shall be a
pointer to the initial element of a character array
7.24.2.2 Library 7.24.2.2
412 Committee Draft -- August 3, 1998 WG14/N843
large enough to accept the sequence and a
terminating null character, which will be added
automatically.
If an l length modifier is present, the
corresponding argument shall be a pointer to the
initial element of an array of wchar_t large enough
to accept the sequence and the terminating null wide
character, which will be added automatically.
[ Matches a nonempty sequence of wide characters from
a set of expected characters (the scanset).
If no l length modifier is present, characters from
the input field are converted as if by repeated
calls to the wcrtomb function, with the conversion
state described by an mbstate_t object initialized
to zero before the first wide character is
converted. The corresponding argument shall be a
pointer to the initial element of a character array
large enough to accept the sequence and a
terminating null character, which will be added
automatically.
If an l length modifier is present, the
corresponding argument shall be a pointer to the
initial element of an array of wchar_t large enough
to accept the sequence and the terminating null wide
character, which will be added automatically.
The conversion specifier includes all subsequent
wide characters in the format string, up to and
including the matching right bracket (]). The wide
characters between the brackets (the scanlist)
compose the scanset, unless the wide character after
the left bracket is a circumflex (^), in which case
the scanset contains all wide characters that do not
appear in the scanlist between the circumflex and
the right bracket. If the conversion specifier
begins with [] or [^], the right bracket wide
character is in the scanlist and the next following |
right bracket wide character is the matching right |
bracket that ends the specification; otherwise the |
first following right bracket wide character is the
one that ends the specification. If a - wide
character is in the scanlist and is not the first,
nor the second where the first wide character is a
^, nor the last character, the behavior is
implementation-defined.
p Matches an implementation-defined set of sequences,
which should be the same as the set of sequences
that may be produced by the %p conversion of the
fwprintf function. The corresponding argument shall
7.24.2.2 Library 7.24.2.2
WG14/N843 Committee Draft -- August 3, 1998 413
be a pointer to a pointer to void. The
interpretation of the input item is implementation-
defined. If the input item is a value converted
earlier during the same program execution, the
pointer that results shall compare equal to that
value; otherwise the behavior of the %p conversion
is undefined.
n No input is consumed. The corresponding argument
shall be a pointer to signed integer into which is
to be written the number of wide characters read
from the input stream so far by this call to the
fwscanf function. Execution of a %n directive does
not increment the assignment count returned at the
completion of execution of the fwscanf function. No
argument is converted, but one is consumed. If the |
conversion specification includes an assignment- |
suppressing wide character or a field width, the
behavior is undefined.
% Matches a single % wide character; no conversion or |
assignment occurs. The complete conversion
specification shall be %%.
[#13] If a conversion specification is invalid, the behavior
is undefined.265)
[#14] The conversion specifiers A, E, F, G, and X are also
valid and behave the same as, respectively, a, e, f, g, and
x.
[#15] If end-of-file is encountered during input, conversion
is terminated. If end-of-file occurs before any wide
characters matching the current directive have been read
(other than leading white space, where permitted), execution
of the current directive terminates with an input failure;
otherwise, unless execution of the current directive is
terminated with a matching failure, execution of the
following directive (other than %n, if any) is terminated
with an input failure.
[#16] Trailing white space (including new-line wide
characters) is left unread unless matched by a directive.
The success of literal matches and suppressed assignments is
not directly determinable other than via the %n directive.
[#17] If conversion terminates on a conflicting input wide
character, the offending input wide character is left unread
in the input stream.266)
____________________
265See ``future library directions'' (7.26.12).
7.24.2.2 Library 7.24.2.2
414 Committee Draft -- August 3, 1998 WG14/N843
Returns
[#18] The fwscanf function returns the value of the macro
EOF if an input failure occurs before any conversion.
Otherwise, the function returns the number of input items
assigned, which can be fewer than provided for, or even
zero, in the event of an early matching failure.
[#19] EXAMPLE 1 The call:
#include <stdio.h>
#include <wchar.h>
/* ... */
int n, i; float x; wchar_t name[50];
n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
with the input line:
25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the
value 5.432, and to name the sequence thompson\0.
[#20] EXAMPLE 2 The call:
#include <stdio.h>
#include <wchar.h>
/* ... */
int i; float x; double y;
fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
with input:
56789 0123 56a72
will assign to i the value 56 and to x the value 789.0, will
skip past 0123, and will assign to y the value 56.0. The
next wide character read from the input stream will be a.
Forward references: the wcstod, wcstof, and wcstold
functions (7.24.4.1.1), the wcstol, wcstoll, wcstoul, and |
wcstoull functions (7.24.4.1.2), the wcrtomb function
(7.24.6.3.3).
____________________
266fwscanf pushes back at most one input wide character onto
the input stream. Therefore, some sequences that are
acceptable to wcstod, wcstol, etc., are unacceptable to
fwscanf.
7.24.2.2 Library 7.24.2.2
WG14/N843 Committee Draft -- August 3, 1998 415
7.24.2.3 The swprintf function
Synopsis
[#1]
#include <wchar.h>
int swprintf(wchar_t * restrict s,
size_t n,
const wchar_t * restrict format, ...);
Description
[#2] The swprintf function is equivalent to fwprintf, except
that the argument s specifies an array of wide characters
into which the generated output is to be written, rather
than written to a stream. No more than n wide characters
are written, including a terminating null wide character,
which is always added (unless n is zero).
Returns
[#3] The swprintf function returns the number of wide
characters written in the array, not counting the
terminating null wide character, or a negative value if an |
encoding error occurred or if n or more wide characters were
requested to be written.
7.24.2.4 The swscanf function
Synopsis
[#1]
#include <wchar.h>
int swscanf(const wchar_t * restrict s,
const wchar_t * restrict format, ...);
Description
[#2] The swscanf function is equivalent to fwscanf, except
that the argument s specifies a wide string from which the
input is to be obtained, rather than from a stream.
Reaching the end of the wide string is equivalent to
encountering end-of-file for the fwscanf function.
Returns
[#3] The swscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the swscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.24.2.2 Library 7.24.2.4
416 Committee Draft -- August 3, 1998 WG14/N843
7.24.2.5 The vfwprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
int vfwprintf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vfwprintf function is equivalent to fwprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfwprintf function does not
invoke the va_end macro.267)
Returns
[#3] The vfwprintf function returns the number of wide |
characters transmitted, or a negative value if an output or |
encoding error occurred.
[#4] EXAMPLE The following shows the use of the vfwprintf
function in a general error-reporting routine.
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
void error(char *function_name, wchar_t *format, ...)
{
va_list args;
va_start(args, format);
// print out name of function causing error
fwprintf(stderr, L"ERROR in %s: ", function_name);
// print out remainder of message
vfwprintf(stderr, format, args);
va_end(args);
}
____________________
267As the functions vfwprintf, vswprintf, vfwscanf,
vwprintf, vwscanf, and vswscanf invoke the va_arg macro,
the value of arg after the return is indeterminate.
7.24.2.4 Library 7.24.2.5
WG14/N843 Committee Draft -- August 3, 1998 417
7.24.2.6 The vfwscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
int vfwscanf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vfwscanf function is equivalent to fwscanf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vfwscanf function does not
invoke the va_end macro.267)
Returns
[#3] The vfwscanf function returns the value of the macro
EOF if an input failure occurs before any conversion.
Otherwise, the vfwscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.24.2.7 The vswprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <wchar.h>
int vswprintf(wchar_t * restrict s,
size_t n,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vswprintf function is equivalent to swprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vswprintf function does not
invoke the va_end macro.267)
Returns
[#3] The vswprintf function returns the number of wide
characters written in the array, not counting the
7.24.2.5 Library 7.24.2.7
418 Committee Draft -- August 3, 1998 WG14/N843
terminating null wide character, or a negative value if an |
encoding error occurred or if n or more wide characters were
requested to be generated.
7.24.2.8 The vswscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <wchar.h>
int vswscanf(const wchar_t * restrict s,
const wchar_t * restrict format,
va_list arg);
Description
[#2] The vswscanf function is equivalent to swscanf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vswscanf function does not
invoke the va_end macro.267)
Returns
[#3] The vswscanf function returns the value of the macro
EOF if an input failure occurs before any conversion.
Otherwise, the vswscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.24.2.9 The vwprintf function
Synopsis
[#1]
#include <stdarg.h>
#include <wchar.h>
int vwprintf(const wchar_t * restrict format,
va_list arg);
Description
[#2] The vwprintf function is equivalent to wprintf, with
the variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vwprintf function does not
invoke the va_end macro.267)
Returns
[#3] The vwprintf function returns the number of wide |
7.24.2.7 Library 7.24.2.9
WG14/N843 Committee Draft -- August 3, 1998 419
characters transmitted, or a negative value if an output or |
encoding error occurred.
7.24.2.10 The vwscanf function
Synopsis
[#1]
#include <stdarg.h>
#include <wchar.h>
int vwscanf(const wchar_t * restrict format,
va_list arg);
Description
[#2] The vwscanf function is equivalent to wscanf, with the
variable argument list replaced by arg, which shall have
been initialized by the va_start macro (and possibly
subsequent va_arg calls). The vwscanf function does not
invoke the va_end macro.267)
Returns
[#3] The vwscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the vwscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.24.2.11 The wprintf function
Synopsis
[#1]
#include <wchar.h>
int wprintf(const wchar_t * restrict format, ...);
Description
[#2] The wprintf function is equivalent to fwprintf with the
argument stdout interposed before the arguments to wprintf.
Returns
[#3] The wprintf function returns the number of wide |
characters transmitted, or a negative value if an output or |
encoding error occurred.
7.24.2.9 Library 7.24.2.11
420 Committee Draft -- August 3, 1998 WG14/N843
7.24.2.12 The wscanf function
Synopsis
[#1]
#include <wchar.h>
int wscanf(const wchar_t * restrict format, ...);
Description
[#2] The wscanf function is equivalent to fwscanf with the
argument stdin interposed before the arguments to wscanf.
Returns
[#3] The wscanf function returns the value of the macro EOF
if an input failure occurs before any conversion.
Otherwise, the wscanf function returns the number of input
items assigned, which can be fewer than provided for, or
even zero, in the event of an early matching failure.
7.24.3 Wide-character input/output functions
7.24.3.1 The fgetwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t fgetwc(FILE *stream);
Description
[#2] If a next wide character is present from the input
stream pointed to by stream, the fgetwc function obtains
that wide character and advances the associated file
position indicator for the stream (if defined).
Returns
[#3] The fgetwc function returns the next wide character
from the input stream pointed to by stream. If the stream
is at end-of-file, the end-of-file indicator for the stream
is set and fgetwc returns WEOF. If a read error occurs, the
error indicator for the stream is set and fgetwc returns
WEOF. If an encoding error occurs (including too few
bytes), the value of the macro EILSEQ is stored in errno and
fgetwc returns WEOF.268)
7.24.2.11 Library 7.24.3.1
WG14/N843 Committee Draft -- August 3, 1998 421
7.24.3.2 The fgetws function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wchar_t *fgetws(wchar_t * restrict s,
int n, FILE * restrict stream);
Description
[#2] The fgetws function reads at most one less than the
number of wide characters specified by n from the stream
pointed to by stream into the array pointed to by s. No
additional wide characters are read after a new-line wide
character (which is retained) or after end-of-file. A null
wide character is written immediately after the last wide
character read into the array.
Returns
[#3] The fgetws function returns s if successful. If end-
of-file is encountered and no characters have been read into
the array, the contents of the array remain unchanged and a
null pointer is returned. If a read or encoding error
occurs during the operation, the array contents are
indeterminate and a null pointer is returned.
7.24.3.3 The fputwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t fputwc(wchar_t c, FILE *stream);
Description
[#2] The fputwc function writes the wide character specified
by c to the output stream pointed to by stream, at the
position indicated by the associated file position indicator
for the stream (if defined), and advances the indicator
appropriately. If the file cannot support positioning
requests, or if the stream was opened with append mode, the
____________________
268An end-of-file and a read error can be distinguished by
use of the feof and ferror functions. Also, errno will
be set to EILSEQ by input/output functions only if an
encoding error occurs.
7.24.3.1 Library 7.24.3.3
422 Committee Draft -- August 3, 1998 WG14/N843
character is appended to the output stream.
Returns
[#3] The fputwc function returns the wide character written.
If a write error occurs, the error indicator for the stream
is set and fputwc returns WEOF. If an encoding error
occurs, the value of the macro EILSEQ is stored in errno and
fputwc returns WEOF.
7.24.3.4 The fputws function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fputws(const wchar_t * restrict s,
FILE * restrict stream);
Description
[#2] The fputws function writes the wide string pointed to
by s to the stream pointed to by stream. The terminating
null wide character is not written.
Returns
[#3] The fputws function returns EOF if a write or encoding
error occurs; otherwise, it returns a nonnegative value.
7.24.3.5 The fwide function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int fwide(FILE *stream, int mode);
Description
[#2] The fwide function determines the orientation of the
stream pointed to by stream. If mode is greater than zero,
the function first attempts to make the stream wide
oriented. If mode is less than zero, the function first
attempts to make the stream byte oriented.269) Otherwise,
mode is zero and the function does not alter the orientation
____________________
269If the orientation of the stream has already been
determined, fwide does not change it.
7.24.3.3 Library 7.24.3.5
WG14/N843 Committee Draft -- August 3, 1998 423
of the stream.
Returns
[#3] The fwide function returns a value greater than zero
if, after the call, the stream has wide orientation, a value
less than zero if the stream has byte orientation, or zero
if the stream has no orientation.
7.24.3.6 The getwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t getwc(FILE *stream);
Description
[#2] The getwc function is equivalent to fgetwc, except that
if it is implemented as a macro, it may evaluate stream more
than once, so the argument should never be an expression
with side effects.
Returns
[#3] The getwc function returns the next wide character from
the input stream pointed to by stream, or WEOF.
7.24.3.7 The getwchar function
Synopsis
[#1]
#include <wchar.h>
wint_t getwchar(void);
Description
[#2] The getwchar function is equivalent to getwc with the
argument stdin.
Returns
[#3] The getwchar function returns the next wide character
from the input stream pointed to by stdin, or WEOF.
7.24.3.5 Library 7.24.3.7
424 Committee Draft -- August 3, 1998 WG14/N843
7.24.3.8 The putwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t putwc(wchar_t c, FILE *stream);
Description
[#2] The putwc function is equivalent to fputwc, except that
if it is implemented as a macro, it may evaluate stream more |
than once, so that argument should never be an expression |
with side effects.
Returns
[#3] The putwc function returns the wide character written,
or WEOF.
7.24.3.9 The putwchar function
Synopsis
[#1]
#include <wchar.h>
wint_t putwchar(wchar_t c);
Description
[#2] The putwchar function is equivalent to putwc with the
second argument stdout.
Returns
[#3] The putwchar function returns the character written, or
WEOF.
7.24.3.7 Library 7.24.3.9
WG14/N843 Committee Draft -- August 3, 1998 425
7.24.3.10 The ungetwc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t ungetwc(wint_t c, FILE *stream);
Description
[#2] The ungetwc function pushes the wide character
specified by c back onto the input stream pointed to by
stream. Pushed-back wide characters will be returned by |
subsequent reads on that stream in the reverse order of
their pushing. A successful intervening call (with the
stream pointed to by stream) to a file positioning function
(fseek, fsetpos, or rewind) discards any pushed-back wide
characters for the stream. The external storage
corresponding to the stream is unchanged.
[#3] One wide character of pushback is guaranteed, even if
the call to the ungetwc function follows just after a call
to a formatted wide character input function fwscanf,
vfwscanf, vwscanf, or wscanf. If the ungetwc function is
called too many times on the same stream without an
intervening read or file positioning operation on that
stream, the operation may fail.
[#4] If the value of c equals that of the macro WEOF, the
operation fails and the input stream is unchanged.
[#5] A successful call to the ungetwc function clears the
end-of-file indicator for the stream. The value of the file
position indicator for the stream after reading or
discarding all pushed-back wide characters is the same as it
was before the wide characters were pushed back. For a text
or binary stream, the value of its file position indicator
after a successful call to the ungetwc function is
unspecified until all pushed-back wide characters are read
or discarded.
Returns
[#6] The ungetwc function returns the wide character pushed
back, or WEOF if the operation fails.
7.24.3.9 Library 7.24.3.10
426 Committee Draft -- August 3, 1998 WG14/N843
7.24.4 General wide-string utilities
[#1] The header <wchar.h> declares a number of functions
useful for wide-string manipulation. Various methods are
used for determining the lengths of the arrays, but in all
cases a wchar_t * argument points to the initial (lowest
addressed) element of the array. If an array is accessed
beyond the end of an object, the behavior is undefined.
7.24.4.1 Wide-string numeric conversion functions
7.24.4.1.1 The wcstod, wcstof, and wcstold functions
Synopsis
[#1]
#include <wchar.h>
double wcstod(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
float wcstof(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
long double wcstold(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
Description
[#2] The wcstod, wcstof, and wcstold functions convert the
initial portion of the wide string pointed to by nptr to
double, float, and long double representation, respectively.
First, they decompose the input string into three parts: an
initial, possibly empty, sequence of white-space wide
characters (as specified by the iswspace function), a |
subject sequence resembling a floating-point constant or |
representing an infinity or NaN; and a final wide string of |
one or more unrecognized wide characters, including the
terminating null wide character of the input wide string.
Then, they attempt to convert the subject sequence to a
floating-point number, and return the result.
[#3] The expected form of the subject sequence is an
optional plus or minus sign, then one of the following:
-- a nonempty sequence of decimal digits optionally
containing a decimal-point wide character, then an
optional exponent part as defined for the corresponding
single-byte characters in 6.4.4.2;
-- a 0x or 0X, then a nonempty sequence of hexadecimal
digits optionally containing a decimal-point wide
character, then an optional binary-exponent part as |
defined in 6.4.4.2, where either the decimal-point wide |
character or the binary-exponent part is present;
7.24.4 Library 7.24.4.1.1
WG14/N843 Committee Draft -- August 3, 1998 427
-- one of INF or INFINITY, or any other wide string
equivalent except for case
-- one of NAN or NAN(n-wchar-sequence-opt), or any other
wide string equivalent except for case in the NAN part,
where: |
n-wchar-sequence:
digit
nondigit
n-wchar-sequence digit
n-wchar-sequence nondigit
The subject sequence is defined as the longest initial *
subsequence of the input wide string, starting with the
first non-white-space wide character, that is of the
expected form. The subject sequence contains no wide
characters if the input wide string is not of the expected
form.
[#4] If the subject sequence has the expected form for a
floating-point number, the sequence of wide characters
starting with the first digit or the decimal-point wide
character (whichever occurs first) is interpreted as a
floating constant according to the rules of 6.4.4.2, except
that the decimal-point wide character is used in place of a
period, and that if neither an exponent part, a binary-
exponent part, nor a decimal-point wide character appears, a
decimal point is assumed to follow the last digit in the
wide string. A wide character sequence INF or INFINITY is
interpreted as an infinity, if representable in the return
type, else like a floating constant that is too large for
the range of the return type. A wide character sequence NAN
or NAN(n-wchar-sequence-opt) is interpreted as a quiet NaN,
if supported in the return type, else like a subject
sequence part that does not have the expected form; the
meaning of the n-wchar sequences is
implementation-defined.270) If the subject sequence begins
with a minus sign, the value resulting from the conversion
is negated.271) A pointer to the final wide string is
stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
[#5] If the subject sequence has the hexadecimal form and *
FLT_RADIX is a power of 2, then the value resulting from the
conversion is correctly rounded.
____________________
270An implementation may use the n-wchar sequence to
determine extra information to be represented in the
NaN's significand.
271The functions honor the sign of zero if floating-point |
arithmetic supports signed zeros.
7.24.4.1.1 Library 7.24.4.1.1
428 Committee Draft -- August 3, 1998 WG14/N843
[#6] In other than the "C" locale, additional locale- |
specific subject sequence forms may be accepted. |
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
Recommended practice
[#8] If the subject sequence has the hexadecimal form and
FLT_RADIX is not a power of 2, then the result should be one
of the two numbers in the appropriate internal format that
are adjacent to the hexadecimal floating source value, with
the extra stipulation that the error should have a correct
sign for the current rounding direction.
[#9] If the subject sequence has the decimal form and at
most DECIMAL_DIG (defined in <float.h>) significant digits, |
then the value resulting from the conversion should be
correctly rounded. If the subject sequence D has the
decimal form and more than DECIMAL_DIG significant digits,
consider the two bounding, adjacent decimal strings L and U,
both having DECIMAL_DIG significant digits, such that the
values of L, D, and U satisfy L <= D <= U. The result of
conversion should be one of the (equal or adjacent) values
that would be obtained by correctly rounding L and U
according to the current rounding direction, with the extra
stipulation that the error with respect to D should have a
correct sign for the current rounding direction.272)
Returns
[#10] The functions return the converted value, if any. If |
no conversion could be performed, zero is returned. If the
correct value is outside the range of representable values,
plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned
(according to the return type and sign of the value), and
the value of the macro ERANGE is stored in errno. If the
result underflows (7.12.1), the functions return a value |
whose magnitude is no greater than the smallest normalized
positive number in the return type; whether errno acquires
the value ERANGE is implementation-defined. |
7.24.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull |
functions |
____________________
272DECIMAL_DIG, defined in <float.h>, should be sufficiently |
large that L and U will usually round to the same
internal floating value, but if not will round to
adjacent values.
7.24.4.1.1 Library 7.24.4.1.2
WG14/N843 Committee Draft -- August 3, 1998 429
Synopsis
[#1]
#include <wchar.h>
long int wcstol(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr,
int base);
long long int wcstoll( |
const wchar_t * restrict nptr, |
wchar_t ** restrict endptr, |
int base); |
unsigned long int wcstoul( |
const wchar_t * restrict nptr, |
wchar_t ** restrict endptr, |
int base); |
unsigned long long int wcstoull( |
const wchar_t * restrict nptr, |
wchar_t ** restrict endptr, |
int base); |
Description
[#2] The wcstol, wcstoll, wcstoul, and wcstoull functions |
convert the initial portion of the wide string pointed to by
nptr to long int, long long int, unsigned long int, and |
unsigned long long int representation, respectively. First, |
they decompose the input string into three parts: an
initial, possibly empty, sequence of white-space wide
characters (as specified by the iswspace function), a
subject sequence resembling an integer represented in some
radix determined by the value of base, and a final wide
string of one or more unrecognized wide characters,
including the terminating null wide character of the input
wide string. Then, they attempt to convert the subject |
sequence to an integer, and return the result.
[#3] If the value of base is zero, the expected form of the
subject sequence is that of an integer constant as described
for the corresponding single-byte characters in 6.4.4.1,
optionally preceded by a plus or minus sign, but not
including an integer suffix. If the value of base is
between 2 and 36 (inclusive), the expected form of the
subject sequence is a sequence of letters and digits
representing an integer with the radix specified by base,
optionally preceded by a plus or minus sign, but not
including an integer suffix. The letters from a (or A)
through z (or Z) are ascribed the values 10 through 35; only
letters and digits whose ascribed values are less than that
of base are permitted. If the value of base is 16, the wide
characters 0x or 0X may optionally precede the sequence of
letters and digits, following the sign if present.
7.24.4.1.2 Library 7.24.4.1.2
430 Committee Draft -- August 3, 1998 WG14/N843
[#4] The subject sequence is defined as the longest initial
subsequence of the input wide string, starting with the
first non-white-space wide character, that is of the
expected form. The subject sequence contains no wide
characters if the input wide string is empty or consists
entirely of white space, or if the first non-white-space
wide character is other than a sign or a permissible letter
or digit.
[#5] If the subject sequence has the expected form and the
value of base is zero, the sequence of wide characters
starting with the first digit is interpreted as an integer
constant according to the rules of 6.4.4.1. If the subject
sequence has the expected form and the value of base is
between 2 and 36, it is used as the base for conversion,
ascribing to each letter its value as given above. If the
subject sequence begins with a minus sign, the value |
resulting from the conversion is negated (in the return |
type). A pointer to the final wide string is stored in the
object pointed to by endptr, provided that endptr is not a
null pointer.
[#6] In other than the "C" locale, additional locale-
specific subject sequence forms may be accepted.
[#7] If the subject sequence is empty or does not have the
expected form, no conversion is performed; the value of nptr
is stored in the object pointed to by endptr, provided that
endptr is not a null pointer.
Returns
[#8] The wcstol, wcstoll, wcstoul, and wcstoull functions |
return the converted value, if any. If no conversion could
be performed, zero is returned. If the correct value is
outside the range of representable values, LONG_MIN, |
LONG_MAX, LLONG_MIN, LLONG_MAX, ULONG_MAX, or ULLONG_MAX is |
returned (according to the return type sign of the value, if |
any), and the value of the macro ERANGE is stored in errno. *
7.24.4.2 Wide-string copying functions
7.24.4.1.2 Library 7.24.4.2
WG14/N843 Committee Draft -- August 3, 1998 431
7.24.4.2.1 The wcscpy function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcscpy(wchar_t * restrict s1,
const wchar_t * restrict s2);
Description
[#2] The wcscpy function copies the wide string pointed to
by s2 (including the terminating null wide character) into
the array pointed to by s1.
Returns
[#3] The wcscpy function returns the value of s1.
7.24.4.2.2 The wcsncpy function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsncpy(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wcsncpy function copies not more than n wide
characters (those that follow a null wide character are not
copied) from the array pointed to by s2 to the array pointed
to by s1.273)
[#3] If the array pointed to by s2 is a wide string that is
shorter than n wide characters, null wide characters are
appended to the copy in the array pointed to by s1, until n
wide characters in all have been written.
Returns
[#4] The wcsncpy function returns the value of s1.
____________________
273Thus, if there is no null wide character in the first n
wide characters of the array pointed to by s2, the result
will not be null-terminated.
7.24.4.2 Library 7.24.4.2.2
432 Committee Draft -- August 3, 1998 WG14/N843
7.24.4.3 Wide-string concatenation functions
7.24.4.3.1 The wcscat function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcscat(wchar_t * restrict s1,
const wchar_t * restrict s2);
Description
[#2] The wcscat function appends a copy of the wide string
pointed to by s2 (including the terminating null wide
character) to the end of the wide string pointed to by s1.
The initial wide character of s2 overwrites the null wide
character at the end of s1.
Returns
[#3] The wcscat function returns the value of s1.
7.24.4.3.2 The wcsncat function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsncat(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wcsncat function appends not more than n wide
characters (a null wide character and those that follow it
are not appended) from the array pointed to by s2 to the end
of the wide string pointed to by s1. The initial wide
character of s2 overwrites the null wide character at the
end of s1 A terminating null wide character is always
appended to the result.274)
Returns
[#3] The wcsncat function returns the value of s1.
____________________
274Thus, the maximum number of wide characters that can end
up in the array pointed to by s1 is wcslen(s1)+n+1.
7.24.4.3 Library 7.24.4.3.2
WG14/N843 Committee Draft -- August 3, 1998 433
7.24.4.4 Wide-string comparison functions
[#1] Unless explicitly stated otherwise, the functions
described in this subclause order two wide characters the
same way as two integers of the underlying integer type
designated by wchar_t.
7.24.4.4.1 The wcscmp function
Synopsis
[#1]
#include <wchar.h>
int wcscmp(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcscmp function compares the wide string pointed to
by s1 to the wide string pointed to by s2.
Returns
[#3] The wcscmp function returns an integer greater than,
equal to, or less than zero, accordingly as the wide string
pointed to by s1 is greater than, equal to, or less than the
wide string pointed to by s2.
7.24.4.4.2 The wcscoll function
Synopsis
[#1]
#include <wchar.h>
int wcscoll(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcscoll function compares the wide string pointed
to by s1 to the wide string pointed to by s2, both
interpreted as appropriate to the LC_COLLATE category of the
current locale.
Returns
[#3] The wcscoll function returns an integer greater than,
equal to, or less than zero, accordingly as the wide string
pointed to by s1 is greater than, equal to, or less than the
wide string pointed to by s2 when both are interpreted as
appropriate to the current locale.
7.24.4.4 Library 7.24.4.4.2
434 Committee Draft -- August 3, 1998 WG14/N843
7.24.4.4.3 The wcsncmp function
Synopsis
[#1]
#include <wchar.h>
int wcsncmp(const wchar_t *s1, const wchar_t *s2,
size_t n);
Description
[#2] The wcsncmp function compares not more than n wide
characters (those that follow a null wide character are not
compared) from the array pointed to by s1 to the array
pointed to by s2.
Returns
[#3] The wcsncmp function returns an integer greater than,
equal to, or less than zero, accordingly as the possibly
null-terminated array pointed to by s1 is greater than,
equal to, or less than the possibly null-terminated array
pointed to by s2.
7.24.4.4.4 The wcsxfrm function
Synopsis
[#1]
#include <wchar.h>
size_t wcsxfrm(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wcsxfrm function transforms the wide string pointed
to by s2 and places the resulting wide string into the array
pointed to by s1. The transformation is such that if the
wcscmp function is applied to two transformed wide strings,
it returns a value greater than, equal to, or less than
zero, corresponding to the result of the wcscoll function
applied to the same two original wide strings. No more than
n wide characters are placed into the resulting array
pointed to by s1, including the terminating null wide
character. If n is zero, s1 is permitted to be a null
pointer.
Returns
[#3] The wcsxfrm function returns the length of the
transformed wide string (not including the terminating null
7.24.4.4.2 Library 7.24.4.4.4
WG14/N843 Committee Draft -- August 3, 1998 435
wide character). If the value returned is n or greater, the
contents of the array pointed to by s1 are indeterminate.
[#4] EXAMPLE The value of the following expression is the
length of the array needed to hold the transformation of the
wide string pointed to by s:
1 + wcsxfrm(NULL, s, 0)
7.24.4.5 Wide-string search functions
7.24.4.5.1 The wcschr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcschr(const wchar_t *s, wchar_t c);
Description
[#2] The wcschr function locates the first occurrence of c
in the wide string pointed to by s. The terminating null
wide character is considered to be part of the wide string.
Returns
[#3] The wcschr function returns a pointer to the located
wide character, or a null pointer if the wide character does
not occur in the wide string.
7.24.4.5.2 The wcscspn function
Synopsis
[#1]
#include <wchar.h>
size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcscspn function computes the length of the maximum
initial segment of the wide string pointed to by s1 which
consists entirely of wide characters not from the wide
string pointed to by s2.
Returns
[#3] The wcscspn function returns the length of the segment.
7.24.4.4.4 Library 7.24.4.5.2
436 Committee Draft -- August 3, 1998 WG14/N843
7.24.4.5.3 The wcslen function
Synopsis
[#1]
#include <wchar.h>
size_t wcslen(const wchar_t *s);
Description
[#2] The wcslen function computes the length of the wide
string pointed to by s.
Returns
[#3] The wcslen function returns the number of wide
characters that precede the terminating null wide character.
7.24.4.5.4 The wcspbrk function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcspbrk function locates the first occurrence in
the wide string pointed to by s1 of any wide character from
the wide string pointed to by s2.
Returns
[#3] The wcspbrk function returns a pointer to the wide
character in s1, or a null pointer if no wide character from
s2 occurs in s1.
7.24.4.5.5 The wcsrchr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
Description
[#2] The wcsrchr function locates the last occurrence of c
in the wide string pointed to by s. The terminating null
wide character is considered to be part of the wide string.
7.24.4.5.2 Library 7.24.4.5.5
WG14/N843 Committee Draft -- August 3, 1998 437
Returns
[#3] The wcsrchr function returns a pointer to the wide
character, or a null pointer if c does not occur in the wide
string.
7.24.4.5.6 The wcsspn function
Synopsis
[#1]
#include <wchar.h>
size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcsspn function computes the length of the maximum
initial segment of the wide string pointed to by s1 which
consists entirely of wide characters from the wide string
pointed to by s2.
Returns
[#3] The wcsspn function returns the length of the segment.
7.24.4.5.7 The wcsstr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
Description
[#2] The wcsstr function locates the first occurrence in the
wide string pointed to by s1 of the sequence of wide
characters (excluding the terminating null wide character)
in the wide string pointed to by s2.
Returns
[#3] The wcsstr function returns a pointer to the located
wide string, or a null pointer if the wide string is not
found. If s2 points to a wide string with zero length, the
function returns s1.
7.24.4.5.5 Library 7.24.4.5.7
438 Committee Draft -- August 3, 1998 WG14/N843
7.24.4.5.8 The wcstok function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wcstok(wchar_t * restrict s1,
const wchar_t * restrict s2,
wchar_t ** restrict ptr);
Description
[#2] A sequence of calls to the wcstok function breaks the
wide string pointed to by s1 into a sequence of tokens, each
of which is delimited by a wide character from the wide
string pointed to by s2. The third argument points to a
caller-provided wchar_t pointer into which the wcstok
function stores information necessary for it to continue
scanning the same wide string.
[#3] The first call in a sequence has a non-null first |
argument and stores an initial value in the object pointed |
to by ptr. Subsequent calls in the sequence have a null |
first argument and the object pointed to by ptr is required |
to have the value stored by the previous call in the |
sequence, which is then updated. The separator wide string
pointed to by s2 may be different from call to call.
[#4] The first call in the sequence searches the wide string
pointed to by s1 for the first wide character that is not
contained in the current separator wide string pointed to by
s2. If no such wide character is found, then there are no
tokens in the wide string pointed to by s1 and the wcstok
function returns a null pointer. If such a wide character
is found, it is the start of the first token.
[#5] The wcstok function then searches from there for a wide
character that is contained in the current separator wide
string. If no such wide character is found, the current
token extends to the end of the wide string pointed to by
s1, and subsequent searches in the same wide string for a
token return a null pointer. If such a wide character is
found, it is overwritten by a null wide character, which
terminates the current token.
[#6] In all cases, the wcstok function stores sufficient
information in the pointer pointed to by ptr so that
subsequent calls, with a null pointer for s1 and the
unmodified pointer value for ptr, shall start searching just
past the element overwritten by a null wide character (if
any).
7.24.4.5.7 Library 7.24.4.5.8
WG14/N843 Committee Draft -- August 3, 1998 439
Returns
[#7] The wcstok function returns a pointer to the first wide
character of a token, or a null pointer if there is no
token.
[#8] EXAMPLE
#include <wchar.h>
static wchar_t str1[] = L"?a???b,,,#c";
static wchar_t str2[] = L"\t \t"; |
wchar_t *t, *ptr1, *ptr2;
// t points to the token L"a"
t = wcstok(str1, L"?", &ptr1);
// t points to the token L"??b"
t = wcstok(NULL, L",", &ptr1);
// t is a null pointer
t = wcstok(str2, L" \t", &ptr2); |
// t points to the token L"c"
t = wcstok(NULL, L"#,", &ptr1);
// t is a null pointer
t = wcstok(NULL, L"?", &ptr1);
7.24.4.6 Wide-character array functions
[#1] These functions operate on arrays of type wchar_t whose
size is specified by a separate count argument. These
functions are not affected by locale, and all wchar_t values |
are treated identically. The null wide character and
wchar_t values not corresponding to valid multibyte
characters are not treated specially.
[#2] Unless explicitly stated otherwise, the functions
described in this subclause order two wide characters the
same way as two integers of the underlying integer type
designated by wchar_t.
[#3] Where an argument declared as size_t n determines the
length of the array for a function, n can have the value
zero on a call to that function. Unless stated explicitly
otherwise in the description of a particular function in
this subclause, pointer arguments on such a call shall still
have valid values, as described in 7.1.4. On such a call, a
function that locates a wide character finds no occurrence,
a function that compares two wide character sequences
returns zero, and a function that copies wide characters
copies zero wide characters.
7.24.4.5.8 Library 7.24.4.6
440 Committee Draft -- August 3, 1998 WG14/N843
7.24.4.6.1 The wmemchr function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemchr(const wchar_t *s, wchar_t c,
size_t n);
Description
[#2] The wmemchr function locates the first occurrence of c
in the initial n wide characters of the object pointed to by
s.
Returns
[#3] The wmemchr function returns a pointer to the located
wide character, or a null pointer if the wide character does
not occur in the object.
7.24.4.6.2 The wmemcmp function
Synopsis
[#1]
#include <wchar.h>
int wmemcmp(const wchar_t * s1, const wchar_t * s2,
size_t n);
Description
[#2] The wmemcmp function compares the first n wide
characters of the object pointed to by s1 to the first n
wide characters of the object pointed to by s2.
Returns
[#3] The wmemcmp function returns an integer greater than,
equal to, or less than zero, accordingly as the object
pointed to by s1 is greater than, equal to, or less than the
object pointed to by s2.
7.24.4.6 Library 7.24.4.6.2
WG14/N843 Committee Draft -- August 3, 1998 441
7.24.4.6.3 The wmemcpy function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemcpy(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
Description
[#2] The wmemcpy function copies n wide characters from the
object pointed to by s2 to the object pointed to by s1.
Returns
[#3] The wmemcpy function returns the value of s1.
7.24.4.6.4 The wmemmove function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
size_t n);
Description
[#2] The wmemmove function copies n wide characters from the
object pointed to by s2 to the object pointed to by s1.
Copying takes place as if the n wide characters from the
object pointed to by s2 are first copied into a temporary
array of n wide characters that does not overlap the objects
pointed to by s1 or s2, and then the n wide characters from
the temporary array are copied into the object pointed to by
s1.
Returns
[#3] The wmemmove function returns the value of s1.
7.24.4.6.2 Library 7.24.4.6.4
442 Committee Draft -- August 3, 1998 WG14/N843
7.24.4.6.5 The wmemset function
Synopsis
[#1]
#include <wchar.h>
wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
Description
[#2] The wmemset function copies the value of c into each of
the first n wide characters of the object pointed to by s.
Returns
[#3] The wmemset function returns the value of s.
7.24.5 Wide-character time conversion functions
7.24.5.1 The wcsftime function
Synopsis
[#1]
#include <time.h>
#include <wchar.h>
size_t wcsftime(wchar_t * restrict s,
size_t maxsize,
const wchar_t * restrict format,
const struct tm * restrict timeptr);
Description
[#2] The wcsftime function is equivalent to the strftime
function, except that:
-- The argument s points to the initial element of an
array of wide characters into which the generated
output is to be placed.
-- The argument maxsize indicates the limiting number of
wide characters.
-- The argument format is a wide string and the conversion
specifiers are replaced by corresponding sequences of
wide characters.
-- The return value indicates the number of wide
characters.
Returns
7.24.4.6.4 Library 7.24.5.1
WG14/N843 Committee Draft -- August 3, 1998 443
[#3] If the total number of resulting wide characters
including the terminating null wide character is not more
than maxsize, the wcsftime function returns the number of
wide characters placed into the array pointed to by s not
including the terminating null wide character. Otherwise,
zero is returned and the contents of the array are
indeterminate.
7.24.5.2 The wcsfxtime function
Synopsis
[#1]
#include <time.h>
#include <wchar.h>
size_t wcsfxtime(wchar_t * restrict s,
size_t maxsize,
const wchar_t * restrict format,
const struct tmx * restrict timeptr);
Description
[#2] The wcsfxtime function is equivalent to the wcsftime
function, except that the timeptr parameter has a different
type, and the %z and %Z conversion specifiers depend on both
the tm_zone and tm_isdst members.
7.24.6 Extended multibyte and wide-character conversion
utilities
[#1] The header <wchar.h> declares an extended set of
functions useful for conversion between multibyte characters
and wide characters.
[#2] Most of the following functions -- those that are
listed as ``restartable'', 7.24.6.3 and 7.24.6.4 -- take as
a last argument a pointer to an object of type mbstate_t
that is used to describe the current conversion state from a
particular multibyte character sequence to a wide-character
sequence (or the reverse) under the rules of a particular
setting for the LC_CTYPE category of the current locale.
[#3] The initial conversion state corresponds, for a
conversion in either direction, to the beginning of a new
multibyte character in the initial shift state. A zero-
valued mbstate_t object is (at least) one way to describe an
initial conversion state. A zero-valued mbstate_t object
can be used to initiate conversion involving any multibyte
character sequence, in any LC_CTYPE category setting. If an
mbstate_t object has been altered by any of the functions
described in this subclause, and is then used with a
different multibyte character sequence, or in the other
conversion direction, or with a different LC_CTYPE category
7.24.5.1 Library 7.24.6
444 Committee Draft -- August 3, 1998 WG14/N843
setting than on earlier function calls, the behavior is
undefined.275)
[#4] On entry, each function takes the described conversion
state (either internal or pointed to by an argument) as |
current. The conversion state described by the pointed-to
object is altered as needed to track the shift state, and
the position within a multibyte character, for the
associated multibyte character sequence.
7.24.6.1 Single-byte wide-character conversion functions
7.24.6.1.1 The btowc function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
wint_t btowc(int c);
Description
[#2] The btowc function determines whether c constitutes a
valid (one-byte) multibyte character in the initial shift
state.
Returns
[#3] The btowc returns WEOF if c has the value EOF or if
(unsigned char)c does not constitute a valid (one-byte)
multibyte character in the initial shift state. Otherwise,
it returns the wide-character representation of that
character.
____________________
275Thus a particular mbstate_t object can be used, for
example, with both the mbrtowc and mbsrtowcs functions as
long as they are used to step sequentially through the
same multibyte character string.
7.24.6 Library 7.24.6.1.1
WG14/N843 Committee Draft -- August 3, 1998 445
7.24.6.1.2 The wctob function
Synopsis
[#1]
#include <stdio.h>
#include <wchar.h>
int wctob(wint_t c);
Description
[#2] The wctob function determines whether c corresponds to
a member of the extended character set whose multibyte
character representation is a single byte when in the
initial shift state.
Returns
[#3] The wctob returns EOF if c does not correspond to a
multibyte character with length one in the initial shift
state. Otherwise, it returns the single-byte representation |
of that character as an unsigned char converted to an int.
7.24.6.2 The mbsinit function
Synopsis
[#1]
#include <wchar.h>
int mbsinit(const mbstate_t *ps);
Description
[#2] If ps is not a null pointer, the mbsinit function
determines whether the pointed-to mbstate_t object describes
an initial conversion state.
Returns
[#3] The mbsinit function returns nonzero if ps is a null
pointer or if the pointed-to object describes an initial
conversion state; otherwise, it returns zero.
7.24.6.3 Restartable multibyte/wide-character conversion
functions
[#1] These functions differ from the corresponding multibyte
character functions of 7.20.7 (mblen, mbtowc, and wctomb) in
that they have an extra parameter, ps, of type pointer to
mbstate_t that points to an object that can completely
describe the current conversion state of the associated
multibyte character sequence. If ps is a null pointer, each
7.24.6.1.1 Library 7.24.6.3
446 Committee Draft -- August 3, 1998 WG14/N843
function uses its own internal mbstate_t object instead,
which is initialized at program startup to the initial
conversion state. The implementation behaves as if no
library function calls these functions with a null pointer
for ps.
[#2] Also unlike their corresponding functions, the return
value does not represent whether the encoding is state-
dependent.
7.24.6.3.1 The mbrlen function
Synopsis
[#1]
#include <wchar.h>
size_t mbrlen(const char * restrict s,
size_t n,
mbstate_t * restrict ps);
Description
[#2] The mbrlen function is equivalent to the call:
mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
where internal is the mbstate_t object for the mbrlen
function, except that the expression designated by ps is
evaluated only once.
Returns
[#3] The mbrlen function returns a value between zero and n, |
inclusive, (size_t)-2, or (size_t)-1.
Forward references: the mbrtowc function (7.24.6.3.2).
7.24.6.3.2 The mbrtowc function
Synopsis
[#1]
#include <wchar.h>
size_t mbrtowc(wchar_t * restrict pwc,
const char * restrict s,
size_t n,
mbstate_t * restrict ps);
Description
[#2] If s is a null pointer, the mbrtowc function is
equivalent to the call:
7.24.6.3 Library 7.24.6.3.2
WG14/N843 Committee Draft -- August 3, 1998 447
mbrtowc(NULL, "", 1, ps)
In this case, the values of the parameters pwc and n are
ignored.
[#3] If s is not a null pointer, the mbrtowc function
inspects at most n bytes beginning with the byte pointed to
by s to determine the number of bytes needed to complete the
next multibyte character (including any shift sequences).
If the function determines that the next multibyte character
is completed, it determines the value of the corresponding
wide character and then, if pwc is not a null pointer,
stores that value in the object pointed to by pwc. If the
corresponding wide character is the null wide character, the
resulting state described is the initial conversion state.
Returns
[#4] The mbrtowc function returns the first of the following
that applies (given the current conversion state):
0 if the next n or fewer bytes complete the
multibyte character that corresponds to the
null wide character (which is the value
stored).
positive if the next n or fewer bytes complete a valid
multibyte character (which is the value |
stored); the value returned is the number of
bytes that complete the multibyte character.
(size_t)-2 if the next n bytes contribute to an incomplete
(but potentially valid) multibyte character,
and all n bytes have been processed (no value
is stored).276)
(size_t)-1 if an encoding error occurs, in which case the
next n or fewer bytes do not contribute to a
complete and valid multibyte character (no
value is stored); the value of the macro EILSEQ
is stored in errno, and the conversion state is
undefined.
____________________
276When n has at least the value of the MB_CUR_MAX macro,
this case can only occur if s points at a sequence of
redundant shift sequences (for implementations with
state-dependent encodings).
7.24.6.3.2 Library 7.24.6.3.2
448 Committee Draft -- August 3, 1998 WG14/N843
7.24.6.3.3 The wcrtomb function
Synopsis
[#1]
#include <wchar.h>
size_t wcrtomb(char * restrict s,
wchar_t wc,
mbstate_t * restrict ps);
Description
[#2] If s is a null pointer, the wcrtomb function is
equivalent to the call
wcrtomb(buf, L'\0', ps)
where buf is an internal buffer.
[#3] If s is not a null pointer, the wcrtomb function
determines the number of bytes needed to represent the
multibyte character that corresponds to the wide character
given by wc (including any shift sequences), and stores the
resulting bytes in the array whose first element is pointed
to by s. At most MB_CUR_MAX bytes are stored. If wc is a
null wide character, a null byte is stored, preceded by any
shift sequence needed to restore the initial shift state;
the resulting state described is the initial conversion
state.
Returns
[#4] The wcrtomb function returns the number of bytes stored
in the array object (including any shift sequences). When
wc is not a valid wide character, an encoding error occurs:
the function stores the value of the macro EILSEQ in errno
and returns (size_t)-1; the conversion state is undefined.
7.24.6.4 Restartable multibyte/wide-string conversion
functions
[#1] These functions differ from the corresponding multibyte
string functions of 7.20.8 (mbstowcs and wcstombs) in that
they have an extra parameter, ps, of type pointer to
mbstate_t that points to an object that can completely
describe the current conversion state of the associated
multibyte character sequence. If ps is a null pointer, each
function uses its own internal mbstate_t object instead,
which is initialized at program startup to the initial
conversion state. The implementation behaves as if no
library function calls these functions with a null pointer
for ps.
7.24.6.3.2 Library 7.24.6.4
WG14/N843 Committee Draft -- August 3, 1998 449
[#2] Also unlike their corresponding functions, the
conversion source parameter, src, has a pointer-to-pointer
type. When the function is storing the results of
conversions (that is, when dst is not a null pointer), the
pointer object pointed to by this parameter is updated to
reflect the amount of the source processed by that
invocation.
7.24.6.4.1 The mbsrtowcs function
Synopsis
[#1]
#include <wchar.h>
size_t mbsrtowcs(wchar_t * restrict dst,
const char ** restrict src,
size_t len,
mbstate_t * restrict ps);
Description
[#2] The mbsrtowcs function converts a sequence of multibyte
characters, beginning in the conversion state described by
the object pointed to by ps, from the array indirectly
pointed to by src into a sequence of corresponding wide
characters. If dst is not a null pointer, the converted
characters are stored into the array pointed to by dst.
Conversion continues up to and including a terminating null
character, which is also stored. Conversion stops earlier
in two cases: when a sequence of bytes is encountered that
does not form a valid multibyte character, or (if dst is not
a null pointer) when len codes have been stored into the
array pointed to by dst.277) Each conversion takes place as
if by a call to the mbrtowc function.
[#3] If dst is not a null pointer, the pointer object
pointed to by src is assigned either a null pointer (if
conversion stopped due to reaching a terminating null
character) or the address just past the last multibyte
character converted (if any). If conversion stopped due to
reaching a terminating null character and if dst is not a
null pointer, the resulting state described is the initial
conversion state.
Returns
[#4] If the input conversion encounters a sequence of bytes
that do not form a valid multibyte character, an encoding
error occurs: the mbsrtowcs function stores the value of the
____________________
277Thus, the value of len is ignored if dst is a null
pointer.
7.24.6.4 Library 7.24.6.4.1
450 Committee Draft -- August 3, 1998 WG14/N843
macro EILSEQ in errno and returns (size_t)-1; the conversion
state is undefined. Otherwise, it returns the number of
multibyte characters successfully converted, not including
the terminating null (if any).
7.24.6.4.2 The wcsrtombs function
Synopsis
[#1]
#include <wchar.h>
size_t wcsrtombs(char * restrict dst,
const wchar_t ** restrict src,
size_t len,
mbstate_t * restrict ps);
Description
[#2] The wcsrtombs function converts a sequence of wide
characters from the array indirectly pointed to by src into
a sequence of corresponding multibyte characters, beginning
in the conversion state described by the object pointed to
by ps. If dst is not a null pointer, the converted
characters are then stored into the array pointed to by dst.
Conversion continues up to and including a terminating null
wide character, which is also stored. Conversion stops
earlier in two cases: when a code is reached that does not
correspond to a valid multibyte character, or (if dst is not
a null pointer) when the next multibyte character would
exceed the limit of len total bytes to be stored into the
array pointed to by dst. Each conversion takes place as if
by a call to the wcrtomb function.278)
[#3] If dst is not a null pointer, the pointer object
pointed to by src is assigned either a null pointer (if
conversion stopped due to reaching a terminating null wide
character) or the address just past the last wide character
converted (if any). If conversion stopped due to reaching a
terminating null wide character, the resulting state
described is the initial conversion state.
Returns
[#4] If conversion stops because a code is reached that does
not correspond to a valid multibyte character, an encoding
error occurs: the wcsrtombs function stores the value of the
macro EILSEQ in errno and returns (size_t)-1; the conversion
____________________
278If conversion stops because a terminating null wide
character has been reached, the bytes stored include
those necessary to reach the initial shift state
immediately before the null byte.
7.24.6.4.1 Library 7.24.6.4.2
WG14/N843 Committee Draft -- August 3, 1998 451
state is undefined. Otherwise, it returns the number of
bytes in the resulting multibyte character sequence, not
including the terminating null (if any).
7.24.6.4.2 Library 7.24.6.4.2
452 Committee Draft -- August 3, 1998 WG14/N843
7.25 Wide-character classification and mapping utilities
<wctype.h>
7.25.1 Introduction
[#1] The header <wctype.h> declares three data types, one
macro, and many functions.279)
[#2] The types declared are
wint_t
which is an integer type unchanged by default argument
promotions that can hold any value corresponding to members
of the extended character set, as well as at least one value
that does not correspond to any member of the extended
character set (see WEOF below);280)
wctrans_t
which is a scalar type that can hold values which represent
locale-specific character mappings; and
wctype_t
which is a scalar type that can hold values which represent
locale-specific character classifications.
[#3] The macro defined is
WEOF
which expands to a constant expression of type wint_t whose
value does not correspond to any member of the extended
character set.281) It is accepted (and returned) by several
functions in this subclause to indicate end-of-file, that
is, no more input from a stream. It is also used as a wide-
character value that does not correspond to any member of
the extended character set.
[#4] The functions declared are grouped as follows:
-- Functions that provide wide-character classification;
-- Extensible functions that provide wide-character
classification;
____________________
279See ``future library directions'' (7.26.13).
280wchar_t and wint_t can be the same integer type.
281The value of the macro WEOF may differ from that of EOF
and need not be negative.
7.25 Library 7.25.1
WG14/N843 Committee Draft -- August 3, 1998 453
-- Functions that provide wide-character case mapping;
-- Extensible functions that provide wide-character
mapping.
[#5] For all functions described in this subclause that
accept an argument of type wint_t, the value shall be
representable as a wchar_t or shall equal the value of the
macro WEOF. If this argument has any other value, the
behavior is undefined.
[#6] The behavior of these functions is affected by the
LC_CTYPE category of the current locale.
7.25.2 Wide-character classification utilities
[#1] The header <wctype.h> declares several functions useful
for classifying wide characters.
[#2] The term printing wide character refers to a member of
a locale-specific set of wide characters, each of which
occupies at least one printing position on a display device.
The term control wide character refers to a member of a
locale-specific set of wide characters that are not printing
wide characters.
7.25.2.1 Wide-character classification functions
[#1] The functions in this subclause return nonzero (true)
if and only if the value of the argument wc conforms to that
in the description of the function.
[#2] Except for the iswgraph and iswpunct functions with
respect to printing, white-space, wide characters other than
L' ', each of the following functions returns true for each
wide character that corresponds (as if by a call to the
wctob function) to a character (byte) for which the |
corresponding character testing function from 7.4.1 returns
true.282)
Forward references: the wctob function (7.24.6.1.2).
____________________
282For example, if the expression isalpha(wctob(wc))
evaluates to true, then the call iswalpha(wc) also
returns true. But, if the expression isgraph(wctob(wc))
evaluates to true (which cannot occur for wc == L' ' of
course), then either iswgraph(wc) or iswprint(wc) &&
iswspace(wc) is true, but not both.
7.25.1 Library 7.25.2.1
454 Committee Draft -- August 3, 1998 WG14/N843
7.25.2.1.1 The iswalnum function
Synopsis
[#1]
#include <wctype.h>
int iswalnum(wint_t wc);
Description
[#2] The iswalnum function tests for any wide character for
which iswalpha or iswdigit is true.
7.25.2.1.2 The iswalpha function
Synopsis
[#1]
#include <wctype.h>
int iswalpha(wint_t wc);
Description
[#2] The iswalpha function tests for any wide character for
which iswupper or iswlower is true, or any wide character
that is one of a locale-specific set of alphabetic wide
characters for which none of iswcntrl, iswdigit, iswpunct,
or iswspace is true.283)
7.25.2.1.3 The iswcntrl function
Synopsis
[#1]
#include <wctype.h>
int iswcntrl(wint_t wc);
Description
[#2] The iswcntrl function tests for any control wide
character.
____________________
283The functions iswlower and iswupper test true or false
separately for each of these additional wide characters;
all four combinations are possible.
7.25.2.1 Library 7.25.2.1.3
WG14/N843 Committee Draft -- August 3, 1998 455
7.25.2.1.4 The iswdigit function
Synopsis
[#1]
#include <wctype.h>
int iswdigit(wint_t wc);
Description
[#2] The iswdigit function tests for any wide character that
corresponds to a decimal-digit character (as defined in
5.2.1).
7.25.2.1.5 The iswgraph function
Synopsis
[#1]
#include <wctype.h>
int iswgraph(wint_t wc);
Description
[#2] The iswgraph function tests for any wide character for
which iswprint is true and iswspace is false.284)
7.25.2.1.6 The iswlower function
Synopsis
[#1]
#include <wctype.h>
int iswlower(wint_t wc);
Description
[#2] The iswlower function tests for any wide character that
corresponds to a lowercase letter or is one of a locale-
specific set of wide characters for which none of iswcntrl,
iswdigit, iswpunct, or iswspace is true.
____________________
284Note that the behavior of the iswgraph and iswpunct |
functions may differ from their corresponding functions |
in 7.4.1 with respect to printing, white-space, basic
execution characters other than ' '.
7.25.2.1.3 Library 7.25.2.1.6
456 Committee Draft -- August 3, 1998 WG14/N843
7.25.2.1.7 The iswprint function
Synopsis
[#1]
#include <wctype.h>
int iswprint(wint_t wc);
Description
[#2] The iswprint function tests for any printing wide
character.
7.25.2.1.8 The iswpunct function
Synopsis
[#1]
#include <wctype.h>
int iswpunct(wint_t wc);
Description
[#2] The iswpunct function tests for any printing wide
character that is one of a locale-specific set of
punctuation wide characters for which neither iswspace nor
iswalnum is true.284)
7.25.2.1.9 The iswspace function
Synopsis
[#1]
#include <wctype.h>
int iswspace(wint_t wc);
Description
[#2] The iswspace function tests for any wide character that
corresponds to a locale-specific set of white-space wide
characters for which none of iswalnum, iswgraph, or iswpunct
is true.
7.25.2.1.6 Library 7.25.2.1.9
WG14/N843 Committee Draft -- August 3, 1998 457
7.25.2.1.10 The iswupper function
Synopsis
[#1]
#include <wctype.h>
int iswupper(wint_t wc);
Description
[#2] The iswupper function tests for any wide character that
corresponds to an uppercase letter or is one of a locale-
specific set of wide characters for which none of iswcntrl,
iswdigit, iswpunct, or iswspace is true.
7.25.2.1.11 The iswxdigit function
Synopsis
[#1]
#include <wctype.h>
int iswxdigit(wint_t wc);
Description
[#2] The iswxdigit function tests for any wide character
that corresponds to a hexadecimal-digit character (as
defined in 6.4.4.1).
7.25.2.2 Extensible wide-character classification functions
[#1] The functions wctype and iswctype provide extensible
wide-character classification as well as testing equivalent
to that performed by the functions described in the previous
subclause (7.25.2.1).
7.25.2.2.1 The iswctype function
Synopsis
[#1]
#include <wctype.h>
int iswctype(wint_t wc, wctype_t desc);
Description
[#2] The iswctype function determines whether the wide
character wc has the property described by desc. The
current setting of the LC_CTYPE category shall be the same
as during the call to wctype that returned the value desc.
7.25.2.1.9 Library 7.25.2.2.1
458 Committee Draft -- August 3, 1998 WG14/N843
[#3] Each of the following expressions has a truth-value
equivalent to the call to the wide-character classification
function (7.25.2.1) in the comment that follows the
expression:
iswctype(wc, wctype("alnum")) // iswalnum(wc)
iswctype(wc, wctype("alpha")) // iswalpha(wc)
iswctype(wc, wctype("cntrl")) // iswcntrl(wc)
iswctype(wc, wctype("digit")) // iswdigit(wc)
iswctype(wc, wctype("graph")) // iswgraph(wc)
iswctype(wc, wctype("lower")) // iswlower(wc)
iswctype(wc, wctype("print")) // iswprint(wc)
iswctype(wc, wctype("punct")) // iswpunct(wc)
iswctype(wc, wctype("space")) // iswspace(wc)
iswctype(wc, wctype("upper")) // iswupper(wc)
iswctype(wc, wctype("xdigit")) // iswxdigit(wc)
Returns
[#4] The iswctype function returns nonzero (true) if and
only if the value of the wide character wc has the property
described by desc.
7.25.2.2.2 The wctype function
Synopsis
[#1]
#include <wctype.h>
wctype_t wctype(const char *property);
Description
[#2] The wctype function constructs a value with type
wctype_t that describes a class of wide characters
identified by the string argument property.
[#3] The strings listed in the description of the iswctype
function shall be valid in all locales as property arguments
to the wctype function.
Returns
[#4] If property identifies a valid class of wide characters
according to the LC_CTYPE category of the current locale,
the wctype function returns a nonzero value that is valid as
the second argument to the iswctype function; otherwise, it
returns zero.
Forward references: the iswctype function (7.25.2.2.1).
7.25.2.2.1 Library 7.25.2.2.2
WG14/N843 Committee Draft -- August 3, 1998 459
7.25.3 Wide-character mapping utilities
[#1] The header <wctype.h> declares several functions useful
for mapping wide characters.
7.25.3.1 Wide-character case mapping functions
7.25.3.1.1 The towlower function
Synopsis
[#1]
#include <wctype.h>
wint_t towlower(wint_t wc);
Description
[#2] The towlower function converts an uppercase letter to a
corresponding lowercase letter.
Returns
[#3] If the argument is a wide character for which iswupper
is true and there are one or more corresponding wide
characters, as specified by the current locale, for which
iswlower is true, the towlower function returns one of the
corresponding wide characters (always the same one for any
given locale); otherwise, the argument is returned
unchanged.
7.25.3.1.2 The towupper function
Synopsis
[#1]
#include <wctype.h>
wint_t towupper(wint_t wc);
Description
[#2] The towupper function converts a lowercase letter to a
corresponding uppercase letter.
Returns
[#3] If the argument is a wide character for which iswlower
is true and there are one or more corresponding wide
characters, as specified by the current locale, for which
iswupper is true, the towupper function returns one of the
corresponding characters (always the same one for any given
locale); otherwise, the argument is returned unchanged.
7.25.3 Library 7.25.3.1.2
460 Committee Draft -- August 3, 1998 WG14/N843
7.25.3.2 Extensible wide-character case mapping functions
[#1] The functions wctrans and towctrans provide extensible
wide-character mapping as well as case mapping equivalent to
that performed by the functions described in the previous
subclause (7.25.3.1).
7.25.3.2.1 The towctrans function
Synopsis
[#1]
#include <wctype.h>
wint_t towctrans(wint_t wc, wctrans_t desc);
Description
[#2] The towctrans function maps the wide character wc using
the mapping described by desc. The current setting of the
LC_CTYPE category shall be the same as during the call to
wctrans that returned the value desc.
[#3] Each of the following expressions behaves the same as
the call to the wide-character case-mapping function
(7.25.3.1) in the comment that follows the expression:
towctrans(wc, wctrans("tolower")) /* towlower(wc) */
towctrans(wc, wctrans("toupper")) /* towupper(wc) */
Returns
[#4] The towctrans function returns the mapped value of wc
using the mapping described by desc.
7.25.3.2.2 The wctrans function
Synopsis
[#1]
#include <wctype.h>
wctrans_t wctrans(const char *property);
Description
[#2] The wctrans function constructs a value with type
wctrans_t that describes a mapping between wide characters
identified by the string argument property.
[#3] The strings listed in the description of the towctrans
function shall be valid in all locales as property arguments
to the wctrans function.
7.25.3.2 Library 7.25.3.2.2
WG14/N843 Committee Draft -- August 3, 1998 461
Returns
[#4] If property identifies a valid mapping of wide
characters according to the LC_CTYPE category of the current
locale, the wctrans function returns a nonzero value that is
valid as the second argument to the towctrans function;
otherwise, it returns zero.
7.25.3.2.2 Library 7.25.3.2.2
462 Committee Draft -- August 3, 1998 WG14/N843
7.26 Future library directions
[#1] The following names are grouped under individual
headers for convenience. All external names described below
are reserved no matter what headers are included by the
program.
7.26.1 Complex arithmetic <complex.h>
[#1] The function names
cerf cexpm1 clog2
cerfc clog10 cgamma
cexp2 clog1p clgamma
and the same names suffixed with f or l are reserved for the
functions with complex arguments and return values.
7.26.2 Character handling <ctype.h>
[#1] Function names that begin with either is or to, and a
lowercase letter (possibly followed by any combination of
digits, letters, and underscore) may be added to the
declarations in the <ctype.h> header.
7.26.3 Errors <errno.h>
[#1] Macros that begin with E and a digit or E and an
uppercase letter (possibly followed by any combination of
digits, letters, and underscore) may be added to the
declarations in the <errno.h> header.
7.26.4 Format conversion of integer types <inttypes.h>
[#1] Macro names beginning with PRI or SCN followed by any |
lower case letter or X may be added to the macros defined in
the <inttypes.h> header.
7.26.5 Localization <locale.h>
[#1] Macros that begin with LC_ and an uppercase letter
(possibly followed by any combination of digits, letters,
and underscore) may be added to the definitions in the
<locale.h> header.
7.26.6 Signal handling <signal.h>
[#1] Macros that begin with either SIG and an uppercase
letter or SIG_ and an uppercase letter (possibly followed by
any combination of digits, letters, and underscore) may be
added to the definitions in the <signal.h> header. |
7.26 Library 7.26.6
WG14/N843 Committee Draft -- August 3, 1998 463
7.26.7 Boolean type and values <stdbool.h> |
[#1] The ability to undefine and perhaps then redefine the |
macros bool, true, and false is an obsolescent feature.
7.26.8 Integer types <stdint.h>
[#1] Type names beginning with int or uint and ending with
_t may be added to the types defined in the <stdint.h>
header. Macro names beginning with INT or UINT and ending
with _MAX or _MIN, may be added to the macros defined in the
<stdint.h> header.
7.26.9 Input/output <stdio.h>
[#1] Lowercase letters may be added to the conversion |
specifiers and length modifiers in fprintf and fscanf.
Other characters may be used in extensions.
[#2] The use of ungetc on a binary stream where the file
position indicator is zero prior to the call is an
obsolescent feature.
7.26.10 General utilities <stdlib.h>
[#1] Function names that begin with str and a lowercase
letter (possibly followed by any combination of digits,
letters, and underscore) may be added to the declarations in
the <stdlib.h> header.
7.26.11 String handling <string.h>
[#1] Function names that begin with str, mem, or wcs and a
lowercase letter (possibly followed by any combination of
digits, letters, and underscore) may be added to the
declarations in the <string.h> header.
7.26.12 Extended multibyte and wide-character utilities
<wchar.h>
[#1] Function names that begin with wcs and a lowercase
letter (possibly followed by any combination of digits,
letters, and underscore) may be added to the declarations in
the <wchar.h> header.
[#2] Lowercase letters may be added to the conversion |
specifiers and length modifiers in fwprintf and fwscanf.
Other characters may be used in extensions.
7.26.7 Library 7.26.12
464 Committee Draft -- August 3, 1998 WG14/N843
7.26.13 Wide-character classification and mapping utilities
<wctype.h>
[#1] Function names that begin with is or to and a lowercase
letter (possibly followed by any combination of digits,
letters, and underscore) may be added to the declarations in
the <wctype.h> header.
7.26.13 Library 7.26.13
WG14/N843 Committee Draft -- August 3, 1998 465
Annex A
(informative)
Language syntax summary
[#1] NOTE The notation is described in the introduction to
clause 6 (Language).
A.1 Lexical grammar
A.1.1 Lexical elements
(6.4) token:
keyword
identifier
constant
string-literal
punctuator
(6.4) preprocessing-token:
header-name
identifier
pp-number
character-constant
string-literal
punctuator
each universal-character-name that cannot be one of the above|
each non-white-space character that cannot be one of the above
A.1.2 Keywords
(6.4.1) keyword: one of
auto enum restrict unsigned
break extern return void
case float short volatile
char for signed while
const goto sizeof _Bool |
continue if static _Complex
default inline struct _Imaginary
do int switch
double long typedef
else register union
A.1.3 Identifiers
(6.4.2) identifier: |
identifier-nondigit ||
identifier identifier-nondigit ||
identifier digit ||
A Language syntax summary A.1.3
466 Committee Draft -- August 3, 1998 WG14/N843
(6.4.2) identifier-nondigit: |
nondigit
universal-character-name |
other implementation-defined characters |
(6.4.2) nondigit: one of
universal-character-name
_ a b c d e f g h i j k l m
n o p q r s t u v w x y z
A B C D E F G H I J K L M
N O P Q R S T U V W X Y Z
(6.4.2) digit: one of
0 1 2 3 4 5 6 7 8 9
A.1.4 Universal character names
(6.4.3) universal-character-name:
\u hex-quad
\U hex-quad hex-quad
(6.4.3) hex-quad:
hexadecimal-digit hexadecimal-digit
hexadecimal-digit hexadecimal-digit
A.1.5 Constants
(6.4.4) constant:
integer-constant
floating-constant
enumeration-constant
character-constant
(6.4.4.1) integer-constant:
decimal-constant integer-suffix-opt
octal-constant integer-suffix-opt
hexadecimal-constant integer-suffix-opt
(6.4.4.1) decimal-constant:
nonzero-digit
decimal-constant digit
(6.4.4.1) octal-constant:
0
octal-constant octal-digit
(6.4.4.1) hexadecimal-constant:
hexadecimal-prefix hexadecimal-digit
hexadecimal-constant hexadecimal-digit
(6.4.4.1) hexadecimal-prefix: one of
0x 0X
A.1.3 Language syntax summary A.1.5
WG14/N843 Committee Draft -- August 3, 1998 467
(6.4.4.1) nonzero-digit: one of
1 2 3 4 5 6 7 8 9
(6.4.4.1) octal-digit: one of
0 1 2 3 4 5 6 7
(6.4.4.1) hexadecimal-digit: one of
0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
(6.4.4.1) integer-suffix:
unsigned-suffix long-suffix-opt |
unsigned-suffix long-long-suffix |
long-suffix unsigned-suffix-opt |
long-long-suffix unsigned-suffix-opt |
(6.4.4.1) unsigned-suffix: one of
u U
(6.4.4.1) long-suffix: one of
l L
(6.4.4.1) long-long-suffix: one of
ll LL
(6.4.4.2) floating-constant:
decimal-floating-constant
hexadecimal-floating-constant
(6.4.4.2) decimal-floating-constant:
fractional-constant exponent-part-opt floating-suffix-opt
digit-sequence exponent-part floating-suffix-opt
(6.4.4.2) hexadecimal-floating-constant:
hexadecimal-prefix hexadecimal-fractional-constant
binary-exponent-part floating-suffix-opt
hexadecimal-prefix hexadecimal-digit-sequence
binary-exponent-part floating-suffix-opt
(6.4.4.2) fractional-constant:
digit-sequence-opt . digit-sequence
digit-sequence .
(6.4.4.2) exponent-part:
e sign-opt digit-sequence
E sign-opt digit-sequence
(6.4.4.2) sign: one of
+ -
A.1.5 Language syntax summary A.1.5
468 Committee Draft -- August 3, 1998 WG14/N843
(6.4.4.2) digit-sequence:
digit
digit-sequence digit
(6.4.4.2) hexadecimal-fractional-constant:
hexadecimal-digit-sequence-opt .
hexadecimal-digit-sequence
hexadecimal-digit-sequence .
(6.4.4.2) binary-exponent-part:
p sign-opt digit-sequence
P sign-opt digit-sequence
(6.4.4.2) hexadecimal-digit-sequence:
hexadecimal-digit
hexadecimal-digit-sequence hexadecimal-digit
(6.4.4.2) floating-suffix: one of
f l F L
(6.4.4.3) enumeration-constant:
identifier
(6.4.4.4) character-constant:
'c-char-sequence'
L'c-char-sequence'
(6.4.4.4) c-char-sequence:
c-char
c-char-sequence c-char
(6.4.4.4) c-char: *
any member of the source character set except
the single-quote ', backslash \, or new-line character
escape-sequence
(6.4.4.4) escape-sequence:
simple-escape-sequence
octal-escape-sequence
hexadecimal-escape-sequence
universal-character-name |
(6.4.4.4) simple-escape-sequence: one of
\' \" \? \\
\a \b \f \n \r \t \v
(6.4.4.4) octal-escape-sequence:
\ octal-digit
\ octal-digit octal-digit
\ octal-digit octal-digit octal-digit
A.1.5 Language syntax summary A.1.5
WG14/N843 Committee Draft -- August 3, 1998 469
(6.4.4.4) hexadecimal-escape-sequence:
\x hexadecimal-digit
hexadecimal-escape-sequence hexadecimal-digit
A.1.6 String literals
(6.4.5) string-literal:
"s-char-sequence-opt"
L"s-char-sequence-opt"
(6.4.5) s-char-sequence:
s-char
s-char-sequence s-char
(6.4.5) s-char: *
any member of the source character set except
the double-quote ", backslash \, or new-line character
escape-sequence
A.1.7 Punctuators
(6.4.6) punctuator: one of
[ ] ( ) { } . ->
++ -- & * + - ~ !
/ % << >> < > <= >= == != ^ | && ||
? : ; ...
= *= /= %= += -= <<= >>= &= ^= |=
, # ## |
<: :> <% %> %: %:%: |
A.1.8 Header names
(6.4.7) header-name:
<h-char-sequence>
"q-char-sequence"
(6.4.7) h-char-sequence:
h-char
h-char-sequence h-char
(6.4.7) h-char:
any member of the source character set except
the new-line character and >
(6.4.7) q-char-sequence:
q-char
q-char-sequence q-char
(6.4.7) q-char:
any member of the source character set except
the new-line character and "
A.1.5 Language syntax summary A.1.8
470 Committee Draft -- August 3, 1998 WG14/N843
A.1.9 Preprocessing numbers
(6.4.8) pp-number:
digit
. digit
pp-number digit
pp-number identifier-nondigit |
pp-number e sign
pp-number E sign
pp-number p sign
pp-number P sign
pp-number .
A.2 Phrase structure grammar
A.2.1 Expressions
(6.5.1) primary-expr:
identifier
constant
string-literal
( expression )
(6.5.2) postfix-expr:
primary-expr
postfix-expr [ expression ]
postfix-expr ( argument-expression-list-opt )
postfix-expr . identifier
postfix-expr -> identifier
postfix-expr ++
postfix-expr --
( type-name ) { initializer-list }
( type-name ) { initializer-list , }
(6.5.2) argument-expression-list:
assignment-expr
argument-expression-list , assignment-expr
(6.5.3) unary-expr:
postfix-expr
++ unary-expr
-- unary-expr
unary-operator cast-expr
sizeof unary-expr
sizeof ( type-name )
(6.5.3) unary-operator: one of
& * + - ~ !
(6.5.4) cast-expr:
unary-expr
( type-name ) cast-expr
A.1.9 Language syntax summary A.2.1
WG14/N843 Committee Draft -- August 3, 1998 471
(6.5.5) multiplicative-expr:
cast-expr
multiplicative-expr * cast-expr
multiplicative-expr / cast-expr
multiplicative-expr % cast-expr
(6.5.6) additive-expr:
multiplicative-expr
additive-expr + multiplicative-expr
additive-expr - multiplicative-expr
(6.5.7) shift-expr:
additive-expr
shift-expr << additive-expr
shift-expr >> additive-expr
(6.5.8) relational-expr:
shift-expr
relational-expr < shift-expr
relational-expr > shift-expr
relational-expr <= shift-expr
relational-expr >= shift-expr
(6.5.9) equality-expr:
relational-expr
equality-expr == relational-expr
equality-expr != relational-expr
(6.5.10) AND-expr:
equality-expr
AND-expr & equality-expr
(6.5.11) exclusive-OR-expr:
AND-expr
exclusive-OR-expr ^ AND-expr
(6.5.12) inclusive-OR-expr:
exclusive-OR-expr
inclusive-OR-expr | exclusive-OR-expr
(6.5.13) logical-AND-expr:
inclusive-OR-expr
logical-AND-expr && inclusive-OR-expr
(6.5.14) logical-OR-expr:
logical-AND-expr
logical-OR-expr || logical-AND-expr
(6.5.15) conditional-expr:
logical-OR-expr
logical-OR-expr ? expr : conditional-expr
A.2.1 Language syntax summary A.2.1
472 Committee Draft -- August 3, 1998 WG14/N843
(6.5.16) assignment-expr:
conditional-expr
unary-expr assignment-operator assignment-expr
(6.5.16) assignment-operator: one of
= *= /= %= += -= <<= >>= &= ^= |=
(6.5.17) expression:
assignment-expr
expression , assignment-expr
(6.6) constant-expr:
conditional-expr
A.2.2 Declarations
(6.7) declaration:
declaration-specifiers init-declarator-list-opt ;
(6.7) declaration-specifiers:
storage-class-specifier declaration-specifiers-opt
type-specifier declaration-specifiers-opt
type-qualifier declaration-specifiers-opt
function-specifier declaration-specifiers-opt
(6.7) init-declarator-list:
init-declarator
init-declarator-list , init-declarator
(6.7) init-declarator:
declarator
declarator = initializer
(6.7.1) storage-class-specifier:
typedef
extern
static
auto
register
A.2.1 Language syntax summary A.2.2
WG14/N843 Committee Draft -- August 3, 1998 473
(6.7.2) type-specifier:
void
char
short
int
long
float
double
signed
unsigned
_Bool |
_Complex
_Imaginary
struct-or-union-specifier
enum-specifier
typedef-name
(6.7.2.1) struct-or-union-specifier:
struct-or-union identifier-opt { struct-declaration-list }
struct-or-union identifier
(6.7.2.1) struct-or-union:
struct
union
(6.7.2.1) struct-declaration-list:
struct-declaration
struct-declaration-list struct-declaration
(6.7.2.1) struct-declaration:
specifier-qualifier-list struct-declarator-list ;
(6.7.2.1) specifier-qualifier-list:
type-specifier specifier-qualifier-list-opt
type-qualifier specifier-qualifier-list-opt
(6.7.2.1) struct-declarator-list:
struct-declarator
struct-declarator-list , struct-declarator
(6.7.2.1) struct-declarator:
declarator
declarator-opt : constant-expr
(6.7.2.2) enum-specifier:
enum identifier-opt { enumerator-list }
enum identifier-opt { enumerator-list , }
enum identifier
(6.7.2.2) enumerator-list:
enumerator
enumerator-list , enumerator
A.2.2 Language syntax summary A.2.2
474 Committee Draft -- August 3, 1998 WG14/N843
(6.7.2.2) enumerator:
enumeration-constant
enumeration-constant = constant-expression
(6.7.3) type-qualifier:
const
restrict
volatile
(6.7.4) function-specifier:
inline
(6.7.5) declarator:
pointer-opt direct-declarator
(6.7.5) direct-declarator:
identifier
( declarator )
direct-declarator [ assignment-expr-opt ]
direct-declarator [ * ]
direct-declarator ( parameter-type-list )
direct-declarator ( identifier-list-opt )
(6.7.5) pointer:
* type-qualifier-list-opt
* type-qualifier-list-opt pointer
(6.7.5) type-qualifier-list:
type-qualifier
type-qualifier-list type-qualifier
(6.7.5) parameter-type-list:
parameter-list
parameter-list , ...
(6.7.5) parameter-list:
parameter-declaration
parameter-list , parameter-declaration
(6.7.5) parameter-declaration:
declaration-specifiers declarator
declaration-specifiers abstract-declarator-opt
(6.7.5) identifier-list:
identifier
identifier-list , identifier
(6.7.6) type-name:
specifier-qualifier-list abstract-declarator-opt
(6.7.6) abstract-declarator:
pointer
pointer-opt direct-abstract-declarator
A.2.2 Language syntax summary A.2.2
WG14/N843 Committee Draft -- August 3, 1998 475
(6.7.6) direct-abstract-declarator:
( abstract-declarator )
direct-abstract-declarator-opt [ assignment-expr-opt ]
direct-abstract-declarator [ * ]
direct-abstract-declarator-opt ( parameter-type-list-opt )
(6.7.7) typedef-name:
identifier
(6.7.8) initializer:
assignment-expr
{ initializer-list }
{ initializer-list , }
(6.7.8) initializer-list:
designation-opt initializer
initializer-list , designation-opt initializer
(6.7.8) designation:
designator-list =
(6.7.8) designator-list:
designator
designator-list designator
(6.7.8) designator:
[ constant-expression ]
. identifier
A.2.3 Statements
(6.8) statement:
labeled-statement
compound-statement
expression-statement
selection-statement
iteration-statement
jump-statement
(6.8.1) labeled-statement:
identifier : statement
case constant-expr : statement
default : statement
(6.8.2) compound-statement:
{ block-item-list-opt }
(6.8.2) block-item-list:
block-item
block-item-list block-item
A.2.2 Language syntax summary A.2.3
476 Committee Draft -- August 3, 1998 WG14/N843
(6.8.2) block-item:
declaration
statement
(6.8.3) expression-statement:
expression-opt ;
(6.8.4) selection-statement:
if ( expression ) statement
if ( expression ) statement else statement
switch ( expression ) statement
(6.8.5) iteration-statement:
while ( expression ) statement
do statement while ( expression ) ;
for ( expr-opt ; expr-opt ; expr-opt ) statement
for ( declaration ; expr-opt ; expr-opt ) statement
(6.8.6) jump-statement:
goto identifier ;
continue ;
break ;
return expression-opt ;
A.2.4 External definitions
(6.9) translation-unit:
external-declaration
translation-unit external-declaration
(6.9) external-declaration:
function-definition
declaration
(6.9.1) function-definition:
declaration-specifiers declarator declaration-list-opt compound-statement
(6.9.1) declaration-list:
declaration
declaration-list declaration
A.3 Preprocessing directives
(6.10) preprocessing-file:
group-opt
(6.10) group:
group-part
group group-part
A.2.3 Language syntax summary A.3
WG14/N843 Committee Draft -- August 3, 1998 477
(6.10) group-part:
pp-tokens-opt new-line
if-section
control-line
(6.10.1) if-section:
if-group elif-groups-opt else-group-opt endif-line
(6.10.1) if-group:
# if constant-expr new-line group-opt
# ifdef identifier new-line group-opt
# ifndef identifier new-line group-opt
(6.10.1) elif-groups:
elif-group
elif-groups elif-group
(6.10.1) elif-group:
# elif constant-expr new-line group-opt
(6.10.1) else-group:
# else new-line group-opt
(6.10.1) endif-line:
# endif new-line
control-line:
(6.10.2) # include pp-tokens new-line
(6.10.3) # define identifier replacement-list new-line
(6.10.3) # define identifier lparen identifier-list-opt )
replacement-list new-line
(6.10.3) # define identifier lparen ... ) replacement-list new-line
(6.10.3) # define identifier lparen identifier-list , ... )
replacement-list new-line
(6.10.3) # undef identifier new-line
(6.10.4) # line pp-tokens new-line
(6.10.5) # error pp-tokens-opt new-line
(6.10.6) # pragma pp-tokens-opt new-line
(6.10.7) # new-line
(6.10.3) lparen:
the left-parenthesis character without preceding white space
(6.10.3) replacement-list:
pp-tokens-opt
(6.10) pp-tokens:
preprocessing-token
pp-tokens preprocessing-token
(6.10) new-line:
the new-line character
A.3 Language syntax summary A.3
478 Committee Draft -- August 3, 1998 WG14/N843
Annex B
(informative)
Library summary
B.1 Diagnostics <assert.h>
NDEBUG
void assert(int expression);
B.2 Complex <complex.h>
complex imaginary I
_Complex_I _Imaginary_I
#pragma STDC CX_LIMITED_RANGE on-off-switch
double complex cacos(double complex z);
float complex cacosf(float complex z);
long double complex cacosl(long double complex z);
double complex casin(double complex z);
float complex casinf(float complex z);
long double complex casinl(long double complex z);
double complex catan(double complex z);
float complex catanf(float complex z);
long double complex catanl(long double complex z);
double complex ccos(double complex z);
float complex ccosf(float complex z);
long double complex ccosl(long double complex z);
double complex csin(double complex z);
float complex csinf(float complex z);
long double complex csinl(long double complex z);
double complex ctan(double complex z);
float complex ctanf(float complex z);
long double complex ctanl(long double complex z);
double complex cacosh(double complex z);
float complex cacoshf(float complex z);
long double complex cacoshl(long double complex z);
double complex casinh(double complex z);
float complex casinhf(float complex z);
long double complex casinhl(long double complex z);
double complex catanh(double complex z);
float complex catanhf(float complex z);
long double complex catanhl(long double complex z);
double complex ccosh(double complex z);
float complex ccoshf(float complex z);
long double complex ccoshl(long double complex z);
double complex csinh(double complex z);
float complex csinhf(float complex z);
long double complex csinhl(long double complex z);
double complex ctanh(double complex z);
float complex ctanhf(float complex z);
long double complex ctanhl(long double complex z);
double complex cexp(double complex z);
float complex cexpf(float complex z);
long double complex cexpl(long double complex z);
B Library summary B.2
WG14/N843 Committee Draft -- August 3, 1998 479
double complex clog(double complex z);
float complex clogf(float complex z);
long double complex clogl(long double complex z);
double cabs(double complex z);
float cabsf(float complex z);
long double cabsl(long double complex z);
double complex cpow(double complex x, double complex y);
float complex cpowf(float complex x, float complex y);
long double complex cpowl(long double complex x,
long double complex y);
double complex csqrt(double complex z);
float complex csqrtf(float complex z);
long double complex csqrtl(long double complex z);
double carg(double complex z);
float cargf(float complex z);
long double cargl(long double complex z);
double cimag(double complex z);
float cimagf(float complex z);
long double cimagl(long double complex z);
double complex conj(double complex z);
float complex conjf(float complex z);
long double complex conjl(long double complex z);
double complex cproj(double complex z);
float complex cprojf(float complex z);
long double complex cprojl(long double complex z);
double creal(double complex z);
float crealf(float complex z);
long double creall(long double complex z);
B.3 Character handling <ctype.h>
int isalnum(int c);
int isalpha(int c);
int iscntrl(int c);
int isdigit(int c);
int isgraph(int c);
int islower(int c);
int isprint(int c);
int ispunct(int c);
int isspace(int c);
int isupper(int c);
int isxdigit(int c);
int tolower(int c);
int toupper(int c);
B.2 Library summary B.3
480 Committee Draft -- August 3, 1998 WG14/N843
B.4 Errors <errno.h>
EDOM EILSEQ ERANGE errno
B.5 Floating-point environment <fenv.h>
fenv_t FE_OVERFLOW FE_TOWARDZERO
fexcept_t FE_UNDERFLOW FE_UPWARD
FE_DIVBYZERO FE_ALL_EXCEPT FE_DFL_ENV
FE_INEXACT FE_DOWNWARD
FE_INVALID FE_TONEAREST
#pragma STDC FENV_ACCESS on-off-switch
void feclearexcept(int excepts);
void fegetexceptflag(fexcept_t *flagp,
int excepts);
void feraiseexcept(int excepts);
void fesetexceptflag(const fexcept_t *flagp, int excepts);
int fetestexcept(int excepts);
int fegetround(void);
int fesetround(int round);
void fegetenv(fenv_t *envp);
int feholdexcept(fenv_t *envp);
void fesetenv(const fenv_t *envp);
void feupdateenv(const fenv_t *envp);
B.6 Characteristics of floating types <float.h>
FLT_ROUNDS DBL_MIN_EXP FLT_MAX
FLT_EVAL_METHOD LDBL_MIN_EXP DBL_MAX
FLT_RADIX FLT_MIN_10_EXP LDBL_MAX
FLT_MANT_DIG DBL_MIN_10_EXP FLT_EPSILON
DBL_MANT_DIG LDBL_MIN_10_EXP DBL_EPSILON
LDBL_MANT_DIG FLT_MAX_EXP LDBL_EPSILON
DECIMAL_DIG |DBL_MAX_EXP FLT_MIN
FLT_DIG LDBL_MAX_EXP DBL_MIN
DBL_DIG FLT_MAX_10_EXP LDBL_MIN
LDBL_DIG DBL_MAX_10_EXP
FLT_MIN_EXP LDBL_MAX_10_EXP
B.7 Format conversion of integer types <inttypes.h>
PRId8 PRIi16 PRIo32 PRIu64
PRId16 PRIi32 PRIo64 PRIuLEAST8
PRId32 PRIi64 PRIoLEAST8 PRIuLEAST16
PRId64 PRIiLEAST8 PRIoLEAST16 PRIuLEAST32
PRIdLEAST8 PRIiLEAST16 PRIoLEAST32 PRIuLEAST64
PRIdLEAST16 PRIiLEAST32 PRIoLEAST64 PRIuFAST8
PRIdLEAST32 PRIiLEAST64 PRIoFAST8 PRIuFAST16
PRIdLEAST64 PRIiFAST8 PRIoFAST16 PRIuFAST32
PRIdFAST8 PRIiFAST16 PRIoFAST32 PRIuFAST64
PRIdFAST16 PRIiFAST32 PRIoFAST64 PRIuMAX
PRIdFAST32 PRIiFAST64 PRIoMAX PRIuPTR
PRIdFAST64 PRIiMAX PRIoPTR PRIx8
PRIdMAX PRIiPTR PRIu8 PRIx16
PRIdPTR PRIo8 PRIu16 PRIx32
PRIi8 PRIo16 PRIu32 PRIx64
B.4 Library summary B.7
WG14/N843 Committee Draft -- August 3, 1998 481
PRIxLEAST8 SCNd8 SCNiFAST32 SCNuLEAST32
PRIxLEAST16 SCNd16 SCNiFAST64 SCNuLEAST64
PRIxLEAST32 SCNd32 SCNiMAX SCNuFAST8
PRIxLEAST64 SCNd64 SCNiPTR SCNuFAST16
PRIxFAST8 SCNdLEAST8 SCNo8 SCNuFAST32
PRIxFAST16 SCNdLEAST16 SCNo16 SCNuFAST64
PRIxFAST32 SCNdLEAST32 SCNo32 SCNuMAX
PRIxFAST64 SCNdLEAST64 SCNo64 SCNuPTR
PRIxMAX SCNdFAST8 SCNoLEAST8 SCNx8
PRIxPTR SCNdFAST16 SCNoLEAST16 SCNx16
PRIX8 SCNdFAST32 SCNoLEAST32 SCNx32
PRIX16 SCNdFAST64 SCNoLEAST64 SCNx64
PRIX32 SCNdMAX SCNoFAST8 SCNxLEAST8
PRIX64 SCNdPTR SCNoFAST16 SCNxLEAST16
PRIXLEAST8 SCNi8 SCNoFAST32 SCNxLEAST32
PRIXLEAST16 SCNi16 SCNoFAST64 SCNxLEAST64
PRIXLEAST32 SCNi32 SCNoMAX SCNxFAST8
PRIXLEAST64 SCNi64 SCNoPTR SCNxFAST16
PRIXFAST8 SCNiLEAST8 SCNu8 SCNxFAST32
PRIXFAST16 SCNiLEAST16 SCNu16 SCNxFAST64
PRIXFAST32 SCNiLEAST32 SCNu32 SCNxMAX
PRIXFAST64 SCNiLEAST64 SCNu64 SCNxPTR
PRIXMAX SCNiFAST8 SCNuLEAST8
PRIXPTR SCNiFAST16 SCNuLEAST16
intmax_t strtoimax(const char * restrict nptr,
char ** restrict endptr, int base);
uintmax_t strtoumax(const char * restrict nptr,
char ** restrict endptr, int base);
intmax_t wcstoimax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
uintmax_t wcstoumax(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
B.8 Alternative spellings <iso646.h>
and bitor not_eq xor
and_eq compl or xor_eq
bitand not or_eq
B.9 Sizes of integer types <limits.h>
CHAR_BIT CHAR_MAX INT_MIN ULONG_MAX
SCHAR_MIN MB_LEN_MAX INT_MAX LLONG_MIN
SCHAR_MAX SHRT_MIN UINT_MAX LLONG_MAX
UCHAR_MAX SHRT_MAX LONG_MIN ULLONG_MAX
CHAR_MIN USHRT_MAX LONG_MAX
B.7 Library summary B.9
482 Committee Draft -- August 3, 1998 WG14/N843
B.10 Localization <locale.h>
struct lconv LC_ALL LC_CTYPE LC_NUMERIC
NULL LC_COLLATE LC_MONETARY LC_TIME
char *setlocale(int category, const char *locale);
struct lconv *localeconv(void);
B.11 Mathematics <math.h>
float_t INFINITY FP_SUBNORMAL FP_ILOGB0 *
double_t NAN FP_ZERO FP_ILOGBNAN
HUGE_VAL FP_INFINITE FP_FAST_FMA
HUGE_VALF FP_NAN FP_FAST_FMAF
HUGE_VALL FP_NORMAL FP_FAST_FMAL
#pragma STDC FP_CONTRACT on-off-switch
int fpclassify(real-floating x);
int isfinite(real-floating x);
int isinf(real-floating x);
int isnan(real-floating x);
int isnormal(real-floating x);
int signbit(real-floating x);
double acos(double x);
float acosf(float x);
long double acosl(long double x);
double asin(double x);
float asinf(float x);
long double asinl(long double x);
double atan(double x);
float atanf(float x);
long double atanl(long double x);
double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
double cos(double x);
float cosf(float x);
long double cosl(long double x);
double sin(double x);
float sinf(float x);
long double sinl(long double x);
double tan(double x);
float tanf(float x);
long double tanl(long double x);
double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);
double asinh(double x);
float asinhf(float x);
long double asinhl(long double x);
double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);
double cosh(double x);
float coshf(float x);
long double coshl(long double x);
double sinh(double x);
B.10 Library summary B.11
WG14/N843 Committee Draft -- August 3, 1998 483
float sinhf(float x);
long double sinhl(long double x);
double tanh(double x);
float tanhf(float x);
long double tanhl(long double x);
double exp(double x);
float expf(float x);
long double expl(long double x);
double exp2(double x);
float exp2f(float x);
long double exp2l(long double x);
double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);
double frexp(double value, int *exp);
float frexpf(float value, int *exp);
long double frexpl(long double value, int *exp);
int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);
double ldexp(double x, int exp);
float ldexpf(float x, int exp);
long double ldexpl(long double x, int exp);
double log(double x);
float logf(float x);
long double logl(long double x);
double log10(double x);
float log10f(float x);
long double log10l(long double x);
double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);
double log2(double x);
float log2f(float x);
long double log2l(long double x);
double logb(double x);
float logbf(float x);
long double logbl(long double x);
double modf(double value, double *iptr);
float modff(float value, float *iptr);
long double modfl(long double value, long double *iptr);
double scalbn(double x, int n);
float scalbnf(float x, int n);
long double scalbnl(long double x, int n);
double scalbln(double x, long int n);
float scalblnf(float x, long int n);
long double scalblnl(long double x, long int n);
double cbrt(double x);
float cbrtf(float x);
long double cbrtl(long double x);
double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);
double hypot(double x, double y);
B.11 Library summary B.11
484 Committee Draft -- August 3, 1998 WG14/N843
float hypotf(float x, float y);
long double hypotl(long double x, long double y);
double pow(double x, double y);
float powf(float x, float y);
long double powl(long double x, long double y);
double sqrt(double x);
float sqrtf(float x);
long double sqrtl(long double x);
double erf(double x);
float erff(float x);
long double erfl(long double x);
double erfc(double x);
float erfcf(float x);
long double erfcl(long double x);
double lgamma(double x); *
float lgammaf(float x);
long double lgammal(long double x);
double tgamma(double x); |
float tgammaf(float x); |
long double tgammal(long double x); |
double ceil(double x);
float ceilf(float x);
long double ceill(long double x);
double floor(double x);
float floorf(float x);
long double floorl(long double x);
double nearbyint(double x);
float nearbyintf(float x);
long double nearbyintl(long double x);
double rint(double x);
float rintf(float x);
long double rintl(long double x);
long int lrint(double x); *
long int lrintf(float x);
long int lrintl(long double x);
long long int llrint(double x); |
long long int llrintf(float x); |
long long int llrintl(long double x); |
double round(double x);
float roundf(float x);
long double roundl(long double x);
long int lround(double x); *
long int lroundf(float x);
long int lroundl(long double x);
long long int llround(double x); |
long long int llroundf(float x); |
long long int llroundl(long double x); |
double trunc(double x);
float truncf(float x);
long double truncl(long double x);
double fmod(double x, double y);
float fmodf(float x, float y);
long double fmodl(long double x, long double y);
double remainder(double x, double y);
B.11 Library summary B.11
WG14/N843 Committee Draft -- August 3, 1998 485
float remainderf(float x, float y);
long double remainderl(long double x, long double y);
double remquo(double x, double y, int *quo);
float remquof(float x, float y, int *quo);
long double remquol(long double x, long double y,
int *quo);
double copysign(double x, double y);
float copysignf(float x, float y);
long double copysignl(long double x, long double y);
double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);
double nextafter(double x, double y);
float nextafterf(float x, float y);
long double nextafterl(long double x, long double y);
double nextafterx(double x, long double y);
float nextafterxf(float x, long double y);
long double nextafterxl(long double x, long double y);
double fdim(double x, double y);
float fdimf(float x, float y);
long double fdiml(long double x, long double y);
double fmax(double x, double y);
float fmaxf(float x, float y);
long double fmaxl(long double x, long double y);
double fmin(double x, double y);
float fminf(float x, float y);
long double fminl(long double x, long double y);
double fma(double x, double y, double z);
float fmaf(float x, float y, float z);
long double fmal(long double x, long double y,
long double z);
int isgreater(real-floating x, real-floating y);
int isgreaterequal(real-floating x, real-floating y);
int isless(real-floating x, real-floating y);
int islessequal(real-floating x, real-floating y);
int islessgreater(real-floating x, real-floating y);
int isunordered(real-floating x, real-floating y);
B.12 Nonlocal jumps <setjmp.h>
jmp_buf
int setjmp(jmp_buf env);
void longjmp(jmp_buf env, int val);
B.13 Signal handling <signal.h>
sig_atomic_t SIG_IGN SIGILL SIGTERM
SIG_DFL SIGABRT SIGINT
SIG_ERR SIGFPE SIGSEGV
void (*signal(int sig, void (*func)(int)))(int);
int raise(int sig);
B.11 Library summary B.13
486 Committee Draft -- August 3, 1998 WG14/N843
B.14 Variable arguments <stdarg.h>
va_list
type va_arg(va_list ap, type);
void va_copy(va_list dest, va_list src);
void va_end(va_list ap);
void va_start(va_list ap, parmN);
B.15 Boolean type and values <stdbool.h>
bool
true
false
__bool_true_false_are_defined
B.16 Common definitions <stddef.h>
ptrdiff_t size_t wchar_t NULL
offsetof(type, member-designator)
B.17 Integer types <stdint.h>
int8_t INT32_MIN UINT_FAST8_MAX
int16_t INT64_MIN UINT_FAST16_MAX
int32_t INT8_MAX UINT_FAST32_MAX
int64_t INT16_MAX UINT_FAST64_MAX
uint8_t INT32_MAX INTPTR_MIN
uint16_t INT64_MAX INTPTR_MAX
uint32_t UINT8_MAX UINTPTR_MAX
uint64_t UINT16_MAX INTMAX_MIN
int_least8_t UINT32_MAX INTMAX_MAX
int_least16_t UINT64_MAX UINTMAX_MAX
int_least32_t INT_LEAST8_MIN PTRDIFF_MIN
int_least64_t INT_LEAST16_MIN PTRDIFF_MAX
uint_least8_t INT_LEAST32_MIN SIG_ATOMIC_MIN
uint_least16_t INT_LEAST64_MIN SIG_ATOMIC_MAX
uint_least32_t INT_LEAST8_MAX SIZE_MAX
uint_least64_t INT_LEAST16_MAX WCHAR_MIN
int_fast8_t INT_LEAST32_MAX WCHAR_MAX
int_fast16_t INT_LEAST64_MAX WINT_MIN
int_fast32_t UINT_LEAST8_MAX WINT_MAX
int_fast64_t UINT_LEAST16_MAX INT8_C(value)
uint_fast8_t UINT_LEAST32_MAX INT16_C(value)
uint_fast16_t UINT_LEAST64_MAX INT32_C(value)
uint_fast32_t INT_FAST8_MIN INT64_C(value)
uint_fast64_t INT_FAST16_MIN UINT8_C(value)
intptr_t INT_FAST32_MIN UINT16_C(value)
uintptr_t INT_FAST64_MIN UINT32_C(value)
intmax_t INT_FAST8_MAX UINT64_C(value)
uintmax_t INT_FAST16_MAX INTMAX_C(value)
INT8_MIN INT_FAST32_MAX UINTMAX_C(value)
INT16_MIN INT_FAST64_MAX
B.14 Library summary B.17
WG14/N843 Committee Draft -- August 3, 1998 487
B.18 Input/output <stdio.h>
size_t _IOLBF FILENAME_MAX TMP_MAX
FILE _IONBF L_tmpnam stderr
fpos_t BUFSIZ SEEK_CUR stdin
NULL EOF SEEK_END stdout
_IOFBF FOPEN_MAX SEEK_SET
int remove(const char *filename);
int rename(const char *old, const char *new);
FILE *tmpfile(void);
char *tmpnam(char *s);
int fclose(FILE *stream);
int fflush(FILE *stream);
FILE *fopen(const char * restrict filename,
const char * restrict mode);
FILE *freopen(const char * restrict filename,
const char * restrict mode,
FILE * restrict stream);
void setbuf(FILE * restrict stream,
char * restrict buf);
int setvbuf(FILE * restrict stream,
char * restrict buf,
int mode, size_t size);
int fprintf(FILE * restrict stream,
const char * restrict format, ...);
int fscanf(FILE * restrict stream,
const char * restrict format, ...);
int printf(const char * restrict format, ...);
int scanf(const char * restrict format, ...);
int snprintf(char * restrict s, size_t n,
const char * restrict format, ...);
int sprintf(char * restrict s,
const char * restrict format, ...);
int sscanf(const char * restrict s,
const char * restrict format, ...);
int vfprintf(FILE * restrict stream,
const char * restrict format,
va_list arg);
int vfscanf(FILE * restrict stream,
const char * restrict format,
va_list arg);
int vprintf(const char * restrict format,
va_list arg);
int vscanf(const char * restrict format,
va_list arg);
int vsnprintf(char * restrict s, size_t n,
const char * restrict format,
va_list arg);
int vsprintf(char * restrict s,
const char * restrict format,
va_list arg);
int vsscanf(const char * restrict s,
const char * restrict format,
va_list arg);
B.18 Library summary B.18
488 Committee Draft -- August 3, 1998 WG14/N843
int fgetc(FILE *stream);
char *fgets(char * restrict s, int n,
FILE * restrict stream);
int fputc(int c, FILE *stream);
int fputs(const char * restrict s,
FILE * restrict stream);
int getc(FILE *stream);
int getchar(void);
char *gets(char *s);
int putc(int c, FILE *stream);
int putchar(int c);
int puts(const char *s);
int ungetc(int c, FILE *stream);
size_t fread(void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
size_t fwrite(const void * restrict ptr,
size_t size, size_t nmemb,
FILE * restrict stream);
int fgetpos(FILE * restrict stream,
fpos_t * restrict pos);
int fseek(FILE *stream, long int offset, int whence);
int fsetpos(FILE *stream, const fpos_t *pos);
long int ftell(FILE *stream);
void rewind(FILE *stream);
void clearerr(FILE *stream);
int feof(FILE *stream);
int ferror(FILE *stream);
void perror(const char *s);
B.19 General utilities <stdlib.h>
size_t ldiv_t EXIT_FAILURE MB_CUR_MAX
wchar_t lldiv_t EXIT_SUCCESS
div_t NULL RAND_MAX
double atof(const char *nptr);
int atoi(const char *nptr);
long int atol(const char *nptr);
long long int atoll(const char *nptr);
double strtod(const char * restrict nptr,
char ** restrict endptr);
float strtof(const char * restrict nptr,
char ** restrict endptr);
long double strtold(const char * restrict nptr,
char ** restrict endptr);
long int strtol(const char * restrict nptr,
char ** restrict endptr, int base);
long long int strtoll(const char * restrict nptr,
char ** restrict endptr, int base);
unsigned long int strtoul(
const char * restrict nptr,
char ** restrict endptr,
int base);
unsigned long long int strtoull(
const char * restrict nptr,
B.18 Library summary B.19
WG14/N843 Committee Draft -- August 3, 1998 489
char ** restrict endptr,
int base);
int rand(void);
void srand(unsigned int seed);
void *calloc(size_t nmemb, size_t size);
void free(void *ptr);
void *malloc(size_t size);
void *realloc(void *ptr, size_t size);
void abort(void);
int atexit(void (*func)(void));
void exit(int status);
char *getenv(const char *name);
int system(const char *string);
void *bsearch(const void *key, const void *base,
size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
void qsort(void *base, size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
int abs(int j);
long int labs(long int j); *
long long int llabs(long long int j); *
div_t div(int numer, int denom); |
ldiv_t ldiv(long int numer, long int denom); |
lldiv_t lldiv(long long int numer,
long long int denom);
int mblen(const char *s, size_t n);
int mbtowc(wchar_t * restrict pwc,
const char * restrict s,
size_t n);
int wctomb(char *s, wchar_t wchar);
size_t mbstowcs(wchar_t * restrict pwcs,
const char * restrict s,
size_t n);
size_t wcstombs(char * restrict s,
const wchar_t * restrict pwcs,
size_t n);
B.20 String handling <string.h>
size_t
NULL
void *memcpy(void * restrict s1,
const void * restrict s2,
size_t n);
void *memmove(void *s1, const void *s2, size_t n);
char *strcpy(char * restrict s1,
const char * restrict s2);
char *strncpy(char * restrict s1,
const char * restrict s2,
size_t n);
char *strcat(char * restrict s1,
const char * restrict s2);
char *strncat(char * restrict s1,
const char * restrict s2,
size_t n);
B.19 Library summary B.20
490 Committee Draft -- August 3, 1998 WG14/N843
int memcmp(const void *s1, const void *s2, size_t n);
int strcmp(const char *s1, const char *s2);
int strcoll(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t n);
size_t strxfrm(char * restrict s1,
const char * restrict s2,
size_t n);
void *memchr(const void *s, int c, size_t n);
char *strchr(const char *s, int c);
size_t strcspn(const char *s1, const char *s2);
char *strpbrk(const char *s1, const char *s2);
char *strrchr(const char *s, int c);
size_t strspn(const char *s1, const char *s2);
char *strstr(const char *s1, const char *s2);
char *strtok(char * restrict s1,
const char * restrict s2);
void *memset(void *s, int c, size_t n);
char *strerror(int errnum);
size_t strlen(const char *s);
B.21 Type-generic math <tgmath.h>
acos sqrt fmod nearbyint
asin fabs frexp nextafter
atan atan2 tgamma |nextafterx
acosh cbrt hypot remainder
asinh ceil ilogb remquo
atanh copysign ldexp rint
cos erf lgamma round
sin erfc llrint scalbn
tan exp2 llround scalbln
cosh expm1 log10 trunc
sinh fdim log1p carg
tanh floor log2 cimag
exp fma logb conj
log fmax lrint cproj
pow fmin lround creal
B.22 Date and time <time.h>
NULL _LOCALTIME time_t
CLOCKS_PER_SEC size_t struct tm
_NO_LEAP_SECONDS clock_t struct tmx
clock_t clock(void);
double difftime(time_t time1, time_t time0);
time_t mktime(struct tm *timeptr);
time_t mkxtime(struct tmx *timeptr);
time_t time(time_t *timer);
char *asctime(const struct tm *timeptr);
char *ctime(const time_t *timer);
struct tm *gmtime(const time_t *timer);
struct tm *localtime(const time_t *timer);
size_t strftime(char * restrict s,
size_t maxsize,
const char * restrict format,
const struct tm * restrict timeptr);
B.20 Library summary B.22
WG14/N843 Committee Draft -- August 3, 1998 491
size_t strfxtime(char * restrict s,
size_t maxsize,
const char * restrict format,
const struct tmx * restrict timeptr);
struct tmx *zonetime(const time_t *timer);
B.23 Extended multibyte and wide-character utilities
<wchar.h>
wchar_t wint_t NULL WEOF
size_t struct tm WCHAR_MAX
mbstate_t struct tmx WCHAR_MIN
int fwprintf(FILE * restrict stream,
const wchar_t * restrict format, ...);
int fwscanf(FILE * restrict stream,
const wchar_t * restrict format, ...);
int swprintf(wchar_t * restrict s,
size_t n,
const wchar_t * restrict format, ...);
int swscanf(const wchar_t * restrict s,
const wchar_t * restrict format, ...);
int vfwprintf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
int vfwscanf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
int vswprintf(wchar_t * restrict s,
size_t n,
const wchar_t * restrict format,
va_list arg);
int vswscanf(const wchar_t * restrict s,
const wchar_t * restrict format,
va_list arg);
int vwprintf(const wchar_t * restrict format,
va_list arg);
int vwscanf(FILE * restrict stream,
const wchar_t * restrict format,
va_list arg);
int wprintf(const wchar_t * restrict format, ...);
int wscanf(const wchar_t * restrict format, ...);
wint_t fgetwc(FILE *stream);
wchar_t *fgetws(wchar_t * restrict s,
int n, FILE * restrict stream);
wint_t fputwc(wchar_t c, FILE *stream);
int fputws(const wchar_t * restrict s,
FILE * restrict stream);
int fwide(FILE *stream, int mode);
wint_t getwc(FILE *stream);
wint_t getwchar(void);
wint_t putwc(wchar_t c, FILE *stream);
wint_t putwchar(wchar_t c);
wint_t ungetwc(wint_t c, FILE *stream);
double wcstod(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
B.22 Library summary B.23
492 Committee Draft -- August 3, 1998 WG14/N843
float wcstof(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
long double wcstold(const wchar_t * restrict nptr,
wchar_t ** restrict endptr);
long int wcstol(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
long long int wcstoll(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
unsigned long int wcstoul(const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
unsigned long long int wcstoull(
const wchar_t * restrict nptr,
wchar_t ** restrict endptr, int base);
wchar_t *wcscpy(wchar_t * restrict s1,
const wchar_t * restrict s2);
wchar_t *wcsncpy(wchar_t * restrict s1,
const wchar_t * restrict s2, size_t n);
wchar_t *wcscat(wchar_t * restrict s1,
const wchar_t * restrict s2);
wchar_t *wcsncat(wchar_t * restrict s1,
const wchar_t * restrict s2, size_t n);
int wcscmp(const wchar_t *s1, const wchar_t *s2);
int wcscoll(const wchar_t *s1, const wchar_t *s2);
int wcsncmp(const wchar_t *s1, const wchar_t *s2,
size_t n);
size_t wcsxfrm(wchar_t * restrict s1,
const wchar_t * restrict s2, size_t n);
wchar_t *wcschr(const wchar_t *s, wchar_t c);
size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
size_t wcslen(const wchar_t *s);
wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
wchar_t *wcstok(wchar_t * restrict s1,
const wchar_t * restrict s2,
wchar_t ** restrict ptr);
wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
int wmemcmp(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
wchar_t *wmemcpy(wchar_t * restrict s1,
const wchar_t * restrict s2,
size_t n);
wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
size_t n);
wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
size_t wcsftime(wchar_t *s, size_t maxsize,
const wchar_t *format, const struct tm *timeptr);
size_t wcsfxtime(wchar_t *s, size_t maxsize,
const wchar_t *format, const struct tmx *timeptr);
wint_t btowc(int c);
int wctob(wint_t c);
int mbsinit(const mbstate_t *ps);
B.23 Library summary B.23
WG14/N843 Committee Draft -- August 3, 1998 493
size_t mbrlen(const char * restrict s, size_t n,
mbstate_t * restrict ps);
size_t mbrtowc(wchar_t * restrict pwc,
const char * restrict s, size_t n,
mbstate_t * restrict ps);
size_t wcrtomb(char * restrict s, wchar_t wc,
mbstate_t * restrict ps);
size_t mbsrtowcs(wchar_t * restrict dst,
const char ** restrict src, size_t len,
mbstate_t * restrict ps);
size_t wcsrtombs(char * restrict dst,
const wchar_t ** restrict src, size_t len,
mbstate_t * restrict ps);
B.24 Wide-character classification and mapping utilities
<wctype.h>
wint_t wctrans_t wctype_t WEOF
int iswalnum(wint_t wc);
int iswalpha(wint_t wc);
int iswcntrl(wint_t wc);
int iswdigit(wint_t wc);
int iswgraph(wint_t wc);
int iswlower(wint_t wc);
int iswprint(wint_t wc);
int iswpunct(wint_t wc);
int iswspace(wint_t wc);
int iswupper(wint_t wc);
int iswxdigit(wint_t wc);
int iswctype(wint_t wc, wctype_t desc);
wctype_t wctype(const char *property);
wint_t towlower(wint_t wc);
wint_t towupper(wint_t wc);
wint_t towctrans(wint_t wc, wctrans_t desc);
wctrans_t wctrans(const char *property);
B.23 Library summary B.24
494 Committee Draft -- August 3, 1998 WG14/N843
Annex C
(informative)
Sequence points
[#1] The following are the sequence points described in
5.1.2.3:
-- The call to a function, after the arguments have been
evaluated (6.5.2.2).
-- The end of the first operand of the following
operators: logical AND && (6.5.13); logical OR ||
(6.5.14); conditional ? (6.5.15); comma , (6.5.17).
-- The end of a full declarator: declarators (6.7.5);
-- The end of a full expression: an initializer (6.7.8);
the expression in an expression statement (6.8.3); the
controlling expression of a selection statement (if or
switch) (6.8.4); the controlling expression of a while
or do statement (6.8.5); each of the three expressions
of a for statement (6.8.5.3); the expression in a
return statement (6.8.6.4).
-- Immediately before a library function returns (7.1.4).
-- After the actions associated with each formatted
input/output function conversion specifier (7.19.6,
7.24.2).
-- Immediately before and immediately after each call to a
comparison function, and also between any call to a
comparison function and any movement of the objects
passed as arguments to that call (7.20.5).
C Sequence points C
WG14/N843 Committee Draft -- August 3, 1998 495
Annex D |
(informative) |
Formal model of sequence points |
D.1 Introduction |
[#1] This annex defines a formal algorithm for determining |
whether any given expression or set of expressions meets the |
requirements of 6.5 and therefore whether or not it involves |
unspecified or undefined behavior.
[#2] An implementation is not required to follow the model |
defined in this annex. In particular, the model assumes |
serial evaluation, but parallel evaluation is equally valid. |
However, an implementation should ensure -- for all |
expressions that are not determined to be undefined in this |
model -- that expressions are evaluated in a way that will |
yield one of the results specified by this model, and that |
each volatile object is accessed exactly the number of times |
determined by the model. |
D.2 Basic concepts |
[#1] This model operates in terms of ``events''. An |
expression or set of expressions give rise to a number of |
events and some constraints on their order of occurrence. |
All possible arrangements that meet those constraints are |
then examined. If any of these arrangements involves |
undefined or unspecified behavior then so does the |
expression or set of expressions. |
D.2.1 Events |
[#1] An event is one of: |
-- reading the value of a byte, |
-- writing a value to a byte, |
-- designation of a byte in an object, |
-- a function call, |
-- a sequence point. |
[#2] A ``write'' event does not mean that the value is |
stored immediately, but that it will be stored before the |
next sequence point. The model automatically takes this |
into account. |
D Formal model of sequence points D.2.1
496 Committee Draft -- August 3, 1998 WG14/N843
D.2.2 Function calls |
[#1] Where an expression involves a function call, that call |
is ``atomic'' for the purposes of this model. There must be |
a sequence point immediately before (see 6.5.2.2) and after |
each function call (either because it ends in a full |
expression, or because it is required by 7.1.4), and so it |
can be seen that the effects of the call -- for the |
purposes of the surrounding expression -- can be determined |
purely by the read and write events involved in it, ignoring |
their ordering. These events cannot be interspersed with |
events from outside the call. Therefore this model treats a |
function call as being a sequence point. |
D.2.3 Short circuits and optimization |
[#1] The &&, ||, and ?: operators are ``short circuiting'' |
-- the way in which an expression containing them is |
evaluated depends on the operands. The model described in |
this annex handles this. |
[#2] Other expressions can sometimes be optimized, for |
example because the result of an operator can be determined |
from only some of the operands; the most obvious case is |
multiplication by constant zero. Not only does this model |
require the other operand be evaluated in this case, but all |
the implications of this model must continue to hold even |
where an optimizing implementation could store values in |
objects earlier than the model would allow.285) |
D.2.4 Notation |
[#1] Events are written as follows: |
R(a) read the byte at address a; |
W(a) write the byte at address a; |
L(a) an lvalue designating the byte at address a; |
F(e) the call to the function designated by e; |
S a sequence point; |
D a dummy event with no effect. |
[#2] For L, R, and W events, the address a may also |
represent a bit-field within a byte in certain |
circumstances; this is written a:bf when it occurs. |
____________________
285Of course, provided the relevant side-effects take place
as if the model were followed, any optimization that
yields a valid result (as specified in D.1) is permitted.
D.2.2 Formal model of sequence points D.2.4
WG14/N843 Committee Draft -- August 3, 1998 497
[#3] If it is necessary to distinguish separate events of |
the same kind, this is done by placing a number or name in |
braces after the event (such as ``R(a, n){5}'' or |
``S{pre}''). |
[#4] In addition, the following notation is used: |
X < Y for each event P in those indicated by X, and |
each event Q in those indicated by Y, P must |
occur before Q; |
R(a, n) R(a), R(a + 1), ... , R(a + n - 1) |
W(a, n) W(a), W(a + 1), ... , W(a + n - 1) |
L(a, n) L(a), L(a + 1), ... , L(a + n - 1) |
E(e) the events and constraints of expression e; |
V(e) the events and constraints of expression e, but |
with each L(a) event replaced by a (different) |
dummy event D; |
Z(e) the size (in bytes) of an object with the same |
type as the expression e (or 1 if e has function |
type). |
D.3 Operation of the model |
[#1] The model is operated in the following stages: |
-- transforming each expression, |
-- identifying events and constraints, |
-- analysis of all possible orders of events. |
[#2] Where more than one expression is involved, each is |
processed through the first two stages separately, and then |
combined as given in D.4 before the last stage. |
D.3.1 Transformation |
[#1] The first stage of analysis of an expression is to |
transform it to a canonical form. To do this:
D.2.4 Formal model of sequence points D.3.1
498 Committee Draft -- August 3, 1998 WG14/N843
each expression of the form is replaced by the form |
e->field (*(e)).field |
e1[e2] *((e1)+(e2)) |
&*e e |
e1 && e2 where e1 is zero (e1) |
where e1 is nonzero ((e1) , (e2)) |
e1 || e2 where e1 is zero ((e1) , (e2)) |
where e1 is nonzero (e1) |
e1 ? e2 : e3 where e1 is zero ((e1) , (e3)) |
where e1 is nonzero ((e1) , (e2)) |
[#2] Note that the &&, ||, and ?: operators require multiple |
analyses to be made; the expression involves undefined |
behavior in those situations where the corresponding case |
does; if the value of e1 is unspecified, the expression |
involves undefined behavior if either alternative does. |
[#3] Finally, wherever 6.5 requires an lvalue not of array |
type to be converted to the value stored in the designated |
object, replace the lvalue expression e by the expression $e |
and where it requires an lvalue of array type to be |
converted to a pointer to the first element of the array, or |
an lvalue of function type to be converted to a pointer to |
the function, replace it by the expression @e (where $ and @ |
are notional operators introduced by the model).
[#4] |
D.3.2 Event identification |
[#1] Each sub-expression gives rise to a set of events and |
constraints on events as follows.
[#2] A constant or string literal does not give rise to any |
events. A parenthesized expression gives rise to the same |
events and constraints that the unparenthesized version |
would.
[#3] An identifier x gives rise to L(a, Z(x)), where a is |
the address of x. This includes the case where x has an |
array type. However, an identifier with function type does |
not give rise to any events. If x has register storage |
class, it still has a notional address even though a program |
cannot determine that address using the & or @ operators.
[#4] A compound literal (type){e1, e2, ...} gives rise to |
L(a, Z(type)) plus the constraints E(e1) < L(a, Z(type)), |
E(e2) < L(a, Z(type)), etc., where a is the address of the |
object generated by the compound literal.
[#5] A type name with variably modified type and containing |
the expressions e1, e2, etc. (in array declarators) gives |
rise to all the events and constraints from V(e1), V(e2), |
etc. (with no constraints between these).
D.3.1 Formal model of sequence points D.3.2
WG14/N843 Committee Draft -- August 3, 1998 499
[#6] All other expressions give rise to events and |
constraints as follows:
Expression Events and constraints |
$e E(e), but replacing each L(a) by R(a). |
@e V(e). |
e0(e1, e2, ...) E(e0), E(e1), E(e2), etc., plus new | |
F(e0), | |
E(e0) < F(e0), E(e1) < F(e0), E(e2) < | |
F(e0), etc. | |
e.field E(e), but if this contains L(a, Z(e)) | |
for some address a then that is replaced | |
by L(a + b, Z(e.field)), where b is the | |
offset of the field in the structure or | |
union type. If e has structure (not | |
union) type and the field is a bit- | |
field, the event identifies only that | |
bit-field within the byte(s). | |
++e --e | E(e), but replacing each L(a) by the | |
e++ e-- | pair [R(a), W(a)], with the constraint | |
R(a) < W(a) for each such pair. | |
&e V(e). |
*e E(e), plus new L(a, Z(*e)), where a is | |
the address pointed to, and the | |
constraint E(e) < L(a, Z(*e)). | |
sizeof e | V(e) or V(type) if e or type has | |
sizeof (type)| variably modified type, otherwise none. | |
+e -e !e ~e E(e). |
(type)e V(e), E(type). |
e1 <op> e2 E(e1), E(e2). |
e1, e2 E(e1), E(e2), plus new S, | |
E(e1) < S, S < E(e2). | |
e1 = e2 E(e1), but replacing each L(a) by W(a), | |
E(e2), | |
E(e2) < W(a) for each W(a) created by | |
the replacement. | |
e1 <op=> e2 E(e1), but replacing each L(a) by the | |
pair [R(a), W(a)], E(e2), and for each | |
W(a) created by the replacement the | |
constraints [E(e2), R(a)] < W(a) where | |
the R(a) is the corresponding event | |
created by the replacement. | |
<op> is any of * / % + - << >> < > <= >= == != & ^ ||
<op=> is any of *= /= %= += -= <<= >>= &= ^= |= |
D.3.2 Formal model of sequence points D.3.2
500 Committee Draft -- August 3, 1998 WG14/N843
D.3.3 Event analysis |
[#1] When all events and constraints in the expression have |
been determined, every possible arrangement of the remaining |
events286) that obeys the constraints is considered.
[#2] If an arrangement contains W(a) followed by either R(a) |
or W(a) (for the same address a) without an intervening S or |
F event, the expression involves undefined behavior. |
[#3] Otherwise, if two different arrangements would have |
different effects then it is unspecified which results.287)
[#4] If an R(a) event applies to a volatile object, this is |
an access to the object. If there is more than one R(a) |
event for the same volatile object, the model shows which |
possible orderings can apply to the accesses for each |
purpose; if the value of the expression depends on the order |
of these accesses and the model permits more than one order, |
which order is used is unspecified. |
D.4 Application |
D.4.1 Expressions |
[#1] For each expression statement, and for each full |
expression in a selection, iteration, or jump statement, the |
expression is considered separately in its normal place in |
the sequence of execution. |
[#2] For each array declarator involving a variably modified |
type, and for each initializer list, the events of all the |
individual expressions are considered together with no |
constraints applying between events from two different full |
expressions. |
____________________
286There will be no L(a) events remaining, since they
represent lvalues and these will have been made the
operand of some operator, possibly a $ operator.
287This will occur if one arrangement contains W(a){1}
followed by either R(a){2} or W(a){3} and the other
arrangement contains either R(a){2} or W(a){3} followed
by W(a){1} (in each case possibly with other events
intervening).
D.3.3 Formal model of sequence points D.4.1
WG14/N843 Committee Draft -- August 3, 1998 501
D.4.2 Signals |
[#1] If program execution is interrupted by a signal where |
the handler returns to the caller, the behavior is as if an |
F event for the signal handler were inserted at an |
unspecified place in the sequence of events forming the full |
expression or array declarator being evaluated at the time |
of the signal. |
D.4.3 Floating-point environment |
[#1] For the purposes of this model, the floating-point |
exception flags constitute a single object and the remainder |
of the floating-point environment another single object. |
Any W event to the latter implies a W event to the former |
with the same constraints and with no constraint between the |
two.
[#2] If the state of the FENV_ACCESS pragma is on, then any |
operation that sets a floating-point exception flag implies |
a W event for the floating-point exception flags (``WX'') |
with the following constraints:
Operations Constraints |
$e | WX occurs after every event associated | |
+e -e !e ~e| with the sub-expression | |
e1 <op> e2 | |
++e --e | WX has the same constraints as the W | |
e++ e-- | events generated in the analysis of the | |
e1 = e2 | sub-expression, but may occur before any | |
e1 <op=> e2| or all of those W events. | |
[#3] Notwithstanding D.3.3, if an arrangement contains more |
than one W event for the floating-point exception flags |
without an intervening S or F event, the behavior is not |
undefined but it is unspecified which of the flags |
associated with the W events will be set (though at least |
one of those flags will be set).288) |
____________________
288If it were undefined to write twice to the flags between
sequence points, it would not be practical to use the
facilities of the <fenv.h> header in complicated
expressions.
D.4.2 Formal model of sequence points D.4.3
502 Committee Draft -- August 3, 1998 WG14/N843
D.5 Examples |
[#1] In these examples the type int and all pointer types |
have a size of 1, double has a size of 3, and addresses are |
in the range 1000 to 1999. In each case it is the final |
line that is being analyzed. |
[#2] EXAMPLE 1
int x, y, z; |
x = y + z; |
[#3] The canonical form is: |
x = $y + $z |
[#4] The events and constraints identified by each sub- |
expression are:
x: L(1000){1} |
y: L(1234){2} |
z: L(1666){3} |
$y: R(1234){4} |
$z: R(1666){5} |
+: {4}, {5} |
=: W(1000){6}, {4}, {5}, [{4}, {5}] < {6} |
[#5] Since each address only appears in one R or W event, |
there is no undefined behavior. |
|
[#6] EXAMPLE 2
int z, y; |
x = y++; // already in canonical form |
[#7] The events and constraints identified by each sub- |
expression are:
x: L(1000){1} |
y: L(1234){2} |
y++: R(1234){3}, W(1234){4}, {3} < {4} |
=: W(1000){5}, {3}, {4}, {3} < {4}, [{3}, {4}] < {5}|
[#8] There is only one possible ordering: |
R(1234) : W(1234) : W(1000) |
[#9] Again, each address appears in only one event, so |
clearly there is no undefined behavior. |
|
[#10] EXAMPLE 3
D.5 Formal model of sequence points D.5
WG14/N843 Committee Draft -- August 3, 1998 503
int x; |
x = ++x; // already in canonical form |
[#11] The events and constraints identified by each sub- |
expression are:
x: L(1000){1} [the x that is the left operand of =]|
x: L(1000){2} [the x that is the operand of ++]|
++x: R(1000){3}, W(1000){4}, {3} < {4} |
=: W(1000){5}, {3}, {4}, {3} < {4}, [{3}, {4}] < {5}|
[#12] Even though there is still only one possible ordering, |
this time the same address appears in two separate W events |
without an intervening sequence point, and so the behavior |
is undefined. |
|
[#13] EXAMPLE 4
int x; |
x += x * x; |
[#14] The canonical form is: |
x += $x * $x; |
[#15] The events and constraints identified by each sub- |
expression are:
x: L(1000){1} [the x that is the left operand of =]|
x: L(1000){2} [the x that is the left operand of *]|
x: L(1000){3} [the x that is the right operand of *]|
$x: R(1000){4} [derived from {2}] |
$x: R(1000){5} [derived from {3}] |
*: {4}, {5} |
+=: R(1000){6}, W(1000){7}, {4}, {5}, [{4}, {5}, {6}] < {7}|
[#16] The address 1000 appears in all four of the remaining |
events, and this time there are six permitted orderings but |
none of the 6 involve undefined behavior, and so the |
expression is valid. If x had volatile-qualified type, it |
would be unspecified which of the three reads would be used |
for each of the three operands of the (implied) x + x * x. |
[#17] EXAMPLE 5
int x; |
extern int f(int); |
x = f(x++); |
[#18] The canonical form is: |
D.5 Formal model of sequence points D.5
504 Committee Draft -- August 3, 1998 WG14/N843
x = (@f)(x++) |
[#19] The events and constraints identified by each sub- |
expression are:
x: L(1000){1} [the x that is the left operand of =]|
x: L(1000){2} [the x that is operand of ++]|
x++: R(1000){3}, W(1000){4}, {3} < {4} |
f: none |
@f: none |
call: {3}, {4}, F(f){5}, {3} < {4}, [{3}, {4}] < {5}|
=: W(1000){6}, {3}, {4}, {5}, {3} < {4}, [{3}, {4}] < {5}, [{3}, {4}, {5}] < {6}|
[#20] The four events have one possible ordering: |
R(1000) : W(1000) : F(f) : W(1000) |
[#21] It is therefore clear that x is incremented before the |
function call starts execution, that the result of the |
function is stored in x, and that the expression is valid. |
If the function has some other form of access to x, it will |
see the incremented value, and any value it stores in x will |
be lost.
[#22] If the expression is replaced by: |
x = 2 * f(x++); |
the analysis is effectively the same -- the multiplication |
by a constant adds no new events. And if it is replaced by:
x = 0 * f(x++); |
the analysis continues to remain the same; an optimizing |
implementation can determine that x is set to 0, but it must |
still make the incremented value of x available to the |
function.
[#23] EXAMPLE 6
int x, y; |
(x=y) + x; |
[#24] The canonical form is: |
(x=$y)+$x |
[#25] The events and constraints identified by each sub- |
expression are:
D.5 Formal model of sequence points D.5
WG14/N843 Committee Draft -- August 3, 1998 505
x: L(1000){1} [the x that is the left operand of =]|
y: L(1234){2} |
x: L(1000){3} [the x that is the right operand of +]|
$y: R(1234){4} |
=: W(1000){5}, {4}, {4} < {5} |
$x: R(1000){6} |
+: {4}, {5}, {6}, {4} < {5} |
[#26] There are three possible orderings: |
{4} : {5} : {6} R(1234) : W(1000) : R(1000) |
{4} : {6} : {5} R(1234) : R(1000) : W(1000) |
{6} : {4} : {5} R(1000) : R(1234) : W(1000) |
[#27] The first of the three involves reading address 1000 |
after writing it -- without an intervening sequence point |
-- and so the expression is undefined.
[#28] EXAMPLE 7
int x, y, z; |
(x=y) + (x=z); |
[#29] The canonical form is: |
(x=$y)+(x=$z) |
[#30] The events and constraints identified by each sub- |
expression are:
x: L(1000){1} [the x that is set to y] |
y: L(1234){2} |
x: L(1000){3} [the x that is set to z] |
z: L(1666){4} |
$y: R(1234){5} |
x=$y: W(1000){6}, {5}, {5} < {6} |
$z: R(1666){7} |
x=$z: W(1000){8}, {7}, {7} < {8} |
+: {5}, {6}, {7}, {8}, {5} < {6}, {7} < {8} |
[#31] There are six possible orderings, but all involve {6} |
and {8} not separated by a sequence point, and so the |
expression is undefined.
[#32] EXAMPLE 8 To demonstrate the rules for arrays: |
double x [5]; |
int y = 3; |
x[y] /= (double) &x[y]; |
[#33] The canonical form is: |
D.5 Formal model of sequence points D.5
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*(@x+$y) /= (double)(@x+$y); |
[#34] The events and constraints identified by each sub- |
expression are:
x: L(1000,15){1} [the x to the left of the =]|
y: L(1666){2} [the y to the left of the =]|
x: L(1000,15){3} [the x to the right of the =]|
y: L(1666){4} [the y to the right of the =]|
@x: D{5} [derived from {1}] |
$y: R(1666){6} [derived from {2}] |
+: {5}, {6} |
x[y]: {5}, {6}, L(1009,3){7}, [{5}, {6}] < {7}|
@x: D{8} [derived from {3}] |
$y: R(1666){9} [derived from {4}] |
+: {8}, {9} |
double: none |
cast: {8}, {9} |
/=: {5}, {6}, R(1009,3){10}, W(1009,3){11},|
{5} < {10}, {5} < {11}, {6} < {10}, {6} < {11},|
{8}, {9}, [{8}, {9}, {10}] < {11} |
[#35] The only purpose of D events is to preserve ordering |
in cases like [{22} < D, D < {23}] and so {5} and {8} can be |
ignored. This leaves the events:
R(1666){6}, R(1666){9}, R(1009,3){10}, W(1009,3){11} |
and the constraints: |
{6} < {10}, {6} < {11}, {9} < {11}, {10} < {11} |
[#36] This permits three orderings: |
R(1666){6} : R(1009,3) : R(1666){9} : W(1009,3) |
R(1666){6} : R(1666){9} : R(1009,3) : W(1009,3) |
R(1666){9} : R(1666){6} : R(1009,3) : W(1009,3) |
[#37] None of these involve undefined behavior. |
[#38] EXAMPLE 9 To demonstrate the rules for structures: |
int x; |
struct s { double p; int q; double r; } y; |
x = y.q; |
[#39] The canonical form is: |
x = $(y.q) |
[#40] The events and constraints identified by each sub- |
expression are:
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x: L(1000){1} |
y: L(1230,7){2} |
y.q: L(1233,1){3} |
$(y.q): R(1233){4} |
=: W(1000){5}, {4}, {4} < {5} |
[#41] EXAMPLE 10
struct s { double p; int q; int r; } *x, y; |
x = &y; |
x->q = x->r; |
[#42] The canonical form is: |
(*$x).q = $((*$x).r) |
[#43] The events and constraints identified by each sub- |
expression are:
x: L(1000){1} [part of the left operand of the =]|
x: L(1000){2} [part of the right operand of the =]|
$x: R(1000){3} [derived from {1}] |
*$x: {3}, L(1220,5){4}, {3} < {4} |
x->q: {3}, L(1223,1){5}, {3} < {5} |
$x: R(1000){6} [derived from {2}] |
*$x: {6}, L(1220,5){7}, {6} < {7} |
x->r: {6}, L(1224,1){8}, {6} < {8} |
$(x->r): {6}, R(1224,1){9}, {6} < {9} |
=: {3}, W(1223,1){10}, {3} < {10}, {6}, {9}, {6} < {9}, [{6}, {9}] < {10}|
[#44] These constraints allow three orderings: |
{3} : {6} : {9} : {10} |
{6} : {3} : {9} : {10} |
{6} : {9} : {3} : {10} |
and it is clear that all of these are valid. |
[#45] EXAMPLE 11 To illustrate the rules for bit-fields: |
struct { int x : 10; int y : 3; } s; |
s.y = 4; |
s.x = s.y++; |
[#46] This is already in canonical form. |
[#47] The events and constraints identified by each sub- |
expression are:
D.5 Formal model of sequence points D.5
508 Committee Draft -- August 3, 1998 WG14/N843
s: L(1000){1} [part of s.x] |
s: L(1000){2} [part of s.y] |
s.x: L(1000:0-9){3} [refers only to the bits of field x]|
s.y: L(1000:10-12){4} [refers only to the bits of field y]|
s.y++: R(1000:10-12){5}, W(1000:10-12){6}, {5} < {6}|
=: W(1000:0-9){6}, {4}, {5}, {4} < {5}, [{4}, {5}] < {6}|
[#48] There is only one possible ordering: |
R(1000:10-12), W(1000:10-12), W(1000:0-9) |
[#49] Since the two W events identify different bit-fields, |
there is no undefined behavior.
[#50] However, if the type was a union instead of a |
structure, there would be no bit-fields in the events, and |
the final ordering would be:
R(1000), W(1000), W(1000) |
which of course involves undefined behavior. |
[#51] EXAMPLE 12
int x; |
x++ && x--; |
[#52] This expression has two canonical forms, depending on |
whether x is or is not initially zero:
x++ // x is initially 0 |
x++ , x-- // x is not initially 0 |
[#53] In this case it is clear that only the latter needs to |
be examined further, but this might not be the case in more |
complex expression. Doing so, the events and constraints |
identified by each sub-expression are:
x: L(1000){1} [the x in x++] |
x: L(1000){2} [the x in x--] |
x++: R(1000){3}, W(1000){4}, {3} < {4} |
x--: R(1000){5}, W(1000){6}, {5} < {6} |
,: {3}, {4}, {3} < {4}, {5}, {6}, {5} < {6}, S{7}, [{3}, {4}] < {7}, {7} < [{5}, {6}]|
[#54] There is only one possible ordering, and this has two |
W events to the same address, but these are separated by an |
S event and so the expression is valid. It is clear that |
the decrement must apply to the incremented variable.
[#55] EXAMPLE 13
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int x, y; |
x++ * y++ ? x-- : y--; |
[#56] Again there are two canonical forms: |
x++ * y++ , x-- // x and y both initially nonzero |
x++ * y++ , y-- // either x or y initially zero |
[#57] In each case the analysis follows the lines above. |
The first case yields:
R(1000){1}, W(1000){2}, R(1234){3}, W(1234){4}, S{5}, R(1000){6}, W(1000){7},|
{1} < {2}, {1} < {5}, {2} < {5}, {3} < {4}, {3} < {5}, {4} < {5}, {5} < {6}, {5} < {7}, {6} < {7}|
[#58] There are six possible orderings, but all place a |
sequence point between the first and second writes to x.
[#59] EXAMPLE 14
int x[2], *y; |
y = x; |
*y = f(y++); |
[#60] The canonical form is: |
*$y = (@f)(y++) |
[#61] The events and constraints identified by each sub- |
expression are:
y: L(1234){1} [the y on the left of the =] |
y: L(1234){2} [the y that is the operand of y++]|
y++: R(1234){3}, W(1234){4}, {3} < {4} |
f: none |
@f: none |
call: {3}, {4}, {3} < {4}, F(f){5}, [{3}, {4}] < {5}|
$y: R(1234){6} [derived from {1}] |
*$y: {6}, L(X){7}, {6} < {7} |
=: {6}, W(X){8}, {6} < {8}, {3}, {4}, {5}, {3} < {4}, [{3}, {4}] < {5}, [{3}, {4}, {5}] < {8}|
where X is the location pointed to by y at the point of the |
* operator.
[#62] One possible ordering is: |
R(1234){3} : W(1234){4} : R(1234){6} : F(f){5} : W(X){8}|
and therefore the expression involves undefined behavior. |
[#63] EXAMPLE 15
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int x[2], y; |
y = 0; |
x[y] = f(y++); |
[#64] The canonical form is: |
*(@x+$y) = (@f)(y++) |
[#65] The events and constraints identified by each sub- |
expression are:
x: L(1000,2){1} |
y: L(1234){2} [the y on the left of the =] |
y: L(1234){3} [the y that is the operand of y++]|
@x: D{4} |
$y: R(1234){5} [derived from {1}] |
+: {4}, {5} |
x[y]: {4}, {5}, L(X){6}, [{4}, {5}] < {6} |
where X is 1000 plus the value determined at {5}|
y++: R(1234){7}, W(1234){8}, {7} < {8} |
f: none |
@f: none |
call: {7}, {8}, {7} < {8}, F(f){9}, [{7}, {8}] < {9}|
=: {4}, {5}, W(X){10}, [{4}, {5}] < {10}, {7}, {8}, {9},|
{7} < {8}, {8} < {9}, {7} < {9}, [{7}, {8}, {9}] < {10}|
[#66] One possible ordering is: |
D{4} : R(1234){7} : W(1234){8} : R(1234){5} : F(f){9} : W(X){10}|
and therefore the expression involves undefined behavior. |
[#67] EXAMPLE 16
int x = 5; |
int a [x][x++]; |
[#68] There are two expressions to be considered, and their |
canonical forms are:
$x |
x++ |
[#69] The first generates the event: |
R(1000){1} |
and the second the events and constraints: |
R(1000){2}, W(1000){3}, {2} < {3} |
[#70] There are no constraints between {1} and the other two |
events, and so they can occur in any of three orders. One |
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of these arrangements puts W(1000) before R(1000) and so the |
declaration as a whole involves undefined behavior.
D.5 Formal model of sequence points D.5
512 Committee Draft -- August 3, 1998 WG14/N843
Annex E
(informative)
Implementation limits
[#1] The contents of the header <limits.h> are given below, |
in alphabetical order. The minimum magnitudes shown shall
be replaced by implementation-defined magnitudes with the
same sign. The values shall all be constant expressions
suitable for use in #if preprocessing directives. The
components are described further in 5.2.4.2.1.
#define CHAR_BIT 8
#define CHAR_MAX UCHAR_MAX or SCHAR_MAX
#define CHAR_MIN 0 or SCHAR_MIN
#define INT_MAX +32767
#define INT_MIN -32767
#define LONG_MAX +2147483647
#define LONG_MIN -2147483647
#define LLONG_MAX +9223372036854775807
#define LLONG_MIN -9223372036854775807
#define MB_LEN_MAX 1
#define SCHAR_MAX +127
#define SCHAR_MIN -127
#define SHRT_MAX +32767
#define SHRT_MIN -32767
#define UCHAR_MAX 255
#define USHRT_MAX 65535
#define UINT_MAX 65535
#define ULONG_MAX 4294967295
#define ULLONG_MAX 18446744073709551615
[#2] The contents of the header <float.h> are given below. |
All integer values, except FLT_ROUNDS, shall be constant |
expressions suitable for use in #if preprocessing |
directives; all floating values shall be constant |
expressions. The components are described further in |
5.2.4.2.2. |
[#3] The values given in the following list shall be |
replaced by implementation-defined expressions:
#define FLT_EVAL_METHOD
#define FLT_ROUNDS
[#4] The values given in the following list shall be |
replaced by implementation-defined constant expressions that
are greater or equal in magnitude (absolute value) to those
shown, with the same sign:
E Implementation limits E
WG14/N843 Committee Draft -- August 3, 1998 513
#define DBL_DIG 10
#define DBL_MANT_DIG
#define DBL_MAX_10_EXP +37
#define DBL_MAX_EXP
#define DBL_MIN_10_EXP -37
#define DBL_MIN_EXP
#define DECIMAL_DIG 10 |
#define FLT_DIG 6
#define FLT_MANT_DIG
#define FLT_MAX_10_EXP +37
#define FLT_MAX_EXP
#define FLT_MIN_10_EXP -37
#define FLT_MIN_EXP
#define FLT_RADIX 2
#define LDBL_DIG 10
#define LDBL_MANT_DIG
#define LDBL_MAX_10_EXP +37
#define LDBL_MAX_EXP
#define LDBL_MIN_10_EXP -37
#define LDBL_MIN_EXP
[#5] The values given in the following list shall be |
replaced by implementation-defined constant expressions with |
values that are greater than or equal to those shown:
#define DBL_MAX 1E+37
#define FLT_MAX 1E+37
#define LDBL_MAX 1E+37
[#6] The values given in the following list shall be |
replaced by implementation-defined constant expressions with |
(positive) values that are less than or equal to those |
shown:
#define DBL_EPSILON 1E-9
#define DBL_MIN 1E-37
#define FLT_EPSILON 1E-5
#define FLT_MIN 1E-37
#define LDBL_EPSILON 1E-9
#define LDBL_MIN 1E-37
E Implementation limits E
514 Committee Draft -- August 3, 1998 WG14/N843
Annex F
(normative)
IEC 60559 floating-point arithmetic
F.1 Introduction
[#1] This annex specifies C language support for the IEC
60559 floating-point standard. The IEC 60559 floating-point
standard is specifically Binary floating-point arithmetic
for microprocessor systems, second edition (IEC 60559:1989),
previously designated IEC 559:1989 and as IEEE Standard for
Binary Floating-Point Arithmetic (ANSI/IEEE 754-1985). IEEE
Standard for Radix-Independent Floating-Point Arithmetic
(ANSI/IEEE 854-1987) generalizes the binary standard to
remove dependencies on radix and word length. IEC 60559
generally refers to the floating-point standard, as in IEC
60559 operation, IEC 60559 format, etc. An implementation
that defines __STDC_IEC_559__ conforms to the specifications
in this annex. Where a binding between the C language and
IEC 60559 is indicated, the IEC 60559-specified behavior is
adopted by reference, unless stated otherwise.
F.2 Types
[#1] The C floating types match the IEC 60559 formats as
follows:
-- The float type matches the IEC 60559 single format.
-- The double type matches the IEC 60559 double format.
-- The long double type matches an IEC 60559 extended
format,289) else a non-IEC 60559 extended format, else
the IEC 60559 double format.
Any non-IEC 60559 extended format used for the long double
type shall have more precision than IEC 60559 double and at
least the range of IEC 60559 double.290)
Recommended practice
[#2] The long double type should match an IEC 60559 extended
format.
____________________
289Extended is IEC 60559's double-extended data format.
Extended refers to both the common 80-bit and quadruple
128-bit IEC 60559 formats.
290A non-IEC 60559 long double type is required to provide
infinity and NaNs, as its values include all double
values.
F IEC 60559 floating-point arithmetic F.2
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F.2.1 Infinities, signed zeros, and NaNs
[#1] This specification does not define the behavior of
signaling NaNs.291) It generally uses the term NaN to
denote quiet NaNs. The NAN and INFINITY macros and the nan
functions in <math.h> provide designations for IEC 60559
NaNs and infinities.
F.3 Operators and functions
[#1] C operators and functions provide IEC 60559 required
and recommended facilities as listed below.
-- The +, -, *, and / operators provide the IEC 60559 add,
subtract, multiply, and divide operations.
-- The sqrt function in <math.h> provides the IEC 60559
square root operation.
-- The remainder function in <math.h> provides the IEC
60559 remainder operation. The remquo function in
<math.h> provides the same operation but with
additional information.
-- The rint function in <math.h> provides the IEC 60559
operation that rounds a floating-point number to an
integer value (in the same precision). The C nearbyint
function in <math.h> provides the nearbyinteger
function recommended in the Appendix to IEEE standard
854.
-- The conversions for floating types provide the IEC
60559 conversions between floating-point precisions.
-- The conversions from integer to floating types provide
the IEC 60559 conversions from integer to floating
point.
-- The conversions from floating to integer types provide
IEC 60559-like conversions but always round toward
zero.
-- The lrint and llrint functions in <math.h> provide the
IEC 60559 conversions, which honor the directed
rounding mode, from floating point to the long int and
long long int integer formats. The lrint and llrint
functions can be used to implement IEC 60559
conversions from floating to other integer formats.
____________________
291Since NaNs created by IEC 60559 operations are always
quiet, quiet NaNs (along with infinities) are sufficient
for closure of the arithmetic.
F.2 IEC 60559 floating-point arithmetic F.3
516 Committee Draft -- August 3, 1998 WG14/N843
-- The translation time conversion of floating constants
and the strtod, fprintf, fscanf, and related library
functions in <stdlib.h>, <stdio.h>, and <wchar.h>
provide IEC 60559 binary-decimal conversions. The
strtold function in <stdlib.h> provides the conv
function recommended in the Appendix to IEEE standard
854.
-- The relational and equality operators provide IEC 60559
comparisons. IEC 60559 identifies a need for
additional comparison predicates to facilitate writing
code that accounts for NaNs. The comparison macros
(isgreater, isgreaterequal, isless, islessequal,
islessgreater, and isunordered) in <math.h> supplement
the language operators to address this need. The
islessgreater and isunordered macros provide
respectively a quiet version of the <> predicate and
the unordered predicate recommended in the Appendix to
IEC 60559.
-- The feclearexcept, feraiseexcept, and fetestexcept
functions in <fenv.h> provide the facility to test and
alter the IEC 60559 floating-point exception flags.
The fegetexceptflag and fesetexceptflag functions in
<fenv.h> provide the facility to save and restore all
five status flags at one time. These functions are
used in conjunction with the type fexcept_t and the
exception macros (FE_INEXACT, FE_DIVBYZERO,
FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in
<fenv.h>.
-- The fegetround and fesetround functions in <fenv.h>
provide the facility to select among the IEC 60559
directed rounding modes represented by the rounding
direction macros (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD,
FE_TOWARDZERO) also in <fenv.h>.
-- The fegetenv, feholdexcept, fesetenv, and feupdateenv
functions in <fenv.h> provide a facility to manage the
floating-point environment, comprising the IEC 60559
status flags and control modes.
-- The copysign function in <math.h> provides the copysign
function recommended in the Appendix to IEC 60559.
-- The unary minus (-) operator provides the minus (-)
operation recommended in the Appendix to IEC 60559.
-- The scalbn and scalbln functions in <math.h> provides |
the scalb function recommended in the Appendix to IEC
60559.
-- The logb function in <math.h> provides the logb
function recommended in the Appendix to IEC 60559, but
F.3 IEC 60559 floating-point arithmetic F.3
WG14/N843 Committee Draft -- August 3, 1998 517
following the newer specifications in IEEE 854.
-- The nextafter and nextafterx functions in <math.h>
provide the nextafter function recommended in the
Appendix to IEC 60559 (but with a minor change to
better handle signed zeros).
-- The isfinite macro in <math.h> provides the finite
function recommended in the Appendix to IEC 60559.
-- The isnan macro in <math.h> provides the isnan function
recommended in the Appendix to IEC 60559.
-- The signbit macro and the fpclassify macro in <math.h>,
used in conjunction with the number classification
macros (FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL,
FP_ZERO), provide the facility of the class function
recommended in the Appendix to IEC 60559 (except that
fpclassify does not distinguish signaling from quiet
NaNs).
F.4 Floating to integer conversion
[#1] If the floating value is infinite or NaN or if the
integral part of the floating value exceeds the range of the
integer type, then the invalid exception is raised and the
resulting value is unspecified. Whether conversion of non-
integer floating values whose integral part is within the
range of the integer type raises the inexact exception is
unspecified.292)
F.5 Binary-decimal conversion
[#1] Conversion from the widest supported IEC 60559 format
to decimal with DECIMAL_DIG digits and back is the identity
function.293)
[#2] Conversions involving IEC 60559 formats follow all
____________________
292ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754),
directly specifies that floating-to-integer conversions
raise the inexact exception for non-integer in-range
values. In those cases where it matters, library
functions can be used to effect such conversions with or
without raising the inexact exception. See rint, lrint,
llrint, and nearbyint in <math.h>.
293If the minimum-width IEC 60559 extended format (64 bits
of precision) is supported, DECIMAL_DIG shall be at least
21. If IEC 60559 double (53 bits of precision) is the
widest IEC 60559 format supported, then DECIMAL_DIG shall
be at least 17. (By contrast, LDBL_DIG and DBL_DIG are
19 and 15, respectively, for these formats.)
F.3 IEC 60559 floating-point arithmetic F.5
518 Committee Draft -- August 3, 1998 WG14/N843
pertinent recommended practice. In particular, conversion
between any supported IEC 60559 format and decimal with
DECIMAL_DIG or fewer significant digits is correctly
rounded.
F.6 Contracted expressions
[#1] A contracted expression treats infinities, NaNs, signed
zeros, subnormals, and the rounding directions in a manner
consistent with the basic arithmetic operations covered by
IEC 60559.
Recommended practice
[#2] A contracted expression should raise exceptions in a
manner generally consistent with the basic arithmetic
operations. A contracted expression should deliver the same
value as its uncontracted counterpart, else should be
correctly rounded (once).
F.7 Environment
[#1] The floating-point environment defined in <fenv.h>
includes the IEC 60559 exception status flags and directed-
rounding control modes. It includes also IEC 60559 dynamic
rounding precision and trap enablement modes, if the
implementation supports them.294)
F.7.1 Environment management
[#1] IEC 60559 requires that floating-point operations
implicitly raise exception status flags, and that rounding
control modes can be set explicitly to affect result values
of floating-point operations. When the state for the
FENV_ACCESS pragma (defined in <fenv.h>) is on, these
changes to the floating-point state are treated as side
effects which respect sequence points.295)
____________________
294This specification does not require dynamic rounding
precision nor trap enablement modes.
295If the state for the FENV_ACCESS pragma is off, the
implementation is free to assume the modes will be the
default ones and the flags will not be tested, which
allows certain optimizations (see F.8).
F.5 IEC 60559 floating-point arithmetic F.7.1
WG14/N843 Committee Draft -- August 3, 1998 519
F.7.2 Translation
[#1] During translation the IEC 60559 default modes are in
effect:
-- The rounding direction mode is rounding to nearest.
-- The rounding precision mode (if supported) is set so
that results are not shortened.
-- Trapping or stopping (if supported) is disabled on all
exceptions.
Recommended practice
[#2] The implementation should produce a diagnostic message
for each translation-time floating-point exception, other
than inexact;296) the implementation should then proceed
with the translation of the program.
F.7.3 Execution
[#1] At program startup the floating-point environment is
initialized as prescribed by IEC 60559:
-- All exception status flags are cleared.
-- The rounding direction mode is rounding to nearest.
-- The dynamic rounding precision mode (if supported) is
set so that results are not shortened.
-- Trapping or stopping (if supported) is disabled on all
exceptions.
F.7.4 Constant expressions
[#1] An arithmetic constant expression of floating type,
other than one in an initializer for an object that has
static storage duration, is evaluated (as if) during |
execution; thus, it is affected by any operative modes and
raises exceptions as required by IEC 60559 (provided the
state for the FENV_ACCESS pragma is on).297)
[#2] EXAMPLE
____________________
296As floating constants are converted to appropriate
internal representations at translation time, their
conversion is subject to default rounding modes and
raises no execution-time exceptions (even where the state
of the FENV_ACCESS pragma is on). Library functions, for
example strtod, provide execution-time conversion of
numeric strings.
F.7.2 IEC 60559 floating-point arithmetic F.7.4
520 Committee Draft -- August 3, 1998 WG14/N843
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
void f(void)
{
float w[] = { 0.0/0.0 }; // raises an exception
static float x = 0.0/0.0; // does not raise an exception
float y = 0.0/0.0; // raises an exception
double z = 0.0/0.0; // raises an exception
/* ... */
}
[#3] For the static initialization, the division is done at
translation time, raising no (execution-time) exceptions.
On the other hand, for the three automatic initializations
the invalid division occurs at execution time.
F.7.5 Initialization
[#1] All computation for automatic initialization is done |
(as if) at execution time; thus, it is affected by any
operative modes and raises exceptions as required by IEC
60559 (provided the state for the FENV_ACCESS pragma is on).
All computation for initialization of objects that have
static storage duration is done (as if) at translation time.
[#2] EXAMPLE
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
void f(void)
{
float u[] = { 1.1e75 }; // raises exceptions
static float v = 1.1e75; // does not raise exceptions
float w = 1.1e75; // raises exceptions
double x = 1.1e75; // may raise exceptions
float y = 1.1e75f; // may raise exceptions
long double z = 1.1e75; // does not raise exceptions
/* ... */
}
[#3] The static initialization of v raises no (execution-
time) exceptions because its computation is done at
translation time. The automatic initialization of u and w
____________________
297Where the state for the FENV_ACCESS pragma is on, results
of inexact expressions like 1.0/3.0 are affected by
rounding modes set at execution time, and expressions
such as 0.0/0.0 and 1.0/0.0 generate execution-time
exceptions. The programmer can achieve the efficiency of
translation-time evaluation through static
initialization, such as
const static double one_third = 1.0/3.0;
F.7.4 IEC 60559 floating-point arithmetic F.7.5
WG14/N843 Committee Draft -- August 3, 1998 521
require an execution-time conversion to float of the wider
value 1.1e75, which raises exceptions. The automatic
initializations of x and y entail execution-time conversion;
however, in some expression evaluation methods, the
conversions is not to a narrower format, in which case no
exception is raised.298) The automatic initialization of z
entails execution-time conversion, but not to a narrower
format, so no exception is raised. Note that the
conversions of the floating constants 1.1e75 and 1.1e75f to
their internal representations occur at translation time in
all cases.
F.7.6 Changing the environment
[#1] Operations defined in 6.5 and functions and macros
defined for the standard libraries change flags and modes
just as indicated by their specifications (including
conformance to IEC 60559). They do not change flags or
modes (so as to be detectable by the user) in any other
cases.
[#2] If the argument to the feraiseexcept function in
<fenv.h> represents IEC 60559 valid coincident exceptions
for atomic operations (namely overflow and inexact, or
underflow and inexact) then overflow or underflow is raised
before inexact.
F.8 Optimization
[#1] This section identifies code transformations that might
subvert IEC 60559-specified behavior, and others that do
not.
F.8.1 Global transformations
[#1] Floating-point arithmetic operations and external
function calls may entail side effects which optimization
shall honor, at least where the state of the FENV_ACCESS
pragma is on. The flags and modes in the floating-point
environment may be regarded as global variables; floating-
point operations (+, *, etc.) implicitly read the modes and
write the flags.
[#2] Concern about side effects may inhibit code motion and
removal of seemingly useless code. For example, in
____________________
298Use of float_t and double_t variables increases the
likelihood of translation-time computation. For example,
the automatic initialization
double_t x = 1.1e75;
could be done at translation time, regardless of the
expression evaluation method.
F.7.5 IEC 60559 floating-point arithmetic F.8.1
522 Committee Draft -- August 3, 1998 WG14/N843
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
void f(double x)
{
/* ... */
for (i = 0; i < n; i++) x + 1;
/* ... */
}
x + 1 might raise exceptions, so cannot be removed. And
since the loop body might not execute (maybe 0 >= n), x + 1
cannot be moved out of the loop. (Of course these
optimizations are valid if the implementation can rule out
the nettlesome cases.)
[#3] This specification does not require support for trap
handlers that maintain information about the order or count
of exceptions. Therefore, between function calls exceptions
need not be precise: the actual order and number of
occurrences of exceptions (> 1) may vary from what the
source code expresses. Thus the preceding loop could be
treated as
if (0 < n) x + 1;
F.8.2 Expression transformations
[#1]
x / 2 <-> x * 0.5 Although similar transformations
involving inexact constants
generally do not yield
numerically equivalent
expressions, if the constants are
exact then such transformations
can be made on IEC 60559 machines
and others that round perfectly.
1 * x and x / 1 -> x The expressions 1 * x, x / 1, and
x are equivalent (on IEC 60559
machines, among others).299)
x / x -> 1.0 The expressions x / x and 1.0 are
not equivalent if x can be zero,
infinite, or NaN.
x - y <-> x + (-y) The expressions x - y, x + (-y),
and (-y) + x are equivalent (on
IEC 60559 machines, among
____________________
299Strict support for signaling NaNs -- not required by
this specification -- would invalidate these and other
transformations that remove arithmetic operators.
F.8.1 IEC 60559 floating-point arithmetic F.8.2
WG14/N843 Committee Draft -- August 3, 1998 523
others).
x - y <-> -(y - x) The expressions x - y and -(y -
x) are not equivalent because 1 -
1 is +0 but -(1 - 1) is -0 (in
the default rounding
direction).300)
x - x -> 0.0 The expressions x - x and 0.0 are
not equivalent if x is a NaN or
infinite.
0 * x -> 0.0 The expressions 0 * x and 0.0 are
not equivalent if x is a NaN,
infinite, or -0.
x + 0 -> x The expressions x + 0 and x are
not equivalent if x is -0,
because (-0) + (+0) yields +0 (in
the default rounding direction),
not -0.
x - 0 -> x (+0) - (+0) yields -0 when
rounding is downward (toward -),
but +0 otherwise, and (-0) - (+0)
always yields -0; so, if the
state of the FENV_ACCESS pragma
is off, promising default
rounding, then the implementation
can replace x - 0 by x, even if x
might be zero.
-x <-> 0 - x The expressions -x and 0 - x are
not equivalent if x is +0,
because -(+0) yields -0, but 0 -
(+0) yields +0 (unless rounding
is downward).
____________________
300IEC 60559 prescribes a signed zero to preserve
mathematical identities across certain discontinuities.
Examples include:
1/(1/±)is±
and
conj(csqrt(z))iscsqrt(conj(z)),
for complex z.
F.8.2 IEC 60559 floating-point arithmetic F.8.2
524 Committee Draft -- August 3, 1998 WG14/N843
F.8.3 Relational operators
[#1]
x != x -> false The statement x != x is true if x
is a NaN.
x == x -> true The statement x == x is false if
x is a NaN.
x < y -> isless(x,y) (and similarly for <=, >, >=)
Though numerically equal, these
expressions are not equivalent
because of side effects when x or
y is a NaN and the state of the
FENV_ACCESS pragma is on. This
transformation, which would be
desirable if extra code were
required to cause the invalid
exception for unordered cases,
could be performed provided the
state of the FENV_ACCESS pragma
is off.
The sense of relational operators shall be maintained. This
includes handling unordered cases as expressed by the source
code.
[#2] EXAMPLE
// calls g and raises invalid
// if a and b are unordered
if (a < b)
f();
else
g();
is not equivalent to
// calls f and raises invalid
// if a and b are unordered
if (a >= b)
g();
else
f();
nor to
F.8.3 IEC 60559 floating-point arithmetic F.8.3
WG14/N843 Committee Draft -- August 3, 1998 525
// calls f without raising invalid
// if a and b are unordered
if (isgreaterequal(a,b))
g();
else
f();
nor, unless the state of the FENV_ACCESS pragma is off, to
// calls g without raising invalid
// if a and b are unordered
if (isless(a,b))
f();
else
g();
but is equivalent to
if (!(a < b))
g();
else
f();
F.8.4 Constant arithmetic
[#1] The implementation shall honor exceptions raised by
execution-time constant arithmetic wherever the state of the
FENV_ACCESS pragma is on. (See F.7.4 and F.7.5.) An
operation on constants that raises no exception can be
folded during translation, except, if the state of the
FENV_ACCESS pragma is on, a further check is required to
assure that changing the rounding direction to downward does
not alter the sign of the result,301) and implementations
that support dynamic rounding precision modes shall assure
further that the result of the operation raises no exception
when converted to the semantic type of the operation. |
____________________
3010 - 0 yields -0 instead of +0 just when the rounding
direction is downward.
F.8.3 IEC 60559 floating-point arithmetic F.8.4
526 Committee Draft -- August 3, 1998 WG14/N843
F.9 Mathematics <math.h> |
[#1] This subclause contains specifications of <math.h>
facilities that are particularly suited for IEC 60559
implementations.
[#2] The Standard C macro HUGE_VAL and its float and long
double analogs, HUGE_VALF and HUGE_VALL, expand to
expressions whose values are positive infinities.
[#3] Special cases for functions in <math.h> are covered
directly or indirectly by IEC 60559. The functions that IEC
60559 specifies directly are identified in F.3. The other
functions in <math.h> treat infinities, NaNs, signed zeros,
subnormals, and (provided the state of the FENV_ACCESS
pragma is on) the exception flags in a manner consistent
with the basic arithmetic operations covered by IEC 60559.
[#4] The invalid and divide-by-zero exceptions are raised as
specified in subsequent subclauses of this annex.
[#5] The overflow exception is raised whenever an infinity
-- or, because of rounding direction, a maximal-magnitude
finite number -- is returned in lieu of a value whose
magnitude is too large.
[#6] The underflow exception is raised whenever a result is
tiny (essentially subnormal or zero) and suffers loss of
accuracy.302)
[#7] Whether or when the trigonometric, hyperbolic, base-e
exponential, base-e logarithmic, error, and log gamma
functions raise the inexact exception is implementation-
defined. For other functions, the inexact exception is
raised whenever the rounded result is not identical to the
mathematical result.
[#8] Whether the inexact exception may be raised when the
rounded result actually does equal the mathematical result
is implementation-defined. Whether the underflow (and
inexact) exception may be raised when a result is tiny but
not inexact is implementation-defined.303) Otherwise, as
implied by F.7.6, the <math.h> functions do not raise
spurious exceptions (detectable by the user).
____________________
302IEC 60559 allows different definitions of underflow.
They all result in the same values, but differ on when
the exception is raised.
303It is intended that undeserved underflow and inexact
exceptions are raised only if determining inexactness
would be too costly.
F.9 IEC 60559 floating-point arithmetic F.9
WG14/N843 Committee Draft -- August 3, 1998 527
[#9] Whether the functions honor the rounding direction mode
is implementation-defined.
[#10] Functions with a NaN argument return a NaN result and |
raise no exception, except where stated otherwise.
[#11] The specifications in the following subclauses append
to the definitions in <math.h>. For families of functions,
the specifications apply to all of the functions even though
only the principal function is shown. |
Recommended practice |
[#12] If a function with one or more NaN arguments returns a |
NaN result, the result should be the same as one of the NaN |
arguments (converted to its parameter type), except perhaps |
for the sign.
F.9.1 Trigonometric functions
F.9.1.1 The acos functions
[#1]
-- acos(1) returns +0.
-- acos(x) returns a NaN and raises the invalid exception
for |x|>1.
F.9.1.2 The asin functions
[#1]
-- asin(±0) returns ±0.
-- asin(x) returns a NaN and raises the invalid exception
for |x|>1.
F.9.1.3 The atan functions
[#1]
-- atan(±0) returns ±0.
-- atan(±) returns ±pi/2.
F.9 IEC 60559 floating-point arithmetic F.9.1.3
528 Committee Draft -- August 3, 1998 WG14/N843
F.9.1.4 The atan2 functions
[#1]
-- atan2(±0, x) returns ±0, for x>0. |
-- atan2(±0, +0) returns ±0.304) |
-- atan2(±0, x) returns ±pi, for x<0. |
-- atan2(±0, -0) returns ±pi. |
-- atan2(y, ±0) returns pi/2 for y>0. |
-- atan2(y, ±0) returns -pi/2 for y<0. |
-- atan2(±y, ) returns ±0, for finite y>0. |
-- atan2(±, x) returns ±pi/2, for finite x. |
-- atan2(±y, -) returns ±pi, for finite y>0. |
-- atan2(±, ) returns ±pi/4. |
-- atan2(±, -) returns ±3pi/4. |
F.9.1.5 The cos functions
[#1]
-- cos(±0) returns 1.
-- cos(±) returns a NaN and raises the invalid exception.
F.9.1.6 The sin functions
[#1]
-- sin(±0) returns ±0.
-- sin(±) returns a NaN and raises the invalid exception.
____________________
304atan2(0, 0) does not raise the invalid exception, nor |
does atan2(y, 0) raise the divide-by-zero exception. |
F.9.1.3 IEC 60559 floating-point arithmetic F.9.1.6
WG14/N843 Committee Draft -- August 3, 1998 529
F.9.1.7 The tan functions
[#1]
-- tan(±0) returns ±0.
-- tan(±) returns a NaN and raises the invalid exception.
F.9.2 Hyperbolic functions
F.9.2.1 The acosh functions
[#1]
-- acosh(1) returns +0.
-- acosh(+) returns +.
-- acosh(x) returns a NaN and raises the invalid exception
if x<1.
F.9.2.2 The asinh functions
[#1]
-- asinh(±0) returns ±0.
-- asinh(±) returns ±.
F.9.2.3 The atanh functions
[#1]
-- atanh(±0) returns ±0.
-- atanh(±1) returns ± and raises the divide-by-zero
exception.
-- atanh(x) returns a NaN and raises the invalid exception
if |x|>1.
F.9.1.6 IEC 60559 floating-point arithmetic F.9.2.3
530 Committee Draft -- August 3, 1998 WG14/N843
F.9.2.4 The cosh functions
[#1]
-- cosh(±0) returns 1.
-- cosh(±) returns +.
F.9.2.5 The sinh functions
[#1]
-- sinh(±0) returns ±0.
-- sinh(±) returns ±.
F.9.2.6 The tanh functions
[#1]
-- tanh(±0) returns ±0.
-- tanh(±) returns ±1.
F.9.3 Exponential and logarithmic functions
F.9.3.1 The exp functions
[#1]
-- exp(±0) returns 1.
-- exp(+) returns +.
-- exp(-) returns +0.
F.9.3.2 The exp2 functions
[#1]
-- exp2(±0) returns 1.
-- exp2(+) returns +.
-- exp2(-) returns +0.
F.9.2.3 IEC 60559 floating-point arithmetic F.9.3.2
WG14/N843 Committee Draft -- August 3, 1998 531
F.9.3.3 The expm1 functions
[#1]
-- expm1(±0) returns ±0.
-- expm1(+) returns +.
-- expm1(-) returns -1.
F.9.3.4 The frexp functions
[#1]
-- frexp(±0, exp) returns ±0, and stores 0 in the object |
pointed to by exp.
-- frexp(±, exp) returns ±, and stores an unspecified |
value in the object pointed to by exp. |
-- frexp(x, exp) stores an unspecified value in the object |
pointed to by exp (and returns a NaN) when x is a NaN. |
-- frexp raises no exception.
[#2] On a binary system, frexp is equivalent to the comma
expression
( (*exp = (value == 0) ? 0 :
(int)(1 + logb(value))), scalbn(value, -(*exp)) )
F.9.3.5 The ilogb functions
[#1] No additional requirements.
F.9.3.6 The ldexp functions
[#1] On a binary system, ldexp(x, exp) is equivalent to |
scalbn(x, exp) |
F.9.3.2 IEC 60559 floating-point arithmetic F.9.3.6
532 Committee Draft -- August 3, 1998 WG14/N843
F.9.3.7 The log functions
[#1]
-- log(±0) returns - and raises the divide-by-zero
exception.
-- log(1) returns +0.
-- log(x) returns a NaN and raises the invalid exception
if x<0.
-- log(+) returns +.
F.9.3.8 The log10 functions
[#1]
-- log10(±0) returns - and raises the divide-by-zero
exception.
-- log10(1) returns +0.
-- log10(x) returns a NaN and raises the invalid exception
if x < 0.
-- log10(+) returns +.
F.9.3.9 The log1p functions
[#1]
-- log1p(±0) returns ±0.
-- log1p(-1) returns - and raises the divide-by-zero
exception.
-- log1p(x) returns a NaN and raises the invalid exception
if x<-1.
-- log1p(+) returns +.
F.9.3.6 IEC 60559 floating-point arithmetic F.9.3.9
WG14/N843 Committee Draft -- August 3, 1998 533
F.9.3.10 The log2 functions
[#1]
-- log2(±0) returns - and raises the divide-by-zero
exception.
-- log2(x) returns a NaN and raises the invalid exception
if x<0.
-- log2(+) returns +.
F.9.3.11 The logb functions
[#1]
-- logb(±) returns +.
-- logb(±0) returns - and raises the divide-by-zero
exception.
F.9.3.12 The modf functions
[#1]
-- modf(value, iptr) returns a result with the same sign |
as the argument value.
-- modf(±, iptr) returns ±0 and stores ± in the object |
pointed to by iptr.
-- modf of a NaN argument stores a NaN in the object |
pointed to by iptr (and returns a NaN).
[#2] modf behaves as though implemented by
#include <math.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
double modf(double value, double *iptr)
{
int save_round = fegetround();
fesetround(FE_TOWARDZERO);
*iptr = nearbyint(value);
fesetround(save_round);
return copysign(
isinf(value) ? 0.0 :
value - (*iptr), value);
}
F.9.3.9 IEC 60559 floating-point arithmetic F.9.3.12
534 Committee Draft -- August 3, 1998 WG14/N843
F.9.3.13 The scalbn and scalbln functions |
[#1]
-- scalbn(x, n) returns x if x is infinite or zero. |
-- scalbn(x, 0) returns x. |
F.9.4 Power and absolute value functions
F.9.4.1 The cbrt functions
[#1]
-- cbrt(±) returns ±.
-- cbrt(±0) returns ±0.
F.9.4.2 The fabs functions
[#1]
-- fabs(±0) returns +0.
-- fabs(±) returns +.
F.9.4.3 The hypot functions
[#1]
-- hypot(x, y), hypot(y, x), and hypot(x, -y) are |
equivalent.
-- hypot(x, y) returns + if x is infinite, even if y is a |
NaN.
-- hypot(x, ±0) is equivalent to fabs(x). |
F.9.4.4 The pow functions
[#1]
-- pow(x, ±0) returns 1 for any x, even a NaN. |
-- pow(x, +) returns + for |x|>1. |
-- pow(x, +) returns +0 for |x|<1. |
-- pow(x, -) returns +0 for |x|>1. |
-- pow(x, -) returns + for |x|<1. |
-- pow(+, y) returns + for y>0. |
F.9.3.13 IEC 60559 floating-point arithmetic F.9.4.4
WG14/N843 Committee Draft -- August 3, 1998 535
-- pow(+, y) returns +0 for y<0. |
-- pow(-, y) returns - for y an odd integer > 0. |
-- pow(-, y) returns + for y>0 and not an odd integer. |
-- pow(-, y) returns -0 for y an odd integer < 0. |
-- pow(-, y) returns +0 for y<0 and not an odd integer. |
-- pow(±1, ±) returns a NaN and raises the invalid |
exception.
-- pow(x, y) returns a NaN and raises the invalid |
exception for finite x<0 and finite non-integer y.
-- pow(±0, y) returns ± and raises the divide-by-zero |
exception for y an odd integer < 0.
-- pow(±0, y) returns + and raises the divide-by-zero |
exception for y<0 and not an odd integer.
-- pow(±0, y) returns ±0 for y an odd integer > 0. |
-- pow(±0, y) returns +0 for y>0 and not an odd integer. |
F.9.4.5 The sqrt functions
[#1] sqrt is fully specified as a basic arithmetic operation
in IEC 60559.
F.9.5 Error and gamma functions
F.9.5.1 The erf functions
[#1]
-- erf(±0) returns ±0.
-- erf(±) returns ±1.
F.9.4.4 IEC 60559 floating-point arithmetic F.9.5.1
536 Committee Draft -- August 3, 1998 WG14/N843
F.9.5.2 The erfc functions
[#1]
-- erfc(+) returns +0.
-- erfc(-) returns 2.
F.9.5.3 The lgamma functions
[#1]
-- lgamma(+) returns +.
-- lgamma(x) returns + and raises the divide-by-zero
exception if x is a negative integer or zero.
-- lgamma(-) returns +.
F.9.5.4 The tgamma functions |
[#1]
-- tgamma(+) returns +. |
-- tgamma(x) returns a NaN and raises the invalid |
exception if x is a negative integer or zero.
-- tgamma(-) returns a NaN and raises the invalid |
exception.
F.9.6 Nearest integer functions
F.9.6.1 The ceil functions
[#1]
-- ceil(x) returns x if x is ± or ±0.
The double version of ceil behaves as though implemented by
#include <math.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
double ceil(double x)
{
double result;
int save_round = fegetround();
fesetround(FE_UPWARD);
result = rint(x); // or nearbyint instead of rint
fesetround(save_round);
return result;
}
F.9.5.1 IEC 60559 floating-point arithmetic F.9.6.1
WG14/N843 Committee Draft -- August 3, 1998 537
F.9.6.2 The floor functions
[#1]
-- floor(x) returns x if x is ± or ±0.
See the sample implementation for ceil in F.9.6.1.
F.9.6.3 The nearbyint functions
[#1] The nearbyint functions use IEC 60559 rounding |
according to the current rounding direction. They do not |
raise the inexact exception if the result differs in value |
from the argument.
F.9.6.4 The rint functions
[#1] The rint functions differ from the nearbyint functions |
only in that they do raise the inexact exception if the |
result differs in value from the argument.
-- rint(±0) returns ±0 (for all rounding directions).
-- rint(±) returns ± (for all rounding directions).
F.9.6.5 The lrint and llrint functions |
[#1] The lrint and llrint functions provide floating-to- |
integer conversion as prescribed by IEC 60559. They round |
according to the current rounding direction. If the rounded
value is outside the range of the return type, the numeric |
result is unspecified and the invalid exception is raised. |
When they raise no other exception and the result differs |
from the argument, they raise the inexact exception.
F.9.6.6 The round functions
[#1] The double version of round behaves as though
implemented by
F.9.6.1 IEC 60559 floating-point arithmetic F.9.6.6
538 Committee Draft -- August 3, 1998 WG14/N843
#include <math.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
double round(double x)
{
double result;
fenv_t save_env;
feholdexcept(&save_env);
result = rint(x);
if (fetestexcept(FE_INEXACT)) {
fesetround(FE_TOWARDZERO);
result = rint(copysign(0.5 + fabs(x), x));|
}
feupdateenv(&save_env);
return result;
}
The round functions may, but are not required to, raise the |
inexact exception for non-integer numeric arguments, as this
implementation does. |
F.9.6.7 The lround and llround functions |
[#1] The lround and llround functions differ from the lrint |
and llrint functions with the default rounding direction |
just in that the lround and llround functions round halfway |
cases away from zero, and may (but need not) raise the
inexact exception for non-integer arguments that round to |
within the range of the return type.
F.9.6.8 The trunc functions
[#1] The trunc functions use IEC 60559 rounding toward zero |
(regardless of the current rounding direction).
F.9.7 Remainder functions
F.9.7.1 The fmod functions
[#1]
-- fmod(±0, y) returns ±0 if y is not zero. |
-- fmod(x, y) returns a NaN and raises the invalid |
exception if x is infinite or y is zero.
-- fmod(x, ±) returns x if x is not infinite. |
The double version of fmod behaves as though implemented by
F.9.6.6 IEC 60559 floating-point arithmetic F.9.7.1
WG14/N843 Committee Draft -- August 3, 1998 539
#include <math.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
double fmod(double x, double y)
{
double result;
result = remainder(fabs(x), (y = fabs(y)));
if (signbit(result)) result += y;
return copysign(result, x);
}
F.9.7.2 The remainder functions
[#1] The remainder functions are fully specified as a basic |
arithmetic operation in IEC 60559.
F.9.7.3 The remquo functions
[#1] The remquo functions follow the specifications for the |
remainder functions. They have no further specifications |
special to IEC 60559 implementations.
F.9.8 Manipulation functions
F.9.8.1 The copysign functions
[#1] copysign is specified in the Appendix to IEC 60559.
F.9.8.2 The nan functions
[#1] All IEC 60559 implementations support quiet NaNs, in
all floating formats.
F.9.8.3 The nextafter functions
[#1]
-- nextafter(x, y) raises the overflow and inexact |
exceptions if x is finite and the function value is
infinite.
-- nextafter(x, y) raises the underflow and inexact |
exceptions if the function value is subnormal or zero
and x!=y.
F.9.7.1 IEC 60559 floating-point arithmetic F.9.8.3
540 Committee Draft -- August 3, 1998 WG14/N843
F.9.8.4 The nextafterx functions
No additional requirements.
F.9.9 Maximum, minimum, and positive difference functions
F.9.9.1 The fdim functions
[#1] No additional requirements. |
F.9.9.2 The fmax functions
[#1]
-- If just one argument is a NaN, the fmax functions |
return the other argument (if both arguments are NaNs, |
the functions return a NaN).
The body of the fmax function might be305)
{ return (isgreaterequal(x, y) ||
isnan(y)) ? x : y; }
F.9.9.3 The fmin functions
[#1] The fmin functions are analogous to the fmax functions. |
See F.9.9.2.
F.9.10 Floating point multiply-add
F.9.10.1 The fma functions
[#1]
-- fma(x, y, z) computes the sum z plus the product x |
times y, correctly rounded once.
-- fma(x, y, z) returns a NaN and optionally raises the |
invalid exception if one of x and y is infinite, the
other is zero, and z is a NaN.
-- fma(x, y, z) returns a NaN and raises the invalid |
exception if one of x and y is infinite, the other is
zero, and z is not a NaN.
-- fma(x, y, z) returns a NaN and raises the invalid |
exception if x times y is an exact infinity and z is
also an infinity but with the opposite sign.
____________________
305Ideally, fmax would be sensitive to the sign of zero, for
example fmax(-0.0, +0.0) would return +0; however, |
implementation in software might be impractical.
F.9.8.3 IEC 60559 floating-point arithmetic F.9.10.1
WG14/N843 Committee Draft -- August 3, 1998 541
Annex G
(informative)
IEC 60559-compatible complex arithmetic
G.1 Introduction
[#1] This annex supplements annex F to specify complex
arithmetic for compatibility with IEC 60559 real floating-
point arithmetic. An implementation supports this
specification if and only if it defines the macro
__STD_IEC_559_COMPLEX__.
G.2 Types
[#1] There are three imaginary types, designated as float
_Imaginary, double _Imaginary, and long double _Imaginary.
The imaginary types (along with the real floating and
complex types) are floating types.
[#2] For imaginary types, the corresponding real type is
given by deleting the keyword _Imaginary from the type name.
[#3] Each imaginary type has the same representation and
alignment requirements as the corresponding real type. The
value of an object of imaginary type is the value of the
real representation times the imaginary unit.
[#4] The imaginary type domain comprises the imaginary |
types.
G.3 Conversions
G.3.1 Imaginary types
[#1] Conversions among imaginary types follow rules
analogous to those for real floating types.
G.3.2 Real and imaginary
[#1] When a value of imaginary type is converted to a real
type, the result is a positive zero.
[#2] When a value of real type is converted to an imaginary
type, the result is a positive imaginary zero.
G IEC 60559-compatible complex arithmetic G.3.2
542 Committee Draft -- August 3, 1998 WG14/N843
G.3.3 Imaginary and complex
[#1] When a value of imaginary type is converted to a
complex type, the real part of the complex result value is a
positive zero and the imaginary part of the complex result
value is determined by the conversion rules for the
corresponding real types.
[#2] When a value of complex type is converted to an
imaginary type, the real part of the complex value is
discarded and the value of the imaginary part is converted
according to the conversion rules for the corresponding real
types.
G.4 Binary operators
[#1] The following subclauses supplement 6.5 in order to
specify the type of the result for an operation with an
imaginary operand.
[#2] For most operand types, the value of the result of a
binary operator with an imaginary or complex operand is
completely determined, with reference to real arithmetic, by
the usual mathematical formula. For some operand types, the
usual mathematical formula is problematic because of its
treatment of infinities and because of undue overflow or
underflow; in these cases the result satisfies certain
properties (specified in G.4.1), but is not completely
determined.
G.4.1 Multiplicative operators
Semantics
[#1] If one operand has real type and the other operand has
imaginary type, then the result has imaginary type. If both
operands have imaginary type, then the result has real type.
(If either operand has complex type, then the result has
complex type.)
[#2] If the operands are not both complex, then the result
and exception behavior of the * operator is defined by the |
usual mathematical formula:
|| | |
* || u | iv | u+iv
-----++------------+-------------+-------------
x || xu | i(xv) | (xu)+i(xv)
-----++------------+-------------+-------------
iy || i(yu) | -yv | (-yv)+i(yu)
-----++------------+-------------+-------------
x+iy ||(xu)+i(yu) | (-yv)+i(xv) |
[#3] If the second operand is not complex, then the result
and exception behavior of the / operator is defined by the |
G.3.3 IEC 60559-compatible complex arithmetic G.4.1
WG14/N843 Committee Draft -- August 3, 1998 543
usual mathematical formula:
|| |
/ || u | iv
-----++--------------+---------------
x || x/u | i(-x/v)
-----++--------------+---------------
iy || i(y/u) | y/v
-----++--------------+---------------
x+iy ||(x/u)+i(y/u) | (y/v)+i(-x/v) |
[#4] A complex or imaginary value with at least one infinite
part is regarded as an infinity (even if its other part is a
NaN). A complex or imaginary value is a finite number if
each of its parts is a finite number (neither infinite nor
NaN). A complex or imaginary value is a zero if each of its
parts is a zero. The * and / operators satisfy the
following infinity properties for all real, imaginary, and
complex operands:306)
-- if one operand is an infinity and the other operand is
a nonzero finite number or an infinity, then the result
of the * operator is an infinity;
-- if the first operand is an infinity and the second
operand is a finite number, then the result of the /
operator is an infinity;
-- if the first operand is a finite number and the second
operand is an infinity, then the result of the /
operator is a zero;
-- if the first operand is a nonzero finite number or an
infinity and the second operand is a zero, then the
result of the / operator is an infinity.
[#5] If both operands of the * operator are complex or if
the second operand of the / operator is complex, the
operator raises exceptions if appropriate for the
calculation of the parts of the result, and may raise
spurious exceptions.
[#6] EXAMPLE 1 Multiplication of double _Complex operands
could be implemented as follows. Note that the imaginary
unit I has imaginary type (see G.5).
____________________
306These properties are already implied for those cases
covered in the tables, but are required for all cases (at
least where the state for CX_LIMITED_RANGE is off).
G.4.1 IEC 60559-compatible complex arithmetic G.4.1
544 Committee Draft -- August 3, 1998 WG14/N843
#include <math.h>
#include <complex.h>
/* Multiply z * w ... */
double complex _Cmultd(double complex z, double complex w)
{
#pragma STDC FP_CONTRACT OFF
double a, b, c, d, ac, bd, ad, bc, x, y;
a = creal(z); b = cimag(z)
c = creal(w); d = cimag(w);
ac = a * c; bd = b * d;
ad = a * d; bc = b * c;
x = ac - bd;
y = ad + bc;
/* Recover infinities that computed as NaN+iNaN ... */
if (isnan(x) && isnan(y)) {
int recalc = 0;
if ( isinf(a) || isinf(b) ) { /* z is infinite */
/* "Box" the infinity ... */
a = copysign(isinf(a) ? 1.0 : 0.0, a);
b = copysign(isinf(b) ? 1.0 : 0.0, b);
/* Change NaNs in the other factor to 0 ... */
if (isnan(c)) c = copysign(0.0, c);
if (isnan(d)) d = copysign(0.0, d);
recalc = 1;
}
if ( isinf(c) || isinf(d) ) { /* w is infinite */
/* "Box" the infinity ... */
c = copysign(isinf(c) ? 1.0 : 0.0, c);
d = copysign(isinf(d) ? 1.0 : 0.0, d);
/* Change NaNs in the other factor to 0 ... */
if (isnan(a)) a = copysign(0.0, a);
if (isnan(b)) b = copysign(0.0, b);
recalc = 1;
}
if (!recalc) {
/* *Recover infinities from overflow cases ... */
if (isinf(ac) || isinf(bd) ||
isinf(ad) || isinf(bc)) {
/* Change all NaNs to 0 ... */
if (isnan(a)) a = copysign(0.0, a);
if (isnan(b)) b = copysign(0.0, b);
if (isnan(c)) c = copysign(0.0, c);
if (isnan(d)) d = copysign(0.0, d);
recalc = 1;
}
}
if (recalc) {
x = INFINITY * ( a * c - b * d );
y = INFINITY * ( a * d + b * c );
}
}
return x + I * y;
}
G.4.1 IEC 60559-compatible complex arithmetic G.4.1
WG14/N843 Committee Draft -- August 3, 1998 545
[#7] This implementation achieves the required treatment of |
infinities at the cost of only one isnan test in ordinary |
(finite) cases. It is less than ideal in that undue |
overflow and underflow may occur.
[#8] EXAMPLE 2 Division of two double _Complex operands
could be implemented as follows.
G.4.1 IEC 60559-compatible complex arithmetic G.4.1
546 Committee Draft -- August 3, 1998 WG14/N843
#include <math.h>
#include <complex.h>
/* Divide z / w ... */
double complex _Cdivd(double complex z, double complex w)
{
#pragma STDC FP_CONTRACT OFF
double a, b, c, d, logbw, denom, x, y;
int ilogbw = 0;
a = creal(z); b = cimag(z);
c = creal(w); d = cimag(w);
logbw = logb(fmax(fabs(c), fabs(d)));
if (isfinite(logbw)) {
ilogbw = (int)logbw;
c = scalbn(c, -ilogbw);
d = scalbn(d, -ilogbw);
}
denom = c * c + d * d;
x = scalbn((a * c + b * d) / denom, -ilogbw);
y = scalbn((b * c - a * d) / denom, -ilogbw);
/*
* Recover infinities and zeros that computed
* as NaN+iNaN; the only cases are non-zero/zero,
* infinite/finite, and finite/infinite, ...
*/
if (isnan(x) && isnan(y)) {
if ((denom == 0.0) &&
(!isnan(a) || !isnan(b))) {
x = copysign(INFINITY, c) * a;
y = copysign(INFINITY, c) * b;
}
else if ((isinf(a) || isinf(b)) &&
isfinite(c) && isfinite(d)) {
a = copysign(isinf(a) ? 1.0 : 0.0, a);
b = copysign(isinf(b) ? 1.0 : 0.0, b);
x = INFINITY * ( a * c + b * d );
y = INFINITY * ( b * c - a * d );
}
else if (isinf(logbw) &&
isfinite(a) && isfinite(b)) {
c = copysign(isinf(c) ? 1.0 : 0.0, c);
d = copysign(isinf(d) ? 1.0 : 0.0, d);
x = 0.0 * ( a * c + b * d );
y = 0.0 * ( b * c - a * d );
}
}
return x + I * y;
}
[#9] Scaling the denominator alleviates the main overflow
and underflow problem, which is more serious than for
multiplication. In the spirit of the multiplication example
above, this code does not defend against overflow and
underflow in the calculation of the numerator. Scaling with
G.4.1 IEC 60559-compatible complex arithmetic G.4.1
WG14/N843 Committee Draft -- August 3, 1998 547
the scalbn function, instead of with division, provides
better roundoff characteristics.
G.4.2 Additive operators
Semantics
[#1] If one operand has real type and the other operand has
imaginary type, then the result has complex type. If both
operands have imaginary type, then the result has imaginary
type. (If either operand has complex type, then the result
has complex type.)
[#2] In all cases the result and exception behavior of a +
or - operator is defined by the usual mathematical formula: |
|| | |
+ or - || u | iv | u+iv
-------++-------------+--------------+--------------
x || x±u | x±iv | (x±u)±iv
-------++-------------+--------------+--------------
iy || ±u+iy | i(y±v) | ±u+i(y±v)
-------++-------------+--------------+--------------
x+iy || (x±u)+iy | x+i(y±v) | (x±u)+i(y±v)
G.5 Complex arithmetic <complex.h> |
[#1] The macros
imaginary
and
_Imaginary_I
are defined, and the macro
I
is defined to be _Imaginary_I (7.3).
[#2] This subclause contains specifications for the
<complex.h> functions that are particularly suited to IEC
60559 implementations.
[#3] The functions are continuous onto both sides of their
branch cuts, taking into account the sign of zero. For
example, csqrt(-2 ± 0*I) == ±sqrt(2)*I.
[#4] Since complex and imaginary values are composed of real
values, each function may be regarded as computing real
values from real values. Except as noted, the functions
treat real infinities, NaNs, signed zeros, subnormals, and
the exception flags in a manner consistent with the
G.4.1 IEC 60559-compatible complex arithmetic G.5
548 Committee Draft -- August 3, 1998 WG14/N843
specifications for real functions in F.9.307)
[#5] The functions cimag, conj, cproj, and creal are fully
specified for all implementations, including IEC 60559 ones,
in 7.3.9. These functions raise no exceptions.
[#6] Each of the functions cabs and carg is specified by a
formula in terms of a real function (whose special cases are
covered in annex F):
cabs(x+iy) = hypot(x, y) |
carg(x+iy) = atan2(y, x) |
[#7] Each of the functions casin, catan, ccos, csin, ctan,
and cpow is specified implicitly by a formula in terms of
other complex functions (whose special cases are specified
below):
casin(z) = -i casinh(iz) |
catan(z) = -i catanh(iz) |
ccos(z) = ccosh(iz) |
csin(z) = -i csinh(iz) |
ctan(z) = -i ctanh(iz) |
cpow(z, c) = cexp(c clog(z)) |
[#8] For the other functions, the following subclauses
specify behavior for special cases, including treatment of
the invalid and divide-by-zero exceptions. For families of
functions, the specifications apply to all of the functions
even though only the principal function is shown. For a
function f satisfying f(conj(z))=conj(f(z)), the |
specification for the upper half-plane implies the
specification for the lower half-plane; if also the
function f is either even, f(-z)=f(z), or odd, f(-z)=-f(z),
then the specification for the first quadrant implies the
specification for the other three quadrants. |
[#9] In the following subclauses, cis(y) is defined as |
cos(y)+isin(y).
G.5.1 Trigonometric functions
____________________
307As noted in G.4.1, a complex value with at least one
infinite part is regarded as an infinity even if its
other part is a NaN.
G.5 IEC 60559-compatible complex arithmetic G.5.1
WG14/N843 Committee Draft -- August 3, 1998 549
G.5.1.1 The cacos functions
[#1]
-- cacos(conj(z)) = conj(cacos(z)). |
-- cacos(±0+i0) returns /2-i0. |
-- cacos(-+i) returns 3/4-i. |
-- cacos(++i) returns /4-i. |
-- cacos(x+i) returns /2-i, for finite x. |
-- cacos(-+iy) returns -i, for positive-signed finite y. |
-- cacos(++iy) returns +0-i, for positive-signed finite y. |
-- cacos(±+iNaN) returns NaN±i (where the sign of the |
imaginary part of the result is unspecified).
-- cacos(±0+iNaN) returns /2+iNaN. |
-- cacos(NaN+i) returns NaN-i. |
-- cacos(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for nonzero finite x. |
-- cacos(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for finite y. |
-- cacos(NaN+iNaN) returns NaN+iNaN. |
G.5.2 Hyperbolic functions
G.5.2.1 The cacosh functions
[#1]
-- cacosh(conj(z)) = conj(cacosh(z)). |
-- cacosh(±0+i0) returns +0+i/2. |
-- cacosh(-+i) returns ++i3/4. |
-- cacosh(++i) returns ++i/4. |
-- cacosh(x+i) returns ++i/2, for finite x. |
-- cacosh(-+iy) returns ++i, for positive-signed finite y. |
-- cacosh(++iy) returns ++i0, for positive-signed finite |
y.
G.5.1 IEC 60559-compatible complex arithmetic G.5.2.1
550 Committee Draft -- August 3, 1998 WG14/N843
-- cacosh(NaN+i) returns ++iNaN. |
-- cacosh(±+iNaN) returns ++iNaN. |
-- cacosh(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for finite x. |
-- cacosh(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for finite y. |
-- cacosh(NaN+iNaN) returns NaN+iNaN. |
G.5.2.2 The casinh functions
-- casinh(conj(z)) = conj(casinh(z)) and casinh is odd. |
-- casinh(+0+i0) returns 0+i0. |
-- casinh(+i) returns ++i/4. |
-- casinh(x+i) returns ++i/2 for positive-signed finite x. |
-- casinh(++iy) returns ++i0 for positive-signed finite y. |
-- casinh(NaN+i) returns ±+iNaN (where the sign of the |
real part of the result is unspecified).
-- casinh(++iNaN) returns ++iNaN. |
-- casinh(NaN+i0) returns NaN+i0. |
-- casinh(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for finite nonzero y. |
-- casinh(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for finite x. |
-- casinh(NaN+iNaN) returns NaN+iNaN. |
G.5.2.3 The catanh functions
[#1]
-- catanh(conj(z)) = conj(catanh(z)) and catanh is odd. |
-- catanh(+0+i0) returns +0+i0. |
-- catanh(++i) returns +0+i/2. |
-- catanh(++iy) returns +0+i/2, for finite positive-signed |
y.
-- catanh(x+i) returns +0+i/2, for finite positive-signed |
x.
G.5.2.1 IEC 60559-compatible complex arithmetic G.5.2.3
WG14/N843 Committee Draft -- August 3, 1998 551
-- catanh(+0+iNaN) returns +0+iNaN. |
-- catanh(NaN+i) returns ±0+i/2 (where the sign of the |
real part of the result is unspecified).
-- catanh(++iNaN) returns +0+iNaN. |
-- catanh(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for finite y. |
-- catanh(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for nonzero finite x. |
-- catanh(NaN+iNaN) returns NaN+iNaN. |
G.5.2.4 The ccosh functions
[#1]
-- ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even. |
-- ccosh(+0+i0) returns 1+i0. |
-- ccosh(+0+i) returns NaN±i0 (where the sign of the |
imaginary part of the result is unspecified) and raises |
the invalid exception.
-- ccosh(++i0) returns ++i0. |
-- ccosh(++i) returns ++iNaN and raises the invalid |
exception.
-- ccosh(x+i) returns NaN+iNaN and raises the invalid |
exception, for finite nonzero x.
-- ccosh(++iy) returns +cis(y), for finite nonzero y. |
-- ccosh(+0+iNaN) returns NaN±i0 (where the sign of the |
imaginary part of the result is unspecified).
-- ccosh(++iNaN) returns ++iNaN. |
-- ccosh(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for finite nonzero x. |
-- ccosh(NaN+i0) returns NaN±i0 (where the sign of the |
imaginary part of the result is unspecified).
-- ccosh(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for all nonzero numbers y. |
-- ccosh(NaN+iNaN) returns NaN+iNaN. |
G.5.2.3 IEC 60559-compatible complex arithmetic G.5.2.4
552 Committee Draft -- August 3, 1998 WG14/N843
G.5.2.5 The csinh functions
[#1]
-- csinh(conj(z)) = conj(csinh(z)) and csinh is odd. |
-- csinh(+0+i0) returns +0+i0. |
-- csinh(+0+i) returns ±0+iNaN (where the sign of the real |
part of the result is unspecified) and raises the
invalid exception.
-- csinh(++i0) returns ++i0. |
-- csinh(++i) returns ±+iNaN (where the sign of the real |
part of the result is unspecified) and raises the
invalid exception.
-- csinh(++iy) returns +cis(y), for positive finite y. |
-- csinh(x+i) returns NaN+iNaN and raises the invalid |
exception, for positive finite x.
-- csinh(+0+iNaN) returns ±0+iNaN (where the sign of the |
real part of the result is unspecified).
-- csinh(++iNaN) returns ±+iNaN (where the sign of the |
real part of the result is unspecified).
-- csinh(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for finite nonzero x. |
-- csinh(NaN+i0) returns NaN+i0. |
-- csinh(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for all nonzero numbers y. |
-- csinh(NaN+iNaN) returns NaN+iNaN. |
G.5.2.6 The ctanh functions
[#1]
-- ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd. |
-- ctanh(+0+i0) returns +0+i0. |
-- ctanh(++iy) returns 1+i0, for all positive-signed |
numbers y.
-- ctanh(x+i) returns NaN+iNaN and raises the invalid |
exception, for finite x.
G.5.2.4 IEC 60559-compatible complex arithmetic G.5.2.6
WG14/N843 Committee Draft -- August 3, 1998 553
-- ctanh(++iNaN) returns 1±i0 (where the sign of the |
imaginary part of the result is unspecified).
-- ctanh(NaN+i0) returns NaN+i0. |
-- ctanh(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for all nonzero numbers y. |
-- ctanh(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for finite x. |
-- ctanh(NaN+iNaN) returns NaN+iNaN. |
G.5.3 Exponential and logarithmic functions
G.5.3.1 The cexp functions
[#1]
-- cexp(conj(z)) = conj(cexp(z)). |
-- cexp(±0+i0) returns 1+i0. |
-- cexp(++i0) returns ++i0. |
-- cexp(-+i) returns ±0±i0 (where the signs of the real |
and imaginary parts of the result are unspecified).
-- cexp(++i) returns ±+iNaN and raises the invalid |
exception (where the sign of the real part of the |
result is unspecified).
-- cexp(x+i) returns NaN+iNaN and raises the invalid |
exception, for finite x.
-- cexp(-+iy) returns +0cis(y), for finite y. |
-- cexp(++iy) returns +cis(y), for finite nonzero y. |
-- cexp(-+iNaN) returns ±0±i0 (where the signs of the real |
and imaginary parts of the result are unspecified).
-- cexp(++iNaN) returns ±+iNaN (where the sign of the real |
part of the result is unspecified).
-- cexp(NaN+i0) returns NaN+i0. |
-- cexp(NaN+iy) returns NaN+iNaN and optionally raises the |
invalid exception, for all non-zero numbers y. |
-- cexp(x+iNaN) returns NaN+iNaN and optionally raises the |
invalid exception, for finite x. |
G.5.2.6 IEC 60559-compatible complex arithmetic G.5.3.1
554 Committee Draft -- August 3, 1998 WG14/N843
-- cexp(NaN+iNaN) returns NaN+iNaN. |
G.5.3.2 The clog functions
[#1]
-- clog(conj(z)) = conj(clog(z)). |
-- clog(0+i0) returns -+i and raises the divide-by-zero |
exception.
-- clog(+0+i0) returns -+i0 and raises the divide-by-zero |
exception.
-- clog(-+i) returns ++i3/4. |
-- clog(++i) returns ++i/4. |
-- clog(x+i) returns ++i/2, for finite x. |
-- clog(-+iy) returns ++i, for finite positive-signed y. |
-- clog(++iy) returns ++i0, for finite positive-signed y. |
-- clog(±+iNaN) returns ++iNaN. |
-- clog(NaN+i) returns ++iNaN. |
-- clog(x+iNaN) returns NaN+iNaN and optionally raises the |
invalid exception, for finite x. |
-- clog(NaN+iy) returns NaN+iNaN and optionally raises the |
invalid exception, for finite y. |
-- clog(NaN+iNaN) returns NaN+iNaN. |
G.5.4 Power and absolute-value functions
G.5.4.1 The csqrt functions
[#1]
-- csqrt(conj(z)) = conj(csqrt(z)). |
-- csqrt(±0+i0) returns +0+i0. |
-- csqrt(-+iy) returns +0+i, for finite positive-signed y. |
-- csqrt(++iy) returns ++i0, for finite positive-signed y. |
-- csqrt(x+i) returns ++i, for all x (including NaN). |
-- csqrt(-+iNaN) returns NaN±i (where the sign of the |
imaginary part of the result is unspecified).
G.5.3.1 IEC 60559-compatible complex arithmetic G.5.4.1
WG14/N843 Committee Draft -- August 3, 1998 555
-- csqrt(++iNaN) returns ++iNaN. |
-- csqrt(x+iNaN) returns NaN+iNaN and optionally raises |
the invalid exception, for finite x. |
-- csqrt(NaN+iy) returns NaN+iNaN and optionally raises |
the invalid exception, for finite y. |
-- csqrt(NaN+iNaN) returns NaN+iNaN. |
G.6 Type-generic math <tgmath.h> |
[#1] Type-generic macros that accept complex arguments also
accept imaginary arguments. If an argument is imaginary,
the macro expands to an expression whose type is real,
imaginary, or complex, as appropriate for the particular
function: if the argument is imaginary, then the types of
cos, cosh, fabs, carg, cimag, and creal are real; the types
of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are
imaginary; and the types of the others are complex.
[#2] Given an imaginary argument, each of the type-generic
macros cos, sin, tan, cosh, sinh, tanh, asin, atan, asinh,
atanh is specified by a formula in terms of real functions:
cos(iy) = cosh(y) |
sin(iy) = i sinh(y) |
tan(iy) = i tanh(y) |
cosh(iy) = cos(y) |
sinh(iy) = i sin(y) |
tanh(iy) = i tan(y) |
asin(iy) = i asinh(y) |
atan(iy) = i atanh(y) |
asinh(iy) = i asin(y) |
atanh(iy) = i atan(y) |
G.5.4.1 IEC 60559-compatible complex arithmetic G.6
556 Committee Draft -- August 3, 1998 WG14/N843
Annex H
(informative)
Language independent arithmetic
H.1 Introduction
[#1] This annex documents the extent to which the C language
supports the ISO/IEC 10967-1 standard for language-
independent arithmetic (LIA-1). LIA-1 is more general than
IEC 60559 (annex F) in that it covers integer and diverse
floating-point arithmetics.
H.2 Types
[#1] The relevant C arithmetic types meet the requirements
of LIA-1 types if an implementation adds notification of
exceptional arithmetic operations and meets the 1 unit in
the last place (ULP) accuracy requirement (LIA-1 subclause
5.2.8).
H.2.1 Boolean type
[#1] The LIA-1 data type Boolean is implemented by the C
data type bool with values of true and false, all from
<stdbool.h>.
H.2.2 Integer types
[#1] The signed C integer types int, long int, long long
int, and the corresponding unsigned types are compatible
with LIA-1. If an implementation adds support for the LIA-1
exceptional values integer_overflow and undefined, then
those types are LIA-1 conformant types. C's unsigned
integer types are ``modulo'' in the LIA-1 sense in that
overflows or out-of-bounds results silently wrap. An
implementation that defines signed integer types as also
being modulo need not detect integer overflow, in which
case, only integer divide-by-zero need be detected.
[#2] The parameters for the integer data types can be
accessed by the following:
maxint INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX,
ULONG_MAX, ULLONG_MAX
minint INT_MIN, LONG_MIN, LLONG_MIN
[#3] The parameter ``bounded'' is always true, and is not
provided. The parameter ``minint'' is always 0 for the
unsigned types, and is not provided for those types.
H Language independent arithmetic H.2.2
WG14/N843 Committee Draft -- August 3, 1998 557
H.2.2.1 Integer operations
[#1] The integer operations on integer types are the
following:
addI x + y
subI x - y
mulI x * y
divI, divtI x / y
remI, remtI x % y
negI - x
absI abs(x), labs(x), llabs(x)
eqI x == y
neqI x != y
lssI x < y
leqI x <= y
gtrI x > y
geqI x >= y
where x and y are expressions of the same integer type.
H.2.3 Floating-point types
[#1] The C floating-point types float, double, and long
double are compatible with LIA-1. If an implementation adds
support for the LIA-1 exceptional values underflow,
floating_overflow, and undefined, then those types are
conformant with LIA-1. An implementation that uses IEC
60559 floating-point formats and operations (see annex F)
along with IEC 60559 status flags and traps has LIA-1
conformant types.
H.2.3.1 Floating-point parameters
[#1] The parameters for a floating point data type can be
accessed by the following:
r FLT_RADIX
p FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG
H.2.2.1 Language independent arithmetic H.2.3.1
558 Committee Draft -- August 3, 1998 WG14/N843
emax FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP
emin FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP
[#2] The derived constants for the floating point types are
accessed by the following:
fmax FLT_MAX, DBL_MAX, LDBL_MAX
fminN FLT_MIN, DBL_MIN, LDBL_MIN
epsilon FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON
rnd_style FLT_ROUNDS
H.2.3.2 Floating-point operations
[#1] The floating-point operations on floating-point types
are the following:
addF x + y
subF x - y
mulF x * y
divF x / y
negF - x
absF fabsf(x), fabs(x), fabsl(x)
exponentF 1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x)
scaleF scalbnf(x, n), scalbn(x, n), scalbnl(x, n),
scalblnf(x, li), scalbln(x, li), scalblnl(x, li)
intpartF modff(x, &y), modf(x, &y), modfl(x, &y)
fractpartF modff(x, &y), modf(x, &y), modfl(x, &y)
eqF x == y
neqF x != y
lssF x < y
leqF x <= y
gtrF x > y
geqF x >= y
where x and y are expressions of the same floating point
H.2.3.1 Language independent arithmetic H.2.3.2
WG14/N843 Committee Draft -- August 3, 1998 559
type, n is of type int, and li is of type long int.
H.2.3.3 Rounding styles
[#1] The C Standard requires all floating types to use the
same radix and rounding style, so that only one identifier
for each is provided to map to LIA-1.
[#2] The FLT_ROUNDS parameter can be used to indicate the
LIA-1 rounding styles:
truncate FLT_ROUNDS == 0
nearest FLT_ROUNDS == 1
other FLT_ROUNDS != 0 && FLT_ROUNDS != 1
provided that an implementation extends FLT_ROUNDS to cover
the rounding style used in all relevant LIA-1 operations,
not just addition as in C.
H.2.4 Type conversions
[#1] The LIA-1 type conversions are the following type
casts:
cvtI'->I (int)i, (long int)i, (long long int)i, (unsigned
int)i, (unsigned long int)i, (unsigned long long
int)i
cvtF->I (int)x, (long int)x, (long long int)x, (unsigned
int)x, (unsigned long int)x, (unsigned long long
int)x
cvtI->F (float)i, (double)i, (long double)i
cvtF'->F (float)x, (double)x, (long double)x
[#2] In the above conversions from floating to integer, the
use of (cast)x can be replaced with (cast)round(x),
(cast)rint(x), (cast)nearbyint(x), (cast)trunc(x),
(cast)ceil(x), or (cast)floor(x). In addition, C's
floating-point to integer conversion functions, lrint(),
llrint(), lround(), and llround(), can be used. They all
meet LIA-1's requirements on floating to integer rounding
for in-range values. For out-of-range values, the
conversions shall silently wrap for the modulo types.
[#3] The fmod() function is useful for doing silent wrapping
to unsigned integer types, e.g., fmod( fabs(rint(x)),
65536.0 ) or (0.0 <= (y = fmod( rint(x), 65536.0 )) ? y :
65536.0 + y) will compute an integer value in the range 0.0
to 65535.0 which can then be cast to unsigned short int.
But, the remainder() function is not useful for doing silent
H.2.3.2 Language independent arithmetic H.2.4
560 Committee Draft -- August 3, 1998 WG14/N843
wrapping to signed integer types, e.g., remainder( rint(x),
65536.0 ) will compute an integer value in the range
-32767.0 to +32768.0 which is not, in general, in the range
of signed short int.
[#4] C's conversions (casts) from floating-point to
floating-point can meet LIA-1 requirements if an
implementation uses round-to-nearest (IEC 60559 default).
[#5] C's conversions (casts) from integer to floating-point
can meet LIA-1 requirements if an implementation uses round-
to-nearest.
H.3 Notification
[#1] Notification is the process by which a user or program
is informed that an exceptional arithmetic operation has
occurred. C's operations are compatible with LIA-1 in that
C allows an implementation to cause a notification to occur
when any arithmetic operation returns an exceptional value
as defined in LIA-1 clause 5.
H.3.1 Notification alternatives
[#1] LIA-1 requires at least the following two alternatives
for handling of notifications: setting indicators or trap-
and-terminate. LIA-1 allows a third alternative: trap-and-
resume.
[#2] An implementation need only support a given
notification alternative for the entire program. An
implementation may support the ability to switch between
notification alternatives during execution, but is not
required to do so. An implementation can provide separate
selection for each kind of notification, but this is not
required.
[#3] C allows an implementation to provide notification.
C's SIGFPE (for traps) and FE_INVALID, FE_DIVBYZERO,
FE_OVERFLOW, FE_UNDERFLOW (for indicators) can provide LIA-1
notification.
[#4] C's signal handlers are compatible with LIA-1. Default
handling of SIGFPE can provide trap-and-terminate behavior.
User-provided signal handlers for SIGFPE allow for trap-and-
resume behavior.
H.3.1.1 Indicators
[#1] C's <fenv.h> status flags are compatible with the LIA-1
indicators.
[#2] The following mapping is for floating-point types:
H.2.4 Language independent arithmetic H.3.1.1
WG14/N843 Committee Draft -- August 3, 1998 561
undefined FE_INVALID, FE_DIVBYZERO
floating_overflow FE_OVERFLOW
underflow FE_UNDERFLOW
[#3] The floating-point indicator interrogation and
manipulation operations are:
set_indicators feraiseexcept(i)
clear_indicators feclearexcept(i)
test_indicators fetestexcept(i)
current_indicators fetestexcept(FE_ALL_EXCEPT)
where i is an expression of type int representing a subset
of the LIA-1 indicators.
[#4] C allows an implementation to provide the following
LIA-1 required behavior: at program termination if any
indicator is set the implementation shall send an
unambiguous and ``hard to ignore'' message (see LIA-1
subclause 6.1.2)
[#5] LIA-1 does not make the distinction between floating-
point and integer for undefined. This documentation makes
that distinction because <fenv.h> covers only the floating-
point indicators.
H.3.1.2 Traps
[#1] C is compatible with LIA-1's trap requirements. An
implementation can provide an alternative of notification
through termination with a ``hard-to-ignore'' message (see
LIA-1 subclause 6.1.3).
[#2] LIA-1 does not require that traps be precise.
[#3] C does require that SIGFPE be the signal corresponding
to arithmetic exceptions, if there is any signal raised for
them.
[#4] C supports signal handlers for SIGFPE and allows
trapping of arithmetic exceptions. When arithmetic
exceptions do trap, C's signal-handler mechanism allows
trap-and-terminate (either default implementation behavior
or user replacement for it) or trap-and-resume, at the
programmer's option.
H.3.1.1 Language independent arithmetic H.3.1.2
562 Committee Draft -- August 3, 1998 WG14/N843
Annex I
(normative)
Universal character names for identifiers
[#1] This clause lists the hexadecimal code values that are
valid in universal character names in identifiers.
[#2] This table is reproduced unchanged from ISO/IEC TR
10176, produced by ISO/IEC JTC1/SC22/WG20, except for the
omission of ranges that are part of the required basic
source character set.
Latin: 00AA, 00BA, 00C0-00D6, 00D8-00F6, 00F8-01F5,
01FA-0217, 0250-02A8, 1E00-1E9B, 1EA0-1EF9,
207F
Greek: 0386, 0388-038A, 038C, 038E-03A1, 03A3-03CE,
03D0-03D6, 03DA, 03DC, 03DE, 03E0, 03E2-03F3,
1F00-1F15, 1F18-1F1D, 1F20-1F45, 1F48-1F4D,
1F50-1F57, 1F59, 1F5B, 1F5D, 1F5F-1F7D,
1F80-1FB4, 1FB6-1FBC, 1FC2-1FC4, 1FC6-1FCC,
1FD0-1FD3, 1FD6-1FDB, 1FE0-1FEC, 1FF2-1FF4,
1FF6-1FFC
Cyrillic: 0401-040C, 040E-044F, 0451-045C, 045E-0481,
0490-04C4, 04C7-04C8, 04CB-04CC, 04D0-04EB,
04EE-04F5, 04F8-04F9
Armenian: 0531-0556, 0561-0587
Hebrew: 05B0-05B9, 05BB-05BD, 05BF, 05C1-05C2,
05D0-05EA, 05F0-05F2
Arabic: 0621-063A, 0640-0652, 0670-06B7, 06BA-06BE,
06C0-06CE, 06D0-06DC, 06E5-06E8, 06EA-06ED
Devanagari: 0901-0903, 0905-0939, 093E-094D, 0950-0952,
0958-0963
Bengali: 0981-0983, 0985-098C, 098F-0990, 0993-09A8,
09AA-09B0, 09B2, 09B6-09B9, 09BE-09C4,
09C7-09C8, 09CB-09CD, 09DC-09DD, 09DF-09E3,
09F0-09F1
Gurmukhi: 0A02, 0A05-0A0A, 0A0F-0A10, 0A13-0A28,
0A2A-0A30, 0A32-0A33, 0A35-0A36, 0A38-0A39,
0A3E-0A42, 0A47-0A48, 0A4B-0A4D, 0A59-0A5C,
0A5E, 0A74
Gujarati: 0A81-0A83, 0A85-0A8B, 0A8D, 0A8F-0A91,
0A93-0AA8, 0AAA-0AB0, 0AB2-0AB3, 0AB5-0AB9,
0ABD-0AC5, 0AC7-0AC9, 0ACB-0ACD, 0AD0, 0AE0
I Universal character names for identifiers I
WG14/N843 Committee Draft -- August 3, 1998 563
Oriya: 0B01-0B03, 0B05-0B0C, 0B0F-0B10, 0B13-0B28,
0B2A-0B30, 0B32-0B33, 0B36-0B39, 0B3E-0B43,
0B47-0B48, 0B4B-0B4D, 0B5C-0B5D, 0B5F-0B61
Tamil: 0B82-0B83, 0B85-0B8A, 0B8E-0B90, 0B92-0B95,
0B99-0B9A, 0B9C, 0B9E-0B9F, 0BA3-0BA4,
0BA8-0BAA, 0BAE-0BB5, 0BB7-0BB9, 0BBE-0BC2,
0BC6-0BC8, 0BCA-0BCD
Telugu: 0C01-0C03, 0C05-0C0C, 0C0E-0C10, 0C12-0C28,
0C2A-0C33, 0C35-0C39, 0C3E-0C44, 0C46-0C48,
0C4A-0C4D, 0C60-0C61
Kannada: 0C82-0C83, 0C85-0C8C, 0C8E-0C90, 0C92-0CA8,
0CAA-0CB3, 0CB5-0CB9, 0CBE-0CC4, 0CC6-0CC8,
0CCA-0CCD, 0CDE, 0CE0-0CE1
Malayalam: 0D02-0D03, 0D05-0D0C, 0D0E-0D10, 0D12-0D28,
0D2A-0D39, 0D3E-0D43, 0D46-0D48, 0D4A-0D4D,
0D60-0D61
Thai: 0E01-0E3A, 0E40-0E5B
Lao: 0E81-0E82, 0E84, 0E87-0E88, 0E8A, 0E8D,
0E94-0E97, 0E99-0E9F, 0EA1-0EA3, 0EA5, 0EA7,
0EAA-0EAB, 0EAD-0EAE, 0EB0-0EB9, 0EBB-0EBD,
0EC0-0EC4, 0EC6, 0EC8-0ECD, 0EDC-0EDD
Tibetan: 0F00, 0F18-0F19, 0F35, 0F37, 0F39, 0F3E-0F47,
0F49-0F69, 0F71-0F84, 0F86-0F8B, 0F90-0F95,
0F97, 0F99-0FAD, 0FB1-0FB7, 0FB9
Georgian: 10A0-10C5, 10D0-10F6
Hiragana: 3041-3093, 309B-309C
Katakana: 30A1-30F6, 30FB-30FC
Bopomofo: 3105-312C
CJK Unified Ideographs: 4E00-9FA5
Hangul: AC00-D7A3
Digits: 0660-0669, 06F0-06F9, 0966-096F, 09E6-09EF,
0A66-0A6F, 0AE6-0AEF, 0B66-0B6F, 0BE7-0BEF,
0C66-0C6F, 0CE6-0CEF, 0D66-0D6F, 0E50-0E59,
0ED0-0ED9, 0F20-0F33
Special characters: 00B5, 00B7, 02B0-02B8, 02BB, 02BD-02C1,
02D0-02D1, 02E0-02E4, 037A, 0559, 093D, 0B3D,
1FBE, 203F-2040, 2102, 2107, 210A-2113, 2115,
2118-211D, 2124, 2126, 2128, 212A-2131,
2133-2138, 2160-2182, 3005-3007, 3021-3029
I Universal character names for identifiers I
564 Committee Draft -- August 3, 1998 WG14/N843
Annex J
(informative)
Common warnings
[#1] An implementation may generate warnings in many
situations, none of which are specified as part of this |
International Standard. The following are a few of the more
common situations.
[#2]
-- A new struct or union type appears in a function |
prototype (6.2.1, 6.7.2.3). |
-- A block with initialization of an object that has
automatic storage duration is jumped into (6.2.4).
-- An implicit narrowing conversion is encountered, such
as the assignment of a long int or a double to an int,
or a pointer to void to a pointer to any type other
than a character type (6.3).
-- An integer character constant includes more than one
character or a wide character constant includes more
than one multibyte character (6.4.4.4).
-- The characters /* are found in a comment (6.4.7).
-- An ``unordered'' binary operator (not comma, && or ||)
contains a side-effect to an lvalue in one operand, and
a side-effect to, or an access to the value of, the
identical lvalue in the other operand (6.5).
-- A function is called but no prototype has been supplied
(6.5.2.2).
-- The arguments in a function call do not agree in number
and type with those of the parameters in a function
definition that is not a prototype (6.5.2.2).
-- An object is defined but not used (6.7).
-- A value is given to an object of an enumeration type
other than by assignment of an enumeration constant
that is a member of that type, or an enumeration
variable that has the same type, or the value of a
function that returns the same enumeration type
(6.7.2.2).
-- An aggregate has a partly bracketed initialization
(6.7.7).
J Common warnings J
WG14/N843 Committee Draft -- August 3, 1998 565
-- A statement cannot be reached (6.8).
-- A statement with no apparent effect is encountered
(6.8).
-- A constant expression is used as the controlling
expression of a selection statement (6.8.4).
-- An incorrectly formed preprocessing group is
encountered while skipping a preprocessing group
(6.10.1).
-- An unrecognized #pragma directive is encountered
(6.10.6).
J Common warnings J
566 Committee Draft -- August 3, 1998 WG14/N843
Annex K
(informative)
Portability issues
[#1] This annex collects some information about portability
that appears in this International Standard.
K.1 Unspecified behavior
[#1] The following are unspecified:
-- The manner and timing of static initialization (5.1.2).
-- The termination status returned to the hosted
environment if the return type of main is not |
compatible with int (5.1.2.2.3).
-- The behavior if a printable character is written when
the active position is at the final position of a line
(5.2.2).
-- The behavior if a backspace character is written when
the active position is at the initial position of a
line (5.2.2).
-- The behavior if a horizontal tab character is written
when the active position is at or past the last defined
horizontal tabulation position (5.2.2).
-- The behavior if a vertical tab character is written
when the active position is at or past the last defined
vertical tabulation position (5.2.2).
-- How an extended source character that does not |
correspond to a universal character name counts toward |
the significant initial characters in an external |
identifier (5.2.4.1). |
-- Many aspects of the representations of types (6.2.6).
-- The value of padding bytes when storing values in
structures or unions (6.2.6.1).
-- The value of a union member other than the last one
stored into (6.2.6.1).
-- The representation used when storing a value in an
object that has more than one object representation for
that value (6.2.6.1).
-- The value of padding bits in integer representations
(6.2.6.2).
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-- Whether two string literals result in distinct arrays
(6.4.5).
-- The order in which subexpressions are evaluated and the
order in which side effects take place, except as |
specified for the function-call (), &&, ||, ?:, and
comma operators (6.5).
-- The order in which the function designator, arguments,
and subexpressions within the arguments are evaluated
in a function call (6.5.2.2).
-- The order of side effects among compound literal
initialization list expressions (6.5.2.5).
-- The order in which the operands of an assignment
operator are evaluated (6.5.16).
-- The alignment of the addressable storage unit allocated
to hold a bit-field (6.7.2.1).
-- The choice of using an inline definition or external
definition of a function when both definitions are in
scope (6.7.4).
-- The size of an array when * is written instead of a
size expression (6.7.5.2).
-- Whether side effects are produced when evaluating the
size expression in a declaration of a variable length |
array (6.7.5.2).
-- The layout of storage for function parameters (6.9.1).
-- When a fully expanded macro replacement list contains a
function-like macro name as its last preprocessing
token and the next preprocessing token from the source
file is a (, and the fully expanded replacement of that
macro ends with the name of the first macro and the
next preprocessing token from the source file is again
a (, whether that is considered a nested replacement.
(6.10.3).
-- Whether the # operator inserts a \ character before the |
\ character that begins a universal character name in a |
character constant or string literal (6.10.3.2). |
-- The order in which # and ## operations are evaluated
during macro substitution (6.10.3.2, 6.10.3.3).
-- Whether errno is a macro or an external identifier
(7.5).
K.1 Portability issues K.1
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-- The order of raising floating-point exceptions, except
as stated in F.7.6 (7.6.2.3).
-- The result of rounding when the value is out of range
(7.12.9.5, 7.12.9.7, F.9.6.5).
-- Whether setjmp is a macro or an external identifier
(7.13).
-- Whether va_end is a macro or an external identifier
(7.15.1).
-- The hexadecimal digit left of the decimal point when a
non-normalized floating-point number is printed with an
a or A conversion specifier (7.19.6.1, 7.24.2.1).
-- The value of the file position indicator after a
successful call to the ungetc function for a text
stream, or the ungetwc function for any stream, until
all pushed-back characters are read or discarded
(7.19.7.11, 7.24.3.10).
-- The details of the value stored by the fgetpos function
(7.19.9.1).
-- The details of the value returned by the ftell function
for a text stream (7.19.9.4).
-- The order and contiguity of storage allocated by
successive calls to the calloc, malloc, and realloc
functions (7.20.3).
-- The amount of storage allocated by a successful call to
the calloc, malloc, or realloc function when 0 bytes
was requested (7.20.3).
-- Which of two elements that compare as equal is matched
by the bsearch function (7.20.5.1).
-- The order of two elements that compare as equal in an
array sorted by the qsort function (7.20.5.2).
-- The value of the tm_extlen member of the tmx structure
to which a pointer is returned by the zonetime function
when it has set the tm_ext member to a null pointer
(7.23.1).
-- The encoding of the calendar time returned by the time
function (7.23.2.5).
-- The resulting value when the invalid exception is
raised during IEC 60559 floating to integer conversion
(F.4).
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-- Whether conversion of non-integer IEC 60559 floating
values raises the inexact exception (F.4).
-- The value stored by frexp for a NaN or infinity
(F.9.3.4).
-- The sign of one part of the complex result of several
math functions for certain exceptional values in IEC
60559 compatible implementations (G.5.1.1, G.5.2.2,
G.5.2.3, G.5.2.4, G.5.2.5, G.5.2.6, G.5.3.1, G.5.4.1).
K.2 Undefined behavior
[#1] The behavior is undefined in the following
circumstances:
-- A nonempty source file does not end in a new-line
character, ends in new-line character immediately
preceded by a backslash character, or ends in a partial
preprocessing token or comment (5.1.1.2).
-- Physical source line splicing or token concatenation |
produces a character sequence matching the syntax of a
universal character name (5.1.1.2).
-- A universal character name specifies a character
identifier in the range 00000000 through 00000020 or |
0000007F through 0000009F, or designates a character in
the required source character set (5.1.1.2).
-- A program in a hosted environment does not define a
function named main using one of the two specified
forms (5.1.2.2.1).
-- A character not in the required basic source character
set is encountered in a source file, except in an |
identifier, a character constant, a string literal, a
header name, a comment, or a preprocessing token that
is never converted to a token (5.2.1).
-- An identifier, comment, string literal, character |
constant, or header name contains an invalid multibyte
character or does not begin and end in the initial
shift state (5.2.1.2).
-- The same identifier is used more than once as a label
in the same function (6.2.1).
-- The same identifier has both internal and external
linkage in the same translation unit (6.2.2).
-- The value of an object with automatic storage duration |
is used while it is indeterminate. (6.2.4, 6.7.8, |
6.8.2). |
K.1 Portability issues K.2
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-- An object is referred to when storage is not allocated |
for it (6.2.4).
-- The value of a pointer that referred to an object with
automatic storage duration is used after the storage is
no longer guaranteed to be reserved (6.2.4).
-- A trap representation is accessed by an lvalue
expression that does not have character type (6.2.6.1).
-- A trap representation is produced by a side effect that |
modifies any part of the object using an lvalue
expression that does not have character type.
(6.2.6.1).
-- Two declarations of the same object or function specify
types that are not compatible (6.2.7).
-- Conversion to or from an integer type produces a value
outside the range that can be represented (6.3.1.4).
-- Demotion of one real floating type to another produces *
a value outside the range that can be represented
(6.3.1.5).
-- An lvalue does not designate an object when evaluated |
(6.3.2.1). |
-- A non-array lvalue with an incomplete type is used in a
context that requires the value of the designated
object (6.3.2.1).
-- An lvalue having array type is converted to a pointer
to the initial element of the array, and the array
object has register storage class (6.3.2.1).
-- An attempt is made to use the value of a void
expression, or an implicit or explicit conversion
(except to void) is applied to a void expression
(6.3.2.2).
-- Conversion of a pointer to an integer type produces a
value outside the range that can be represented
(6.3.2.3).
-- Conversion between two pointer types produces a result
that is incorrectly aligned (6.3.2.3).
-- A pointer to a function is converted to point to a
function of a different type and used to call a
function of a type not compatible with the type of the
called function (6.3.2.3).
K.2 Portability issues K.2
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-- An unmatched ' or " character is encountered on a
logical source line during tokenization (6.4).
-- A reserved keyword token is used in translation phase 7
or 8 for some purpose other than as a keyword (6.4.1).
-- A universal character name does not designate a code
value in one of the specified ranges (6.4.2.1). |
-- The first character of an identifier is a universal
character name designating an extended digit (6.4.2.1). |
-- Two identifiers differ only in nonsignificant
characters (6.4.2.1). |
-- An unspecified escape sequence is encountered in a
character constant or a string literal (6.4.4.4).
-- An attempt is made to modify a string literal of either
form (6.4.5).
-- The characters ', \, ", //, or /* are encountered
between the < and > delimiters, or the characters ', \,
//, or /* are encountered between the " delimiters, in
a header name preprocessing token (6.4.7).
-- Between two sequence points, an object is modified more
than once, or is modified and the prior value is
accessed other than to determine the value to be stored
(6.5).
-- An exception occurs during the evaluation of an *
expression (6.5).
-- An object has its stored value accessed other than by
an lvalue expression having one of the following types:
a type compatible with the effective type of the
object, a qualified version of a type compatible with
the effective type of the object, a type that is the
signed or unsigned type corresponding to the effective
type of the object, a type that is the signed or
unsigned type corresponding to a qualified version of
the effective type of the object, an aggregate or union
type that includes one of the aforementioned types
among its members (including, recursively, a member of
a subaggregate or contained union), or a character type
(6.5).
-- For a function call without a function prototype, the
number of arguments does not agree with the number of
parameters (6.5.2.2).
-- For a function call without a function prototype, the
function is defined without a function prototype, and
K.2 Portability issues K.2
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the types of the arguments after promotion are not |
compatible with those of the parameters after |
promotion, with certain exceptions (6.5.2.2).
-- For a function call without a function prototype, the
function is defined with a function prototype, and the
types of the arguments after promotion are not
compatible with the types of the parameters, or the
prototype ends with an ellipsis (6.5.2.2).
-- A function is defined with a type that is not
compatible with the type pointed to by the expression
that denotes the called function (6.5.2.2).
-- An attempt is made to modify the result of a function |
call or to access it after the next sequence point |
(6.5.2.2). |
-- The operand of the unary * operator has an invalid
value (6.5.3.2).
-- A pointer is converted to other than an integer or
pointer type (6.5.4).
-- The value of the second operand of the / or % operator
is zero (6.5.5).
-- Addition or subtraction of a pointer into, or just
beyond, an array object and an integer type produces a
result that does not point into, or just beyond, the
same array object (6.5.6).
-- Addition or subtraction of a pointer into, or just
beyond, an array object and an integer type produces a |
result that points just beyond the array object and is |
used as the operand of a unary * operator that is |
evaluated. (6.5.6). |
-- Pointers that do not point into, or just beyond, the |
same array object are subtracted (6.5.6).
-- An array subscript is out of range, even if an object
is apparently accessible with the given subscript (as
in the lvalue expression a[1][7] given the declaration
int a[4][5]) (6.5.6).
-- The result of subtracting two pointers is not
representable in an object of type ptrdiff_t (6.5.6).
-- An expression is shifted by a negative number or by an *
amount greater than or equal to the width of the
promoted expression (6.5.7).
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-- An expression having signed promoted type is left-
shifted and either the value of the expression is
negative or the result of shifting would be not be
representable in the promoted type. (6.5.7).
-- Pointers that do not point to the same aggregate or
union (nor just beyond the same array object) are
compared using relational operators (6.5.8).
-- An attempt is made to modify the result of a |
conditional operator or to access it after the next |
sequence point (6.5.15). |
-- An attempt is made to modify the result of an |
assignment operator or to access it after the next |
sequence point (6.5.16). |
-- An object is assigned to an inexactly overlapping
object or to an exactly overlapping object with
incompatible type (6.5.16.1).
-- An attempt is made to modify the result of a comma |
operator or to access it after the next sequence point |
(6.5.17). |
-- An expression that is required to be an integer
constant expression does not have an integer type,
contains casts (outside operands to sizeof operators)
other than conversions of arithmetic types to integer
types, or has operands that are not integer constants,
enumeration constants, character constants, fixed-
length sizeof expressions, or immediately-cast floating
constants (6.6).
-- A constant expression in an initializer does not
evaluate to one of the following: an arithmetic
constant expression, a null pointer constant, an
address constant, or an address constant for an object
type plus or minus an integer constant expression
(6.6).
-- An arithmetic constant expression does not have
arithmetic type, contains casts (outside operands to
sizeof operators) other than conversions of arithmetic
types to arithmetic types, or has operands that are not
integer constants, floating constants, enumeration
constants, character constants, or sizeof expressions
(6.6).
-- An address constant is created neither explicitly using
the unary & operator or an integer constant cast to
pointer type, nor implicitly by the use of an
expression of array or function type (6.6).
K.2 Portability issues K.2
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-- The value of an object is accessed by an array-
subscript [], member-access . or ->, address &, or
indirection * operator or a pointer cast in creating an
address constant (6.6).
-- An identifier for an object is declared with no linkage
and the type of the object is incomplete after its
declarator, or after its init-declarator if it has an
initializer (6.7).
-- A function is declared at block scope with an explicit
storage-class specifier other than extern (6.7.1).
-- A structure or union is defined as containing no named
members (6.7.2.1).
-- A bit-field is declared with a type other than a
qualified or unqualified version of _Bool, signed int, |
or unsigned int (6.7.2.1).
-- An attempt is made to access, or generate a pointer to |
just past, a flexible array member of a structure when |
the referenced object provides no elements for that |
array (6.7.2.1).
-- A tag is declared with the bracketed list twice within
the same scope (6.7.2.3).
-- When the complete type is needed, an incomplete
structure or union type is not completed in the same
scope by another declaration of the tag that defines
the content (6.7.2.3).
-- An attempt is made to modify an object defined with a
const-qualified type through use of an lvalue with non-
const-qualified type (6.7.3).
-- An attempt is made to refer to an object defined with a
volatile-qualified type through use of an lvalue with
non-volatile-qualified type (6.7.3).
-- An attempt is made to access an object through a
restrict-qualified pointer and another pointer not
based on it (6.7.3, 6.7.3.1).
-- The specification of a function type includes a type
qualifier (6.7.3).
-- Two qualified types that are required to be compatible
do not have the identically qualified version of a
compatible type (6.7.3).
-- A function with external linkage is declared with an
inline function specifier, but is not also defined in
K.2 Portability issues K.2
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the same translation unit (6.7.4).
-- Two pointer types that are required to be compatible
are not identically qualified, or are not pointers to
compatible types (6.7.5.1).
-- The size expression in an array declaration is not a
constant expression and evaluates at program execution
time to a nonpositive value (6.7.5.2).
-- In a context requiring two array types to be
compatible, they do not have compatible element types,
or their size specifiers evaluate to unequal values
(6.7.5.2).
-- A storage-class specifier or type qualifier modifies
the keyword void as a function parameter type list
(6.7.5.3).
-- In a context requiring two function types to be
compatible, they do not have compatible return types,
or their parameters disagree in use of the ellipsis
terminator or the number and type of parameters (after
default argument promotion, when there is no parameter
type list or when one type is specified by a function
definition with identifier list) (6.7.5.3).
-- The value of an unnamed member of a structure or union *
is used (6.7.8).
-- The initializer for a scalar is neither a single *
expression nor a single expression enclosed in braces
(6.7.8).
-- The initializer for a structure or union object is
neither an initializer list nor a single expression
that has compatible structure or union type (6.7.8).
-- The initializer for an aggregate or union, other than |
an array initialized by a string literal, is not a |
brace-enclosed list of initializers for its elements or |
members. (6.7.8).
-- An identifier with external linkage is used, but in the *
program there does not exist exactly one external
definition for the identifier, or the identifier is not
used and there exist multiple external definitions for
the identifier. (6.9).
-- A function definition includes an identifier list, but
the types of the parameters are not declared in a
following declaration list. (6.9.1).
K.2 Portability issues K.2
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-- A function that accepts a variable number of arguments
is defined without a parameter type list that ends with
the ellipsis notation (6.9.1).
-- An adjusted parameter type in a function definition is
not an object type (6.9.1).
-- The } that terminates a function is reached, and the |
value of the function call is used by the caller |
(6.9.1). |
-- An identifier for an object with internal linkage and
an incomplete type is declared with a tentative
definition (6.9.2).
-- The token defined is generated during the expansion of
a #if or #elif preprocessing directive, or the use of
the defined unary operator does not match one of the
two specified forms prior to macro replacement
(6.10.1).
-- The #include preprocessing directive that results after
expansion does not match one of the two header name
forms (6.10.2).
-- The character sequence in an #include preprocessing
directive does not start with a letter (6.10.2).
-- There are sequences of preprocessing tokens within the
list of macro arguments that would otherwise act as
preprocessing directive lines (6.10.3).
-- The result of the preprocessing operator # is not a
valid character string literal (6.10.3.2).
-- The result of the preprocessing operator ## is not a
valid preprocessing token (6.10.3.3).
-- The #line preprocessing directive that results after
expansion does not match one of the two well-defined
forms, or its digit sequence specifies zero or a number
greater than 2147483647 (6.10.4).
-- A non-STDC #pragma preprocessing directive that is
documented as causing translation failure or some other
form of undefined behavior is encountered (6.10.6).
-- A #pragma STDC preprocessing directive does not match
one of the nine well-defined forms (6.10.6).
-- One of the following identifiers is the subject of a
#define or #undef preprocessing directive: __LINE__,
__FILE__, __DATE__, __TIME__, __STDC__,
__STDC_VERSION__, __STDC_IEC_559__,
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__STDC_IEC_559_COMPLEX__, or defined (6.10.8).
-- An attempt is made to copy an object to an overlapping
object by use of a library function other than memmove
(7).
-- A file with the same name as one of the standard
headers, not provided as part of the implementation, is |
placed in any of the standard places that are searched |
for included source files (7.1.2).
-- A header is included within an external declaration or
definition (7.1.2).
-- A function, object, type, or macro that is specified as
being declared or defined by some standard header is
used before any header that declares or defines it is
included (7.1.2).
-- A standard header is included while a macro is defined
with the same name as a keyword (7.1.2).
-- The program attempts to declare a library function
itself, rather than via a standard header, but the
declaration does not have external linkage (7.1.2).
-- The program declares or defines a reserved identifier
(other than as allowed by 7.1.4) (7.1.3).
-- The program removes the definition of a macro whose
name begins with an underscore and either an uppercase
letter or another underscore (7.1.3).
-- An argument to a library function has an invalid value
or a type not expected by a function with variable
number of arguments (7.1.4).
-- The macro definition of assert is suppressed in order
to access an actual function (7.2).
-- The CX_LIMITED_RANGE pragma is used in any context
other than outside all external declarations or
preceding all explicit declarations and statements
inside a compound statement (7.3.4).
-- The value of an argument to a character handling
function is neither equal to the value of EOF nor
representable as an unsigned char (7.4).
-- A macro definition of errno is suppressed in order to
access an actual object, or the program defines an
identifier with the name errno (7.5).
K.2 Portability issues K.2
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-- The FENV_ACCESS pragma is used in any context other
than outside all external declarations or preceding all
explicit declarations and statements inside a compound
statement (7.6.1).
-- Part of the program tests flags or runs under non-
default mode settings, but was translated with the
state for the FENV_ACCESS pragma off (7.6.1).
-- The exception-mask argument for one of the functions
that provide access to the exception flags has a value
not obtained by bitwise OR of the exception macros
(7.6.2).
-- The fesetexceptflag function is used to set the status
for exception flags not specified in the call to the
fegetexceptflag function that provided the value of the
corresponding fexcept_t object (7.6.2.4).
-- The program modifies the string pointed to by the value
returned by the setlocale function (7.11.1.1).
-- The program modifies the structure pointed to by the
value returned by the localeconv function (7.11.2.1).
-- The FP_CONTRACT pragma is used in any context other
than outside all external declarations or preceding all
explicit declarations and statements inside a compound
statement (7.12.2).
-- An argument to a floating-point classification macro is
not of real floating type (7.12.3).
-- A macro definition of setjmp is suppressed in order to
access an actual function, or the program defines an
identifier with the name setjmp (7.13.1).
-- An invocation of the setjmp macro occurs in a context
other than as the entire controlling expression in a
selection or iteration statement, or in a comparison
with an integer constant expression (possibly as
implied by the unary ! operator) as the entire
controlling expression of a selection or iteration
statement, or as the entire expression of an expression
statement (possibly cast to void) (7.13.2.1).
-- The longjmp function is invoked to restore a
nonexistent environment (7.13.2.1).
-- After a longjmp, there is an attempt to access the
value of an object of automatic storage class with non-
volatile-qualified type, local to the function
containing the invocation of the corresponding setjmp
macro, that was changed between the setjmp invocation
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and longjmp call (7.13.2.1).
-- The longjmp function is invoked from a nested signal
handler (7.13.2.1).
-- The program uses a nonpositive value for a signal
number (7.14).
-- The program specifies an invalid pointer to a signal
handler function (7.14.1.1).
-- A signal handler returns when the signal corresponded
to a computational exception (7.14.1.1).
-- A signal occurs other than as the result of calling the
abort or raise function, and the signal handler calls a
function in the standard library other than the signal
function (for the same signal number) or refers to an
object with static storage duration other than by
assigning a value to an object declared as volatile
sig_atomic_t (7.14.1.1).
-- The value of errno is referred to after a signal
occurred other than as the result of calling the abort
or raise function and the corresponding signal handler
obtained a SIG_ERR return from a call to the signal
function (7.14.1.1).
-- A function with a variable number of arguments attempts
to access its varying arguments other than through a
properly declared and initialized va_list object, or
before the va_start macro is invoked (7.15, 7.15.1.1,
7.15.1.4).
-- The macro va_arg is invoked using the parameter ap that
was passed to a function that invoked the macro va_arg
with the same parameter (7.15).
-- A macro definition of va_start, va_arg, va_copy, or
va_end is suppressed in order to access an actual
function, or the program defines an external identifier
with the name va_end (7.15.1).
-- The va_end macro is invoked without a corresponding
invocation of the va_start or va_copy macro, or vice
versa. (7.15.1, 7.15.1.3, 7.15.1.4).
-- The va_arg macro is invoked when there is no actual
next argument, or with a specified type that is not
compatible with the promoted type of the actual next |
argument, with certain exceptions (7.15.1.1).
-- The parameter parmN of a va_start macro is declared
with the register storage class, with a function or
K.2 Portability issues K.2
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array type, or with a type that is not compatible with
the type that results after application of the default
argument promotions (7.15.1.4).
-- The member-designator parameter of an offsetof macro is
an invalid right operand of the . operator for the type
parameter, or the member-designator parameter
designates a bit-field (7.17).
-- The argument in an instance of one of the integer-
constant macros is not a decimal, octal, or hexadecimal
constant, or it has a value that exceeds the limits for
the corresponding type (7.18.4).
-- A byte input/output function is applied to a wide-
oriented stream, or a wide-character input/output
function is applied to a byte-oriented stream (7.19.2).
-- Use is made of any portion of a file beyond the most |
recent wide character written to a wide-oriented stream
(7.19.2).
-- The value of a pointer to a FILE object is used after
the associated file is closed (7.19.3).
-- The stream for the fflush function points to an input
stream or to an update stream in which the most recent
operation was input (7.19.5.2).
-- The string pointed to by the mode argument in a call to
the fopen function does not exactly match one of the
specified character sequences (7.19.5.3).
-- An output operation on an update stream is followed by
an input operation without an intervening call to the
fflush function or a file positioning function, or an
input operation on an update stream is followed by an
output operation with an intervening call to a file
positioning function (7.19.5.3).
-- An attempt is made to use the contents of the array
that was supplied in a call to the setvbuf function
(7.19.5.6).
-- There are insufficient arguments for the format in a
call to the fprintf, fscanf, fwprintf, or fwscanf
function, or an argument does not have an appropriate
type (7.19.6.1, 7.19.6.2, 7.24.2.1, 7.24.2.2).
-- The format in a call to the fprintf, fscanf, fwprintf,
fwscanf, strftime, strfxtime, wcsftime, or wcsfxtime
function is not a valid multibyte character sequence
that begins and ends in its initial shift state
(7.19.6.1, 7.19.6.2, 7.24.2.1, 7.24.2.2, 7.23.3.5,
K.2 Portability issues K.2
WG14/N843 Committee Draft -- August 3, 1998 581
7.23.3.6, 7.24.5.1, 7.24.5.2).
-- In a call to the fprintf or fwprintf function, a
precision appears with a conversion specifier other
than a, A, d, e, E, f, F, g, G, i, o, s, u, x, or X
(7.19.6.1, 7.24.2.1).
-- A conversion specification for the fprintf, fscanf,
fwprintf, or fwscanf function uses a length modifier
with a conversion specifier in a combination not
specified in this International Standard (7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2).
-- An asterisk is used to denote an argument-supplied
field width or precision, but the corresponding
argument is not provided (7.19.6.1, 7.24.2.1).
-- A conversion specification for the fprintf or fwprintf
function uses a # flag with a conversion specifier
other than a, A, e, E, f, F, g, G, o, x, or X
(7.19.6.1, 7.24.2.1).
-- A conversion specification for the fprintf or fwprintf
function uses a 0 flag with a conversion specifier
other than a, A, d, e, E, f, F, g, G, i, o, u, x, or X
(7.19.6.1, 7.24.2.1).
-- An s conversion specifier is encountered by the fprintf
or fwprintf function, and the argument is missing the
null terminator (unless a precision is specified that
does not require null termination) (7.19.6.1,
7.24.2.1).
-- An n conversion specification includes any flags, an |
assignment-suppressing character, a field width, or a |
precision (7.19.6.1, 7.19.6.2, 7.24.2.1, 7.24.2.2).
-- A % conversion specifier is encountered by the fprintf,
fscanf, fwprintf, or fwscanf function, but the complete
conversion specification is not exactly %% (7.19.6.1,
7.19.6.2, 7.24.2.1, 7.24.2.2).
-- An invalid conversion specification is found in the
format for the fprintf, fscanf, strftime, strfxtime,
fwprintf, fwscanf, wcsftime, or wcsfxtime function
(7.19.6.1, 7.19.6.2, 7.23.3.5, 7.23.3.6, 7.24.2.1,
7.24.2.2, 7.24.5.1, 7.24.5.2).
-- An argument to the fprintf or fwprintf function is not |
the correct type for the corresponding conversion |
specification (7.19.6.1, 7.24.2.1).
-- The number of characters transmitted by a formatted |
output function is greater than INT_MAX (7.19.6.1, |
K.2 Portability issues K.2
582 Committee Draft -- August 3, 1998 WG14/N843
7.19.6.3, 7.19.6.8, 7.19.6.10) |
-- The result of a conversion by the fscanf or fwscanf
function cannot be represented in the corresponding
object, or the receiving object does not have an
appropriate type (7.19.6.2, 7.24.2.2).
-- A c, s, or [ conversion specifier is encountered by the
fscanf or fwscanf function, and the character array
pointed to by the corresponding argument is not large
enough to accept the input sequence (and a null
terminator if the conversion specifier is s or [)
(7.19.6.2, 7.24.2.2).
-- An c, s, or [ conversion specifier with an l qualifier
is encountered by the fscanf or fwscanf function, but
the input is not a valid multibyte character sequence
that begins in the initial shift state (7.19.6.2,
7.24.2.2).
-- The input item for %p conversion by the fscanf or
fwscanf function is not a value converted earlier
during the same program execution (7.19.6.2, 7.24.2.2).
-- The snprintf, sprintf, sscanf, vsnprintf, vsprintf,
mbstowcs, wcstombs, memcpy, strcpy, strncpy, strcat,
strncat, strxfrm, strftime, or strfxtime function, or
any of the functions declared by <wchar.h> (except
where otherwise specified), is used to copy between
overlapping objects (7.19.6.5, 7.19.6.6, 7.19.6.7,
7.19.6.12, 7.19.6.13, 7.20.8.1, 7.20.8.2, 7.21.2.1,
7.21.2.3, 7.21.2.4, 7.21.3.1, 7.21.3.2, 7.21.4.5,
7.23.3.5, 7.23.3.6, 7.24.1). |
-- The vfprintf, vfscanf, vprintf, vscanf, vsnprintf,
vsprintf, vsscanf, vfwprintf, vfwscanf, vswprintf,
vswscanf, vwprintf, or vwscanf. function is called
with an improperly initialized va_list argument
(7.19.6.8, 7.19.6.9, 7.19.6.10, 7.19.6.11, 7.19.6.12,
7.19.6.13, 7.19.6.14, 7.24.2.5, 7.24.2.6, 7.24.2.7,
7.24.2.8, 7.24.2.9, 7.24.2.10).
-- The contents of the array supplied in a call to the
fgets, gets, or fgetws function are used after a read
error occurred (7.19.7.2, 7.19.7.7, 7.24.3.2).
-- The file position indicator for a binary stream is used
after a call to the ungetc function where its value was
zero before the call (7.19.7.11).
-- The file position indicator for a stream is used after
an error occurred during a call to the fread or fwrite
function (7.19.8.1, 7.19.8.2).
K.2 Portability issues K.2
WG14/N843 Committee Draft -- August 3, 1998 583
-- A partial element read by a call to the fread function
is used (7.19.8.1).
-- The fseek function is called for a text stream with
other than SEEK_SET, or with a non-zero offset that was
not returned by a previous successful call to the ftell
function for the same file (7.19.9.2).
-- The fsetpos function is called to set a position that
was not returned by a previous successful call to the
fgetpos function for the same file (7.19.9.3).
-- The value of the result of converting a string to a
number by the atof, atoi, atol, or atoll function
cannot be represented (7.20.1).
-- A non-null pointer returned by a call to the calloc,
malloc, or realloc function with a zero requested size
is used to access an object (7.20.3).
-- The value of a pointer that refers to space deallocated
by a call to the free or realloc function is used
(7.20.3).
-- The pointer argument to the free or realloc function
does not match a pointer earlier returned by calloc,
malloc, or realloc, or the space has been deallocated
by a call to free or realloc (7.20.3.2, 7.20.3.4).
-- The value of the object allocated by the malloc
function is used (7.20.3.3).
-- The value of the newly allocated portion of an object
expanded by the realloc function is used (7.20.3.4).
-- The program executes more than one call to the exit
function (7.20.4.3).
-- The string set up by the getenv or strerror function is
modified by the program (7.20.4.4, 7.21.6.2).
-- A command is executed through the system function in a
way that is documented as causing termination or some
other form of undefined behavior (7.20.4.5).
-- The comparison function called by the bsearch or qsort
function returns ordering values inconsistently
(7.20.5.1, 7.20.5.2).
-- The array being searched by the bsearch function does
not have its elements in proper order (7.20.5.1).
-- The result of an integer arithmetic function (abs, div,
labs, llabs, ldiv, or lldiv) cannot be represented
K.2 Portability issues K.2
584 Committee Draft -- August 3, 1998 WG14/N843
(7.20.6.1, 7.20.6.2).
-- The current shift state is used with a multibyte
character function after the LC_CTYPE category was
changed (7.20.7).
-- A string or wide-string utility function is instructed
to access an array beyond the end of an object (7.21.1,
7.24.4).
-- The contents of the destination array are used after a
call to the strxfrm, strftime, strfxtime, wcsxfrm,
wcsftime, or wcsfxtime function in which the specified
length was too small to hold the entire null-terminated
result (7.21.4.5, 7.23.3.5, 7.23.3.6, 7.24.4.4.4,
7.24.5.1, 7.24.5.2).
-- A non-real argument is supplied for a generic parameter
of a type-generic macro (7.22.1).
-- The tmx structure whose address is passed as an
argument to the mkxtime, strfxtime, or wcsfxtime
function does not provide an appropriate extension
block as required by the implementation (7.23.1).
-- The value of the tm_version member of the tmx structure
pointed to by the argument in a call to the mkxtime
function is not 1 (7.23.2.3, 7.23.2.6).
-- The value of one of the tm_year, tm_mon, tm_mday,
tm_hour, tm_min, tm_sec, tm_leapsecs, tm_zone, or
tm_isdst members of the tm or tmx structure pointed to
by the argument in a call to the mktime or mkxtime
function is drastically out of the normal range
(7.23.2.6).
-- The argument corresponding to an s specifier without an
l qualifier in a call to the fwprintf function does not
point to a valid multibyte character sequence that
begins in the initial shift state (7.24.2.11).
-- The first argument in a call to the wcstok function
does not point to a wide string on the first call or is
not a null pointer for subsequent calls to continue
parsing the same wide string, or when continuing
parsing, the saved pointer value pointed to by the
third argument does not match that stored by the
previous call for the same wide string (7.24.4.5.8).
-- An mbstate_t object is used inappropriately (7.24.6).
-- The conversion state is used after the mbrtowc,
wcrtomb, mbsrtowcs, or wcsrtombs function reports an
encoding error (7.24.6.3.2, 7.24.6.3.3, 7.24.6.4.1,
K.2 Portability issues K.2
WG14/N843 Committee Draft -- August 3, 1998 585
7.24.6.4.2).
-- The value of an argument of type wint_t to a wide-
character classification or mapping function is neither
equal to the value of WEOF nor representable as a
wchar_t (7.25.1).
-- The iswctype function is called using a different
LC_CTYPE category from the one in effect for the call
to the wctype function that returned the description
(7.25.2.2.1).
-- The towctrans function is called using a different
LC_CTYPE category from the one in effect for the call
to the wctrans function that returned the description
(7.25.3.2.1).
K.3 Implementation-defined behavior
[#1] A conforming implementation shall document its choice
of behavior in each of the areas listed in this subclause.
The following are implementation-defined:
K.3.1 Translation
[#1]
-- How a diagnostic is identified (3.8, 5.1.1.3).
-- Whether each nonempty sequence of white-space
characters other than new-line is retained or replaced
by one space character in translation phase 3
(5.1.1.2).
K.3.2 Environment
[#1]
-- The name and type of the function called at program
startup in a freestanding environment (5.1.2.1).
-- The effect of program termination in a freestanding
environment (5.1.2.1).
-- An alternative manner in which the main function may be |
defined (5.1.2.2.1).
-- The values given to the strings pointed to by the argv
argument to main (5.1.2.2.1).
-- What constitutes an interactive device (5.1.2.3).
-- Signals for which the equivalent of signal(sig,
SIG_IGN); is executed at program startup (7.14.1.1).
K.2 Portability issues K.3.2
586 Committee Draft -- August 3, 1998 WG14/N843
-- The form of the status returned to the host environment
to indicate unsuccessful termination when the SIGABRT
signal is raised and not caught (7.20.4.1).
-- The forms of the status returned to the host
environment by the exit function to report successful
and unsuccessful termination (7.20.4.3).
-- The status returned to the host environment by the exit
function if the value of its argument is other than
zero, EXIT_SUCCESS, or EXIT_FAILURE (7.20.4.3).
-- The set of environment names and the method for
altering the environment list used by the getenv
function (7.20.4.4).
-- The manner of execution of the string by the system
function (7.20.4.5).
K.3.3 Identifiers
[#1]
-- Which additional multibyte characters may appear in |
identifiers and their correspondence to universal |
character names (6.4.2).
-- The number of significant initial characters in an |
identifier (5.2.4.1, 6.4.2).
K.3.4 Characters
[#1]
-- The number of bits in a byte (3.4).
-- The values of the members of the execution character
set (5.2.1).
-- The unique value of the member of the execution
character set produced for each of the standard
alphabetic escape sequences (5.2.2).
-- The value of a char object into which has been stored
any character other than a member of the required
source character set (6.2.5).
-- Which of signed char or unsigned char has the same
range, representation, and behavior as ``plain'' char
(6.2.5, 6.3.1.1).
-- The mapping of members of the source character set (in
character constants and string literals) to members of
the execution character set (6.4.4.4).
K.3.2 Portability issues K.3.4
WG14/N843 Committee Draft -- August 3, 1998 587
-- The value of an integer character constant that
contains more than one character or a wide character
constant that contains more than one multibyte
character (6.4.4.4).
-- The value of an integer character constant that
contains a character or escape sequence not represented
in the basic execution character set or a wide
character constant that contains a multibyte character
or escape sequence not represented in the extended
execution character set (6.4.4.4).
-- The current locale used to convert a wide character
constant consisting of a single multibyte character
that maps to a member of the extended execution
character set into a corresponding wide-character code
(6.4.4.4). |
-- The current locale used to convert a wide string |
literal into corresponding wide-character codes |
(6.4.5). |
-- The value of a string literal containing a multibyte |
character or escape sequence not represented in the |
execution character set (6.4.5).
K.3.5 Integers
[#1]
-- Any extended integer types that exist in the
implementation (6.2.5).
-- The rank of any extended integer type relative to
another extended integer type with the same precision
(6.3.1.1).
-- The result of converting an integer to a signed integer
type when the value cannot be represented in an object
of that type (6.3.1.3).
-- The results of some bit-wise operations on signed
integers (6.5).
K.3.6 Floating point
[#1]
-- The accuracy of the floating-point operations and of |
the library functions in <math.h> and <complex.h> that |
return floating-point results (5.2.4.2.2) |
-- Rounding behavior for values of FLT_ROUNDS less than -1
(5.2.4.2.2).
K.3.4 Portability issues K.3.6
588 Committee Draft -- August 3, 1998 WG14/N843
-- Rounding behavior for values of FLT_EVAL_METHOD less
than -1 or greater than 2 (5.2.4.2.2).
-- The direction of rounding when an integer is converted
to a floating-point number that cannot exactly
represent the original value (6.3.1.4).
-- The direction of rounding when a floating-point number
is converted to a narrower floating-point number
(6.3.1.5).
-- How the nearest representable value or the larger or
smaller representable value immediately adjacent to the
nearest representable value is chosen for certain
floating constants (6.4.4.2).
-- Whether and how floating expressions are contracted
when not disallowed by the FP_CONTRACT pragma (6.5).
K.3.7 Arrays and pointers
[#1]
-- The result of converting a pointer to an integer or
vice versa (6.3.2.3).
-- The size of the result of subtracting two pointers to
elements of the same array (6.5.6).
K.3.8 Hints
[#1]
-- The extent to which suggestions made by using the
register storage-class specifier are effective (6.7.1).
-- The extent to which suggestions made by using the
inline function specifier are effective (6.7.4).
K.3.9 Structures, unions, enumerations, and bit-fields
[#1]
-- The behavior when a member of a union object is
accessed using a member of a different type (6.5.2.3).
-- Whether a ``plain'' int bit-field is treated as a
signed int bit-field or as an unsigned int bit-field
(6.7.2).
-- Whether a bit-field can straddle a storage-unit
boundary (6.7.2.1).
K.3.6 Portability issues K.3.9
WG14/N843 Committee Draft -- August 3, 1998 589
-- The order of allocation of bit-fields within a unit
(6.7.2.1).
-- The alignment of non-bit-field members of structures
(6.7.2.1). This should present no problem unless
binary data written by one implementation is read by
another.
-- The integer type compatible with each enumerated type
(6.7.2.2).
K.3.10 Qualifiers
[#1]
-- What constitutes an access to an object that has
volatile-qualified type (6.7.3).
K.3.11 Preprocessing directives
[#1]
-- How sequences in both forms of header names are mapped
to headers or external source file names (6.4.7).
-- Whether the value of a character constant in a constant
expression that controls conditional inclusion matches
the value of the same character constant in the
execution character set (6.10.1).
-- Whether the value of a single-character character
constant in a constant expression that controls
conditional inclusion may have a negative value
(6.10.1).
-- The places that are searched for an included < >
delimited header, and how the places are specified or
the header is identified (6.10.2).
-- How the named source file is searched for in an
included " " delimited header (6.10.2).
-- The method by which preprocessing tokens are combined
into a header name (6.10.2).
-- The nesting limit for #include processing (6.10.2).
-- The behavior on each recognized non-STDC #pragma
directive (6.10.6).
-- The definitions for __DATE__ and __TIME__ when
respectively, the date and time of translation are not
available (6.10.8).
K.3.9 Portability issues K.3.11
590 Committee Draft -- August 3, 1998 WG14/N843
K.3.12 Library functions
[#1]
-- Any library facilities available to a freestanding |
program, other than the minimal set required by clause |
4 (5.1.2.1).
-- The format of the diagnostic printed by the assert
macro (7.2.1.1).
-- The default state for the FENV_ACCESS pragma (7.6.1)
-- The representation of floating point exception flags
stored by the fegetexceptflag function (7.6.2.2).
-- Whether the feraiseexcept function raises the inexact
exception in addition to the overflow or underflow
exception (7.6.2.3).
-- Floating environment macros other than FE_DFL_ENV that
can be used as the argument to the fesetenv or
feupdateenv function (7.6.4.3, 7.6.4.4).
-- Strings other than "C" and "" that may be passed as the
second argument to the setlocale function (7.11.1.1).
-- The types defined for float_t and double_t when the
value of the FLT_EVAL_METHOD macro is less than 0 or
greater than 2 (7.12).
-- The infinity to which the INFINITY macro expands, if
any (7.12).
-- The quiet NaN to which the NAN macro expands, when it
is defined (7.12).
-- Domain errors for the mathematics functions, other than *
those required by this International Standard (7.12.1).
-- The values returned by the mathematics functions, and
whether errno is set to the value of the macro EDOM, on
domain errors (7.12.1).
-- Whether the mathematics functions set errno to the
value of the macro ERANGE on overflow and/or underflow
range errors (7.12.1).
-- The default state for the FP_CONTRACT pragma (7.12.2)
-- Whether a domain error occurs or zero is returned when
the fmod function has a second argument of zero
(7.12.10.1).
K.3.12 Portability issues K.3.12
WG14/N843 Committee Draft -- August 3, 1998 591
-- The base-2 logarithm of the modulus used by the remquo
function in reducing the quotient (7.12.10.3).
-- The set of signals, their semantics, and their default
handling (7.14).
-- If the equivalent of signal(sig, SIG_DFL); is not
executed prior to the call of a signal handler, the
blocking of the signal that is performed (7.14.1.1).
-- Whether the equivalent of signal(sig, SIG_DFL); is
executed prior to the call of a signal handler for the
signal SIGILL (7.14.1.1).
-- Signal values other than SIGFPE, SIGILL, and SIGSEGV
that correspond to a computational exception
(7.14.1.1).
-- The null pointer constant to which the macro NULL
expands (7.17).
-- Whether the last line of a text stream requires a
terminating new-line character (7.19.2).
-- Whether space characters that are written out to a text
stream immediately before a new-line character appear
when read in (7.19.2).
-- The number of null characters that may be appended to
data written to a binary stream (7.19.2).
-- Whether the file position indicator of an append-mode
stream is initially positioned at the beginning or end
of the file (7.19.3).
-- Whether a write on a text stream causes the associated
file to be truncated beyond that point (7.19.3).
-- The characteristics of file buffering (7.19.3).
-- Whether a zero-length file actually exists (7.19.3).
-- The rules for composing valid file names (7.19.3).
-- Whether the same file can be open multiple times
(7.19.3).
-- The nature and choice of encodings used for multibyte
characters in files (7.19.3).
-- The effect of the remove function on an open file
(7.19.4.1).
K.3.12 Portability issues K.3.12
592 Committee Draft -- August 3, 1998 WG14/N843
-- The effect if a file with the new name exists prior to
a call to the rename function (7.19.4.2).
-- Whether an open temporary file is removed upon abnormal
program termination (7.19.4.3).
-- What happens when the tmpnam function is called more
than TMP_MAX times (7.19.4.4).
-- Which changes of mode are permitted (if any), and under |
what circumstances (7.19.5.4). |
-- The style used to print an infinity or NaN, and the
meaning of the n-char-sequence if that style is printed
for a NaN (7.19.6.1, 7.24.2.1).
-- The output for %p conversion in the fprintf or fwprintf
function (7.19.6.1, 7.24.2.1).
-- The interpretation of a - character that is neither the
first nor the last character, nor the second where a ^
character is the first, in the scanlist for %[
conversion in the fscanf or fwscanf function (7.19.6.2,
7.24.2.1).
-- The set of sequences matched by the %p conversion in
the fscanf or fwscanf function (7.19.6.2, 7.24.2.2).
-- The interpretation of the input item corresponding to a
%p conversion in the fscanf or fwscanf function
(7.19.6.2, 7.24.2.2).
-- The value to which the macro errno is set by the
fgetpos, fsetpos, or ftell functions on failure
(7.19.9.1, 7.19.9.3, 7.19.9.4).
-- The meaning of the n-char-sequence in a string
converted by the strtod, strtof, strtold, wcstod,
wcstof, or wcstold function (7.20.1.3, 7.24.4.1.1).
-- Whether or not the strtod, strtof, strtold, wcstod,
wcstof, or wcstold function sets errno to ERANGE when
underflow occurs (7.20.1.3, 7.24.4.1.1).
-- Whether the calloc, malloc, and realloc functions
return a null pointer or a pointer to an allocated
object when the size requested is zero (7.20.3).
-- Whether open output streams are flushed, open streams
are closed, or temporary files are removed when the
abort function is called (7.20.4.1).
-- The termination status returned to the host environment
by the abort function (7.20.4.1).
K.3.12 Portability issues K.3.12
WG14/N843 Committee Draft -- August 3, 1998 593
-- The value returned by the system function when its
argument is not a null pointer (7.20.4.5).
-- The local time zone and Daylight Saving Time (7.23.1).
-- The era for the clock function (7.23.2.1).
-- The positive value for tm_isdst in a normalized tmx
structure (7.23.2.6).
-- The replacement string for the %Z specifier to the
strftime, strfxtime, wcsftime, and wcsfxtime functions
in the "C" locale (7.23.3.5, 7.23.3.6, (7.24.5.1,
7.24.5.2).
-- Whether or when the trigonometric, hyperbolic, base-e
exponential, base-e logarithmic, error, and log gamma
functions raise the inexact exception in an IEC 60559
conformant implementation (F.9).
-- Whether the inexact exception may be raised when the
rounded result actually does equal the mathematical
result in an IEC 60559 conformant implementation (F.9).
-- Whether the underflow (and inexact) exception may be
raised when a result is tiny but not inexact in an IEC
60559 conformant implementation (F.9).
-- Whether the functions honor the rounding direction mode
(F.9).
K.3.13 Architecture
[#1]
-- The values or expressions assigned to the macros *
specified in the headers <float.h>, <limits.h>, and
<stdint.h> (5.2.4.2, 7.18.2, 7.18.3).
-- The number, order, and encoding of bytes in any object |
(when not explicitly specified in this International |
Standard) (6.2.6.1). |
-- The value of the result of the sizeof operator
(6.5.3.4).
K.3.12 Portability issues K.3.13
594 Committee Draft -- August 3, 1998 WG14/N843
K.4 Locale-specific behavior
[#1] The following characteristics of a hosted environment
are locale-specific and shall be documented by the
implementation:
-- Additional members of the execution character set
beyond the required members (5.2.1).
-- The presence, meaning, and representation of additional
multibyte characters in the execution character set
beyond the required single-byte characters (5.2.1.2).
-- The shift states used for the encoding of multibyte
characters (5.2.1.2).
-- The direction of writing of successive printable
characters (5.2.2).
-- The decimal-point character (7.1.1).
-- The set of printing characters (7.4).
-- The set of control characters (7.4).
-- The sets of characters tested for by the isalpha,
islower, ispunct, isspace, or isupper functions
(7.4.1.2, 7.4.1.6, 7.4.1.8, 7.4.1.9, 7.4.1.10).
-- The native environment (7.11.1.1).
-- Additional subject sequences accepted by the string
conversion functions (7.20.1) and the wide string
numeric conversion function (7.24.4.1).
-- The collation sequence of the execution character set
(7.21.4.3).
-- The contents of the error message strings set up by the
strerror function (7.21.6.2).
-- The formats for time and date (7.23.3.5).
-- Character mappings that are supported by the towctrans
function (7.25.1).
-- Character classifications that are supported by the
iswctype function (7.25.1).
-- The set of printing wide characters (7.25.2).
-- The set of control wide characters (7.25.2).
K.4 Portability issues K.4
WG14/N843 Committee Draft -- August 3, 1998 595
-- The sets of wide characters tested for by the iswalpha,
iswlower, iswpunct, iswspace, or iswupper functions
(7.25.2.1.2, 7.25.2.1.6, 7.25.2.1.8, 7.25.2.1.9,
7.25.2.1.10).
K.5 Common extensions
[#1] The following extensions are widely used in many
systems, but are not portable to all implementations. The
inclusion of any extension that may cause a strictly
conforming program to become invalid renders an
implementation nonconforming. Examples of such extensions
are new keywords, extra library functions declared in
standard headers, or predefined macros with names that do
not begin with an underscore.
K.5.1 Environment arguments
[#1] In a hosted environment, the main function receives a
third argument, char *envp[], that points to a null-
terminated array of pointers to char, each of which points
to a string that provides information about the environment
for this execution of the program (5.1.2.2.1).
K.5.2 Specialized identifiers
[#1] Characters other than the underscore _, letters, and
digits, that are not defined in the required source
character set (such as the dollar sign $, or characters in
national character sets) may appear in an identifier
(6.4.2).
K.5.3 Lengths and cases of identifiers
[#1] All characters in identifiers (with or without external
linkage) are significant (6.4.2).
K.5.4 Scopes of identifiers
[#1] A function identifier, or the identifier of an object
the declaration of which contains the keyword extern, has
file scope (6.2.1).
K.5.5 Writable string literals
[#1] String literals are modifiable (in which case,
identical string literals should denote distinct objects)
(6.4.5).
K.4 Portability issues K.5.5
596 Committee Draft -- August 3, 1998 WG14/N843
K.5.6 Other arithmetic types
[#1] Additional arithmetic types, such as __int128, and
their appropriate conversions are defined (6.2.5, 6.3.1.1).
K.5.7 Function pointer casts
[#1] A pointer to an object or to void may be cast to a
pointer to a function, allowing data to be invoked as a
function (6.5.4).
[#2] A pointer to a function may be cast to a pointer to an
object or to void, allowing a function to be inspected or
modified (for example, by a debugger) (6.5.4). |
K.5.8 Extended bit-field types |
[#1] A bit-field may be declared with a type other than |
_Bool, unsigned int, or signed int, with an appropriate |
maximum width (6.7.2.1).
K.5.9 The fortran keyword
[#1] The fortran function specifier may be used in a
function declaration to indicate that calls suitable for
FORTRAN should be generated, or that a different
representation for the external name is to be generated
(6.7.4).
K.5.10 The asm keyword
[#1] The asm keyword may be used to insert assembly language
directly into the translator output; the most common
implementation is via a statement of the form
asm ( character-string-literal );
(6.8).
K.5.11 Multiple external definitions
[#1] There may be more than one external definition for the
identifier of an object, with or without the explicit use of
the keyword extern; if the definitions disagree, or more
than one is initialized, the behavior is undefined (6.9.2).
K.5.6 Portability issues K.5.11
WG14/N843 Committee Draft -- August 3, 1998 597
K.5.12 Predefined macro names
[#1] Macro names that do not begin with an underscore,
describing the translation and execution environments, are
defined by the implementation before translation begins
(6.10.8).
K.5.13 Extra arguments for signal handlers
[#1] Handlers for specific signals may be called with extra
arguments in addition to the signal number (7.14.1.1).
K.5.14 Additional stream types and file-opening modes
[#1] Additional mappings from files to streams may be
supported (7.19.2).
[#2] Additional file-opening modes may be specified by
characters appended to the mode argument of the fopen
function (7.19.5.3).
K.5.15 Defined file position indicator
[#1] The file position indicator is decremented by each
successful call to the ungetc or ungetwc function for a text
stream, except if its value was zero before a call
(7.19.7.11, 7.24.3.10).
K.5.12 Bibliography K.5.15
598 Committee Draft -- August 3, 1998 WG14/N843
Bibliography
1. ``The C Reference Manual'' by Dennis M. Ritchie, a
version of which was published in The C Programming
Language by Brian W. Kernighan and Dennis M. Ritchie,
Prentice-Hall, Inc., (1978). Copyright owned by AT&T.
2. 1984 /usr/group Standard by the /usr/group Standards
Committee, Santa Clara, California, USA, November
1984.
3. ANSI X3/TR-1-82 (1982), American National Dictionary
for Information Processing Systems, Information
Processing Systems Technical Report.
4. ANSI/IEEE 754-1985, American National Standard for
Binary Floating-Point Arithmetic.
5. ANSI/IEEE 854-1988, American National Standard for
Radix-Independent Floating-Point Arithmetic.
6. IEC 60559:1989, Binary floating-point arithmetic for
microprocessor systems, second edition (previously
designated IEC 559:1989).
7. ISO/IEC 646:1991, Information technology -- ISO 7-bit
coded character set for information interchange.
8. ISO/IEC 2382-1:1993, Information technology --
Vocabulary -- Part 1: Fundamental terms.
9. ISO 4217:1995, Codes for the representation of
currencies and funds.
10. ISO 8601:1988, Data elements and interchange formats
-- Information interchange -- Representation of dates
and times.
11. ISO/IEC 9899:1990, Programming languages -- C. *
12. ISO/IEC 9899/COR1:1994, Technical Corrigendum 1.
13. ISO/IEC 9899/COR2:1996, Technical Corrigendum 2.
14. ISO/IEC 9899/AMD1:1995, Amendment 1 to ISO/IEC
9899:1990 C Integrity.
15. ISO/IEC 9945-2:1993, Information technology -- |
Portable Operating System Interface (POSIX) -- Part |
2: Shell and Utilities. |
16. ISO/IEC TR 10176:1998, Information technology --
Guidelines for the preparation of programming language
standards.
Bibliography
WG14/N843 Committee Draft -- August 3, 1998 599
17. ISO/IEC 10646:1993, Information technology -- |
Universal Multiple-Octet Coded Character Set (UCS).
18. ISO/IEC 10967-1:1994, Information technology --
Language independent arithmetic -- Part 1: Integer
and floating point arithmetic.
Bibliography
600 Committee Draft -- August 3, 1998 WG14/N843
Bibliography
WG14/N843 Committee Draft -- August 3, 1998 601
Index
! (logical negation operator), 6.5.3.3
!= (inequality operator), 6.5.9
# operator, 6.10.3.2
# preprocessing directive, 6.10.7
# punctuator, 6.10
## operator, 6.10.3.3
#define preprocessing directive, 6.10.3
#elif preprocessing directive, 6.10.1
#else preprocessing directive, 6.10.1
#endif preprocessing directive, 6.10.1
#error preprocessing directive, 4, 6.10.5 |
#if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, 6.10.1,
7.1.4
#ifdef preprocessing directive, 6.10.1
#ifndef preprocessing directive, 6.10.1
#include preprocessing directive, 5.1.1.2, 6.10.2
#line preprocessing directive, 6.10.4
#pragma preprocessing directive, 6.10.6
#undef preprocessing directive, 6.10.3.5, 7.1.3, 7.1.4
% (remainder operator), 6.5.5
%: (alternative spelling of #), 6.4.6
%:%: (alternative spelling of ##), 6.4.6
%= (remainder assignment operator), 6.5.16.2
%> (alternative spelling of }), 6.4.6
& (address operator), 6.3.2.1, 6.5.3.2
& (bitwise AND operator), 6.5.10
&& (logical AND operator), 6.5.13
&= (bitwise AND assignment operator), 6.5.16.2
' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.9
( ) (cast operator), 6.5.4
( ) (function-call operator), 6.5.2.2
( ) (parentheses punctuator), 6.7.5.3, 6.8.4, 6.8.5
( ){ } (compound-literal operator), 6.5.2.5
* (asterisk punctuator), 6.7.5.1, 6.7.5.2
* (indirection operator), 6.5.2.1, 6.5.3.2
* (multiplication operator), 6.5.5
*= (multiplication assignment operator), 6.5.16.2
+ (addition operator), 6.5.2.1, 6.5.3.2, 6.5.6
+ (unary plus operator), 6.5.3.3
++ (postfix increment operator), 6.3.2.1, 6.5.2.4
++ (prefix increment operator), 6.3.2.1, 6.5.3.1
+= (addition assignment operator), 6.5.16.2
, (comma operator), 6.5.17
, (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, 6.7.2.3,
6.7.8
- (subtraction operator), 6.5.6
- (unary minus operator), 6.5.3.3
-- (postfix decrement operator), 6.3.2.1, 6.5.2.4
-- (prefix decrement operator), 6.3.2.1, 6.5.3.1
-= (subtraction assignment operator), 6.5.16.2
-> (structure/union pointer operator), 6.5.2.3
Index
602 Committee Draft -- August 3, 1998 WG14/N843
. (structure/union member operator), 6.3.2.1, 6.5.2.3
. punctuator, 6.7.8
... (ellipsis punctuator), 6.5.2.2, 6.7.5.3, 6.10.3
/ (division operator), 6.5.5
/* */ (comment delimiters), 6.4.9
// (comment delimiters), 6.4.9
/= (division assignment operator), 6.5.16.2
: (colon punctuator), 6.7.2.1
:> (alternative spelling of ]), 6.4.6
; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3, 6.8.5, 6.8.6
< (less-than operator), 6.5.8
<% (alternative spelling of {), 6.4.6
<: (alternative spelling of [), 6.4.6
<< (left-shift operator), 6.5.7
<<= (left-shift assignment operator), 6.5.16.2
<= (less-than-or-equal-to operator), 6.5.8
<assert.h> header, 7.2, B.1 |
<complex.h> header, 5.2.4.2.2, 7.3, 7.22, 7.26.1, G.5 |
<ctype.h> header, 7.4, 7.26.2
<errno.h> header, 7.5, 7.26.3
<fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, D.4.3, F, H |
<float.h> header, 4, 5.2.4.2.2, 7.7, 7.20.1.3, 7.24.4.1.1 |
<inttypes.h> header, 7.8, 7.26.4
<iso646.h> header, 4, 7.9
<limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10 |
<locale.h> header, 7.11, 7.26.5
<math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.22, F, F.9 |
<setjmp.h> header, 7.13
<signal.h> header, 7.14, 7.26.6
<stdarg.h> header, 4, 6.7.5.3, 7.15
<stdbool.h> header, 4, 7.16, 7.26.7, H |
<stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5,
6.5.3.4, 6.5.6, 7.17
<stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8, 7.18, 7.26.8 |
<stdio.h> header, 7.19, 7.26.9, F |
<stdlib.h> header, 7.20, 7.26.10, F |
<string.h> header, 7.21, 7.26.11 |
<tgmath.h> header, 7.22, G.6 |
<time.h> header, 7.23
<wchar.h> header, 7.19.1, 7.24, 7.26.12, F |
<wctype.h> header, 7.25, 7.26.13 |
= (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.8
= (simple assignment operator), 6.5.16.1
== (equality operator), 6.5.9
> (greater-than operator), 6.5.8
>= (greater-than-or-equal-to operator), 6.5.8
>> (right-shift operator), 6.5.7
>>= (right-shift assignment operator), 6.5.16.2
? : (conditional operator), 6.5.15
?? (trigraph sequences), 5.2.1.1
[ ] (array subscript operator), 6.5.2.1, 6.5.3.2
[ ] (brackets punctuator), 6.7.5.2, 6.7.8
\ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4
\ (escape character), 6.4.4.4
Index
WG14/N843 Committee Draft -- August 3, 1998 603
\" (double-quote escape sequence), 6.4.4.4, 6.4.5, 6.10.9
\\ (backslash escape sequence), 6.4.4.4, 6.10.9
\' (single-quote escape sequence), 6.4.4.4, 6.4.5
\0 (null character), 5.2.1, 6.4.4.4, 6.4.5
padding of binary stream, 7.19.2
\? (question-mark escape sequence), 6.4.4.4
\a (alert escape sequence), 5.2.2, 6.4.4.4
\b (backspace escape sequence), 5.2.2, 6.4.4.4
\f (form-feed escape sequence), 5.2.2, 6.4.4.4, 7.4.1.9
\n (new-line escape sequence), 5.2.2, 6.4.4.4, 7.4.1.9
\octal digits (octal-character escape sequence), 6.4.4.4
\r (carriage-return escape sequence), 5.2.2, 6.4.4.4,
7.4.1.9
\t (horizontal-tab escape sequence), 5.2.2, 6.4.4.4, 7.4.1.9
\U (universal character names), 6.4.3
\u (universal character names), 6.4.3
\v (vertical-tab escape sequence), 5.2.2, 6.4.4.4, 7.4.1.9
\xhexadecimal digits (hexadecimal-character escape
sequence), 6.4.4.4
^ (bitwise exclusive OR operator), 6.5.11
^= (bitwise exclusive OR assignment operator), 6.5.16.2
__bool_true_false_are_defined macro, 7.16
__DATE__ macro, 6.10.8
__FILE__ macro, 6.10.8, 7.2.1.1
__func__ identifier, 6.4.2.2, 7.2.1.1
__LINE__ macro, 6.10.8, 7.2.1.1
__STDC__ macro, 6.10.8
__STDC_CONSTANT_MACROS macro, 7.18.4
__STDC_FORMAT_MACROS macro, 7.8.1
__STDC_IEC_559__ macro, 6.10.8
__STDC_IEC_559_COMPLEX__ macro, 6.10.8
__STDC_ISO_10646__ macro, 6.10.8 |
__STDC_LIMIT_MACROS macro, 7.18.2, 7.18.3
__STDC_VERSION__ macro, 6.10.8
__TIME__ macro, 6.10.8
_Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2 |
_Bool type conversions, 6.3.1.2 |
_Complex types, 6.2.5, 6.7.2 |
_Complex_I macro, 7.3.1
_Imaginary types, 6.7.2, G.2 |
_Imaginary_I macro, 7.3.1, G.5
_IOFBF macro, 7.19.1, 7.19.5.5, 7.19.5.6
_IOLBF macro, 7.19.1, 7.19.5.6
_IONBF macro, 7.19.1, 7.19.5.5, 7.19.5.6
_LOCALTIME macro, 7.23.1, 7.23.2.4, 7.23.2.6, 7.23.3.7
_NO_LEAP_SECONDS macro, 7.23.1, 7.23.2.4, 7.23.2.6, 7.23.3.7
_Pragma operator, 5.1.1.2, 6.10.9 |
{ } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.8, 6.8.2
{ } (compound-literal operator), 6.5.2.5
| (bitwise inclusive OR operator), 6.5.12
|= (bitwise inclusive OR assignment operator), 6.5.16.2
|| (logical OR operator), 6.5.14
~ (bitwise complement operator), 6.5.3.3
Index
604 Committee Draft -- August 3, 1998 WG14/N843
abort function, 7.2.1.1, 7.14.1.1, 7.19.3, 7.20.4.1
abs function, 7.20.6.1 |
absolute-value functions
complex, 7.3.8, G.5.4 |
integer, 7.20.6.1 |
real, 7.12.7, F.9.4 |
abstract declarator, 6.7.6
abstract machine, 5.1.2.3
accuracy, floating-point, 5.2.4.2.2 |
acos functions, 7.12.4.1, F.9.1.1
acos type-generic macro, 7.22.1
acosh functions, 7.12.5.1, F.9.2.1 |
acosh type-generic macro, 7.22.1
active position, 5.2.2
actual argument, 3.2
actual parameter (deprecated), 3.2
addition assignment operator (+=), 6.5.16.2
addition operator (+), 6.5.2.1, 6.5.3.2, 6.5.6
additive expressions, 6.5.6
address constant, 6.6
address operator (&), 6.3.2.1, 6.5.3.2
aggregate initialization, 6.7.8
aggregate types, 6.2.5
alert escape sequence (\a), 5.2.2, 6.4.4.4
alignment, 3.1
structure/union member, 6.7.2.1
allocated storage, order and contiguity, 7.20.3
and macro, 7.9
AND operators
bitwise (&), 6.5.10
bitwise assignment (&=), 6.5.16.2
logical (&&), 6.5.13
and_eq macro, 7.9
ANSI/IEEE 754, F.1 |
ANSI/IEEE 854, F.1 |
argc (main function parameter), 5.1.2.2.1
argument, 3.2
array, 6.9.1
default promotions, 6.5.2.2
function, 6.5.2.2, 6.9.1
macro, substitution, 6.10.3.1
argument, complex, 7.3.9.1 |
argv (main function parameter), 5.1.2.2.1
arithmetic constant expression, 6.6
arithmetic conversions, usual, see usual arithmetic
conversions
arithmetic operators
additive, 6.5.6
bitwise, 6.5.10, 6.5.11, 6.5.12
increment and decrement, 6.5.2.4, 6.5.3.1
multiplicative, 6.5.5
shift, 6.5.7
unary, 6.5.3.3
arithmetic types, 6.2.5
Index
WG14/N843 Committee Draft -- August 3, 1998 605
arithmetic, pointer, 6.5.6
array
argument, 6.9.1
declarator, 6.7.5.2
initialization, 6.7.8
multidimensional, 6.5.2.1
parameter, 6.9.1
storage order, 6.5.2.1
subscript operator ([ ]), 6.5.2.1, 6.5.3.2
subscripting, 6.5.2.1
type, 6.2.5
type conversion, 6.3.2.1
wide-character functions, 7.24.4.6
arrow operator (->), 6.5.2.3
ASCII code set, 5.2.1.1
asctime function, 7.23.3.1
asin functions, 7.12.4.2, F.9.1.2 |
asin type-generic macro, 7.22.1, G.6 |
asinh functions, 7.12.5.2, F.9.2.2 |
asinh type-generic macro, 7.22.1, G.6 |
asm keyword, K.5.10 |
assert macro, 7.2.1.1
assert.h header, 7.2, B.1 |
assignment
compound, 6.5.16.2
conversion, 6.5.16.1
expressions, 6.5.16
operators, 6.3.2.1, 6.5.16
simple, 6.5.16.1
associativity of operators, 6.5
asterisk punctuator (*), 6.7.5.1, 6.7.5.2
atan functions, 7.12.4.3, F.9.1.3 |
atan type-generic macro, 7.22.1, G.6 |
atan2 functions, 7.12.4.4, F.9.1.4 |
atan2 type-generic macro, 7.22.1
atanh functions, 7.12.5.3, F.9.2.3 |
atanh type-generic macro, 7.22.1, G.6 |
atexit function, 7.20.4.2, 7.20.4.3
atof function, 7.20.1, 7.20.1.1
atoi function, 7.20.1, 7.20.1.2
atol function, 7.20.1, 7.20.1.2 |
atoll function, 7.20.1, 7.20.1.2 |
auto storage-class specifier, 6.7.1, 6.9
automatic storage duration, 5.1.2.3, 5.2.3, 6.2.4
backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4
backslash escape sequence (\\), 6.4.4.4, 6.10.9
backspace escape sequence (\b), 5.2.2, 6.4.4.4
basic character set, 5.2.1 |
basic types, 6.2.5
bibliography, K.5.15 |
binary streams, 7.19.2, 7.19.7.11, 7.19.9.2, 7.19.9.4
bit, 3.3
high order, 3.4
Index
606 Committee Draft -- August 3, 1998 WG14/N843
low order, 3.4
bit-field, 6.7.2.1, K.5.8 |
bitand macro, 7.9
bitor macro, 7.9
bitwise operators, 6.5
AND, 6.5.10
AND assignment (&=), 6.5.16.2
complement (~), 6.5.3.3
exclusive OR, 6.5.11
exclusive OR assignment (^=), 6.5.16.2
inclusive OR, 6.5.12
inclusive OR assignment (|=), 6.5.16.2
shift, 6.5.7
block, 6.8.2
block scope, 6.2.1
block structure, 6.2.1
bold type convention, 6.1
bool macro, 7.16 |
boolean type, 6.3.1.2 |
boolean type conversion, 6.3.1.1, 6.3.1.2
braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.8, 6.8.2
brackets operator ([ ]), 6.5.2.1, 6.5.3.2
brackets punctuator ([ ]), 6.7.5.2, 6.7.8
branch cuts, 7.3.3
break statement, 6.8.6.3
broken-down time, 7.23.1, 7.23.2.3, 7.23.3, 7.23.3.1,
7.23.3.3, 7.23.3.4, 7.23.3.5, 7.23.3.7
normalization, 7.23.2.6
bsearch function, 7.20.5, 7.20.5.1
btowc function, 7.24.6.1.1
BUFSIZ macro, 7.19.1, 7.19.2, 7.19.5.5
byte, 3.4, 6.5.3.4
byte input/output functions, 7.19.1
byte-oriented stream, 7.19.2
C program, 5.1.1.1
C++, 7.8.1, 7.18.2, 7.18.3, 7.18.4
cabs functions, 7.3.8.1, G.5 |
type-generic macro for, 7.22.1
cacos functions, 7.3.5.1, G.5.1.1 |
type-generic macro for, 7.22.1
cacosh functions, 7.3.6.1, G.5.2.1 |
type-generic macro for, 7.22.1
calendar time, 7.23.1, 7.23.2.2, 7.23.2.3, 7.23.2.5, *
7.23.3.2, 7.23.3.3, 7.23.3.4, 7.23.3.7
call by value, 6.5.2.2
calloc function, 7.20.3, 7.20.3.1, 7.20.3.2, 7.20.3.4
carg functions, 7.3.9.1, G.5 |
carg type-generic macro, 7.22.1, G.6 |
carriage-return escape sequence (\r), 5.2.2, 6.4.4.4,
7.4.1.9
case label, 6.8.1, 6.8.4.2
case mapping functions
character, 7.4.2
Index
WG14/N843 Committee Draft -- August 3, 1998 607
wide character, 7.25.3.1
extensible, 7.25.3.2
casin functions, 7.3.5.2, G.5 |
type-generic macro for, 7.22.1
casinh functions, 7.3.6.2, G.5.2.2 |
type-generic macro for, 7.22.1
cast expr, 6.5.4 *
cast operator (( )), 6.5.4
catan functions, 7.3.5.3, G.5 |
type-generic macro for, 7.22.1
catanh functions, 7.3.6.3, G.5.2.3 |
type-generic macro for, 7.22.1
cbrt functions, 7.12.7.1, F.9.4.1 |
cbrt type-generic macro, 7.22.1
ccos functions, 7.3.5.4, G.5 |
type-generic macro for, 7.22.1
ccosh functions, 7.3.6.4, G.5.2.4 |
type-generic macro for, 7.22.1
ceil functions, 7.12.9.1, F.9.6.1 |
ceil type-generic macro, 7.22.1
cerf function, 7.26.1
cerfc function, 7.26.1
cexp functions, 7.3.7.1, G.5.3.1 |
type-generic macro for, 7.22.1
cexp2 function, 7.26.1 *
cexpm1 function, 7.26.1
cgamma function, 7.26.1
char type, 6.2.5, 6.3.1.1, 6.7.2
char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, 6.3.1.8 |
CHAR_BIT macro, 5.2.4.2.1
CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1
CHAR_MIN macro, 5.2.4.2.1
character, 3.5
character array initialization, 6.7.8
character case mapping functions, 7.4.2
character classification functions, 7.4.1
wide character
extensible, 7.25.2.2
character constant, 5.1.1.2, 5.2.1, 6.4.4.4
character display semantics, 5.2.2
character handling header, 7.4, 7.11.1.1
character input/output functions, 7.19.7
character sets, 5.2.1
character string literal, see string literal
character testing functions, 7.4.1
character type conversion, 6.3.1.1
character types, 6.2.5, 6.7.8 |
cimag functions, 7.3.9.2, 7.3.9.4, G.5 |
cimag type-generic macro, 7.22.1, G.6 |
cis function, G.5 |
classification functions
character, 7.4.1
wide character, 7.25.2.1
clearerr function, 7.19.10.1
Index
608 Committee Draft -- August 3, 1998 WG14/N843
clgamma function, 7.26.1
clock function, 7.23.2.1
clock_t type, 7.23.1, 7.23.2.1
CLOCKS_PER_SEC macro, 7.23.1, 7.23.2.1
clog functions, 7.3.7.2, G.5.3.2 |
type-generic macro for, 7.22.1
clog10 function, 7.26.1 *
clog1p function, 7.26.1
clog2 function, 7.26.1
collating sequences, 5.2.1
colon punctuator (:), 6.7.2.1
comma operator (,), 6.5.17
comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2, 6.7.2.3,
6.7.8
command processor, 7.20.4.5
comment delimiters (/* */ and //), 6.4.9
comments, 5.1.1.2, 6.4, 6.4.9
common extensions, K.5 |
common initial sequence, 6.5.2.3
common real type, 6.3.1.8 |
common warnings, J |
comparison functions, 7.20.5, 7.20.5.1, 7.20.5.2
string, 7.21.4
wide string, 7.24.4.4
comparison macros, 7.12.14
comparison, pointer, 6.5.8
compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.5
compl macro, 7.9
complement operator (~), 6.5.3.3
complex macro, 7.3.1
complex numbers, 6.2.5, G |
complex type conversion, 6.3.1.6, 6.3.1.7 |
complex type domain, 6.2.5 |
complex types, 6.2.5, 6.7.2 |
complex.h header, 5.2.4.2.2, 7.3, 7.22, 7.26.1, G.5 |
compliance, see conformance
components of time, 7.23.1
composite type, 6.2.7
compound assignment, 6.5.16.2
compound literals, 6.5.2.5
compound statement, 6.8.2
compound-literal operator (( ){ }), 6.5.2.5
concatenation functions
string, 7.21.3
wide string, 7.24.4.3
concatenation, preprocessing, see preprocessing |
concatenation |
conceptual models, 5.1
conditional inclusion, 6.10.1
conditional operator (? :), 6.5.15
conformance, 4
conforming freestanding implementation, 4
conforming hosted implementation, 4
conforming implementation, 4
Index
WG14/N843 Committee Draft -- August 3, 1998 609
conforming program, 4
conj functions, 7.3.9.3, G.5 |
conj type-generic macro, 7.22.1
const type qualifier, 6.7.3
const-qualified type, 6.2.5, 6.3.2.1, 6.7.3
constant expression, 6.6
constants, 6.4.4
as primary expression, 6.5.1
character, 6.4.4.4
enumeration, 6.2.1, 6.4.4.3 |
floating, 6.4.4.2
hexadecimal, 6.4.4.1
integer, 6.4.4.1
octal, 6.4.4.1
constraints, 3.6
content of structure/union/enumeration, 6.7.2.3
contiguity of allocated storage, 7.20.3
continue statement, 6.8.6.2
control character, 5.2.1, 7.4
control wide character, 7.25.2
conversion, 6.3
arithmetic operands, 6.3.1
array, 6.3.2.1
array argument, 6.9.1
array parameter, 6.9.1
boolean, 6.3.1.2 |
boolean, characters, and integers, 6.3.1.1 |
by assignment, 6.5.16.1
by return statement, 6.8.6.4
complex types, 6.3.1.6 |
explicit, 6.3
function, 6.3.2.1
function argument, 6.5.2.2, 6.9.1
function parameter, 6.9.1
imaginary, G.3.1 |
imaginary and complex, G.3.3 |
implicit, 6.3
lvalues and function designators, 6.3.2.1
pointer, 6.3.2.1, 6.3.2.3
real and complex, 6.3.1.7 |
real and imaginary, G.3.2 |
real floating and integer, 6.3.1.4 |
real floating types, 6.3.1.5 |
signed and unsigned integers, 6.3.1.3 |
usual arithmetic, see usual arithmetic conversions
void type, 6.3.2.2
conversion functions
multibyte/wide character
restartable, 7.24.6.3
multibyte/wide-string
restartable, 7.24.6.4
numeric
wide string, 7.24.4.1
single byte
Index
610 Committee Draft -- August 3, 1998 WG14/N843
wide character, 7.24.6.1
time, 7.23.3
wide character
single byte, 7.24.6.1
conversion specifier, 7.19.6.1, 7.19.6.2, 7.24.2.1, 7.24.2.2
conversion state, 7.24.6, 7.24.6.2, 7.24.6.3, 7.24.6.3.2,
7.24.6.3.3, 7.24.6.4, 7.24.6.4.1, 7.24.6.4.2
conversion utilities
multibyte
extended, 7.24.6
wide string
extended, 7.24.6
copying functions
string, 7.21.2
wide string, 7.24.4.2
copysign functions, 7.3.9.4, 7.12.11.1, F.9.8.1 |
copysign type-generic macro, 7.22.1
correctly rounded result, 3.7
corresponding real type, 6.2.5
cos functions, 7.12.4.5, F.9.1.5 |
cos type-generic macro, 7.22.1, G.6 |
cosh functions, 7.12.5.4, F.9.2.4 |
cosh type-generic macro, 7.22.1, G.6 |
cpow functions, 7.3.8.2, G.5 |
type-generic macro for, 7.22.1
cproj functions, 7.3.9.4, G.5 |
cproj type-generic macro, 7.22.1
creal functions, 7.3.9.5, G.5 |
creal type-generic macro, 7.22.1, G.6 |
csin functions, 7.3.5.5, G.5 |
type-generic macro for, 7.22.1
csinh functions, 7.3.6.5, G.5.2.5 |
type-generic macro for, 7.22.1
csqrt functions, 7.3.8.3, G.5.4.1 |
type-generic macro for, 7.22.1
ctan functions, 7.3.5.6, G.5 |
type-generic macro for, 7.22.1
ctanh functions, 7.3.6.6, G.5.2.6 |
type-generic macro for, 7.22.1
ctime function, 7.23.3.2 *
ctype.h header, 7.4, 7.26.2
current object, 6.7.8
CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4
data stream, see streams
date and time header, 7.23
Daylight Saving Time, 7.23.1
DBL_DIG macro, 5.2.4.2.2
DBL_EPSILON macro, 5.2.4.2.2
DBL_MANT_DIG macro, 5.2.4.2.2
DBL_MAX macro, 5.2.4.2.2
DBL_MAX_10_EXP macro, 5.2.4.2.2
DBL_MAX_EXP macro, 5.2.4.2.2
DBL_MIN macro, 5.2.4.2.2
Index
WG14/N843 Committee Draft -- August 3, 1998 611
DBL_MIN_10_EXP macro, 5.2.4.2.2
DBL_MIN_EXP macro, 5.2.4.2.2
decimal constant, 6.4.4.1
decimal digits, 5.2.1
decimal-point character, 7.1.1, 7.11.2.1
DECIMAL_DIG macro, 5.2.4.2.2, 7.12, 7.19.6.1, 7.20.1.3, |
7.24.2.1, 7.24.4.1.1
declaration specifiers, 6.7
declarations, 6.7
function, 6.7.5.3
pointer, 6.7.5.1
structure/union, 6.7.2.1
typedef, 6.7.7
declarator, 6.7.5
abstract, 6.7.6
declarator type derivation, 6.2.5, 6.7.5
decrement operators, see arithmetic operators, increment and
decrement
default argument promotions, 6.5.2.2, 7.8.1
default initialization, 6.7.8
default label, 6.8.1, 6.8.4.2
define preprocessing directive, 6.10.3
defined operator, 6.10.1
definition, 6.7
function, 6.9.1
definitions of terms, 3
derived declarator types, 6.2.5
derived types, 6.2.5
designated initializer, 6.7.8
destringizing, 6.10.9
device input/output, 5.1.2.3
diagnostic message, 3.8, 5.1.1.3
diagnostics, 5.1.1.3
diagnostics header, 7.2
difftime function, 7.23.2.2
digraphs, 6.4.6
direct input/output functions, 7.19.8
display device, 5.2.2
div function, 7.20.6.2 |
div_t type, 7.20
division assignment operator (/=), 6.5.16.2
division operator (/), 6.5.5
do statement, 6.8.5.2
documentation of implementation, 4
domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4,
7.12.5.1, 7.12.5.3, 7.12.6.7, 7.12.6.8, 7.12.6.9,
7.12.6.10, 7.12.6.11, 7.12.7.4, 7.12.7.5, 7.12.8.4, |
7.12.10.1
dot operator (.), 6.5.2.3
double _Complex type, 6.2.5
double _Complex type conversion, 6.3.1.6, 6.3.1.7, 6.3.1.8 |
double _Imaginary type, G.2 |
double type, 6.2.5, 6.4.4.2, 6.7.2
double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, 6.3.1.8 |
Index
612 Committee Draft -- August 3, 1998 WG14/N843
double-precision arithmetic, 5.1.2.3
double-quote escape sequence (\"), 6.4.5
double-quote escape sequence (\"), 6.4.4.4, 6.10.9
double_t type, 7.12
EDOM macro, 7.5, 7.12.1, see also domain error |
effective type, 6.5
EILSEQ macro, 7.5, 7.19.3, 7.24.3.1, 7.24.3.3, 7.24.6.3.2, |
7.24.6.3.3, 7.24.6.4.1, 7.24.6.4.2, see also encoding |
error
element type, 6.2.5
elif preprocessing directive, 6.10.1
ellipsis punctuator (...), 6.5.2.2, 6.7.5.3, 6.10.3
else preprocessing directive, 6.10.1
else statement, 6.8.4.1
empty statement, 6.8.3
encoding error, 7.19.3, 7.24.3.1, 7.24.3.3, 7.24.6.3.2,
7.24.6.3.3, 7.24.6.4.1, 7.24.6.4.2
end-of-file, 7.25.1
end-of-file indicator, 7.19.1, 7.19.5.3, 7.19.7.1, 7.19.7.5,
7.19.7.6, 7.19.7.11, 7.19.9.2, 7.19.9.3, 7.19.10.1,
7.19.10.2, 7.24.3.1, 7.24.3.10
end-of-file macro, see EOF macro
end-of-line indicator, 5.2.1
endif preprocessing directive, 6.10.1
enum type, 6.2.5, 6.7.2, 6.7.2.2
enumerated type, 6.2.5
enumeration, 6.2.5, 6.7.2.2
enumeration constant, 6.2.1, 6.4.4.3 |
enumeration content, 6.7.2.3
enumeration members, 6.7.2.2
enumeration specifiers, 6.7.2.2
enumeration tag, 6.2.3, 6.7.2.3
enumerator, 6.7.2.2
environment, 5
environment functions, 7.20.4
environment list, 7.20.4.4
environmental considerations, 5.2
environmental limits, 5.2.4, 7.13.1.1, 7.19.2, 7.19.3, |
7.19.4.4, 7.19.6.1, 7.20.2.1, 7.20.4.2, 7.24.2.1
EOF macro, 7.4, 7.19.1, 7.19.5.1, 7.19.5.2, 7.19.6.2,
7.19.6.7, 7.19.6.9, 7.19.6.11, 7.19.6.14, 7.19.7.1,
7.19.7.3, 7.19.7.4, 7.19.7.5, 7.19.7.6, 7.19.7.9,
7.19.7.10, 7.19.7.11, 7.24.2.2, 7.24.2.4, 7.24.2.6,
7.24.2.8, 7.24.2.10, 7.24.2.12, 7.24.3.4, 7.24.6.1.1,
7.24.6.1.2, 7.25.1
equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.8
equal-to operator, see equality operator
equality expressions, 6.5.9
equality operator (==), 6.5.9
ERANGE macro, 7.5, 7.8.2.1, 7.8.2.2, 7.12.1, 7.20.1.3, |
7.20.1.4, 7.24.4.1.1, 7.24.4.1.2, see also range error
erf functions, 7.12.8.1, F.9.5.1 |
erf type-generic macro, 7.22.1
Index
WG14/N843 Committee Draft -- August 3, 1998 613
erfc functions, 7.12.8.2, F.9.5.2 |
erfc type-generic macro, 7.22.1
errno macro, 7.3.2, 7.5, 7.8.2.1, 7.8.2.2, 7.12.1, 7.14.1.1, |
7.19.3, 7.19.9.3, 7.19.10.4, 7.20.1, 7.20.1.3, 7.20.1.4, |
7.21.6.2, 7.24.3.1, 7.24.3.3, 7.24.4.1.1, 7.24.4.1.2, |
7.24.6.3.2, 7.24.6.3.3, 7.24.6.4.1, 7.24.6.4.2
errno.h header, 7.5, 7.26.3
error conditions, 7.12.1
error functions, 7.12.8, F.9.5 |
error indicator, 7.19.1, 7.19.5.3, 7.19.7.1, 7.19.7.3,
7.19.7.5, 7.19.7.6, 7.19.7.8, 7.19.7.9, 7.19.9.2,
7.19.10.1, 7.19.10.3, 7.24.3.1, 7.24.3.3
error preprocessing directive, 6.10.5
error, domain, see domain error
error, encoding, see encoding error
error, range, see range error
error-handling functions, 7.19.10, 7.21.6.2
escape character (\), 6.4.4.4
escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.1
evaluation
order, 6.5
exception, 6.5, 7.6, 7.6.2, F.9 |
exclusive OR operators
bitwise (^), 6.5.11
bitwise assignment (^=), 6.5.16.2
executable program, 5.1.1.1
execution character set, 5.2.1
execution environment, 5, 5.1.2, see also environmental
limits
execution sequence, 5.1.2.3, 6.8
exit function, 5.1.2.2.3, 7.19.3, 7.20, 7.20.4.3
EXIT_FAILURE macro, 7.20, 7.20.4.3
EXIT_SUCCESS macro, 7.20, 7.20.4.3
exp functions, 7.12.6.1, F.9.3.1 |
exp type-generic macro, 7.22.1
exp2 functions, 7.12.6.2, F.9.3.2 |
exp2 type-generic macro, 7.22.1
explicit conversion, 6.3
expm1 functions, 7.12.6.3, F.9.3.3 |
expm1 type-generic macro, 7.22.1
exponent part, 6.4.4.2
exponential functions
complex, 7.3.7, G.5.3 |
real, 7.12.6, F.9.3 |
expression, 6.5
assignment, 6.5.16
constant, 6.6
full, 6.8
order of evaluation, 6.5
parenthesized, 6.5.1
primary, 6.5.1
unary, 6.5.3
expression statement, 6.8.3
extended character set, 5.2.1.2
Index
614 Committee Draft -- August 3, 1998 WG14/N843
extended integer types, 6.2.5, 7.18
extended multibyte conversion utilities, 7.24.6
extended wide-string conversion utilities, 7.24.6
extensible wide-character case mapping functions, 7.25.3.2
extensible wide-character classification functions, 7.25.2.2
extern storage-class specifier, 6.2.2, 6.7.1
external definition, 6.9
external identifiers, underscore, 7.1.3
external linkage, 6.2.2
external name, 6.4.2.1
external object definitions, 6.9.2
fabs functions, 7.12.7.2, F.9.4.2 |
fabs type-generic macro, 7.22.1, G.6 |
false macro, 7.16
fclose function, 7.19.5.1
fdim functions, 7.12.12.1, F.9.9.1 |
fdim type-generic macro, 7.22.1
FE_ALL_EXCEPT macro, 7.6
FE_DFL_ENV macro, 7.6, 7.6.4.3, 7.6.4.4
FE_DIVBYZERO macro, 7.6
FE_DOWNWARD macro, 7.6
FE_INEXACT macro, 7.6
FE_INVALID macro, 7.6
FE_OVERFLOW macro, 7.6
FE_TONEAREST macro, 7.6
FE_TOWARDZERO macro, 7.6
FE_UNDERFLOW macro, 7.6
FE_UPWARD macro, 7.6
feclearexcept function, 7.6.2, 7.6.2.1
fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4
fegetexceptflag function, 7.6.2, 7.6.2.2
fegetround function, 7.6, 7.6.3.1
feholdexcept function, 7.6.4.2, 7.6.4.3, 7.6.4.4
fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, D.4.3, F, H |
FENV_ACCESS pragma, 6.10.6, 7.6.1
fenv_t type, 7.6
feof function, 7.19.10.2
feraiseexcept function, 7.6.2, 7.6.2.3
ferror function, 7.19.10.3
fesetenv function, 7.6.4.3
fesetexceptflag function, 7.6.2, 7.6.2.4
fesetround function, 7.6, 7.6.3.2
fetestexcept function, 7.6.2, 7.6.2.5
feupdateenv function, 7.6.4.2, 7.6.4.4
fexcept_t type, 7.6
fflush function, 7.19.5.2, 7.19.5.3
fgetc function, 7.19.1, 7.19.3, 7.19.7.1, 7.19.7.5
fgetpos function, 7.19.2, 7.19.9.1, 7.19.9.3
fgets function, 7.19.1, 7.19.7.2
fgetwc function, 7.19.1, 7.19.3, 7.24.3.1, 7.24.3.6
fgetws function, 7.19.1, 7.24.3.2
field width, 7.19.6.1, 7.24.2.1
file, 7.19.3
Index
WG14/N843 Committee Draft -- August 3, 1998 615
access functions, 7.19.5
name, 7.19.3
operations, 7.19.4
position indicator, 7.19.1, 7.19.2, 7.19.3, 7.19.5.3,
7.19.7.1, 7.19.7.3, 7.19.7.11, 7.19.8.1, 7.19.8.2,
7.19.9.1, 7.19.9.2, 7.19.9.3, 7.19.9.4, 7.19.9.5, |
7.24.3.1, 7.24.3.3, 7.24.3.10, K.5.15
positioning functions, 7.19.9
file scope, 6.2.1, 6.9
FILE type, 7.19.1, 7.19.3
file-opening modes, K.5.14 |
FILENAME_MAX macro, 7.19.1
flags, 7.19.6.1, 7.24.2.1
flexible array member, 6.7.2.1
float _Complex type, 6.2.5
float _Complex type conversion, 6.3.1.6, 6.3.1.7, 6.3.1.8 |
float _Imaginary type, G.2 |
float type, 6.2.5, 6.4.4.2, 6.7.2
float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, 6.3.1.8 |
float.h header, 4, 5.2.4.2.2, 7.7, 7.20.1.3, 7.24.4.1.1 |
float_t type, 7.12
floating constant, 6.4.4.2 *
floating suffix, f or F, 6.4.4.2
floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7 |
floating types, 6.2.5
floating-point accuracy, 5.2.4.2.2 |
floating-point arithmetic functions, 7.12, F.9
floating-point control mode, 7.6
floating-point environment, 7.6
floating-point numbers, 6.2.5
floating-point rounding mode, 5.2.4.2.2
floating-point status flag, 7.6
floor functions, 7.12.9.2, F.9.6.2 |
floor type-generic macro, 7.22.1
FLT_DIG macro, 5.2.4.2.2
FLT_EPSILON macro, 5.2.4.2.2
FLT_EVAL_METHOD macro, 5.2.4.2.2, 7.12
FLT_MANT_DIG macro, 5.2.4.2.2
FLT_MAX macro, 5.2.4.2.2
FLT_MAX_10_EXP macro, 5.2.4.2.2
FLT_MAX_EXP macro, 5.2.4.2.2
FLT_MIN macro, 5.2.4.2.2
FLT_MIN_10_EXP macro, 5.2.4.2.2
FLT_MIN_EXP macro, 5.2.4.2.2
FLT_RADIX macro, 5.2.4.2.2, 7.19.6.1, 7.20.1.3, 7.24.2.1, |
7.24.4.1.1
FLT_ROUNDS macro, 5.2.4.2.2, 7.6, 7.12.13.1
fma functions, 7.12, 7.12.13.1, F.9.10.1 |
fma type-generic macro, 7.22.1
fmax functions, 7.12.12.2, F.9.9.2 |
fmax type-generic macro, 7.22.1
fmin functions, 7.12.12.3, F.9.9.3 |
fmin type-generic macro, 7.22.1
fmod functions, 7.12.10.1, F.9.7.1 |
Index
616 Committee Draft -- August 3, 1998 WG14/N843
fmod type-generic macro, 7.22.1
fopen function, 7.19.5.3, 7.19.5.4
FOPEN_MAX macro, 7.19.1, 7.19.3
for statement, 6.8.5, 6.8.5.3
form-feed character, 5.2.1, 6.4
form-feed escape sequence (\f), 5.2.2, 6.4.4.4, 7.4.1.9
formal argument (deprecated), 3.16
formal parameter, 3.16
formatted input/output functions, 7.11.1.1, 7.19.6
formatted wide-character input/output functions, 7.24.2
fortran keyword, K.5.9 |
forward references, 3.9
FP_CONTRACT pragma, 6.10.6, 7.12.2
FP_FAST_FMA macro, 7.12
FP_FAST_FMAF macro, 7.12
FP_FAST_FMAL macro, 7.12
FP_ILOGB0 macro, 7.12, 7.12.6.5
FP_ILOGBNAN macro, 7.12, 7.12.6.5
FP_INFINITE macro, 7.12
FP_NAN macro, 7.12
FP_NORMAL macro, 7.12
FP_SUBNORMAL macro, 7.12
FP_ZERO macro, 7.12
fpclassify macro, 7.12.3.1
fpos_t type, 7.19.1, 7.19.2
fprintf function, 7.8.1, 7.19.1, 7.19.6.1, 7.19.6.2,
7.19.6.3, 7.19.6.5, 7.19.6.6, 7.19.6.8, 7.24.2.2
fputc function, 5.2.2, 7.19.1, 7.19.3, 7.19.7.3, 7.19.7.8
fputs function, 7.19.1, 7.19.7.4
fputwc function, 5.2.2, 7.19.1, 7.19.3, 7.24.3.3, 7.24.3.8 |
fputws function, 7.19.1, 7.24.3.4
fread function, 7.19.1, 7.19.8.1
free function, 7.20.3.2, 7.20.3.4
freestanding execution environment, 5.1.2, 5.1.2.1
freopen function, 7.19.2, 7.19.5.4
frexp functions, 7.12.6.4, F.9.3.4 |
frexp type-generic macro, 7.22.1
fscanf function, 7.8.1, 7.19.1, 7.19.6.2, 7.19.6.4,
7.19.6.7, 7.19.6.9
fseek function, 7.19.1, 7.19.5.3, 7.19.7.11, 7.19.9.2,
7.19.9.4, 7.19.9.5, 7.24.3.10
fsetpos function, 7.19.2, 7.19.5.3, 7.19.7.11, 7.19.9.1,
7.19.9.3, 7.24.3.10
ftell function, 7.19.9.2, 7.19.9.4
full declarator, 6.7.5
full expression, 6.8
fully buffered stream, 7.19.3
function
argument, 6.5.2.2, 6.9.1
body, 6.9.1
call, 6.5.2.2
library, 7.1.4
declarator, 6.7.5.3, 6.11.3
definition, 6.7.5.3, 6.9.1, 6.11.4
Index
WG14/N843 Committee Draft -- August 3, 1998 617
designator, 6.3.2.1
image, 5.2.3
library, 5.1.1.1, 7.1.4
name length, 6.4.2.1
parameter, 5.1.2.2.1, 6.5.2.2, 6.9.1
pointer casts, K.5.7 |
prototype, 6.2.1, 6.5.2.2, 6.7.5.3, 6.9.1
prototype scope, 6.2.1
recursive call, 6.5.2.2
return, 6.8.6.4
scope, 6.2.1
type, 6.2.5
type conversion, 6.3.2.1
function specifiers, 6.7.4 |
function type, 6.2.5
function-call operator (( )), 6.5.2.2
function-like macro, 6.10.3
future directions
language, 6.11
library, 7.26
fwide function, 7.19.2, 7.24.3.5
fwprintf function, 7.19.1, 7.19.6.2, 7.24.2.1, 7.24.2.2,
7.24.2.3, 7.24.2.5, 7.24.2.11
fwrite function, 7.19.1, 7.19.8.2
fwscanf function, 7.19.1, 7.24.2.2, 7.24.2.4, 7.24.2.6,
7.24.2.12, 7.24.3.10
gamma functions, 7.12.8, F.9.5 |
general utilities, 7.20
wide string, 7.24.4
general wide-string utilities, 7.24.4
getc function, 7.19.1, 7.19.7.5, 7.19.7.6
getchar function, 7.19.1, 7.19.7.6
getenv function, 7.20.4.4
gets function, 7.19.1, 7.19.7.7
getwc function, 7.19.1, 7.24.3.6, 7.24.3.7
getwchar function, 7.19.1, 7.24.3.7
gmtime function, 7.23.3.3
goto statement, 6.2.1, 6.8.1, 6.8.6.1
graphic characters, 5.2.1
greater-than operator (>), 6.5.8
greater-than-or-equal-to operator (>=), 6.5.8
header, 7.1.2
header names, 6.4, 6.4.7, 6.10.2
hexadecimal constant, 6.4.4.1
hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4
hexadecimal prefix, 6.4.4.1
hexadecimal-character escape sequence (\xhexadecimal
digits), 6.4.4.4
high-order bit, 3.4
horizontal-tab character, 5.2.1, 6.4
horizontal-tab escape sequence (\t), 5.2.2, 6.4.4.4, 7.4.1.9
hosted execution environment, 5.1.2, 5.1.2.2
Index
618 Committee Draft -- August 3, 1998 WG14/N843
HUGE_VAL macro, 7.12, 7.12.1, 7.20.1.3, 7.24.4.1.1 |
HUGE_VALF macro, 7.12, 7.12.1, 7.20.1.3, 7.24.4.1.1 |
HUGE_VALL macro, 7.12, 7.12.1, 7.20.1.3, 7.24.4.1.1 |
hyperbolic functions
complex, 7.3.6, G.5.2 |
real, 7.12.5, F.9.2 |
hypot functions, 7.12.7.3, F.9.4.3 |
hypot type-generic macro, 7.22.1
I macro, 7.3.1, 7.3.9.4, G.5 |
identifier, 6.4.2.1, 6.5.1
linkage, 6.2.2
maximum length, 6.4.2.1
name spaces, 6.2.3
reserved, 7.1.3
scope, 6.2.1
type, 6.2.5
identifier list, 6.7.5
identifier nondigit, 6.4.2.1 |
IEC 559, F.1
IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8, 7.3.3, 7.6, |
7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G, H.1
IEEE 754, F.1 |
IEEE 854, F.1 |
IEEE floating-point arithmetic standard, see IEC 60559,
ANSI/IEEE 754, ANSI/IEEE 854
if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2, 6.10.1,
7.1.4
if statement, 6.8.4.1
ifdef preprocessing directive, 6.10.1
ifndef preprocessing directive, 6.10.1
ilogb functions, 7.12, 7.12.6.5, F.9.3.5 |
ilogb type-generic macro, 7.22.1
imaginary macro, 7.3.1, G.5 |
imaginary numbers, G.2 |
imaginary type domain, G.2 |
imaginary types, 6.7.2, G.2
implementation, 3.10
implementation limits, 3.12, 5.2.4.2, 6.4.2.1, 6.7.5, |
6.8.4.2, E
implementation-defined behavior, 3.11, K.3 |
implicit conversion, 6.3
implicit initialization, 6.7.8
include preprocessing directive, 5.1.1.2, 6.10.2
inclusive OR operators
bitwise (|), 6.5.12
bitwise assignment (|=), 6.5.16.2
incomplete type, 6.2.5
increment operators, see arithmetic operators, increment and
decrement
indirection operator (*), 6.5.2.1, 6.5.3.2
inequality operator (!=), 6.5.9
INFINITY macro, 7.3.9.4, 7.12
initial position, 5.2.2
Index
WG14/N843 Committee Draft -- August 3, 1998 619
initial shift state, 5.2.1.2, 7.20.7
initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.8 |
in blocks, 6.8.2
initializer, 6.7.8
permitted form, 6.6
string literal, 6.3.2.1
inline, 6.7.4 |
inner scope, 6.2.1
input failure, 7.19.6.2, 7.24.2.2, 7.24.2.6, 7.24.2.8,
7.24.2.10
input/output functions
character, 7.19.7
direct, 7.19.8
formatted, 7.19.6
wide character, 7.24.2
wide character, 7.24.3
formatted, 7.24.2
input/output header, 7.19
input/output, device, 5.1.2.3
int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2 |
int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, 6.3.1.8 |
INT_FASTn_MAX macros, 7.18.2.3
INT_FASTn_MIN macros, 7.18.2.3
int_fastn_t types, 7.18.1.3
INT_LEASTn_MAX macros, 7.18.2.2
INT_LEASTn_MIN macros, 7.18.2.2
int_leastn_t types, 7.18.1.2
INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5
INT_MIN macro, 5.2.4.2.1, 7.12
integer arithmetic functions, 7.20.6
integer character constant, 6.4.4.4
integer constant, 6.4.4.1
integer constant expression, 6.6
integer conversion rank, 6.3.1.1
integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1, 6.5.2.2,
6.5.3.3, 6.5.7, 6.8.4.2, 7.18.2, 7.18.3, 7.19.6.1,
7.24.2.1
integer suffix, 6.4.4.1
integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4 |
integer types, 6.2.5, 7.18
extended, 7.18
interactive device, 5.1.2.3, 7.19.3, 7.19.5.3
internal linkage, 6.2.2
internal name, 6.4.2.1
interrupt, 5.2.3
INTMAX_C macro, 7.18.4.2
INTMAX_MAX macro, 7.8.2.1, 7.8.2.2, 7.18.2.5 |
INTMAX_MIN macro, 7.8.2.1, 7.8.2.2, 7.18.2.5 |
intmax_t type, 7.18.1.5
INTn_C macros, 7.18.4.1
INTn_MAX macros, 7.18.2.1
INTn_MIN macros, 7.18.2.1
intn_t types, 7.18.1.1
INTPTR_MAX macro, 7.18.2.4
Index
620 Committee Draft -- August 3, 1998 WG14/N843
INTPTR_MIN macro, 7.18.2.4
intptr_t type, 7.18.1.4
inttypes.h header, 7.8, 7.26.4
isalnum function, 7.4.1.1, 7.4.1.8, 7.4.1.9
isalpha function, 7.4.1.1, 7.4.1.2
iscntrl function, 7.4.1.2, 7.4.1.3, 7.4.1.6, 7.4.1.10
isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.4, 7.4.1.6,
7.4.1.10, 7.11.1.1
isfinite macro, 7.12.3.2
isgraph function, 7.4.1.5
isgreater macro, 7.12.14.1
isgreaterequal macro, 7.12.14.2
isinf macro, 7.12.3.3
isless macro, 7.12.14.3
islessequal macro, 7.12.14.4
islessgreater macro, 7.12.14.5
islower function, 7.4.1.2, 7.4.1.6, 7.4.2.1, 7.4.2.2
isnan macro, 7.12.3.4
isnormal macro, 7.12.3.5
ISO 4217, 2, 7.11.2.1 *
ISO 8601, 2, 7.23.3.5 *
ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8 |
ISO/IEC 2382-1, 2, 3
ISO/IEC 646, 2, 5.2.1.1 |
ISO/IEC 9945-2, 7.11
ISO/IEC TR 10176, I |
iso646.h header, 4, 7.9
isprint function, 5.2.2, 7.4.1.7
ispunct function, 7.4.1.2, 7.4.1.6, 7.4.1.8, 7.4.1.10
isspace function, 7.4.1.2, 7.4.1.6, 7.4.1.8, 7.4.1.9, |
7.4.1.10, 7.19.6.2, 7.20.1.3, 7.20.1.4, 7.24.2.2
isunordered macro, 7.12.14.6
isupper function, 7.4.1.2, 7.4.1.10, 7.4.2.1, 7.4.2.2
iswalnum function, 7.25.2.1.1, 7.25.2.1.8, 7.25.2.1.9,
7.25.2.2.1
iswalpha function, 7.25.2.1.1, 7.25.2.1.2, 7.25.2.2.1
iswcntrl function, 7.25.2.1.2, 7.25.2.1.3, 7.25.2.1.6,
7.25.2.1.10, 7.25.2.2.1
iswctype function, 7.25.2.2.1, 7.25.2.2.2
iswdigit function, 7.25.2.1.1, 7.25.2.1.2, 7.25.2.1.4,
7.25.2.1.6, 7.25.2.1.10, 7.25.2.2.1
iswgraph function, 7.25.2.1, 7.25.2.1.5, 7.25.2.1.9,
7.25.2.2.1
iswlower function, 7.25.2.1.2, 7.25.2.1.6, 7.25.2.2.1,
7.25.3.1.1, 7.25.3.1.2
iswprint function, 5.2.2, 7.25.2.1.5, 7.25.2.1.7, 7.25.2.2.1 |
iswpunct function, 7.25.2.1, 7.25.2.1.2, 7.25.2.1.6,
7.25.2.1.8, 7.25.2.1.9, 7.25.2.1.10, 7.25.2.2.1
iswspace function, 7.19.6.2, 7.24.2.2, 7.24.4.1.1, |
7.24.4.1.2, 7.25.2.1.2, 7.25.2.1.5, 7.25.2.1.6, |
7.25.2.1.8, 7.25.2.1.9, 7.25.2.1.10, 7.25.2.2.1
iswupper function, 7.25.2.1.2, 7.25.2.1.10, 7.25.2.2.1,
7.25.3.1.1, 7.25.3.1.2
iswxdigit function, 7.25.2.1.11, 7.25.2.2.1
Index
WG14/N843 Committee Draft -- August 3, 1998 621
isxdigit function, 7.4.1.11, 7.11.1.1
italic type convention, 3, 6.1
iteration statements, 6.8.5
jmp_buf type, 7.13
jump statements, 6.8.6
keywords, 6.4.1
L_tmpnam macro, 7.19.1, 7.19.4.4
label name, 6.2.1, 6.2.3
labeled statement, 6.8.1
labs function, 7.20.6.1 |
language, 6
future directions, 6.11
syntax summary, A
Latin alphabet, 5.2.1
LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1
LC_COLLATE macro, 7.11, 7.11.1.1, 7.21.4.3, 7.24.4.4.2
LC_CTYPE macro, 7.11, 7.11.1.1, 7.20, 7.20.7, 7.20.8,
7.24.6, 7.25.1, 7.25.2.2.1, 7.25.2.2.2, 7.25.3.2.1,
7.25.3.2.2
LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1
LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1
LC_TIME macro, 7.11, 7.11.1.1, 7.23.3.5
lconv structure type, 7.11
LDBL_DIG macro, 5.2.4.2.2
LDBL_EPSILON macro, 5.2.4.2.2
LDBL_MANT_DIG macro, 5.2.4.2.2
LDBL_MAX macro, 5.2.4.2.2
LDBL_MAX_10_EXP macro, 5.2.4.2.2
LDBL_MAX_EXP macro, 5.2.4.2.2
LDBL_MIN macro, 5.2.4.2.2
LDBL_MIN_10_EXP macro, 5.2.4.2.2
LDBL_MIN_EXP macro, 5.2.4.2.2
ldexp functions, 7.12.6.6, F.9.3.6 |
ldexp type-generic macro, 7.22.1
ldiv function, 7.20.6.2 |
ldiv_t type, 7.20
leading underscore in identifiers, 7.1.3
left-shift assignment operator (<<=), 6.5.16.2
left-shift operator (<<), 6.5.7
length
external name, 6.4.2.1
function name, 6.4.2.1
identifier, 6.4.2.1
internal name, 6.4.2.1
length function, 7.20.7.1, 7.21.6.3, 7.24.4.5.3, 7.24.6.3.1
length modifier, 7.19.6.1, 7.19.6.2, 7.24.2.1, 7.24.2.2
less-than operator (<), 6.5.8
less-than-or-equal-to operator (<=), 6.5.8
letter, 7.1.1
lexical elements, 5.1.1.2, 6.4
lgamma functions, 7.12.8.3, F.9.5.3 |
Index
622 Committee Draft -- August 3, 1998 WG14/N843
lgamma type-generic macro, 7.22.1
library, 5.1.1.1, 7
future directions, 7.26
summary, B |
terms, 7.1.1
use of functions, 7.1.4
limits
environmental, see environmental limits
numerical, see numerical limits
translation, see translation limits
limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10 |
line buffered stream, 7.19.3
line number, 6.10.4, 6.10.8 |
line preprocessing directive, 6.10.4
lines, 5.1.1.2, 7.19.2
preprocessing directive, 6.10
linkage of identifiers, 6.2.2
llabs function, 7.20.6.1 |
lldiv function, 7.20.6.2 |
lldiv_t type, 7.20
LLONG_MAX macro, 5.2.4.2.1, 7.20.1.4, 7.24.4.1.2 |
LLONG_MIN macro, 5.2.4.2.1, 7.20.1.4, 7.24.4.1.2 |
llrint functions, 7.12.9.5, F.9.6.5 |
llrint type-generic macro, 7.22.1
llround functions, 7.12.9.7, F.9.6.7 |
llround type-generic macro, 7.22.1
local time, 7.23.1
locale, 3.13
locale-specific behavior, 3.13, K.4 |
locale.h header, 7.11, 7.26.5
localeconv function, 7.11.1.1, 7.11.2.1
localization, 7.11
localtime function, 7.23.2.3, 7.23.3.4
log functions, 7.12.6.7, F.9.3.7 |
log type-generic macro, 7.22.1
log10 functions, 7.12.6.8, F.9.3.8 |
log10 type-generic macro, 7.22.1
log1p functions, 7.12.6.9, F.9.3.9 |
log1p type-generic macro, 7.22.1
log2 functions, 7.12.6.10, F.9.3.10 |
log2 type-generic macro, 7.22.1
logarithmic functions
complex, 7.3.7, G.5.3 |
real, 7.12.6, F.9.3 |
logb functions, 7.12.6.11, F.9.3.11 |
logb type-generic macro, 7.22.1
logical operators
AND (&&), 6.5.13
negation (!), 6.5.3.3
OR (||), 6.5.14
logical source lines, 5.1.1.2
long double _Complex type, 6.2.5
long double _Complex type conversion, 6.3.1.6, 6.3.1.7, |
6.3.1.8
Index
WG14/N843 Committee Draft -- August 3, 1998 623
long double _Imaginary type, G.2 |
long double suffix, l or L, 6.4.4.2
long double type, 6.2.5, 6.4.4.2, 6.7.2
long double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7, |
6.3.1.8
long int type, 6.2.5, 6.3.1.1, 6.7.2
long int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, 6.3.1.8 |
long integer suffix, l or L, 6.4.4.1
long long int type, 6.2.5, 6.3.1.1, 6.7.2
long long int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, |
6.3.1.8
long long integer suffix, ll or LL, 6.4.4.1
LONG_MAX macro, 5.2.4.2.1, 7.20.1.4, 7.23.2.6, 7.24.4.1.2 |
LONG_MIN macro, 5.2.4.2.1, 7.20.1.4, 7.24.4.1.2 |
longjmp function, 7.13.1.1, 7.13.2.1
loop body, 6.8.5
low-order bit, 3.4
lrint functions, 7.12.9.5, F.9.6.5 |
lrint type-generic macro, 7.22.1
lround functions, 7.12.9.7, F.9.6.7 |
lround type-generic macro, 7.22.1
lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16
machine dependency, K.3 |
macro argument substitution, 6.10.3.1
macro definition
library function, 7.1.4
macro invocation, 6.10.3
macro name, 5.2.4.1, 6.10.3
predefined, 6.10.8
redefinition, 6.10.3
scope, 6.10.3.5
macro parameter, 6.10.3
macro preprocessor, 6.10
macro replacement, 6.10.3
magnitude, complex, 7.3.8.1 |
main function, 5.1.2.2.1, 5.1.2.2.3, 7.19.3
malloc function, 7.20.3, 7.20.3.2, 7.20.3.3, 7.20.3.4
manipulation functions
complex, 7.3.9
real, 7.12.11, F.9.8 |
mapping utilities
wide character, 7.25.3
matching failure, 7.19.6.2, 7.24.2.2, 7.24.2.6, 7.24.2.8,
7.24.2.10
math.h header, 5.2.4.2.2, 6.5, 7.12, 7.22, F, F.9 |
maximum functions, 7.12.12, F.9.9 |
MB_CUR_MAX macro, 7.1.1, 7.20, 7.20.7.2, 7.20.7.3,
7.24.6.3.3
MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.20
mblen function, 7.20.7.1, 7.24.6.3
mbrlen function, 7.24.6.3.1
mbrtowc function, 7.19.3, 7.19.6.1, 7.19.6.2, 7.24.2.1,
7.24.2.2, 7.24.6.3.1, 7.24.6.3.2, 7.24.6.4.1
Index
624 Committee Draft -- August 3, 1998 WG14/N843
mbsinit function, 7.24.6.2
mbsrtowcs function, 7.24.6.4.1
mbstate_t type, 7.19.2, 7.19.3, 7.19.6.1, 7.19.6.2, 7.24.1,
7.24.2.1, 7.24.2.2, 7.24.6, 7.24.6.2, 7.24.6.3,
7.24.6.3.1, 7.24.6.4
mbstowcs function, 6.4.5, 7.20.8.1, 7.24.6.4 |
mbtowc function, 7.20.7.1, 7.20.7.2, 7.20.8.1, 7.24.6.3
member access operators (. and ->), 6.5.2.3
member alignment, 6.7.2.1
memchr function, 7.21.5.1
memcmp function, 7.21.4, 7.21.4.1
memcpy function, 7.21.2.1
memmove function, 7.21.2.2
memory management functions, 7.20.3
memset function, 7.21.6.1
minimum functions, 7.12.12, F.9.9 |
minus operator, unary, 6.5.3.3
mktime function, 7.23.2.3, 7.23.2.4
mkxtime function, 7.23.2.4, 7.23.2.6
modf functions, 7.12.6.12, F.9.3.12 |
modifiable lvalue, 6.3.2.1
modulus functions, 7.12.6.12
modulus, complex, 7.3.8.1 |
multibyte character, 3.14, 5.2.1.2, 6.4.4.4, 7.20.7, 7.20.8
multibyte character functions, 7.20.7, 7.20.8
multibyte conversion functions
wide character
restartable, 7.24.6.3
wide string
restartable, 7.24.6.4
multibyte string, 7.1.1 |
multibyte string functions, 7.20.8
multibyte/wide-character conversion functions
restartable, 7.24.6.3
multibyte/wide-string conversion functions
restartable, 7.24.6.4
multidimensional array, 6.5.2.1
multiple external definitions, K.5.11 |
multiplication assignment operator (*=), 6.5.16.2
multiplication operator (*), 6.5.5
multiplicative expressions, 6.5.5
n-char sequence, 7.20.1.3 |
n-wchar sequence, 7.24.4.1.1
name
external, 6.4.2.1
file, 7.19.3
internal, 6.4.2.1
label, 6.2.3
structure/union member, 6.2.3
name spaces, 6.2.3
named label, 6.8.1
NaN, 5.2.4.2.2 *
nan functions, 7.12.11.2, F.9.8.2 |
Index
WG14/N843 Committee Draft -- August 3, 1998 625
NAN macro, 7.12
NDEBUG macro, 7.2
nearbyint functions, 7.12.9.3, 7.12.9.4, F.9.6.3 |
nearbyint type-generic macro, 7.22.1
nearest integer functions, 7.12.9, F.9.6 |
negation operator (!), 6.5.3.3
new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4
new-line escape sequence (\n), 5.2.2, 6.4.4.4, 7.4.1.9
nextafter functions, 7.12.11.3, 7.12.11.4, F.9.8.3 |
nextafter type-generic macro, 7.22.1
nextafterx functions, 7.12.11.4, F.9.8.4 |
nextafterx type-generic macro, 7.22.1
no linkage, 6.2.2
nongraphic characters, 5.2.2, 6.4.4.4
nonlocal jumps header, 7.13
norm, complex, 7.3.8.1 |
normalization of broken-down times, 7.23.2.6
not macro, 7.9
not-equal-to operator, see inequality operator
not_eq macro, 7.9
null character (\0), 5.2.1, 6.4.4.4, 6.4.5
padding of binary stream, 7.19.2
NULL macro, 7.11, 7.17, 7.19.1, 7.20, 7.21.1, 7.23.1, 7.24.1
null pointer, 6.3.2.3
null pointer constant, 6.3.2.3
null preprocessing directive, 6.10.7
null statement, 6.8.3
null wide character, 7.1.1
numeric conversion functions
wide string, 7.24.4.1
numerical limits, 5.2.4.2
object, 3.15
object type, 6.2.5
object-like macro, 6.10.3
obsolescence, 6.11, 7.26
octal constant, 6.4.4.1
octal digit, 6.4.4.1, 6.4.4.4
octal-character escape sequence (\octal digits), 6.4.4.4
offsetof macro, 7.17
on-off switch, 6.10.6
operand, 6.4.6, 6.5
operating system, 5.1.2.1, 7.20.4.5
operations on files, 7.19.4
operator, 6.4.6
operators, 6.5
assignment, 6.5.16
associativity, 6.5
equality, 6.5.9
multiplicative, 6.5.5
postfix, 6.5.2
precedence, 6.5
preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9
relational, 6.5.8
Index
626 Committee Draft -- August 3, 1998 WG14/N843
shift, 6.5.7
unary, 6.5.3
unary arithmetic, 6.5.3.3
or macro, 7.9
OR operators
bitwise exclusive (^), 6.5.11
bitwise exclusive assignment (^=), 6.5.16.2
bitwise inclusive (|), 6.5.12
bitwise inclusive assignment (|=), 6.5.16.2
logical (||), 6.5.14
or_eq macro, 7.9
order of allocated storage, 7.20.3
order of evaluation of expressions, 6.5
ordinary identifier name space, 6.2.3
orientation of stream, 7.19.2, 7.24.3.5
outer scope, 6.2.1
padding
binary stream, 7.19.2
structure/union, 6.7.2.1
parameter, 3.16
array, 6.9.1
ellipsis, 6.7.5.3, 6.10.3
function, 6.5.2.2, 6.9.1
macro, 6.10.3
main function, 5.1.2.2.1
program, 5.1.2.2.1
parameter type list, 6.7.5.3
parentheses punctuator (( )), 6.7.5.3, 6.8.4, 6.8.5
parenthesized expression, 6.5.1
parse state, 7.19.2 |
permitted form of initializer, 6.6
perror function, 7.19.10.4
phase angle, complex, 7.3.9.1 |
physical source lines, 5.1.1.2
placemarker, 6.10.3.3
plus operator, unary, 6.5.3.3
pointer arithmetic, 6.5.6
pointer comparison, 6.5.8
pointer declarator, 6.7.5.1
pointer operator (->), 6.5.2.3
pointer to function, 6.5.2.2
pointer type, 6.2.5
pointer type conversion, 6.3.2.1, 6.3.2.3
pointer, null, 6.3.2.3
portability, 4, K |
position indicator, file, see file position indicator
positive difference, 7.12.12.1
positive difference functions, 7.12.12, F.9.9 |
postfix decrement operator (--), 6.3.2.1, 6.5.2.4
postfix expressions, 6.5.2
postfix increment operator (++), 6.3.2.1, 6.5.2.4
pow functions, 7.12.7.4, F.9.4.4 |
pow type-generic macro, 7.22.1
Index
WG14/N843 Committee Draft -- August 3, 1998 627
power functions
complex, 7.3.8, G.5.4 |
real, 7.12.7, F.9.4 |
pp-number, 6.4.8
pragma operator, 6.10.9
pragma preprocessing directive, 6.10.6, 6.11.5
precedence of operators, 6.5
precedence of syntax rules, 5.1.1.2
precision, 6.2.6.2, 6.3.1.1, 6.3.1.8, 7.19.6.1, 7.24.2.1 |
predefined macro names, 6.10.8, K.5.12 |
prefix decrement operator (--), 6.3.2.1, 6.5.3.1
prefix increment operator (++), 6.3.2.1, 6.5.3.1
preprocessing concatenation, 6.10.3.3
preprocessing directives, 5.1.1.2, 6.10
preprocessing file, 5.1.1.1, 6.10 |
preprocessing numbers, 6.4, 6.4.8
preprocessing operators
#, 6.10.3.2
##, 6.10.3.3
_Pragma, 5.1.1.2, 6.10.9 |
defined, 6.10.1
preprocessing tokens, 5.1.1.2, 6.4, 6.10
preprocessing translation unit, 5.1.1.1
preprocessor, 6.10
PRIcFASTn macros, 7.8.1
PRIcLEASTn macros, 7.8.1
PRIcMAX macros, 7.8.1
PRIcn_C macros, 7.8.1
PRIcPTR macros, 7.8.1
primary expression, 6.5.1
printf function, 7.19.1, 7.19.6.3, 7.19.6.10
printing character, 5.2.2, 7.4, 7.4.1.7
printing wide character, 7.25.2
program diagnostics, 7.2.1
program execution, 5.1.2.2.2, 5.1.2.3
program file, 5.1.1.1
program image, 5.1.1.2
program name (argv[0]), 5.1.2.2.1
program parameters, 5.1.2.2.1
program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1
program structure, 5.1.1.1
program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3, 5.1.2.3
program, conforming, 4
program, strictly conforming, 4
promotions
default argument, 6.5.2.2
integer, 5.1.2.3, 6.3.1.1
prototype, see function prototype
pseudo-random sequence functions, 7.20.2
PTRDIFF_MAX macro, 7.18.3
PTRDIFF_MIN macro, 7.18.3
ptrdiff_t type, 7.17, 7.18.3
punctuators, 6.4.6
putc function, 7.19.1, 7.19.7.8, 7.19.7.9
Index
628 Committee Draft -- August 3, 1998 WG14/N843
putchar function, 7.19.1, 7.19.7.9
puts function, 7.19.1, 7.19.7.10
putwc function, 7.19.1, 7.24.3.8, 7.24.3.9
putwchar function, 7.19.1, 7.24.3.9
qsort function, 7.20.5, 7.20.5.2
qualified types, 6.2.5
qualified version of type, 6.2.5
question-mark escape sequence (\?), 6.4.4.4
quiet NaN, 5.2.4.2.2
raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.20.4.1
rand function, 7.20, 7.20.2.1, 7.20.2.2
RAND_MAX macro, 7.20, 7.20.2.1
range error, 7.12.1, 7.12.5.3, 7.12.5.4, 7.12.5.5, 7.12.6.1,
7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6, 7.12.6.7,
7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.13, 7.12.7.3,
7.12.7.4, 7.12.8.2, 7.12.8.3, 7.12.8.4, 7.12.9.5, |
7.12.11.3, 7.12.12.1 |
rank, see integer conversion rank
real floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7 |
real floating types, 6.2.5
real type domain, 6.2.5 |
real types, 6.2.5
realloc function, 7.20.3, 7.20.3.2, 7.20.3.4
recommended practice, 3.17
recursion, 6.5.2.2
recursive function call, 6.5.2.2
redefinition of macro, 6.10.3
reentrancy, 5.1.2.3, 5.2.3
library functions, 7.1.4
referenced type, 6.2.5
register storage-class specifier, 6.7.1, 6.9
relational expressions, 6.5.8
reliability of data, interrupted, 5.1.2.3
remainder assignment operator (%=), 6.5.16.2
remainder functions, 7.12.10, F.9.7 |
remainder functions, 7.12.10.2, 7.12.10.3, F.9.7.2 |
remainder operator (%), 6.5.5
remainder type-generic macro, 7.22.1
remove function, 7.19.4.1, 7.19.4.4
remquo functions, 7.12.10.3, F.9.7.3 |
remquo type-generic macro, 7.22.1
rename function, 7.19.4.2
rescanning and replacement, 6.10.3.4
reserved identifiers, 7.1.3
reserved words, 6.4.1
restartable multibyte/wide-character conversion functions,
7.24.6.3
restartable multibyte/wide-string conversion functions,
7.24.6.4
restore calling environment function, 7.13.2
restrict type qualifier, 6.7.3, 6.7.3.1
restrict-qualified type, 6.2.5, 6.7.3
Index
WG14/N843 Committee Draft -- August 3, 1998 629
restrictions on registers, K.3.8 |
return statement, 6.8.6.4
rewind function, 7.19.5.3, 7.19.7.11, 7.19.9.5, 7.24.3.10
right-shift assignment operator (>>=), 6.5.16.2
right-shift operator (>>), 6.5.7
rint functions, 7.12.9.4, F.9.6.4 |
rint type-generic macro, 7.22.1
round functions, 7.12.9.6, F.9.6.6 |
round type-generic macro, 7.22.1
rounding mode, floating point, 5.2.4.2.2
rvalue, 6.3.2.1
save calling environment function, 7.13.1
scalar types, 6.2.5
scalbln function, 7.12.6.13, F.9.3.13 |
scalbln type-generic macro, 7.22.1
scalbn function, 7.12.6.13, F.9.3.13 |
scalbn type-generic macro, 7.22.1
scanf function, 7.19.1, 7.19.6.4, 7.19.6.11
scanlist, 7.19.6.2, 7.24.2.2
scanset, 7.19.6.2, 7.24.2.2
SCHAR_MAX macro, 5.2.4.2.1
SCHAR_MIN macro, 5.2.4.2.1
SCNcFASTn macros, 7.8.1
SCNcLEASTn macros, 7.8.1
SCNcMAX macros, 7.8.1
SCNcn_C macros, 7.8.1
SCNcPTR macros, 7.8.1
scope of externals, 6.9.2
scope of identifier, 6.2.1
search functions
string, 7.21.5
utility, 7.20.5
wide string, 7.24.4.5
SEEK_CUR macro, 7.19.1, 7.19.9.2
SEEK_END macro, 7.19.1, 7.19.9.2
SEEK_SET macro, 7.19.1, 7.19.9.2
selection statements, 6.8.4
self-referential structure, 6.7.2.3
semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3, 6.8.5, 6.8.6
separate compilation, 5.1.1.1
separate translation, 5.1.1.1
sequence points, 5.1.2.3, 6.5, 6.8, 7.1.4, 7.19.6, 7.20.5, |
7.24.2, C, D
sequencing of statements, 6.8
setbuf function, 7.19.3, 7.19.5.5
setjmp macro, 7.13.1.1, 7.13.2.1
setjmp.h header, 7.13
setlocale function, 7.11.1.1, 7.11.2.1
setvbuf function, 7.19.1, 7.19.3, 7.19.5.5, 7.19.5.6
shift expressions, 6.5.7
shift sequence, 7.1.1
shift states, 5.2.1.2, 7.20.7
short int type, 6.2.5, 6.3.1.1, 6.7.2
Index
630 Committee Draft -- August 3, 1998 WG14/N843
short int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, |
6.3.1.8
SHRT_MAX macro, 5.2.4.2.1
SHRT_MIN macro, 5.2.4.2.1
side effects, 5.1.2.3, 6.5
SIG_ATOMIC_MAX macro, 7.18.3
SIG_ATOMIC_MIN macro, 7.18.3
sig_atomic_t type, 7.14, 7.14.1.1, 7.18.3
SIG_DFL macro, 7.14, 7.14.1.1
SIG_ERR macro, 7.14, 7.14.1.1
SIG_IGN macro, 7.14, 7.14.1.1
SIGABRT macro, 7.14, 7.20.4.1
SIGFPE macro, 7.14, 7.14.1.1
SIGILL macro, 7.14, 7.14.1.1
SIGINT macro, 7.14
signal function, 7.14.1.1
signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1
signal handler arguments, K.5.13 |
signal handling functions, 7.14.1
signal.h header, 7.14, 7.26.6
signaling NaN, 5.2.4.2.2
signals, 5.1.2.3, 5.2.3, 7.14.1
signbit macro, 7.12.3.6
signed char type, 6.2.5
signed character, 6.3.1.1
signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1 |
signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, 6.3.1.8 |
signed types, 6.2.5, 6.7.2
significand part, 6.4.4.2
SIGSEGV macro, 7.14, 7.14.1.1
SIGTERM macro, 7.14
simple assignment operator (=), 6.5.16.1
sin functions, 7.12.4.6, F.9.1.6 |
sin type-generic macro, 7.22.1, G.6 |
single-byte character, 5.2.1.2
single-byte wide-character conversion functions, 7.24.6.1
single-precision arithmetic, 5.1.2.3
single-quote escape sequence (\'), 6.4.4.4, 6.4.5
sinh functions, 7.12.5.5, F.9.2.5 |
sinh type-generic macro, 7.22.1, G.6 |
SIZE_MAX macro, 7.18.3
size_t type, 7.17, 7.18.3, 7.19.1, 7.20, 7.21.1, 7.23.1,
7.24.1
sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4
snprintf function, 7.19.6.5, 7.19.6.12
sorting utility functions, 7.20.5
source character set, 5.1.1.2, 5.2.1
source file, 5.1.1.1 |
name, 6.10.4, 6.10.8
source file inclusion, 6.10.2
source lines, 5.1.1.2
source text, 5.1.1.2
space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.9
sprintf function, 7.19.6.6, 7.19.6.13
Index
WG14/N843 Committee Draft -- August 3, 1998 631
sqrt functions, 7.12.7.5, F.9.4.5 |
sqrt type-generic macro, 7.22.1
srand function, 7.20.2.2
sscanf function, 7.19.6.7, 7.19.6.14
standard error stream, 7.19.1, 7.19.3, 7.19.10.4
standard headers, 4, 7.1.2
<assert.h>, 7.2, B.1 |
<complex.h>, 5.2.4.2.2, 7.3, 7.22, 7.26.1, G.5 |
<ctype.h>, 7.4, 7.26.2
<errno.h>, 7.5, 7.26.3
<fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, D.4.3, F, H |
<float.h>, 4, 5.2.4.2.2, 7.7, 7.20.1.3, 7.24.4.1.1 |
<inttypes.h>, 7.8, 7.26.4
<iso646.h>, 4, 7.9
<limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10 |
<locale.h>, 7.11, 7.26.5
<math.h>, 5.2.4.2.2, 6.5, 7.12, 7.22, F, F.9 |
<setjmp.h>, 7.13
<signal.h>, 7.14, 7.26.6
<stdarg.h>, 4, 6.7.5.3, 7.15
<stdbool.h>, 4, 7.16, 7.26.7, H |
<stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5, 6.5.3.4,
6.5.6, 7.17
<stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.18, 7.26.8 |
<stdio.h>, 7.19, 7.26.9, F |
<stdlib.h>, 7.20, 7.26.10, F |
<string.h>, 7.21, 7.26.11 |
<tgmath.h>, 7.22, G.6 |
<time.h>, 7.23
<wchar.h>, 7.19.1, 7.24, 7.26.12, F |
<wctype.h>, 7.25, 7.26.13 |
standard input stream, 7.19.1, 7.19.3
standard integer types, 6.2.5 |
standard output stream, 7.19.1, 7.19.3
standard signed integer types, 6.2.5
state-dependent encoding, 5.2.1.2, 7.20.7
statements, 6.8
break, 6.8.6.3
compound, 6.8.2
continue, 6.8.6.2
do, 6.8.5.2
else, 6.8.4.1
expression, 6.8.3
for, 6.8.5.3
goto, 6.8.6.1
if, 6.8.4.1
iteration, 6.8.5
jump, 6.8.6
labeled, 6.8.1
null, 6.8.3
return, 6.8.6.4
selection, 6.8.4
sequencing, 6.8
switch, 6.8.4.2
Index
632 Committee Draft -- August 3, 1998 WG14/N843
while, 6.8.5.1
static storage duration, 6.2.4
static storage-class specifier, 6.2.2, 6.2.4, 6.7.1
stdarg.h header, 4, 6.7.5.3, 7.15
stdbool.h header, 4, 7.16, 7.26.7, H |
STDC, 6.10.6, 6.11.5
stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4, 6.4.5,
6.5.3.4, 6.5.6, 7.17
stderr macro, 7.19.1, 7.19.2, 7.19.3
stdin macro, 7.19.1, 7.19.2, 7.19.3, 7.19.6.4, 7.19.7.6,
7.19.7.7, 7.24.2.12, 7.24.3.7
stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.18, 7.26.8 |
stdio.h header, 7.19, 7.26.9, F |
stdlib.h header, 7.20, 7.26.10, F |
stdout macro, 7.19.1, 7.19.2, 7.19.3, 7.19.6.3, 7.19.7.9,
7.19.7.10, 7.24.2.11, 7.24.3.9
storage duration, 6.2.4
storage order of array, 6.5.2.1
storage-class specifiers, 6.7.1, 6.11.2
strcat function, 7.21.3.1
strchr function, 7.21.5.2
strcmp function, 7.21.4, 7.21.4.2
strcoll function, 7.11.1.1, 7.21.4.3, 7.21.4.5
strcpy function, 7.21.2.3
strcspn function, 7.21.5.3
streams, 7.19.2, 7.20.4.3, K.5.14 |
fully buffered, 7.19.3
line buffered, 7.19.3
orientation, 7.19.2
standard error, 7.19.1, 7.19.3
standard input, 7.19.1, 7.19.3
standard output, 7.19.1, 7.19.3
unbuffered, 7.19.3
strerror function, 7.19.10.4, 7.21.6.2
strftime function, 7.11.1.1, 7.23.3, 7.23.3.5, 7.23.3.6,
7.24.5.1
strfxtime function, 7.11.1.1, 7.23.3, 7.23.3.6
strictly conforming program, 4
string, 7.1.1
comparison functions, 7.21.4
concatenation functions, 7.21.3
conversion functions, 7.11.1.1, 7.20.1
copying functions, 7.21.2
library function conventions, 7.21.1
literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.8
miscellaneous functions, 7.21.6
search functions, 7.21.5
string handling header, 7.21
string.h header, 7.21, 7.26.11 |
stringizing, 6.10.3.2, 6.10.9
strlen function, 7.21.6.3
strncat function, 7.21.3.2
strncmp function, 7.21.4, 7.21.4.4
strncpy function, 7.21.2.4
Index
WG14/N843 Committee Draft -- August 3, 1998 633
strpbrk function, 7.21.5.4
strrchr function, 7.21.5.5
strspn function, 7.21.5.6
strstr function, 7.21.5.7
strtod function, 7.12.11.2, 7.19.6.2, 7.20.1.3, 7.24.2.2 |
strtof function, 7.12.11.2, 7.20.1.3 |
strtoimax function, 7.8.2.1
strtok function, 7.21.5.8
strtol function, 7.8.2.1, 7.19.6.2, 7.20.1.2, 7.20.1.4, |
7.24.2.2
strtold function, 7.12.11.2, 7.20.1.3 |
strtoll function, 7.8.2.1, 7.20.1.2, 7.20.1.4 |
strtoul function, 7.8.2.1, 7.19.6.2, 7.20.1.2, 7.20.1.4, |
7.24.2.2
strtoull function, 7.8.2.1, 7.20.1.2, 7.20.1.4 |
strtoumax function, 7.8.2.1 |
struct hack, see flexible array member
structure
arrow operator (->), 6.5.2.3
content, 6.7.2.3
dot operator (.), 6.5.2.3
initialization, 6.7.8
member alignment, 6.7.2.1
member name space, 6.2.3
member operator (.), 6.3.2.1, 6.5.2.3
pointer operator (->), 6.5.2.3
specifier, 6.7.2.1
tag, 6.2.3, 6.7.2.3
type, 6.2.5, 6.7.2.1
strxfrm function, 7.11.1.1, 7.21.4.5
subscripting, 6.5.2.1
subtraction assignment operator (-=), 6.5.16.2
subtraction operator (-), 6.5.6
suffix
floating constant, 6.4.4.2
integer constant, 6.4.4.1
switch body, 6.8.4.2
switch case label, 6.8.1, 6.8.4.2
switch default label, 6.8.1, 6.8.4.2
switch statement, 6.8.1, 6.8.4.2
swprintf function, 7.24.2.3, 7.24.2.7
swscanf function, 7.24.2.4, 7.24.2.8
syntactic categories, 6.1
syntax notation, 6.1
syntax rule precedence, 5.1.1.2
syntax summary, language, A
system function, 7.20.4.5
tab characters, 5.2.1, 6.4
tag name space, 6.2.3
tags, 6.7.2.3
tan functions, 7.12.4.7, F.9.1.7 |
tan type-generic macro, 7.22.1, G.6 |
tanh functions, 7.12.5.6, F.9.2.6 |
Index
634 Committee Draft -- August 3, 1998 WG14/N843
tanh type-generic macro, 7.22.1, G.6 |
tentative definition, 6.9.2
text streams, 7.19.2, 7.19.7.11, 7.19.9.2, 7.19.9.4
tgamma functions, 7.12.8.4, F.9.5.4 |
tgamma type-generic macro, 7.22.1 |
tgmath.h header, 7.22, G.6
time
broken down, 7.23.2.3, 7.23.3, 7.23.3.1, 7.23.3.3,
7.23.3.4, 7.23.3.5, 7.23.3.7
calendar, 7.23.1, 7.23.2.2, 7.23.2.3, 7.23.2.5, 7.23.3.2,
7.23.3.3, 7.23.3.4, 7.23.3.7
components, 7.23.1
conversion functions, 7.23.3
local, 7.23.1
manipulation functions, 7.23.2
time function, 7.23.2.5
time.h header, 7.23
time_t type, 7.23.1
tm structure type, 7.23.1, 7.24.1
TMP_MAX macro, 7.19.1, 7.19.4.4
tmpfile function, 7.19.4.3, 7.20.4.3
tmpnam function, 7.19.1, 7.19.4.4
tmx structure type, 7.23.1, 7.24.1
token, 5.1.1.2, 6.4, see also preprocessing tokens
token concatenation, 6.10.3.3
token pasting, 6.10.3.3
tolower function, 7.4.2.1
toupper function, 7.4.2.2
towctrans function, 7.25.3.2.1, 7.25.3.2.2
towlower function, 7.25.3.1.1, 7.25.3.2.1
towupper function, 7.25.3.1.2, 7.25.3.2.1
translation environment, 5, 5.1.1
translation limits, 5.2.4.1
translation phases, 5.1.1.2
translation unit, 5.1.1.1, 6.9
trap representation, 6.2.6.1
trigonometric functions
complex, 7.3.5, G.5.1 |
real, 7.12.4, F.9.1 |
trigraph sequences, 5.1.1.2, 5.2.1.1
true macro, 7.16
trunc functions, 7.12.9.8, F.9.6.8 |
trunc type-generic macro, 7.22.1
truncation toward zero, 6.5.5
type, 6.2.5 |
type category, 6.2.5
type conversion, 6.3
type definitions, 6.7.7
type domain, G.2 |
type names, 6.7.6
type qualifiers, 6.7.3
type specifiers, 6.7.2
type-generic macros, 7.22, G.6 |
typedef declaration, 6.7.7
Index
WG14/N843 Committee Draft -- August 3, 1998 635
typedef storage-class specifier, 6.7.1, 6.7.7
types, 6.2.5
character, 6.7.8 |
compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.5
complex, 6.2.5
composite, 6.2.7
const qualified, 6.7.3
conversions, 6.3
imaginary, G.2 |
restrict qualified, 6.7.3
volatile qualified, 6.7.3
UCHAR_MAX macro, 5.2.4.2.1
UINT_FASTn_MAX macros, 7.18.2.3
uint_fastn_t types, 7.18.1.3
UINT_LEASTn_MAX macros, 7.18.2.2
uint_leastn_t types, 7.18.1.2
UINT_MAX macro, 5.2.4.2.1
UINTMAX_C macro, 7.18.4.2
UINTMAX_MAX macro, 7.8.2.1, 7.8.2.2, 7.18.2.5 |
uintmax_t type, 7.18.1.5
UINTn_C macros, 7.18.4.1
UINTn_MAX macros, 7.18.2.1
uintn_t types, 7.18.1.1
UINTPTR_MAX macro, 7.18.2.4
uintptr_t type, 7.18.1.4
ULLONG_MAX macro, 5.2.4.2.1, 7.20.1.4, 7.24.4.1.2 |
ULONG_MAX macro, 5.2.4.2.1, 7.20.1.4, 7.24.4.1.2 |
unary arithmetic operators, 6.5.3.3
unary expressions, 6.5.3
unary minus operator (-), 6.5.3.3
unary operators, 6.5.3
unary plus operator (+), 6.5.3.3
unbuffered stream, 7.19.3
undef preprocessing directive, 6.10.3.5, 7.1.3, 7.1.4
undefined behavior, 3.18, K.2 |
underscore character, 6.4.2.1
underscore, leading, in identifier, 7.1.3
ungetc function, 7.19.1, 7.19.7.11, 7.19.9.2, 7.19.9.3
ungetwc function, 7.19.1, 7.24.3.10
union
arrow operator (->), 6.5.2.3
content, 6.7.2.3
dot operator (.), 6.5.2.3
initialization, 6.7.8
member alignment, 6.7.2.1
member name space, 6.2.3
member operator (.), 6.3.2.1, 6.5.2.3
pointer operator (->), 6.5.2.3
specifier, 6.7.2.1
tag, 6.2.3, 6.7.2.3
type, 6.2.5, 6.7.2.1
universal character name, 6.4.3 |
unqualified type, 6.2.5
Index
636 Committee Draft -- August 3, 1998 WG14/N843
unqualified version of type, 6.2.5
unsigned integer suffix, u or U, 6.4.4.1
unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1 |
unsigned type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4, 6.3.1.8 |
unsigned types, 6.2.5, 6.7.2
unspecified behavior, 3.19, K.1 |
use of library functions, 7.1.4
USHRT_MAX macro, 5.2.4.2.1
usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6, 6.5.8, |
6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15
utilities
general
wide string, 7.24.4
va_arg macro, 7.15, 7.15.1, 7.15.1.1, 7.15.1.2, 7.15.1.4,
7.19.6.8, 7.19.6.9, 7.19.6.10, 7.19.6.11, 7.19.6.12,
7.19.6.13, 7.19.6.14, 7.24.2.5, 7.24.2.6, 7.24.2.7,
7.24.2.8, 7.24.2.9, 7.24.2.10
va_copy macro, 7.15, 7.15.1, 7.15.1.2
va_end macro, 7.15, 7.15.1, 7.15.1.3, 7.15.1.4, 7.19.6.8,
7.19.6.9, 7.19.6.10, 7.19.6.11, 7.19.6.12, 7.19.6.13,
7.19.6.14, 7.24.2.5, 7.24.2.6, 7.24.2.7, 7.24.2.8,
7.24.2.9, 7.24.2.10
va_list type, 7.15, 7.15.1.1, 7.15.1.2, 7.15.1.3
va_start macro, 7.15, 7.15.1, 7.15.1.1, 7.15.1.2, 7.15.1.3,
7.15.1.4, 7.19.6.8, 7.19.6.9, 7.19.6.10, 7.19.6.11,
7.19.6.12, 7.19.6.13, 7.19.6.14, 7.24.2.5, 7.24.2.6,
7.24.2.7, 7.24.2.8, 7.24.2.9, 7.24.2.10
variable arguments, 6.10.3, 7.15
variable arguments header, 7.15
variable length array, 6.7.5, 6.7.5.2
variably modified type, 6.7.5, 6.7.5.2
vertical-tab character, 5.2.1, 6.4
vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4, 7.4.1.9
vfprintf function, 7.19.1, 7.19.6.8
vfscanf function, 7.19.1, 7.19.6.8, 7.19.6.9
vfwprintf function, 7.19.1, 7.24.2.5
vfwscanf function, 7.19.1, 7.24.2.6, 7.24.3.10
visibility of identifier, 6.2.1
void expression, 6.3.2.2
void function parameter, 6.7.5.3
void type, 6.2.5, 6.3.2.2, 6.7.2
void type conversion, 6.3.2.2
volatile storage, 5.1.2.3
volatile type qualifier, 6.7.3
volatile-qualified type, 6.2.5, 6.7.3
vprintf function, 7.19.1, 7.19.6.8, 7.19.6.10
vscanf function, 7.19.1, 7.19.6.8, 7.19.6.11
vsnprintf function, 7.19.6.8, 7.19.6.12
vsprintf function, 7.19.6.8, 7.19.6.13
vsscanf function, 7.19.6.8, 7.19.6.14
vswprintf function, 7.24.2.7
vswscanf function, 7.24.2.8
vwprintf function, 7.19.1, 7.24.2.9
Index
WG14/N843 Committee Draft -- August 3, 1998 637
vwscanf function, 7.19.1, 7.24.2.10, 7.24.3.10
warnings, J |
wchar.h header, 7.19.1, 7.24, 7.26.12, F
WCHAR_MAX macro, 7.18.3, 7.24.1
WCHAR_MIN macro, 7.18.3, 7.24.1
wchar_t type, 6.4.4.4, 6.4.5, 6.7.8, 6.10.8, 7.17, 7.18.3, |
7.20, 7.24.1
wcrtomb function, 7.19.3, 7.19.6.2, 7.24.2.2, 7.24.6.3.3,
7.24.6.4.2
wcscat function, 7.24.4.3.1
wcschr function, 7.24.4.5.1
wcscmp function, 7.24.4.4.1, 7.24.4.4.4
wcscoll function, 7.24.4.4.2, 7.24.4.4.4
wcscpy function, 7.24.4.2.1
wcscspn function, 7.24.4.5.2
wcsftime function, 7.24.5.1, 7.24.5.2
wcsfxtime function, 7.24.5.2
wcslen function, 7.24.4.5.3
wcsncat function, 7.24.4.3.2
wcsncmp function, 7.24.4.4.3
wcsncpy function, 7.24.4.2.2
wcspbrk function, 7.24.4.5.4
wcsrchr function, 7.24.4.5.5
wcsrtombs function, 7.24.6.4.2
wcsspn function, 7.24.4.5.6
wcsstr function, 7.24.4.5.7
wcstod function, 7.19.6.2, 7.24.2.2
wcstod function, 7.24.4.1.1
wcstof function, 7.24.4.1.1
wcstoimax function, 7.8.2.2 |
wcstok function, 7.24.4.5.8
wcstol function, 7.8.2.2, 7.19.6.2, 7.24.2.2, 7.24.4.1.2 |
wcstold function, 7.24.4.1.1
wcstoll function, 7.8.2.2, 7.24.4.1.2 |
wcstombs function, 7.20.8.2, 7.24.6.4
wcstoul function, 7.8.2.2, 7.19.6.2, 7.24.2.2, 7.24.4.1.2 |
wcstoull function, 7.8.2.2, 7.24.4.1.2 |
wcstoumax function, 7.8.2.2 |
wcsxfrm function, 7.24.4.4.4
wctob function, 7.24.6.1.2, 7.25.2.1
wctomb function, 7.20.7.3, 7.20.8.2, 7.24.6.3
wctrans function, 7.25.3.2.1, 7.25.3.2.2
wctrans_t type, 7.25.1, 7.25.3.2.2
wctype function, 7.25.2.2.1, 7.25.2.2.2
wctype.h header, 7.25, 7.26.13 |
wctype_t type, 7.25.1, 7.25.2.2.2
WEOF macro, 7.24.1, 7.24.3.1, 7.24.3.3, 7.24.3.6, 7.24.3.7,
7.24.3.8, 7.24.3.9, 7.24.3.10, 7.24.6.1.1, 7.25.1
while statement, 6.8.5.1
white space, 5.1.1.2, 6.4, 6.10, 7.4.1.9, 7.25.2.1.9
white-space characters, 6.4
wide character, 6.4.4.4, 7.1.1 |
array functions, 7.24.4.6
Index
638 Committee Draft -- August 3, 1998 WG14/N843
case mapping functions, 7.25.3.1
extensible, 7.25.3.2
classification functions, 7.25.2.1
extensible, 7.25.2.2
constant, 6.4.4.4
formatted input/output functions, 7.24.2
input functions, 7.19.1
input/output functions, 7.19.1, 7.24.3
mapping utilities, 7.25.3
output functions, 7.19.1
single-byte conversion functions, 7.24.6.1
wide string, 7.1.1
wide string literal, see string literal
wide-oriented stream, 7.19.2
wide-string comparison functions, 7.24.4.4
wide-string concatenation functions, 7.24.4.3
wide-string copying functions, 7.24.4.2
wide-string numeric conversion functions, 7.24.4.1
wide-string search functions, 7.24.4.5
width, 6.2.6.2 |
WINT_MAX macro, 7.18.3
WINT_MIN macro, 7.18.3
wint_t type, 7.18.3, 7.24.1, 7.25.1
wmemchr function, 7.24.4.6.1
wmemcmp function, 7.24.4.6.2
wmemcpy function, 7.24.4.6.3
wmemmove function, 7.24.4.6.4
wmemset function, 7.24.4.6.5
wprintf function, 7.19.1, 7.24.2.9, 7.24.2.11
wscanf function, 7.19.1, 7.24.2.10, 7.24.2.12, 7.24.3.10
xor macro, 7.9
xor_eq macro, 7.9
zonetime function, 7.23.2.4, 7.23.3.7
Index
Contents
1. Scope .............................................. 1
2. Normative references ............................... 2
3. Terms and definitions .............................. 2
4. Conformance ........................................ 6
5. Environment ........................................ 8
5.1 Conceptual models ............................ 8
5.1.1 Translation environment ............. 8
5.1.2 Execution environments .............. 10
5.2 Environmental considerations ................. 18
5.2.1 Character sets ...................... 18
5.2.2 Character display semantics ......... 20
5.2.3 Signals and interrupts .............. 21
5.2.4 Environmental limits ................ 21
6. Language ........................................... 31
6.1 Notation ..................................... 31
6.2 Concepts ..................................... 31
6.2.1 Scopes of identifiers ............... 31
6.2.2 Linkages of identifiers ............. 32
6.2.3 Name spaces of identifiers .......... 34
6.2.4 Storage durations of objects ........ 34
6.2.5 Types ............................... 35
6.2.6 Representations of types ............ 40
6.2.7 Compatible type and composite type .. 43
6.3 Conversions .................................. 45
6.3.1 Arithmetic operands ................. 45
6.3.2 Other operands ...................... 49
6.4 Lexical elements ............................. 53
6.4.1 Keywords ............................ 54
6.4.2 Identifiers ......................... 55
6.4.3 Universal character names ........... 57
6.4.4 Constants ........................... 58
6.4.5 String literals ..................... 66
6.4.6 Punctuators ......................... 67
6.4.7 Header names ........................ 68
6.4.8 Preprocessing numbers ............... 69
6.4.9 Comments ............................ 70
6.5 Expressions .................................. 71
6.5.1 Primary expressions ................. 73
6.5.2 Postfix operators ................... 74
6.5.3 Unary operators ..................... 83
6.5.4 Cast operators ...................... 87
6.5.5 Multiplicative operators ............ 88
6.5.6 Additive operators .................. 89
6.5.7 Bitwise shift operators ............. 91
6.5.8 Relational operators ................ 92
6.5.9 Equality operators .................. 93
6.5.10
i
Bitwise AND operator ................ 94
6.5.11 Bitwise exclusive OR operator ....... 95
6.5.12 Bitwise inclusive OR operator ....... 95
6.5.13 Logical AND operator ................ 96
6.5.14 Logical OR operator ................. 96
6.5.15 Conditional operator ................ 97
6.5.16 Assignment operators ................ 98
6.5.17 Comma operator ...................... 101
6.6 Constant expressions ......................... 103
6.7 Declarations ................................. 105
6.7.1 Storage-class specifiers ............ 106
6.7.2 Type specifiers ..................... 107
6.7.3 Type qualifiers ..................... 117
6.7.4 Function specifiers ................. 122
6.7.5 Declarators ......................... 124
6.7.6 Type names .......................... 133
6.7.7 Type definitions .................... 134
6.7.8 Initialization ...................... 136
6.8 Statements ................................... 144
6.8.1 Labeled statements .................. 144
6.8.2 Compound statement, or block ........ 145
6.8.3 Expression and null statements ...... 145
6.8.4 Selection statements ................ 146
6.8.5 Iteration statements ................ 149
6.8.6 Jump statements ..................... 150
6.9 External definitions ......................... 155
6.9.1 Function definitions ................ 156
6.9.2 External object definitions ......... 158
6.10 Preprocessing directives ..................... 160
6.10.1 Conditional inclusion ............... 162
6.10.2 Source file inclusion ............... 164
6.10.3 Macro replacement ................... 166
6.10.4 Line control ........................ 174
6.10.5 Error directive ..................... 175
6.10.6 Pragma directive .................... 175
6.10.7 Null directive ...................... 176
6.10.8 Predefined macro names .............. 176
6.10.9 Pragma operator ..................... 177
6.11 Future language directions ................... 179
6.11.1 Character escape sequences .......... 179
6.11.2 Storage-class specifiers ............ 179
6.11.3 Function declarators ................ 179
6.11.4 Function definitions ................ 179
6.11.5 Pragma directives ................... 179
7. Library ............................................ 180
7.1 Introduction ................................. 180
7.1.1 Definitions of terms ................ 180
7.1.2 Standard headers .................... 181
7.1.3 Reserved identifiers ................ 182
7.1.4 Use of library functions ............ 183
7.2 Diagnostics <assert.h> ....................... 186
7.2.1 Program diagnostics ................. 186
7.3
ii
Complex arithmetic <complex.h> ............... 188
7.3.1 Introduction ........................ 188
7.3.2 Conventions ......................... 189
7.3.3 Branch cuts ......................... 189
7.3.4 The CX_LIMITED_RANGE pragma ......... 189
7.3.5 Trigonometric functions ............. 190
7.3.6 Hyperbolic functions ................ 193
7.3.7 Exponential and logarithmic
functions ........................... 195
7.3.8 Power and absolute-value functions .. 196
7.3.9 Manipulation functions .............. 198
7.4 Character handling <ctype.h> ................. 201
7.4.1 Character testing functions ......... 201
7.4.2 Character case mapping functions .... 205
7.5 Errors <errno.h> ............................. 207
7.6 Floating-point environment <fenv.h> .......... 208
7.6.1 The FENV_ACCESS pragma .............. 210
7.6.2 Exceptions .......................... 211
7.6.3 Rounding ............................ 214
7.6.4 Environment ......................... 215
7.7 Characteristics of floating types <float.h> .. 218
7.8 Format conversion of integer types
<inttypes.h> ................................. 219
7.8.1 Macros for format specifiers ........ 219
7.8.2 Conversion functions for greatest-
width integer types ................. 221
7.9 Alternative spellings <iso646.h> ............. 223
7.10 Sizes of integer types <limits.h> ............ 224
7.11 Localization <locale.h> ...................... 225
7.11.1 Locale control ...................... 226
7.11.2 Numeric formatting convention
inquiry ............................. 227
7.12 Mathematics <math.h> ......................... 233
7.12.1 Treatment of error conditions ....... 235
7.12.2 The FP_CONTRACT pragma .............. 236
7.12.3 Classification macros ............... 236
7.12.4 Trigonometric functions ............. 240
7.12.5 Hyperbolic functions ................ 243
7.12.6 Exponential and logarithmic
functions ........................... 246
7.12.7 Power and absolute-value functions .. 253
7.12.8 Error and gamma functions ........... 255
7.12.9 Nearest integer functions ........... 257
7.12.10 Remainder functions ................. 261
7.12.11 Manipulation functions .............. 263
7.12.12 Maximum, minimum, and positive
difference functions ................ 265
7.12.13 Floating multiply-add ............... 267
7.12.14 Comparison macros ................... 268
7.13 Nonlocal jumps <setjmp.h> .................... 272
7.13.1 Save calling environment ............ 272
7.13.2 Restore calling environment ......... 273
7.14 Signal handling <signal.h> ................... 275
7.14.1
iii
Specify signal handling ............. 276
7.14.2 Send signal ......................... 277
7.15 Variable arguments <stdarg.h> ................ 279
7.15.1 Variable argument list access
macros .............................. 279
7.16 Boolean type and values <stdbool.h> .......... 284
7.17 Common definitions <stddef.h> ................ 285
7.18 Integer types <stdint.h> ..................... 286
7.18.1 Integer types ....................... 286
7.18.2 Limits of specified-width integer
types ............................... 289
7.18.3 Limits of other integer types ....... 291
7.18.4 Macros for integer constants ........ 292
7.19 Input/output <stdio.h> ....................... 294
7.19.1 Introduction ........................ 294
7.19.2 Streams ............................. 296
7.19.3 Files ............................... 298
7.19.4 Operations on files ................. 301
7.19.5 File access functions ............... 303
7.19.6 Formatted input/output functions .... 308
7.19.7 Character input/output functions .... 333
7.19.8 Direct input/output functions ....... 339
7.19.9 File positioning functions .......... 340
7.19.10 Error-handling functions ............ 343
7.20 General utilities <stdlib.h> ................. 346
7.20.1 String conversion functions ......... 347
7.20.2 Pseudo-random sequence generation
functions ........................... 352
7.20.3 Memory management functions ......... 354
7.20.4 Communication with the environment .. 356
7.20.5 Searching and sorting utilities ..... 359
7.20.6 Integer arithmetic functions ........ 361
7.20.7 Multibyte character functions ....... 362
7.20.8 Multibyte string functions .......... 365
7.21 String handling <string.h> ................... 367
7.21.1 String function conventions ......... 367
7.21.2 Copying functions ................... 367
7.21.3 Concatenation functions ............. 369
7.21.4 Comparison functions ................ 370
7.21.5 Search functions .................... 373
7.21.6 Miscellaneous functions ............. 378
7.22 Type-generic math <tgmath.h> ................. 380
7.22.1 Type-generic macros ................. 380
7.23 Date and time <time.h> ....................... 383
7.23.1 Components of time .................. 383
7.23.2 Time manipulation functions ......... 385
7.23.3 Time conversion functions ........... 390
7.24 Extended multibyte and wide-character
utilities <wchar.h> .......................... 398
7.24.1 Introduction ........................ 398
7.24.2 Formatted wide-character
input/output functions .............. 399
7.24.3 Wide-character input/output
functions
iv
........................... 420
7.24.4 General wide-string utilities ....... 426
7.24.5 Wide-character time conversion
functions ........................... 442
7.24.6 Extended multibyte and wide-
character conversion utilities ...... 443
7.25 Wide-character classification and mapping
utilities <wctype.h> ......................... 452
7.25.1 Introduction ........................ 452
7.25.2 Wide-character classification
utilities ........................... 453
7.25.3 Wide-character mapping utilities .... 459
7.26 Future library directions .................... 462
7.26.1 Complex arithmetic <complex.h> ...... 462
7.26.2 Character handling <ctype.h> ........ 462
7.26.3 Errors <errno.h> .................... 462
7.26.4 Format conversion of integer types
<inttypes.h> ........................ 462
7.26.5 Localization <locale.h> ............. 462
7.26.6 Signal handling <signal.h> .......... 462
7.26.7 Boolean type and values
<stdbool.h> ......................... 463
7.26.8 Integer types <stdint.h> ............ 463
7.26.9 Input/output <stdio.h> .............. 463
7.26.10 General utilities <stdlib.h> ........ 463
7.26.11 String handling <string.h> .......... 463
7.26.12 Extended multibyte and wide-
character utilities <wchar.h> ....... 463
7.26.13 Wide-character classification and
mapping utilities <wctype.h> ........ 464
Annex A (informative) Language syntax summary ......... 465
A.1 Lexical grammar .............................. 465
A.2 Phrase structure grammar ..................... 470
A.3 Preprocessing directives ..................... 476
Annex B (informative) Library summary ................. 478
B.1 Diagnostics <assert.h> ....................... 478
B.2 Complex <complex.h> .......................... 478
B.3 Character handling <ctype.h> ................. 479
B.4 Errors <errno.h> ............................. 480
B.5 Floating-point environment <fenv.h> .......... 480
B.6 Characteristics of floating types <float.h> .. 480
B.7 Format conversion of integer types
<inttypes.h> ................................. 480
B.8 Alternative spellings <iso646.h> ............. 481
B.9 Sizes of integer types <limits.h> ............ 481
B.10 Localization <locale.h> ...................... 482
B.11 Mathematics <math.h> ......................... 482
B.12 Nonlocal jumps <setjmp.h> .................... 485
B.13 Signal handling <signal.h> ................... 485
B.14 Variable arguments <stdarg.h> ................ 486
B.15 Boolean type and values <stdbool.h> .......... 486
B.16
v
Common definitions <stddef.h> ................ 486
B.17 Integer types <stdint.h> ..................... 486
B.18 Input/output <stdio.h> ....................... 487
B.19 General utilities <stdlib.h> ................. 488
B.20 String handling <string.h> ................... 489
B.21 Type-generic math <tgmath.h> ................. 490
B.22 Date and time <time.h> ....................... 490
B.23 Extended multibyte and wide-character
utilities <wchar.h> .......................... 491
B.24 Wide-character classification and mapping
utilities <wctype.h> ......................... 493
Annex C (informative) Sequence points ................. 494
Annex D (informative) Formal model of sequence
points ................................................. 495
D.1 Introduction ................................. 495
D.2 Basic concepts ............................... 495
D.3 Operation of the model ....................... 497
D.4 Application .................................. 500
D.5 Examples ..................................... 502
Annex E (informative) Implementation limits ........... 512
Annex F (normative) IEC 60559 floating-point
arithmetic ............................................. 514
F.1 Introduction ................................. 514
F.2 Types ........................................ 514
F.3 Operators and functions ...................... 515
F.4 Floating to integer conversion ............... 517
F.5 Binary-decimal conversion .................... 517
F.6 Contracted expressions ....................... 518
F.7 Environment .................................. 518
F.8 Optimization ................................. 521
F.9 Mathematics <math.h> ......................... 526
Annex G (informative) IEC 60559-compatible complex
arithmetic ............................................. 541
G.1 Introduction ................................. 541
G.2 Types ........................................ 541
G.3 Conversions .................................. 541
G.4 Binary operators ............................. 542
G.5 Complex arithmetic <complex.h> ............... 547
G.6 Type-generic math <tgmath.h> ................. 555
Annex H (informative) Language independent
arithmetic ............................................. 556
H.1 Introduction ................................. 556
H.2 Types ........................................ 556
H.3 Notification ................................. 560
Annex I (normative) Universal character names for
identifiers ............................................ 562
vi
Annex J (informative) Common warnings ................. 564
Annex K (informative) Portability issues .............. 566
K.1 Unspecified behavior ......................... 566
K.2 Undefined behavior ........................... 569
K.3 Implementation-defined behavior .............. 585
K.4 Locale-specific behavior ..................... 594
K.5 Common extensions ............................ 595
Bibliography ....................................... 598
Index .............................................. 601
vii
viii
Foreword
[#1] ISO (the International Organization for
Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide
standardization. National bodies that are member of ISO or
IEC participate in the development of International
Standards through technical committees established by the
respective organization to deal with particular fields of
technical activity. ISO and IEC technical committees
collaborate in fields of mutual interest. Other
international organizations, governmental and non-
governmental, in liaison with ISO and IEC, also take part in
the work.
[#2] International Standards are drafted in accordance with
the rules given in the ISO/IEC Directives, Part 3. |
Accordingly, annexes F and I form a normative part of this
standard; this foreword, the introduction, notes, footnotes,
examples, annexes A, B, C, D, E, G, H, J, K, the |
bibliography, and the index are for information only.
[#3] In the field of information technology, ISO and IEC
have established a joint technical committee, ISO/IEC JTC 1.
Draft International Standards adopted by the joint technical
committee are circulated to national bodies for voting.
Publication as an International Standard requires approval
by at least 75% of the national bodies casting a vote.
[#4] International Standard ISO/IEC 9899 was prepared by
Joint Technical Committee ISO/IEC JTC 1, ``Information
Technology'', subcommittee 22, ``Programming languages,
their environments and system software interfaces''.
Introduction
[#1] With the introduction of new devices and extended
character sets, new features may be added to this
International Standard. Subclauses in the language and
library clauses warn implementors and programmers of usages
which, though valid in themselves, may conflict with future
additions.
[#2] Certain features are obsolescent, which means that they
may be considered for withdrawal in future revisions of this
International Standard. They are retained because of their
widespread use, but their use in new implementations (for
implementation features) or new programs (for language
[6.11] or library features [7.26]) is discouraged.
[#3] This International Standard is divided into four major
subdivisions:
-- the introduction and preliminary elements;
-- the characteristics of environments that translate and
execute C programs;
-- the language syntax, constraints, and semantics;
-- the library facilities.
[#4] Examples are provided to illustrate possible forms of
the constructions described. Footnotes are provided to
emphasize consequences of the rules described in that
subclause or elsewhere in this International Standard.
References are used to refer to other related subclauses. |
Recommendations are provided to give advice or guidance to |
implementors. Annexes provide additional information and |
summarize the information contained in this International
Standard. A bibliography lists documents that were referred |
to during the preparation of the standard.
[#5] The language clause (clause 6) is derived from ``The C
Reference Manual''.
[#6] The library clause (clause 7) is based on the 1984
/usr/group Standard.
Programming languages -- C
ABSTRACT
(Cover sheet to be provided by ISO Secretariat.)
This International Standard specifies the form and
establishes the interpretation of programs expressed in the
programming language C. Its purpose is to promote
portability, reliability, maintainability, and efficient
execution of C language programs on a variety of computing
systems.
Clauses are included that detail the C language itself and
the contents of the C language execution library. Annexes
summarize aspects of both of them, and enumerate factors
that influence the portability of C programs.
Although this International Standard is intended to guide
knowledgeable C language programmers as well as implementors
of C language translation systems, the document itself is
not designed to serve as a tutorial.