A conforming implementation shall produce at least one diagnostic message (identified in an implementation-defined manner) for every translation unit that contains a violation of any syntax rule or constraint.

A conforming implementation shall produce at least one diagnostic message (identified in an implementation-defined manner) for every translation unit that contains a violation of any syntax rule or constraint, even if the behavior is also explicitly specified as undefined or implementation-defined.

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.

15 nested levels of compound statements, iteration control structures, and selection control structures

15 nested levels of compound statements, iteration statements, and selection statements

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.

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.

If the declaration of an identifier for an object or a function contains the storage-class specifier extern, the identifier has the same linkage as any visible declaration of the identifier with file scope. If there is no visible declaration with file scope, the identifier has external linkage.

For an identifier declared with the storage-class specifier extern in a scope in which a prior declaration of that identifier is visible^*, if the prior declaration specifies internal or external linkage, the linkage of the identifier at the latter declaration becomes 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. [Footnote *: As specified in 6.1.2.1, the latter declaration might hide the prior declaration.]

For an identifier with external or internal linkage declared in the same scope as another declaration for that identifier, the type of the identifier becomes the composite type.

For an identifier with internal or external linkage declared in a scope in which a prior declaration of that identifier is visible^*, if the prior declaration specifies internal or external linkage, the type of the identifier at the latter declaration becomes the composite type.
[Footnote *: As specified in 6.1.2.1, the latter declaration might hide the prior declaration.]

Header name preprocessing tokens shall only appear within a #include preprocessing directive.

A header name preprocessing token is recognized only within a #include preprocessing directive.

An object shall have its stored value accessed only by an lvalue expression that has one of the following types:³⁶

the declared type of the object,

a qualified version of the declared type of the object,

An object shall have its stored value accessed only by an lvalue expression that has one of the following types:³⁶

a type compatible with the declared type of the object,

a qualified version of a type compatible with the declared type of the object,

The value of the function call expression is specified in 6.6.6.4.

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 6.6.6.4. Otherwise, the function call has type void.

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 parenthesis is then converted to the type of the outer assignment-expression, that is, long type.

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.

occurs prior to the declaration that defines the content

occurs prior to the } following the struct-declaration-list that defines the content

An enumeration type is compatible with some integral type. An implementation may delay the choice of which integral type until all enumeration constants have been seen. Thus in:

enum f { c = sizeof(enum f) };

the behavior is undefined since the size of the respective enumeration type is not necessarily known when sizeof is encountered.

In a parameter declaration, a single typedef name in parentheses is taken to be an abstract declarator that specifies a function with a single parameter, not as redundant parentheses around the identifier for a declarator.

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.

(For each parameter declared with function or array type, its type for these comparisons is the one that results from conversion to a pointer type, as in 6.7.1. For each parameter declared with qualified type, its type for these comparisons is the unqualified version of its declared type.)

(In the determination of type compatibility and of a composite type, each parameter declared with function or array type is taken as having the type that results from conversion to a pointer type, as in 6.7.1, and each parameter declared with qualified type is taken as having the unqualified version of its declared type.)

All unnamed structure or union members are ignored during initialization.

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. A union object containing only unnamed members has indeterminate value even after initialization.

If an object that has static storage duration is not initialized explicitly, it is initialized implicitly as if every member that has arithmetic type were assigned 0 and every member that has pointer type were assigned a null pointer constant.

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 zero;

- 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.

The initial value of the object is that of the expression.

The initial value of the object, including unnamed members, is that of the expression.

If the expression has a type different from that of the function in which it appears, it is converted as if it were assigned to an object of that type.

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 toan object having the return type of the function.^*
[Footnote *: The return statement is not an assignment. The overlap restriction in subclause 6.3.16.1 does not apply to the case of function return.]

In:

   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();

the behavior is defined.

If at the end of the translation unit containing

int i[];

the array i still has incomplete type, the array is assumed to have one element. This element is initialized to zero on program startup.

A new-line character ends the preprocessing directive even if it occurs within what would otherwise be an invocation of a function-like macro.

In the definition of an object-like macro, if the first character of a replacement list is not a character required by subclause 5.2.1, then there shall be white-space separation between the identifier and the replacement list.^*
[Footnote *: This allows an implementation to choose to interpret the directive:

#define THIS$AND$THAT(a, b) ((a) + (b))

as defining a function-like macro THIS$AND$THAT, rather than an object-like macro THIS. Whichever choice it makes, it must also issue a diagnostic.]

#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:

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 catenation operator.

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 g

However, if the identifier is declared or defined in more than one header,

However, if an identifier is declared or defined in more than one header,

and the following, each of which expands to a positive integral constant expression that is the signal number corresponding to the specified condition:

and the following, which expand to positive integral constant expressions with distinct values that are the signal numbers, each corresponding to the specified condition:

For o conversion, it increases the precision to force the first digit of the result to be a zero.

For o conversion, it increases the precision, if and only if necessary, to force the first digit of the result to be a zero.

An input item is defined as the longest matching sequence of input characters, unless that exceeds a specified field width, in which case it is the initial subsequence of that length in the sequence.

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.

If conversion terminates on a conflicting input character, the offending input character is left unread in the input stream.

No argument is converted, but one is consumed. If the conversion specification with this conversion specifier is not one of %n, %ln, or %hn, the behavior is undefined.

If conversion terminates on a conflicting input character, the offending input character is left unread in the input stream.^*
[Footnote *: fscanf pushes back at most one input character onto the input stream. Therefore, some sequences that are acceptable to strtod, strtol, or strtoul are unacceptable to fscanf.]

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 3 is assigned to i.

a value returned by an earlier call to the ftell function

a value returned by an earlier successful call to the ftell function

a value obtained from an earlier call to the fgetpos function

a value obtained from an earlier successful call to the fgetpos function

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 must still have valid values, as described in subclause 7.1.7. 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.

if (mktime(&time_str) == -1)

   if (mktime(&ime_str) == (time_t)-1)

A program contains no function called main (5.1.2.2.1).

A storage-class specifier or type qualifier modifies the keyword void as a function parameter type list (6.5.4.3).

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]) (6.3.6).

A fully expanded macro replacement list contains a function-like macro name as its last preprocessing token (6.8.3).

A call to a library function exceeds an environmental limit (7.9.2, 7.9.3, 7.9.4.4, 7.9.6.1, 7.10.2.1).

static storage-class specifier, 3.1.2.2, 6.1.2.4, 6.5.1, 6.7

static storage-class specifier, 6.1.2.2, 6.1.2.4, 6.5.1, 6.7