Submitter: Blaine Garst
Submission Date: 2013-07-31
Source: WG 14
Reference Document:
N1736
Version: 1.0
Date: October 2013
Subject:Use byte instead of character for memcmp, memcpy
Summary
It has been noted that the descriptions for 7.24.2.1memcpy
, 7.24.2.2 memmove
and 7.24.4.1 memcmp
are written using the term character which is inconsistent with their design as memory functions. Moreover, if one then reads 3.7.2 as allowing character to mean multibyte character, it is thought that confusion could arise as to whether the number of multibyte characters should be supplied rather than the number of bytes.
Although it is clear by 7.24.1 String function conventions paragraph 3
For all functions in this sub clause, each character shall be interpreted as if it had the type unsigned char
that the number of bytes to be used corresponds to the size of a unsigned char
, one has to reference 6.2.6 Representation of types to learn that unsigned char
is in fact a single byte (consisting of CHAR_BIT
bits).
It would be simpler and more to the point if the three memory functions describe their count parameter n
in terms of bytes.
Suggested Technical Corrigendum
memcpy
Change 7.24.2.1 p 2 first sentence from
Thememcpy
function copiesn
characters from the object pointed to bys2
into the object pointed to bys1
.
to
Thememcpy
function copiesn
bytes from the object pointed to bys2
into the object pointed to bys1
.
memmove
Change 7.24.2.2 p 2 from
Thememmove
function copiesn
characters from the object pointed to bys2
into the object pointed to bys1
. Copying takes place as if then
characters from the object pointed to bys2
are first copied into a temporary array ofn
characters that does not overlap the objects pointed to bys1
ands2
, and then then
characters from the temporary array are copied into the object pointed to bys1
.
to
Thememmove
function copiesn
bytes from the object pointed to bys2
into the object pointed to bys1
. Copying takes place as if then
bytes from the object pointed to bys2
are first copied into a temporary array ofn
bytes that does not overlap the objects pointed to bys1
ands2
, and then then
bytes from the temporary array are copied into the object pointed to bys1
.
memcmp
Change 7.24.4.1 p 2 from
Thememcmp
function compares the firstn
characters of the object pointed to bys1
to the firstn
characters of the object pointed to bys2
.
to
Thememcmp
function compares the firstn
bytes of the object pointed to bys1
to the firstn
bytes of the object pointed to bys2
.
Proposed Committee Response
After reviewing the original motivation and suggestion for change, it was noted by the project editor that "character" is used in several distinct contexts, and that it would be inappropriate to simply improve one area without a comprehensive review of all uses such that the existing consistency of uses of character be replaced in a consistent new manner, as yet undetermined. As it stands, although careful reading is strictly required, it is correct and as such this is not a defect.