Defect Report #446

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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 7.24.2.1 memcpy, 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

The memcpy function copies n characters from the object pointed to by s2 into the object pointed to by s1.

to

The memcpy function copies n bytes from the object pointed to by s2 into the object pointed to by s1.

memmove

Change 7.24.2.2 p 2 from

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.

to

The memmove function copies n bytes from the object pointed to by s2 into the object pointed to by s1. Copying takes place as if the n bytes from the object pointed to by s2 are first copied into a temporary array of n bytes that does not overlap the objects pointed to by s1 and s2, and then the n bytes from the temporary array are copied into the object pointed to by s1.

memcmp

Change 7.24.4.1 p 2 from

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.

to

The memcmp function compares the first n bytes of the object pointed to by s1 to the first n bytes of the object pointed to by s2.
Oct 2013 meeting

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.


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