Issue 0484: invalid characters in strcoll()

This issue has been automatically converted from the original issue lists and some formatting may not have been preserved.

Authors: WG14, Fred J. Tydeman
Date: 2015-06-23
Reference document: N1944
Submitted against: C11 / C17
Status: Closed
Converted from: n2396.htm

Summary

7.24.4.3 strcoll makes the assumption that the result of comparing two strings can only have one of three outcomes: greater than, equal to, or less than. However, there is a fourth outcome that is possible: not comparable.

I have been told that there are locales or codesets that have strings of bytes that do not form valid characters. Those invalid characters could be considered Not-a-Character (similar to Not-a-Number for floating-point). And, they are not comparable to anything.

I do not know if the same issue can apply to wchar_t. If so, then 7.29.4.4.1 wcscmp(), 7.29.4.4.3 wcsncmp(), and 7.29.4.4.5 wmemcmp() have the same problem.

Suggested Technical Corrigendum

Replace the start of 7.24.4.3, paragraph 3,

The strcoll ...

with

If either string contains invalid characters, errno is set to an implementation defined value and the return value is unspecified; otherwise, errno is left alone and the strcoll ...

The same change should also be applied to 7.29.4.4.2 wcscoll.

Comment from WG14 on 2016-10-21:

Oct 2015 meeting

Committee Discussion

The committee agrees that the standard does not specify behavior under these conditions and as such there is undefined behavior by way of §7.1.4p1 “If an argument to a function has an invalid value … the behavior is undefined”. There is strong sentiment to keep the library fast and that imposing new requirements to set errno is to be generally avoided. Whereas POSIX does define behavior that sets errno under these conditions, it is explicitly the intent of the committee to leave such behavior undefined in the standard to allow such refinements by others.

Proposed Committee Response

By way of §7.1.4p1 “If an argument to a function has an invalid value … the behavior is undefined” the behavior of strcoll in the face of invalid input is already clearly undefined. The committee wishes to leave it so specified. This latitude allows POSIX to further refine the semantics according to their needs. We therefore do not accept the Proposed Technical Corrigendum.