Issue 0273: meaning of __STDC_ISO_10646__

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

Authors: Clive D.W. Feather <clive@demon.net>, UK C Panel
Date: 2001-09-07
Submitted against: C99
Status: Fixed
Fixed in: C99 TC2
Converted from: summary-c99.htm, dr_273.htm

Problem

6.10.8 reads in part:

__STDC_ISO_10646__

An integer 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.

Firstly, this wording is less than optimal, in that it could be read as making an implementation non-conforming if wchar_t has a value that does not correspond to an ISO 10646 (Unicode) character. Since Unicode has gaps in the encoding tables, this would mean that no implementation could define this symbol.

Secondly, is this wording meant to put a lower bound on the size of wchar_t, or does the (wchar_t = = Unicode) mapping only apply to those values that wchar_t can take. In other words, if a given version of Unicode defines characters up to U+12345, can WCHAR_MAX be less than 0x12345 on a system that defines this symbol ?

Suggested Technical Corrigendum

Replace the cited text by:

__STDC_ISO_10646__

An integer constant of the form yyyymmL (for example, 199712L). If this symbol is defined, then every character in the "Unicode required set", when stored in an object of type wchar_t, has the same value as the short identifier of that character.

and then either:

The "Unicode required set" consists of all the characters that are defined by ISO/IEC 10646, along with all amendments and technical corrigenda, as of the specified year and month.

if the intent is to put a minimum on the value of WCHAR_MAX, or then:

The "Unicode required set" consists of all the characters that:

• are defined by ISO/IEC 10646, along with all amendments and technical corrigenda, as of the specified year and month; and
• have short identifiers that lie within the range of values that can be represented by the type wchar_t.

Comment from WG14 on 2002-03-07:

Technical Corrigendum

Replace the relevant part of 6.10.8 with:

__STDC_ISO_10646__

An integer constant of the form yyyymmL (for example, 199712L). If this symbol is defined, then every character in the "Unicode required set", when stored in an object of type wchar_t, has the same value as the short identifier of that character. The "Unicode required set" consists of all the characters that are defined by ISO/IEC 10646, along with all amendments and technical corrigenda, as of the specified year and month.