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CWG3237 [cpp.predefined] __STDC_MB_MIGHT_NEQ_WC__ imposes no restrictions #1017
Description
Full name of submitter (unless configured in github; will be published with the issue): Jay Ghiron
Reference (section label): [cpp.predefined]/2.7
Issue description:
The macro __STDC_MB_MIGHT_NEQ_WC__ is not referenced anywhere outside of [cpp.predefined] (not counting the index), and the text therein just talks about the intent if it is defined. There does not appear to be any requirements on code units if it is not defined like there is in C, so it appears that the macro has no actual purpose in C++. Either there should be wording added to enforce that 'x' and L'x' have the same value if __STDC_MB_MIGHT_NEQ_WC__ is not defined, or an entry should be added to [diff.cpp] that says __STDC_MB_MIGHT_NEQ_WC__ has no meaning in C++ if it is not defined.
Activity
[-][cpp.predefined] \_\_STDC_MB_MIGHT_NEQ_WC\_\_ imposes no restrictions[/-][+][cpp.predefined] __STDC_MB_MIGHT_NEQ_WC__ imposes no restrictions[/+]frederick-vs-ja commentedon Oct 2, 2026
The wording in [cpp.predefined]/2.7 looks fine to me as it's mostly copied from the C standard (see https://port70.net/~nsz/c/c23/n3220.html#6.10.10.3p1). IIUC we should add corresponding restrictions to [lex.charset].
jensmaurer commentedon Oct 5, 2026
CWG3237
[-][cpp.predefined] __STDC_MB_MIGHT_NEQ_WC__ imposes no restrictions[/-][+]CWG3237 [cpp.predefined] __STDC_MB_MIGHT_NEQ_WC__ imposes no restrictions[/+]Halalaluyafail3 commentedon Oct 5, 2026
That links to #1011 instead of this issue. The next issue should also link to #1012 instead.
jensmaurer commentedon Oct 5, 2026
Fixed