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10.1223 towupper

POSIX specification:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/towupper.html

Gnulib module: wctype-h

Portability problems fixed by Gnulib:

• This function returns values of which the upper 16 bits are incorrect on some platforms: mingw.
• This function cannot be called from plain inline or extern inline functions on some platforms: macOS 10.8.

Portability problems not fixed by Gnulib:

• On Windows and 32-bit AIX platforms, wchar_t is a 16-bit type and therefore cannot accommodate all Unicode characters. However, the Gnulib function c32toupper, provided by Gnulib module c32toupper, operates on 32-bit wide characters and therefore does not have this limitation.
• This function returns wrong values even for the ASCII characters in a zh_CN.GB18030 locale on some platforms: NetBSD 10.0.