[emmelaich]

I remember that the various is* man pages noted that most of them are only defined if isascii() is true. So I always used e.g. (isascii(x) && ispunct())

FWIW, just looked at the man page (macos) and iswdigit() and isnumber() are mentioned.

[_kst_]

isascii() is not defined by ISO C. (It is defined by POSIX, but POSIX says it may be removed in a future version.)

I see that POSIX explicitly says that isascii(x) is "defined on all integer values" (it should have said "all int values").

Personally I'd rather cast to unsigned char.