test whether a wide character belongs
to a character class
These functions test whether the wide character wc belongs to charclass.
The behaviour is undefined if charclass or wc is invalid. When charclass is retrieved with wctype(3), it becomes invalid when the thread-specific character encoding locale is changed with uselocale(3) or when the global character encoding locale is changed with setlocale(3). When charclass is retrieved with wctype_l(3), it is only valid for use with the same locale argument.
These functions return zero if the character tests false or non-zero if the character tests true.
iswalnum(3), newlocale(3), setlocale(3), towctrans(3), wctype(3)
iswctype() function conforms to
ISO/IEC 9899/AMD1:1995 (“ISO C90, Amendment
IEEE Std 1003.1-2008 (“POSIX.1”).
iswctype() function has been available
since OpenBSD 3.8, and
iswctype_l() since OpenBSD