wctypeconst
wctypeconst is a term used in some C library implementations to denote a compile-time constant value of type wctype_t that represents a wide-character classification. It is intended to allow code to refer to a character class without performing a runtime lookup.
In standard C, wide-character classes are obtained at run time by calling wctype with a string name
Availability and portability are important notes. wctypeconst is not part of the ISO C standard, and its
Commonly supported classification names, when available, include standard categories such as alnum, alpha, digit, space, lower,