#include <wctype.h> int iswupper (wint_t wc);
The wide character class "upper" is a subclass of the wide character class "alpha", and therefore also a subclass of the wide character class "alnum", of the wide character class "graph" and of the wide character class "print".
Being a subclass of the wide character class "print", the wide character class "upper" is disjoint from the wide character class "cntrl".
Being a subclass of the wide character class "graph", the wide character class "upper" is disjoint from the wide character class "space" and its subclass "blank".
Being a subclass of the wide character class "alnum", the wide character class "upper" is disjoint from the wide character class "punct".
Being a subclass of the wide character class "alpha", the wide character class "upper" is disjoint from the wide character class "digit".
The wide character class "upper" contains at least those characters wc which are equal to towupper(wc) and different from towlower(wc).
The wide character class "upper" always contains at least the letters 'A' to 'Z'.
This function is not very appropriate for dealing with Unicode characters, because Unicode knows about three cases: upper, lower and title case.