VMS Help CC, Run-time functions, wcscspn  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Compares the characters in a wide-character string against a set of
  wide characters.  The function returns the length of the initial
  substring comprised entirely of characters that are not in the set
  of wide characters.

  Syntax:

       #include <wchar.h>

       size_t wcscspn (const wchar_t *wstr1, const wchar_t *wstr2);