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

  Determines the number bytes needed to represent the multibyte
  character that corresponds to the specified wide character.

  Syntax:

        #include <wchar.h>

        size_t wcrtomb (char *s, wchar_t wc, mbstate_t *ps);