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

  Writes output to a specified file in wide character format.

  Syntax:

        #include <wchar.h>

        int vswprintf (wchar_t *s,
                       size_t n,
                       const wchar_t *format,
                       va_list arg);