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

  Returns a nonzero integer if its wide-character argument is classed
  as a digit in the program's current locale.  Otherwise, it returns
  0.

  Syntax:

       #include <wctype.h>  (ISO C Standard)
       #include <wchar.h>   (XPG4 Standard)

       int iswdigit (wint_t wc);