/sys$common/syshlp/helplib.hlb CC, Run-time functions, wcsncat  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Appends wide characters from the wide-character string wstr_2 to
  the end of wstr_1.  Up to a maximum of maxchar characters are
  appended to wstr_1.

  Syntax:

       #include <wchar.h>

       wchar_t *wcsncat (wchar_t *wstr_1, const wchar_t *wstr_2,
       size_t maxchar);