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

  Appends not more than maxchar characters from str_2 to the end of
  str_1.

  Syntax:

       #include <string.h>

       char *strncat(char *str_1, const char *str_2, size_t maxchar);