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

  Returns, in OpenVMS terms, the group number from the user
  identification code (UIC).  For example, if the UIC is [313,031],
  313 is the group number.

  Syntax:

       #include <unistd.h>

       gid_t getgid(void);