Description

   The getgrgid_r function updates the group structure pointed to
   by grp and stores a pointer to that structure at the location
   pointed to by result. The structure contains an entry from the
   group database with a matching gid. Storage referenced by the
   group structure is allocated from the memory provided with the
   buffer argument, which is bufsize characters in size. The maximum
   size needed for this buffer can be determined with the _SC_GETGR_
   R_SIZE_MAX parameter of the sysconf function. On error or if the
   requested entry is not found, a NULL pointer is returned at the
   location pointed to by result.