ultrix man page for getgroups

getgroups(2)							System Calls Manual						      getgroups(2)

Name
       getgroups - get group access list

Syntax
       #include <sys/types.h>
       #include <unistd.h>

       int getgroups(gidsetsize, grouplist)
       int gidsetsize;
       int grouplist[];

Description
       The  call  gets	the  current  group access list of the user process and stores it in the array of int grouplist.  The gidsetsize parameter
       indicates the number of entries that can be placed in grouplist.

Return Values
       Upon success, the call returns the number of groups as the value of the function.  No more than NGROUPS, as defined in  <sys/param.h>,  are
       returned.

       A value of -1 indicates that an error occurred, and the error code is stored in the global variable, errno.

Diagnostics
       The call fails under the following conditions:

       [EINVAL]       The gidsetsize argument is smaller than the number of groups in the group set.

       [EFAULT]       The grouplist argument specifies invalid addresses.

Environment
   POSIX
       When your program is compiled in the POSIX environment, the grouplist argument should be defined as follows:

       gid_t	 grouplist[];

       Additionally,  in  the  POSIX environment, if the gidsetsize argument is zero, returns the number of supplemental group IDs associated with
       the calling process, without modifying the array pointed to by the grouplist argument.

See Also
       setgroups(2), initgroups(3x)

																      getgroups(2)