#define _POSIX_C_SOURCE 201800 /* still the same */
#include <grp.h>   /* getgrent */
#include <stdio.h> /* printf */

/* This program prints info about «groups» (which are stored in
 * ‹/etc/group›).  The functions to access group information are
 * analogous to those for accessing user (passwd) information. This
 * program basically prints info from lines 10-13 of ‹/etc/group›.
 * */

int main()
{
    int i, j;

    /* We first skip the first 10 entries because they are quite
     * boring. */

    for ( i = 0; i < 10; ++i )
        getgrent();

    for ( i = 0; i < 3; ++i )
    {
        struct group *grp = getgrent();

        /* Groups have names and identifiers, just like users...
         * let's print those first. */

        printf( "name: %s\n", grp->gr_name );
        printf( "gid: %d\n", grp->gr_gid );

        /* However, users only have a fixed number of fields
         * attached to them.  The situation with groups is somewhat
         * different, because they contain a list of all users which
         * belong to the group. We don't know beforehand how many
         * such entries there are. The information is stored just
         * like ‹argv›: an array of strings. We know we hit the end
         * when we encounter a NULL string (pointer). Let's print
         * all the member users then: */

        for ( j = 0; grp->gr_mem[j]; ++j )
            printf( "member: %s\n", grp->gr_mem[j] );
        printf( "\n" );
    }
}

/* Next: ‹3.txt›. */