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29.15 User and Group Database Example

Here is an example program showing the use of the system database inquiry functions. The program prints some information about the user running the program.

     #include <grp.h>
     #include <pwd.h>
     #include <sys/types.h>
     #include <unistd.h>
     #include <stdlib.h>
     main (void)
       uid_t me;
       struct passwd *my_passwd;
       struct group *my_group;
       char **members;
       /* Get information about the user ID. */
       me = getuid ();
       my_passwd = getpwuid (me);
       if (!my_passwd)
           printf ("Couldn't find out about user %d.\n", (int) me);
           exit (EXIT_FAILURE);
       /* Print the information. */
       printf ("I am %s.\n", my_passwd->pw_gecos);
       printf ("My login name is %s.\n", my_passwd->pw_name);
       printf ("My uid is %d.\n", (int) (my_passwd->pw_uid));
       printf ("My home directory is %s.\n", my_passwd->pw_dir);
       printf ("My default shell is %s.\n", my_passwd->pw_shell);
       /* Get information about the default group ID. */
       my_group = getgrgid (my_passwd->pw_gid);
       if (!my_group)
           printf ("Couldn't find out about group %d.\n",
                   (int) my_passwd->pw_gid);
           exit (EXIT_FAILURE);
       /* Print the information. */
       printf ("My default group is %s (%d).\n",
               my_group->gr_name, (int) (my_passwd->pw_gid));
       printf ("The members of this group are:\n");
       members = my_group->gr_mem;
       while (*members)
           printf ("  %s\n", *(members));
       return EXIT_SUCCESS;

Here is some output from this program:

     I am Throckmorton Snurd.
     My login name is snurd.
     My uid is 31093.
     My home directory is /home/fsg/snurd.
     My default shell is /bin/sh.
     My default group is guest (12).
     The members of this group are: