### 31.15 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>
    #include <stdio.h>

    int
    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));
          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:
      friedman
      tami