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

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