main (void)
{
  char *login;
  int errors = 0;

  login = getlogin ();
  if (login == NULL)
    puts ("getlogin returned NULL, no further tests");
  else
    {
      char name[1024];
      int ret;

      printf ("getlogin returned: `%s'\n", login);

      ret = getlogin_r (name, sizeof (name));
      if (ret == 0)
	{
	  printf ("getlogin_r returned: `%s'\n", name);
	  if (strcmp (name, login) != 0)
	    {
	      puts ("Error: getlogin and getlogin_r returned different names");
	      ++errors;
	    }
	}
      else
	{
	  printf ("Error: getlogin_r returned: %d (%s)\n",
		  ret, strerror (ret));
	  ++errors;
	}
    }

  return errors != 0;
}
The software does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions.