Using the highest layer

Suppose you are writing a program that needs to know how many
users are logged into a remote machine. You might do this by calling a library routine named rnusers, as illustrated here:

   #include <stdio.h>
   

   main(argc, argv)
           int argc;
           char **argv;
   {
           unsigned num;
   

           if (argc < 2) {
                   fprintf(stderr, "usage: rnusers hostname\n");
                   exit(1);
           }
           if ((num = rnusers(argv[1])) < 0) {
                   fprintf(stderr, "error: rnusers\n");
                   exit(-1);
           }
           printf("%d users on %s\n", num, argv[1]);
           exit(0);
   }

The program above could be compiled with:

cc program.c -lrpcsvc -lsocket