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<h4 class="subsection">16.10.3 Datagram Socket Example</h4>

<p>Here is a set of example programs that send messages over a datagram
stream in the local namespace.  Both the client and server programs use
the <code>make_named_socket</code> function that was presented in <a href="Local-Socket-Example.html#Local-Socket-Example">Local Socket Example</a>, to create and name their sockets.

   <p>First, here is the server program.  It sits in a loop waiting for
messages to arrive, bouncing each message back to the sender. 
Obviously this isn't a particularly useful program, but it does show
the general ideas involved.

<pre class="smallexample">     #include &lt;stdio.h&gt;
     #include &lt;errno.h&gt;
     #include &lt;stdlib.h&gt;
     #include &lt;sys/socket.h&gt;
     #include &lt;sys/un.h&gt;
     
     #define SERVER  "/tmp/serversocket"
     #define MAXMSG  512
     
     int
     main (void)
     {
       int sock;
       char message[MAXMSG];
       struct sockaddr_un name;
       size_t size;
       int nbytes;
     
       /* <span class="roman">Remove the filename first, it's ok if the call fails</span> */
       unlink (SERVER);
     
       /* <span class="roman">Make the socket, then loop endlessly.</span> */
       sock = make_named_socket (SERVER);
       while (1)
         {
           /* <span class="roman">Wait for a datagram.</span> */
           size = sizeof (name);
           nbytes = recvfrom (sock, message, MAXMSG, 0,
                              (struct sockaddr *) &amp; name, &amp;size);
           if (nbytes &lt; 0)
             {
               perror ("recfrom (server)");
               exit (EXIT_FAILURE);
             }
     
           /* <span class="roman">Give a diagnostic message.</span> */
           fprintf (stderr, "Server: got message: %s\n", message);
     
           /* <span class="roman">Bounce the message back to the sender.</span> */
           nbytes = sendto (sock, message, nbytes, 0,
                            (struct sockaddr *) &amp; name, size);
           if (nbytes &lt; 0)
             {
               perror ("sendto (server)");
               exit (EXIT_FAILURE);
             }
         }
     }
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