Inet Example (The GNU C Library)

#### 16.6.7 Internet Socket Example ¶

Here is an example showing how to create and name a socket in the Internet namespace. The newly created socket exists on the machine that the program is running on. Rather than finding and using the machine’s Internet address, this example specifies `INADDR_ANY` as the host address; the system replaces that with the machine’s actual address.

    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/socket.h>
    #include <netinet/in.h>

    int
    make_socket (uint16_t port)
    {
      int sock;
      struct sockaddr_in name;

      /* Create the socket. */
      sock = socket (PF_INET, SOCK_STREAM, 0);
      if (sock < 0)
        {
          perror ("socket");
          exit (EXIT_FAILURE);
        }

      /* Give the socket a name. */
      name.sin_family = AF_INET;
      name.sin_port = htons (port);
      name.sin_addr.s_addr = htonl (INADDR_ANY);
      if (bind (sock, (struct sockaddr *) &name, sizeof (name)) < 0)
        {
          perror ("bind");
          exit (EXIT_FAILURE);
        }

      return sock;
    }

Here is another example, showing how you can fill in a `sockaddr_in` structure, given a host name string and a port number:

    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <netdb.h>

    void
    init_sockaddr (struct sockaddr_in *name,
                   const char *hostname,
                   uint16_t port)
    {
      struct hostent *hostinfo;

      name->sin_family = AF_INET;
      name->sin_port = htons (port);
      hostinfo = gethostbyname (hostname);
      if (hostinfo == NULL)
        {
          fprintf (stderr, "Unknown host %s.\n", hostname);
          exit (EXIT_FAILURE);
        }
      name->sin_addr = *(struct in_addr *) hostinfo->h_addr;
    }