GNU C Library (libc) Programming Guide - Inet Example

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;
 }