bind

bind

Assigns a Name to a Socket

Portability: UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
PORTABILITY
EXAMPLE
RELATED FUNCTIONS

SYNOPSIS

#include <sys/types.h>
#include <sys/socket.h>

int bind(int s, const void *addr, int addrlen);

DESCRIPTION

bind assigns a name to an unnamed socket s . When a socket is created, it exists in an address family, but it does not have a name assigned to it. Servers use bind to associate themselves with a well-known port. Servers may also use bind to restrict access by other network addresses on a host with multiple network addresses. bind enables a connectionless client to have an address that the server can use for responses.

For addresses in the AF_INET family, addr points to a sockaddr or sockaddr_in structure. addrlen is the length of the address, in bytes. addrlen should be greater than or equal to the size of the sockaddr or sockaddr_in structure. The INADDR_ANY constant in the <netinet/in.h> header file specifies that the network address is not restricted. If the sin_port field of the sockaddr structure is zero, bind chooses a port. Alternatively, a well-known port number can be passed in the sin_port field. Internet host addresses and port numbers in sockaddr_in are always in network byte order. The remainder of the sockaddr or sockaddr_in structure should be 0 .

Upon return, if a port of 0 was specified, the selected port value is filled in. On return, the structure pointed to by addr should be the same as the structure pointed to by getsockname for this socket s .

RETURN VALUE

If bind is successful, it returns a 0 ; otherwise, it returns a -1 and sets errno to indicate the type of error.

PORTABILITY

bind is portable to other environments, including most UNIX systems, that implement BSD sockets.

EXAMPLE

In this example, bind assigns socket s to an arbitrary port without restriction by network address.

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <string.h>
#include <stdio.h>
f()
{
   struct sockaddr_in sa;
   int s;
   struct servent *serv;
   .
   .
   .
      /* Specify the port. */
   memset(&sa,'\0',sizeof(sa));
   sa.sin_family = AF_INET;
   sa.sin_addr.s_addr = INADDR_ANY;
   sa.sin_port = serv->s_port;
   if (bind(s, &sa, sizeof(sa)) == -1) {
      perror("bind() failed");
      return -1;
   }
   .
   .
   .
      /* Let TCP/IP choose the port. */
   memset(&sa,'\0',sizeof(sa));
   sa.sin_family = AF_INET;
   sa.sin_addr.s_addr = INADDR_ANY;
   sa.sin_port = 0;
   if (bind(s, &sa, sizeof(sa)) == -1) {
      perror("bind() failed");
      return -1;
   }
   .
   .
   .
}

RELATED FUNCTIONS

connect , getservbyname , getsockname, htons

Chapter Contents
Previous
Next
Top of Page