connect

connect

Associates a Socket with a Process

Portability: UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
PORTABILITY
EXAMPLE
RELATED FUNCTIONS

SYNOPSIS

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

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

DESCRIPTION

connect attempts to associate socket s with a peer process at address addr . addr is a pointer to a buffer containing the address of the peer socket. addrlen is the length, in bytes, of the buffer pointed to by addr . addrlen should be greater than or equal to the number of bytes in the sockaddr or sockaddr_in structure.

For connection-oriented protocols on blocking sockets, when the establishment of a connection is actually attempted, the call blocks I/O until the connection attempt succeeds or fails. On non-blocking sockets, the call returns immediately, with errno set to EINPROGRESS if the connection could not complete immediately. The caller can then discover whether or not the connection is complete by issuing the select call to determine if the socket is ready for writing.

For sockets that use connectionless protocols, connect enables the socket to register a destination address once, instead of having to specify the same destination address for every read or write operation. By associating a packet with a specific socket, connect provides more information with which to trace the source of the problem if a transmission fails. In this case, connect can be called many times.

RETURN VALUE

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

If errno is set to ECONNREFUSED , reuse of the failed socket descriptor is TCP/IP implementation-specific and unpredictable. However, it is always safe to close and obtain another socket descriptor for subsequent calls to connect .

PORTABILITY

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

EXAMPLE

In this example, connect connects socket s to a specific host and port.

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
f()
{
   struct sockaddr_in sa;
   struct hostent *host;
   struct servent *serv;
   int s;
   .
   .
   .
      /* Specify destination socket address (IP address and */
      /* port number).                                      */
   memset(&sa,'\0',sizeof(sa));
   sa.sin_family = AF_INET;
   memcpy(&sa.sin_addr,host->h_addr,sizeof(sa.sin_addr));
   sa.sin_port = serv->s_port;
      /* Connect to the host and port.                      */
   if (connect(s, &sa, sizeof(sa)) == -1) {
      perror("connect() failed");
      return -1;
   }
   .
   .
   .
}

RELATED FUNCTIONS

accept , select , socket , getpeername

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