CONNECT(2)

NAME
connect - initiate a connection on a socket

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

int connect(int sockfd, struct sockaddr *serv_addr, socklen_t addrlen );

DESCRIPTION
The parameter sockfd is a socket. If it is of type SOCK_DGRAM, this call specifies the peer with which the socket is to be associated; this address is that to which datagrams are to be sent, and the only address from which datagrams are to be received. If the socket is of type SOCK_STREAM , this call attempts to make a connection to another socket. The other socket is specified by serv_addr, which is an address in the communications space of the socket. Each communications space interprets the serv_addr, parameter in its own way. Generally, stream sockets may successfully connect only once; datagram sockets may use connect multiple times to change their association. Datagram sockets may dissolve the association by connecting to an invalid address, such as a null address.

RETURN VALUE
If the connection or binding succeeds, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS
The following are general socket errors only. There may be other domain-specific error codes.

EBADF
    Bad descriptor.

EFAULT
    The socket structure address is outside your address space.

ENOTSOCK
    The descriptor is not associated with a socket.

EISCONN
    The socket is already connected.

ECONNREFUSED
    Connection refused at server.

ETIMEDOUT
    Timeout while attempting connection.

ENETUNREACH
    Network is unreachable.

EADDRINUSE
    Address is already in use.

EINPROGRESS
    The socket is non-blocking and the connection cannot be completed immediately. It is possible to select(2) for completion by selecting the socket for writing. After select indicates writability, use getsockopt(2) to read the SO_ERROR option at level SOL_SOCKET to determine whether connect completed successfully (SO_ERROR is zero) or unsuccessfully (SO_ERROR is one of the usual error codes listed above, explaining the reason for the failure).

EALREADY
    The socket is non-blocking and a previous connection attempt has not yet been completed.

CONFORMING TO
SVr4, 4.4BSD (the connect function first appeared in BSD 4.2). SVr4 documents additional general error codes EADDRNOTAVAIL, EINVAL, EAFNOSUPPORT, EALREADY, EINTR, EPROTOTYPE, ENOSR. It also documents many additional error conditions not described here.

NOTE
The third argument of connect is in reality an int (and this is what BSD 4.* and libc4 and libc5 have). Some POSIX confusion resulted in the present socklen_t. The draft standard has not been adopted yet, but glibc2 already follows it and also has socklen_t. See also accept(2).

SEE ALSO
accept(2), bind(2), listen(2), socket(2), getsockname(2)