View Source: connect(2) - Waikato Linux Users Group

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connect - initiate a connection on a socket
!!SYNOPSIS


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


 __int connect(int__ ''sockfd''__, const struct sockaddr *__''serv_addr''__, socklen_t__ ''addrlen''__);__
!!DESCRIPTION

The file descriptor ''sockfd'' must refer to a socket. If the socket is of type __SOCK_DGRAM__ then the ''serv_addr'' address is the address to which datagrams are sent by default, and the only address from which
datagrams are received. If the socket is of type __SOCK_STREAM__ or __SOCK_SEQPACKET__, this call attempts to make a connection to another socket. The other socket is specified by ''serv_addr'', which is an address
(of length ''addrlen'') in the communications space of the socket. Each communications space interprets the ''serv_addr'' parameter in its own way.

Generally, connection-based protocol sockets may successfully __connect__ only once; connectionless protocol sockets may use __connect__ multiple times to change their association. Connectionless sockets may
dissolve the association by connecting to an address with the ''sa_family'' member of __sockaddr__ set to __AF_UNSPEC__.
!!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]: The file descriptor is not a valid index in the descriptor table.
;[EFAULT]: The socket structure address is outside the user's address space.
;[ENOTSOCK]: The file descriptor is not associated with a socket.
;[EISCONN]: The socket is already connected.
;[ECONNREFUSED]: No one listening on the remote address.
;[ETIMEDOUT]: Timeout while attempting connection. The server may be too busy to accept new connections. Note that for IP sockets the timeout may be very long when syncookies are enabled on the server.
;[ENETUNREACH]: Network is unreachable.
;[EADDRINUSE]: Local address is already in use.
;[EINPROGRESS]: The socket is non-blocking and the connection cannot be completed immediately. It is possible to select(2) or poll(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 here, explaining the reason for the failure).
;[EALREADY]: The socket is non-blocking and a previous connection attempt has not yet been completed.
;[EAGAIN]: No more free local ports or insufficient entries in the routing cache. For __PF_INET__ see the __net.ipv4.ip_local_port_range__ sysctl in ip(7) on how to increase the number of local ports.
;[EAFNOSUPPORT]: The passed address didn't have the correct address family in its ''sa_family'' field.
;[EACCES], [EPERM]: The user tried to connect to a broadcast address without having the socket broadcast flag enabled or the connection request failed because of a local firewall rule.
;[EAFNOSUPPORT]: The address family is not supported by protocol
!!CONFORMING TO


SVr4, 4.4BSD (the __connect__ function first appeared in BSD 4.2). SVr4 documents the additional general error codes [EADDRNOTAVAIL], [EINVAL], [EALREADY], [EINTR], [EPROTOTYPE], and [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).
!!BUGS

Unconnecting a socket by calling __connect__ with a __AF_UNSPEC__ address is not yet implemented.

!!SEE ALSO
accept(2), bind(2), listen(2), socket(2), getsockname(2), CategorySocketSysCalls
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Last edited on Sunday, February 23, 2003 2:26:05 pm by PerryLorier
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