connect

The Windows Sockets connect function establishes a connection to a specifed socket.

int connect (
  SOCKET s,                          
  const struct sockaddr FAR*  name,  
  int namelen                        
);

Parameters

s: [in] A descriptor identifying an unconnected socket.
name: [in] The name of the socket to connect to.
namelen: [in] The length of the name parameter.

Remarks

The connect function is used to create a connection to the specified destination. If the socket, s, is unbound, unique values are assigned to the local association by the system, and the socket is marked as bound.

For connection-oriented sockets (for example, type SOCK_STREAM), an active connection is initiated to the foreign host using name (an address in the name space of the socket; for a detailed description, please see bind and SOCKADDR). When the socket call completes successfully, the socket is ready to send/receive data. If the address member of the structure specified by the name parameter is all zeroes, connect will return the error WSAEADDRNOTAVAIL. Any attempt to re-connect an active connection will fail with the error code WSAEISCONN.

For connection-oriented, nonblocking sockets, it is often not possible to complete the connection immediately. In such a case, this function returns the error WSAEWOULDBLOCK. However, the operation proceeds. When the success or failure outcome becomes known, it may be reported in one of several ways depending on how the client registers for notification. If the client uses the select function, success is reported in the writefds set and failure is reported in the exceptfds set. If the client uses the functions WSAAsyncSelect or WSAEventSelect, the notification is announced with FD_CONNECT and the error code associated with the FD_CONNECT indicates either success or a specific reason for failure

For a connectionless socket (for example, type SOCK_DGRAM), the operation performed by connect is merely to establish a default destination address that will be used on subsequent send/WSASend and recv/WSARecv calls. Any datagrams received from an address other than the destination address specified will be discarded. If the address member of the structure specifed by name is all zeroes, the socket will be "dis-connected." Then, the default remote address will be indeterminate, so send/WSASend and recv/WSARecv calls will return the error code WSAENOTCONN. However, sendto/WSASendTo and recvfrom/WSARecvFrom can still be used. The default destination can be changed by simply calling connect again, even if the socket is already connected. Any datagrams queued for receipt are discarded if name is different from the previous connect.

For connectionless sockets, name can indicate any valid address, including a broadcast address. However, to connect to a broadcast address, a socket must use setsockopt to enable the SO_BROADCAST option. Otherwise, connect will fail with the error code WSAEACCES.

When a connection between sockets is broken, the sockets should be discarded and recreated. When a problem develops on a connected socket, the application must discard and recreate the needed sockets in order to return to a stable point.

Windows CE: Windows CE does not support the WSAEINTR error value.

For IrSocket implementation:

The Af_irda.h file must be explicitly included.
If WSAENETDOWN is returned, an existing IrDA connection was detected at the media access level.
If WSAEADDRINUSE is returned, active connections to a device with a different address exist.
If WSAEINPROGRESS is returned, IAS name resolution failed because another IAS query is in progress. Retry the operation at one second intervals.
If WSAEISCONN is returned, the socket is already connected or an exclusive/multiplexed mode change failed.

IrSockets implements the connect function with addresses of the form sockaddr_irda. Typically, a client application will create a socket with the socket function, scan the immediate vicinity for IrDA devices with the IRLMP_ENUMDEVICES socket option, choose a device from the returned list, form an address, and call connect. There is no difference in blocking and non-blocking semantics.

Return Values

If no error occurs, connect returns zero. Otherwise, it returns SOCKET_ERROR, and a specific error code can be retrieved by calling WSAGetLastError.

On a blocking socket, the return value indicates success or failure of the connection attempt.

With a nonblocking socket, the connection attempt cannot be completed immediately. In this case, connect will return SOCKET_ERROR, and WSAGetLastError will return WSAEWOULDBLOCK. In this case, there are three different steps you can take:

Use the select function to determine the completion of the connection request by checking to see if the socket is writeable.
If the application is using WSAAsyncSelect to indicate interest in connection events, then the application will receive an FD_CONNECT notification indicating that the connect operation is complete (successfully or not).
If the application is using WSAEventSelect to indicate interest in connection events, then the associated event object will be signaled indicating that the connect operation is complete (successfully or not).

Until the connection attempt completes on a nonblocking socket, all subsequent calls to connect on the same socket will fail with the error code WSAEALREADY, and WSAEISCONN when the connection completes successfully. Due to ambiguities in version 1.1 of the Windows Sockets specification, error codes returned from connect while a connection is already pending may vary among implementations. As a result, it is not recommended that applications use multiple calls to connect to detect connection completion. If they do, they must be prepared to handle WSAEINVAL and WSAEWOULDBLOCK error values the same way that they handle WSAEALREADY, to assure robust execution.

If the error code returned indicates the connection attempt failed (that is, WSAECONNREFUSED, WSAENETUNREACH, WSAETIMEDOUT) the application can call connect again for the same socket.

Error Codes

WSANOTINITIALISED	A successful WSAStartup must occur before using this function.
WSAENETDOWN	The network subsystem has failed.
WSAEADDRINUSE	The socket's local address is already in use and the socket was not marked to allow address reuse with SO_REUSEADDR. This error usually occurs when executing bind, but could be delayed until this function if the bind was to a partially wild-card address (involving ADDR_ANY) and if a specific address needs to be committed at the time of this function.
WSAEINTR	The (blocking) Windows Socket 1.1 call was canceled through WSACancelBlockingCall.
WSAEINPROGRESS	A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAEALREADY	A nonblocking connect call is in progress on the specified socket. Note In order to preserve backward compatibility, this error is reported as WSAEINVAL to Windows Sockets 1.1 applications that link to either WINSOCK.DLL or WSOCK32.DLL.
WSAEADDRNOTAVAIL	The remote address is not a valid address (such as ADDR_ANY).
WSAEAFNOSUPPORT	Addresses in the specified family cannot be used with this socket.
WSAECONNREFUSED	The attempt to connect was forcefully rejected.
WSAEFAULT	The name or the namelen parameter is not a valid part of the user address space, the namelen parameter is too small, or the name parameter contains incorrect address format for the associated address family.
WSAEINVAL	The parameter s is a listening socket, or the destination address specified is not consistent with that of the constrained group the socket belongs to.
WSAEISCONN	The socket is already connected (connection-oriented sockets only).
WSAENETUNREACH	The network cannot be reached from this host at this time.
WSAENOBUFS	No buffer space is available. The socket cannot be connected.
WSAENOTSOCK	The descriptor is not a socket.
WSAETIMEDOUT	Attempt to connect timed out without establishing a connection.
WSAEWOULDBLOCK	The socket is marked as nonblocking and the connection cannot be completed immediately.
WSAEACCES	Attempt to connect datagram socket to broadcast address failed because setsockopt option SO_BROADCAST is not enabled.

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