WSAConnect

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11/18/2015

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4/8/2010

This function establishes a connection to another socket application and exchanges connect (Windows Sockets) data.

Syntax

int  WSAConnect(
  SOCKET s,
  const struct sockaddr FAR* name,
  int namelen,
  LPWSABUF lpCallerData,
  LPWSABUF lpCalleeData,
  LPQOS lpSQOS,
  LPQOS lpGQOS 
);

Parameters

s
[in] Descriptor identifying an unconnected socket.

name
[in] Name of the socket in the other application to which to connect.

namelen
[in] Length of the name.

lpCallerData
[in] Pointer to the user data that is to be transferred to the other socket during connection establishment.

lpCalleeData
[out] Pointer to the user data that is to be transferred back from the other socket during connection establishment.

lpSQOS
[in] Reserved.

lpGQOS
[in] Reserved.

Return Value

If no error occurs, this function returns zero. If an error occurs, it returns SOCKET_ERROR, and a specific error code can be retrieved by calling the WSAGetLastError function. On a blocking socket, the return value indicates success or failure of the connection attempt.

Note

The Windows Embedded CE default TCP/UDP service provider does not support the exchange of data at the time of connection for the default service provider. lpCalleeData and lpCallerData should both be NULL.

With a nonblocking socket, the connection attempt cannot be completed immediately. In this case, WSAConnect will return SOCKET_ERROR and WSAGetLastError will return WSAEWOULDBLOCK. The application could perform the following actions:

Use select to determine the completion of the connection request by checking if the socket is writeable.
If your application is using WSAEventSelect to indicate interest in connection events, then the associated event object will be signaled when the connectoperation is complete (successful or not).

For a nonblocking socket, until the connection attempt completes all subsequent calls to WSAConnect on the same socket will fail with the error code WSAEALREADY.

If the return error code indicates the connection attempt failed (that is, WSAECONNREFUSED, WSAENETUNREACH, or WSAETIMEDOUT), the application can call WSAConnect again for the same socket. The following table shows a list of possible error codes.

Error code	Description
WSANOTINITIALISED	A successful WSAStartup call must occur before using this function.
WSAENETDOWN	The network subsystem has failed.
WSAEADDRINUSE	The local address of the socket is already in use and the socket was not marked to allow address reuse with SO_REUSEADDR. This error usually occurs during the execution of the bind (Windows Sockets) function, but it could be delayed until the WSAConnect function if the bind function operates on a partially wildcard address (involving ADDR_ANY) and if a specific address needs to be "committed" at the time of the WSAConnect function.
WSAEINTR	The socket was closed.
WSAEINPROGRESS	A blocking Winsock call is in progress, or the service provider is still processing a callback function.
WSAEALREADY	A nonblocking connect/WSAConnect call is in progress on the specified socket.
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 connectwas rejected.
WSAEFAULT	The name or namelen parameter is not a valid part of the user address space; the namelen parameter is too small; the buffer length for lpCalleeData is too small; or the buffer length for lpCallerData is too large.
WSAEINVAL	The parameter s is a listening socket.
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.
WSAEOPNOTSUPP	The structures specified in lpSQOS and lpGQOS cannot be satisfied.
WSAEPROTONOSUPPORT	The lpCallerData argument is not supported by the service provider.
WSAETIMEDOUT	An attempt to connecttimed out without establishing a connection.
WSAEWOULDBLOCK	The socket is marked as nonblocking and the connection cannot be completed immediately.
WSAEACCES	An attempt to connectdatagram socket to broadcast address failed because setsockopt SO_BROADCAST is not enabled.

Remarks

This function is used to create a connection to the specified destination and to perform a number of other ancillary operations that occur at connecttime. If 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). When this call completes successfully, the socket is ready to send and receive data. If the address parameter of the name structure is all zeroes, WSAConnect will return the error WSAEADDRNOTAVAIL. Any attempt to reconnect 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 cases, 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 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 WSAConnect is merely to establish a default destination address so that the socket can be used on subsequent connection-oriented send and receive operations (send, WSASend, recv, and WSARecv). Any datagrams received from an address other than the destination address specified will be discarded. If the entire name structure is all zeros (not just the address parameter of the name structure), then the socket will be disconnected. 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 WSAConnect again, even if the socket is already connected. Any datagrams queued for receipt are discarded if name is different from the previous WSAConnect call.

For connectionless sockets, name can indicate any valid address, including a broadcast address. However, to connectto a broadcast address, a socket must have setsockopt (Windows Sockets) SO_BROADCAST enabled. Otherwise, WSAConnect will fail with the error code WSAEACCES.

On connectionless sockets, exchange of user-to-user data is not possible and the corresponding parameters will be silently ignored.

The application is responsible for allocating any memory space pointed to directly or indirectly by any of the parameters it specifies.

The lpCallerData parameter is a value parameter that contains any user data that is to be sent along with the connection request. If lpCallerData is NULL, no user data will be passed to the peer. The lpCalleeData parameter is a result parameter that will contain any user data passed back from the other socket as part of the connection establishment in a WSABUF structure. The lpCalleeData->len member initially contains the length of the buffer allocated by the application and pointed to by lpCalleeData->buf. The lpCalleeData->len member will be set to zero if no user data has been passed back. The lpCalleeData information will be valid when the connection operation is complete. For blocking sockets, the connection operation completes when WSAConnect returns. For nonblocking sockets, completion will be after the FD_CONNECT notification has occurred. If lpCalleeData is NULL, no user data will be passed back. The exact format of the user data is specific to the address family to which the socket belongs.

Requirements

Header	winsock2.h
Library	Ws2.lib
Windows Embedded CE	Windows CE .NET 4.0 and later
Windows Mobile	Windows Mobile Version 5.0 and later

共用方式為

WSAConnect

Syntax

Parameters

Return Value

Remarks

Requirements

See Also

Reference

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