WSACleanup function (winsock2.h)

The WSACleanup function terminates use of the Winsock 2 DLL (Ws2_32.dll).


int WSAAPI WSACleanup();

Return value

The return value is zero if the operation was successful. Otherwise, the value SOCKET_ERROR is returned, and a specific error number can be retrieved by calling WSAGetLastError.

In a multithreaded environment, WSACleanup terminates Windows Sockets operations for all threads.

Error code Meaning
A successful WSAStartup call must occur before using this function.
The network subsystem has failed.
A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.


An application or DLL is required to perform a successful WSAStartup call before it can use Windows Sockets services. When it has completed the use of Windows Sockets, the application or DLL must call WSACleanup to deregister itself from a Windows Sockets implementation and allow the implementation to free any resources allocated on behalf of the application or DLL.

When WSACleanup is called, any pending blocking or asynchronous Windows Sockets calls issued by any thread in this process are canceled without posting any notification messages or without signaling any event objects. Any pending overlapped send or receive operations (WSASend, WSASendTo, WSARecv, or WSARecvFrom with an overlapped socket, for example) issued by any thread in this process are also canceled without setting the event object or invoking the completion routine, if one was specified. In this case, the pending overlapped operations fail with the error status WSA_OPERATION_ABORTED.

Sockets that were open when WSACleanup was called are reset and automatically deallocated as if closesocket were called. Sockets that have been closed with closesocket but that still have pending data to be sent can be affected when WSACleanup is called. In this case, the pending data can be lost if the WS2_32.DLL is unloaded from memory as the application exits. To ensure that all pending data is sent, an application should use shutdown to close the connection, then wait until the close completes before calling closesocket and WSACleanup. All resources and internal state, such as queued unposted or posted messages, must be deallocated so as to be available to the next user.

There must be a call to WSACleanup for each successful call to WSAStartup. Only the final WSACleanup function call performs the actual cleanup. The preceding calls simply decrement an internal reference count in the WS2_32.DLL.

Note  WSACleanup does not unregister names (peer names, for example) that may have been registered with a Windows Sockets namespace provider such as Peer Name Resolution Protocol (PNRP) namespace provider.
In Windows Sockets 1.1, attempting to call WSACleanup from within a blocking hook and then failing to check the return code was a common programming error. If a Winsock 1.1 application needs to quit while a blocking call is outstanding, the application has to first cancel the blocking call with WSACancelBlockingCall then issue the WSACleanup call once control has been returned to the application. In Windows Sockets 2, this issue does not exist and the WSACancelBlockingCall function has been removed.

The WSACleanup function typically leads to protocol-specific helper DLLs being unloaded. As a result, the WSACleanup function should not be called from the DllMain function in a application DLL. This can potentially cause deadlocks. For more information, please see the DLL Main Function.

Windows Phone 8: This function is supported for Windows Phone Store apps on Windows Phone 8 and later.

Windows 8.1 and Windows Server 2012 R2: This function is supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and later.


Minimum supported client Windows 8.1, Windows Vista [desktop apps | UWP apps]
Minimum supported server Windows Server 2003 [desktop apps | UWP apps]
Target Platform Windows
Header winsock2.h (include Winsock2.h)
Library Ws2_32.lib
DLL Ws2_32.dll

See also

PNRP Namespace Provider API


Winsock Functions

Winsock Reference