WSACleanup

WSACleanup is a function in the Windows Sockets API (Winsock) used to terminate the process’s use of Winsock. It decrements the internal per-process reference count that was incremented by WSAStartup, and when the count reaches zero, Winsock resources are freed.

Winsock uses a per-process initialization model: a successful WSAStartup call increases the reference count, and WSACleanup should be called once for each successful WSAStartup when the application finishes using Winsock. The cleanup is process-wide rather than per-thread, and you should close all sockets before calling WSACleanup to avoid operating on invalid handles. After WSACleanup reduces the count to zero, further Winsock operations should not be performed until a new WSAStartup is successfully invoked.

Return value and error handling: WSACleanup returns 0 on success. On failure, it returns SOCKET_ERROR and you can retrieve extended error information with WSAGetLastError. A common error is WSA_NOT_INITIALISED, indicating that WSACleanup was called without a prior successful WSAStartup. The function must be matched with a corresponding WSAStartup call; if you call WSACleanup more times than WSAStartup succeeded, you may encounter errors.

Implementation notes: WSACleanup is part of Winsock2. Programs that use Winsock should include Winsock2.h and link against Ws2_32.lib. Proper cleanup helps ensure that system resources are released and that the process can reinitialize Winsock later if needed.