WSAIoctl

WSAIoctl is a Windows Sockets API function used to perform I/O control operations on a socket. It provides a mechanism to query or configure extended options and to obtain information that is not exposed through the standard getsockopt/setsockopt interfaces. WSAIoctl accepts a socket handle, a control code, optional input and output buffers, the sizes of those buffers, and a place to receive the number of bytes returned. It also supports overlapped (asynchronous) operation via a WSAOVERLAPPED structure and an optional completion routine.

The function signature is:

int WSAIoctl(SOCKET s, DWORD dwIoControlCode, LPVOID lpvInBuffer, DWORD cbInBuffer, LPVOID lpvOutBuffer, DWORD cbOutBuffer, LPDWORD lpcbBytesReturned, LPWSAOVERLAPPED lpOverlapped, LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine);

Return value is zero on success and SOCKET_ERROR on failure. When an error occurs, extended error information can be retrieved with WSAGetLastError. If overlapped I/O is used (lpOverlapped is non-NULL), the operation completes asynchronously and the completion routine or WSAGetOverlappedResult can indicate completion.

Common uses include enabling or querying advanced socket capabilities, obtaining network topology or interface information, and other platform-specific controls exposed as IOCTL codes (for example, codes related to interface lists or routing changes). WSAIoctl can also be used to configure non-blocking behavior or to perform other actions beyond standard socket options.

Notes:

- Include Winsock2.h and typically Ws2tcpip.h for some IP-related controls.

- Link against Ws2_32.lib.

- WSAIoctl is complementary to, and more general than, ioctlsocket, and is aimed at advanced scenarios in Windows networking.

See also: ioctlsocket, getsockopt, setsockopt, WSAGetLastError, WSAOVERLAPPED, Ws2_32.lib.