WSAGetLastError

WSAGetLastError is a Winsock API function used to retrieve the last error code that occurred on the calling thread during Windows Sockets operations. It is declared in Winsock2.h and implemented in Ws2_32.dll; programs typically link against Ws2_32.lib. The function returns an int representing a Winsock error code.

Usage involves checking the return value of Winsock functions. When a function fails, it usually indicates failure by returning SOCKET_ERROR (or INVALID_SOCKET for certain operations). In that case, calling WSAGetLastError yields the specific Winsock error code, such as WSAEHOSTUNREACH, WSAETIMEDOUT, WSAECONNREFUSED, WSAENETDOWN, or WSAEWOULDBLOCK. These codes are Winsock-specific and differ from the general GetLastError values.

WSAGetLastError is per-thread. Each thread maintains its own last-error value for Winsock operations, so the last error should be retrieved immediately after a failed Winsock call and before performing further Winsock calls that might overwrite it. In other words, rely on WSAGetLastError to obtain the error after a specific operation and avoid assumptions about the value after other calls.

Related functionality includes WSASetLastError, which can set the thread’s last Winsock error value, though typical usage is to read the error provided by the failing function via WSAGetLastError. For comprehensive error handling, consult the Winsock documentation for the mapping between error codes and network conditions, and ensure proper handling across different Windows versions and environments.