Handling Winsock Errors
Most Windows Sockets 2 functions do not return the specific cause of an error when the function returns. Some Winsock functions return a value of zero if successful. Otherwise, the value SOCKET_ERROR (-1) is returned and a specific error number can be retrieved by calling the WSAGetLastError function. For Winsock functions that return a handle, a return value of INVALID_SOCKET (0xffff) indicates an error and a specific error number can be retrieved by calling WSAGetLastError. For Winsock functions that return a pointer, a return value of NULL indicates an error and a specific error number can be retrieved by calling the WSAGetLastError function.
A Winsock error code can be converted to an HRESULT for use in a remote procedure call (RPC) using HRESULT_FROM_WIN32. In earlier versions of the Platform Software Development Kit (SDK), HRESULT_FROM_WIN32 was defined as a macro in the Winerror.h header file. In the Microsoft Windows Software Development Kit (SDK), HRESULT_FROM_WIN32 is defined as an inline function in the Winerror.h header file.
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