C/C++预处理指令#ifdef,#ifndef

#ifdef如果宏已经定义，则编译下面代码
#ifndef如果宏没有定义，则编译下面代码

#ifdef _SOCKET_ASYNC_IO
		if ((WSAAsyncSelect(s, g_hMainWnd, nMsgID, lEvent)) == SOCKET_ERROR)
			return FALSE;
#else
#ifdef _SOCKET_OVERLAPPED_IO
		if ((WSAAsyncSelect(s, g_hMainWnd, nMsgID, lEvent)) == SOCKET_ERROR)
			return FALSE;
#else
		//		CreateIOCPWorkerThread((int)lEvent);				  
		CreateIOCPWorkerThread((int)1);
		//		InitServerThreadForMsg();

		if (!InitThread(AcceptThread))
			return FALSE;
#endif
#endif