MFC中socket编程时recv设置超时属性后，如果超时返回值是什么？谢谢大家：）

超时,也是 返回： SOCKET_ERROR
用WSAGetLastError() 获取 id 再分析，程序如下：

memset(buff,0x0,buff_size);
if (recv(sock,buff,sizeof(buff),0) == SOCKET_ERROR){
id = WSAGetLastError();
switch (id)
{
case WSANOTINITIALISED: printf("not initialized\n"); break;
case WSASYSNOTREADY: printf("sub sys not ready\n"); break;
case WSAHOST_NOT_FOUND: printf("name server not found\n"); break;
case WSATRY_AGAIN: printf("server fail\n"); break;
case WSANO_RECOVERY: printf("no recovery\n"); break;
case WSAEINPROGRESS: printf("socket blocked by other prog\n"); break;
case WSANO_DATA: printf("no data record\n"); break;
case WSAEINTR: printf("blocking call canciled\n"); break;
case WSAEPROCLIM: printf("limit exceeded\n");
case WSAEFAULT: printf("lpWSAData in startup not valid\n");
default: printf("unknown error id = %d\n",id); break;
};
printf("receive error.\n");
};

SOCKET ERROR