Socket中如何设置连接超时

1. create socket
 struct sockaddr_in addr;
 addr.sin_family = AF_INET;
 // Server address
 addr.sin_addr.s_addr = inet_addr(host);
 // Server port
 addr.sin_port = htons(port);
 // Creating socket
 if ((soc = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == INVALID_SOCKET)
  throw connector_exception("connector: can't create socket");

2. connect
 if (::connect(soc, (struct sockaddr *) &addr, sizeof(addr)) == SOCKET_ERROR)
  throw connector_exception("connector: can't connect.");

3. 设置为非阻塞式socket
   unsigned long ul = 1;
   int ret = ioctlsocket(rec(), FIONBIO, (unsigned long*)&ul);
   if(ret==SOCKET_ERROR)
    log <<"ioctlsocket error" << endl;
4. select socket
   FD_ZERO(&r_readfds);FD_ZERO(&r_exfds);
  FD_SET(rec(), &r_readfds);FD_SET(rec(), &r_exfds);
 if ((iret=select(0,&r_readfds, NULL,&r_exfds,&tv))==SOCKET_ERROR){
每次调用好select后，select 函数自动把r_readfds，r_exfds都设为空，必须重新调用
FD_ZERO(&r_readfds);FD_ZERO(&r_exfds);
FD_SET(rec(), &r_readfds); FD_SET(rec(), &r_exfds);  否则会报10022 WSAEINVAL 错误因为select如果超时会自动清空r_readfds,r_exfds。但是如果不超时，则不清空，所以要调用FD_ZERO(&r_readfds);FD_ZERO(&r_exfds);保证清空

5 参考文献
http://support.microsoft.com/kb/q147714/