//設定非阻塞方式連線
unsigned long ul = 1;
ret = ioctlsocket(cclient, fionbio, (unsigned long*)&ul);
if(ret==socket_error)return 0;
//連線
server.sin_family = af_inet;
server.sin_port = htons(25);
server.sin_addr .s_addr = inet_addr((lpcstr)psmtp);
if(server.sin_addr.s_addr == inaddr_none)
connect(cclient,(const struct sockaddr *)&server,sizeof(server));
//select 模型，即設定超時
struct timeval timeout ;
fd_set r;
fd_zero(&r);
fd_set(cclient, &r);
timeout.tv_sec = 15; //連線超時15秒
timeout.tv_usec =0;
ret = select(0, 0, &r, 0, &timeout);
if ( ret <= 0 )
//一般非鎖定模式套接比較難控制，可以根據實際情況考慮 再設回阻塞模式
unsigned long ul1= 0 ;
ret = ioctlsocket(cclient, fionbio, (unsigned long*)&ul1);
if(ret==socket_error){
::closesocket (cclient);
return 0;
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