socket connect 函数设置超时

[源 = http://www.iprotocolsec.com/2011/08/22/socket-connect-%E5%87%BD%E6%95%B0%E8%AE%BE%E7%BD%AE%E8%B6%85%E6%97%B6/]

众所周知，在进行网络编程的时候，如果使用系统connect函数，无法设置超时，而在连接一个不存在的主机时，将会一直阻塞。

其实在调用connect函数时，将句柄设置为非阻塞，然后调用select函数，可以达到设置超时的效果。

bool connect(char *host,int port, int timeout)
{
    TIMEVAL Timeout;
    Timeout.tv_sec = timeout;
    Timeout.tv_usec = 0;
    struct sockaddr_in address;  /* the libc network address data structure */   

    sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

    address.sin_addr.s_addr = inet_addr(host); /* assign the address */
    address.sin_port = htons(port);            /* translate int2port num */
    address.sin_family = AF_INET;

    //set the socket in non-blocking
    unsigned long iMode = 1;
    int iResult = ioctlsocket(sock, FIONBIO, &iMode);
    if (iResult != NO_ERROR)
    {
        printf("ioctlsocket failed with error: %ld\n", iResult);
    }

    if(connect(sock,(struct sockaddr *)&address,sizeof(address))==false)
    {
        return false;
    }   

    // restart the socket mode
    iMode = 0;
    iResult = ioctlsocket(sock, FIONBIO, &iMode);
    if (iResult != NO_ERROR)
    {
        printf("ioctlsocket failed with error: %ld\n", iResult);
    }

    fd_set Write, Err;
    FD_ZERO(&Write);
    FD_ZERO(&Err);
    FD_SET(sock, &Write);
    FD_SET(sock, &Err);

    // check if the socket is ready
    select(0,NULL,&Write,&Err,&Timeout);
    if(FD_ISSET(sock, &Write))
    {
        return true;
    }

    return false;
}