C connect实现Timeout效果（Linux）

C connect函数是阻塞的，现要实现非阻塞式的connect。

int SocketClient::connectTimeOut(const int &connect_fd, const int &timeout,const sockaddr_in &server)
{
    int error=-1, len;
    len = sizeof(int);
    timeval tm;
    fd_set set;
    unsigned long ul = 1;

    ioctl(connect_fd, FIONBIO, &ul); //设置为非阻塞模式


    bool ret = false;
    if( connect(connect_fd, (struct sockaddr *)&server, sizeof(struct sockaddr)) == -1)
    {
        tm.tv_sec = timeout;
        tm.tv_usec = 0;
        FD_ZERO(&set);
        FD_SET(connect_fd, &set);
        if( select(connect_fd+1, NULL, &set, NULL, &tm) > 0)
        {

            getsockopt(connect_fd, SOL_SOCKET, SO_ERROR, &error, (socklen_t *)&len);

            if(error == 0) ret = true;
            else ret = false;
        } else ret = false;
    }
    else ret = true;
    ul = 0;


  ioctl(connect_fd, FIONBIO, &ul); //设置为阻塞模式

    if(!ret){
        close(connect_fd);
//        fprintf(stderr,"Connect server fail\n");
    }
    return ret;
}