fd_set set;
    struct timeval st_time;
    
    st_time.tv_sec  = 3 * 3;
    st_time.tv_usec = 0;

    while (1)  
    {   
        strcpy(sendbuf, "hello every");

        FD_ZERO(&set);
        FD_SET(sock_cli, &set);
     
        printf("before select. \n");
        int ret = select(sock_cli + 1, &set, (fd_set *)0, (fd_set *)0, &st_time);
        if (ret == 0)
        {   
            printf("select timeout.\n");
        }   
        else if (ret < 0)
        {   
            printf("select error.\n");
            break;
        }   
        else if (ret == 1)
        {   
            if (FD_ISSET(sock_cli, &set))
            {   
                ret = recv(sock_cli, recvbuf, sizeof(recvbuf),0); ///接收  
                if (ret <= 0)
                {   
                    printf("server disconnect..\n");
                    break;
                }   
            }   
        }