void client::clientSendMessage ()

 {

     QByteArray data;

     data.append(ui->clientMessagelineEdit->text());

     tcp->write(data);

     ui->messagetextBrowser->insertPlainText (tr("send message: %1 \n").arg (QString(data)));

 }

void MainWindow::sendMessage()

{

   QByteArray block;//暂时存储我们需要发送的数据

   QDataStream out(&block,QIODevice::WriteOnly);//TCP必须和数据流一起使用

   out.setVersion(QDataStream::Qt_5_7);//设置数据流的版本（服务器和主机版本一定相同）

   out<<(quint16);//强制转化，quint16=unsigned short，向头部添加0为了开辟空间存放文件大小

   out << tr("");

   out.device()->seek();//向头添加数据，类似链表

   out <<(quint16)(block.size()-sizeof(quint16));//文件大小

   //*************利用“套接字”进行服务器和主机的连接和通讯****************//

   QTcpSocket *clientConnection = tcpServer->nextPendingConnection();

   connect(clientConnection,SIGNAL(disconnected()),//断开连接同时删除套接字

                  clientConnection,SLOT(deleteLater()));

   clientConnection->write(block);

   clientConnection->disconnectFromHost();//此函数关闭套接字触发disconnected()函数，接着由上面连接触发deleteLater()删除套接字

   ui->label_3->setText("successful sendmessage");

}