QT UDP send custom structure (message body)

• UDP is a lightweight socket communication with functions such as broadcasting and multicasting. UDP transmits data through data packets, without the problem of sub-packaging and grouping, which is convenient and quick. This article introduces an example of QT UDP communication.

QUdpSocket class

include

• To use QT's QUdpSocket class, you need to add in the pro file:

QT += network

• Add in .h

	#include <QUdpSocket>
	#include <QtNetwork>

Official example

//服务端绑定端口，能够收到固定端口的广播信号。
  void Server::initSocket()
  {
    
    
      udpSocket = new QUdpSocket(this);  //创建对象
      udpSocket->bind(QHostAddress::LocalHost, 7755); //绑定端口
      //当UDP收到消息后，会发送readyRead信号，
      //连接成功有 connected，断开连接有，disconnected信号。
      connect(udpSocket, SIGNAL(readyRead()),
              this, SLOT(readPendingDatagrams())); 
  }
  void Server::readPendingDatagrams()
  {
    
    
      while (udpSocket->hasPendingDatagrams()) {
    
    
      //从缓冲区中读取数据，
          QNetworkDatagram datagram = udpSocket->receiveDatagram();
          //处理数据。
          processTheDatagram(datagram); 
      }
  }

In the official instance

Broadcast and receive custom structure/message body

Informed body

Add msg_type.h file and declare the structure. For example as follows

typedef struct
{
    
    
    unsigned int send_id;       // 发送方的ID（网络的IP、SRIO的ID）
    unsigned int recv_id;       // 接收方的ID（网络的IP、SRIO的ID）
    unsigned int msg_type : 8;  // 消息类型
    unsigned int len : 24;      // 消息长度，字节数
    unsigned int conn_type: 8;  // 连接类型，TCP、UDP等
    unsigned int pkg_num : 8;   // 总的包数（用于组包传输）
    unsigned int pkg_idx : 8;   // 子包索引（用于组包传输），从1计数
    unsigned int rsvd : 8;      // 保留位
    unsigned int check_sum;     // 校验位
    char* load;                 // 消息体地址
} DispCtrlMsg;

broadcast

/**
 * @brief Widget::on_UDPButton_clicked
 * 从6000端口广播消息
 */
void MainWindow::on_udpBroadButton_clicked()
{
    
    
    quint16 targetPort = ui->lineEdit_udpport->text().toUShort();
    DispCtrlMsg *sendMsg = new DispCtrlMsg();
    sendMsg->send_id = QHostAddress(ui->combox_tcpip->currentText()).toIPv4Address();
    sendMsg->msg_type = 0x10;
    sendMsg->conn_type = UDPCONNECTION;
    sendMsg->len = headLength;
    sendMsg->check_sum = sendMsg->send_id + sendMsg->msg_type + sendMsg->conn_type;
    QByteArray str;
    str.append((char*)sendMsg, headLength); 
    //headLength = sizeof(DispCtrlMsg)- sizeof(char*)
    //不发送char*部分的数据。
    udpSocket->writeDatagram(str, QHostAddress::Broadcast, targetPort);
    delete sendMsg;
}

receive

• The receiving end needs to bind ports to accept broadcast packets. After binding the port, if there is a broadcast packet, or the udp connection will send the corresponding signal. The trigger signal of onUDPReadyRead() is: readyRead() (this signal is inherited from QIODevice).

quint16 port = 6000;
udpSocket->bind(port);

receive

void Widget::onUDPReadyRead()
{
    
    
    while (udpSocket->hasPendingDatagrams()) {
    
    
        QHostAddress peerAddr;
        quint16 peerPort;
        QByteArray recvMsg;
        DispCtrlMsg msgHead;
        udpSocket->readDatagram((char*)&msgHead, sizeof(msgHead));
        qDebug() << QString::number(msgHead.msg_type,16).toUpper();
        qDebug() << msgHead.send_id;
        serverIP = msgHead.send_id;
        onConnected();
    }
}