QUdpSocket Echo Server : Client Recv Problem

  • I am writing a simple udp echo server, but have problem about how to recv data in udp client.
    Below is the UDP Server main logic:

    m_oServerSocket = new QUdpSocket(this);
    m_oServerSocket->connect(m_oServerSocket, SIGNAL(readyRead()), this, SLOT(__onServerRecv()));
    m_oServerSocket->bind(QHostAddress::Any, sPort.toInt());

    and in "__onServerRecv()":


    QByteArray datagram;

    QHostAddress sender;
    quint16 senderPort;
    m_oServerSocket->readDatagram(datagram.data(), datagram.size(), &sender, &senderPort);

    QDateTime dt = QDateTime::currentDateTime();
    QString sDtString = dt.toString("yyyy-MM-dd HH:mm:ss");
    QString sLog = ui->txtServerLog->toPlainText();
    sLog = sDtString + " : " + QString::fromUtf8(datagram) + "\n" + sLog;

    m_oServerSocket->writeDatagram(datagram, sender, senderPort);

    I think the Server's Code is OK because I write a simple python client and it works perfectly.But when I write my QUdpSocket Client:

    m_oClientSocket = new QUdpSocket(this);
    m_oClientSocket ->connect(m_oClientSocket , SIGNAL(readyRead()), this, SLOT(__onClientRecv()));

    QString sSendMsg = ui->txtClientSend->text();
    m_oClientSocket->writeDatagram(sSendMsg.toUtf8(), QHostAddress::LocalHost, sPort.toInt());

    the slot "__onClientRecv" is never called, and it means that the client's signal "readyRead" is never triggerred.

    How should I do ?

  • Try something like m_oServerSocket->bind(QHostAddress::Any, sPort.toInt()); for m_oClientSocket.

  • You need to call "QAbstractSocket::connectToHost":http://qt-project.org/doc/qt-4.8/qabstractsocket.html#connectToHost function at your client application and you will be fine.

  • [quote author="VanDerSam" date="1332181472"]Try something like m_oServerSocket->bind(QHostAddress::Any, sPort.toInt()); for m_oClientSocket.[/quote]

    if I use bind in client, I think the client would became server too. And it will open two udp listen port.

  • [quote author="favoritas37" date="1332196902"]You need to call "QAbstractSocket::connectToHost":http://qt-project.org/doc/qt-4.8/qabstractsocket.html#connectToHost function at your client application and you will be fine.[/quote]

    It's OK.
    But I think the Qt's Socket Api is much different from typical C socket api. I mean there is no api corresponding to connectToHost in C socket.

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