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QExtSerialPort port->write Problem

  • I seem to be having difficulty using the PortListener class. If I write to a connected port directly everything is fine. If I write via a public or private function using identical code I get an error:

    “Application.exe has encountered a problem and needs to close.”

    It seems a bizarre problem so I must be missing something really simple. My apologies in advance if this is the case. I have cut the code down to a minimal case that still generates the problem.

    @MainWindow::MainWindow(QWidget *parent): QMainWindow(parent){
    QWidget *w = new QWidget(this);
    scPtr = new Session ();
    QString portName = scPtr->enumerate();
    if (portName == "NULL"){
    qDebug() << "Serial Device NOT FOUND portName = " << portName;
    int i = QMessageBox::warning(this,tr("Connection"),tr("No SerialDevices detected."),QMessageBox::Cancel);
    }else{ qDebug() << "SerialDevice Found. portName = " << portName; }
    PortListener *listener = new PortListener(portName);

    //============ below does not work?===============

    //============ below works======================
    QByteArray ba;
    ba[0] = 254 ;
    ba[1] = 1;
    ba[2] = 255;
    int i = listener->port->write(ba,ba.length());

    void MainWindow::clickTEST0() {
    QByteArray ba;
    ba[0] = 254 ;
    ba[1] = 1;
    ba[2] = 255;
    int i = listener->port->write(ba,ba.length());


    QString Session::enumerate(){
    QList<QextPortInfo> ports = QextSerialEnumerator::getPorts();
    int tempport = 9999;
    QString tempportname = "NULL";
    QString tempfriendname = "NULL";
    QString qstr;
    int portsize = 0;
    for (int i = 0; i < ports.size(); i++) {
    qstr =;
    if (qstr == SerialDeviceString) {
    tempport = i;
    tempportname =;
    tempfriendname =;
    } else {}
    QString portName = tempportname; // update this to use your port of choice
    if (portName == "NULL"){ qDebug() << "SerialDevice NOT FOUND portName = " << portName;
    }else{ qDebug() << " SerialDevice FOUND portName = " << portName; }
    return portName;

    PortListener::PortListener(const QString & portName) { //, int iVal){ //portName = this->enumerate();
    if (portName=="NULL"){ //NOT CONNECTED
    }else{ SetPort(portName); }

    void PortListener::SetPort(const QString & portName){
    this->port = new QextSerialPort(portName, QextSerialPort::EventDriven);
    if (port->open(QIODevice::ReadWrite) == true) {
    connect(port, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
    connect(port, SIGNAL(dsrChanged(bool)), this, SLOT(onDsrChanged(bool)));
    if (!(port->lineStatus() & LS_DSR))
    qDebug() << "warning: device is not turned on";
    qDebug() << "listening for data on" << port->portName();
    else {qDebug() << "device failed to open:" << port->errorString(); }
    emit onReadyWrite("Listener Created!");

  • I have more problem with this class in the past, now i use this project [] Maybe can help you.

  • Thanks for the reply. I am aware of QSerialDevice but I have found QextSerialPort to be extremely reliable and very effective for my requirements. It has enabled me to quickly produce a lot of successful code and I am not particularly keen to start from scratch.

    The line

    PortListener *listener = new PortListener(portName);

    seems to be the problem as it makes listener behave with local scope even though it is a member of the MainWindow class.

  • Ehehe for some user is reliable QextSerialPort, for other is QSerialDevice... why the team not join the force?
    ...this is only my consideration...sorry for the spam.

  • Normally, you should not have to start from scratch at all, since they both simply subclass QIODevice. That means most of your code can stay stable.

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