Question

I want to read a file one line at each second using timer. Once the timer is started, read the first line, after one second, read the second line……

But there is no function to read specific line in QTextStream. Any ideas on how to achieve this?

If I run the following code, it will always returns

 QTextStream: no device
 QTextStream: no device
 QTextStream: no device
 QTextStream: no device

timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(sendmsg()));


void simulatorwindow::on_simON_clicked()
{ 
    simfile = QFileDialog::getOpenFileName(this, tr("Open"),"", tr("Files (*.txt)"));  
    QFile simfile(simfile);
    if (!simfile.open(QIODevice::ReadOnly | QIODevice::Text))
    return; 

    QTextStream textsim(&simfile); 
    timer->start(1000);
    qDebug("Start simulation");
}

void simulatorwindow::on_simOFF_clicked()
{ 
    timer->stop();
    qDebug("Stop simulation");
}

void simulatorwindow::sendmsg()
{ 

    QString line = textsim.readLine();
    QString title = line.section(',', 0,0);
    QString chopped = line.section(',', 1,1);
}

Answer 1

In on_simON_clicked you define textsim as a local variable, and you use a variable of the same name in sendmsg. But it is not the same variable!

In on_simON_clicked you should use the (apparently) member variable instead, as the local variable is not available outside the function. If you turn on more warnings in the compiler you will get a warning about having a local variable “shadow” a member/global variable.