Edit .txt file in QT

Question

I have a txt file to configure settings of a serial device, which looks like this:

`R ref, version, "config_ID",                   menu language, Power timeout (hours), Number of users
R  R1   1        "Template for setting parameters"  ENGLISH        1                      1

`U ref, "user name", language, volume, number of activities
U U1    "Any user"   ENGLISH   100%      1

`A ref, "activity name",    max duration, max cycles, startingPW%, available/hidden
 A A1   "Setup stim levels" 0min          0           0%           AVAILABLE FALSE FALSE TRUE TRUE

  B SA1 1 "Engine tests"
` These limits apply to all phases
`  M ref stim, channel, max current, minPW, maxPW, freq, waveform, output name
   M CH1 1 1 120mA 10us 450us 40Hz ASYM "Channel 1"
   M CH2 1 2 120mA 10us 450us 40Hz ASYM "Channel 2"

   P P0 "Test phase" 0ms NONE 2000ms STOP STOP STOP
`                Delay  RR    rate    PW    
    O CH1 0mA  0ms    0ms   600000ns 180us RATE   
    O CH2 0mA  0ms    0ms   600000ns 180us RATE

in my program , I need to read this file and change some values and save.

for example, in the last lines of the text:

  P P0 "Test phase" 0ms NONE 2000ms STOP STOP STOP
`                Delay  RR    rate    PW    
    O CH1 0mA  0ms    0ms   600000ns 180us RATE   
    O CH2 0mA  0ms    0ms   600000ns 180us RATE

I need to change those PW values (180us) into a value adjusted through a QSlider

ui->verticalSlider_ch1->value()
ui->verticalSlider_ch2->value()

Can you show me how to access those values from the txt file and change it?

p.s.

In the above-mentioned config file, comments are enclosed in backticks `` and replaced with space characters. A single backtick ` starts a comment that continues to the end of the line.

EDIT

From the comments, I tried to breakdown the problem into three parts:

1) Reading the file and extracting the contents of the O lines, 2) using that to present a screen with sliders

   QString filename = "config_keygrip";
   QString path = QCoreApplication::applicationDirPath()+"/"+filename+".txt";
   QFile file(path);

    if(!file.open(QIODevice::ReadOnly  | QIODevice::Text))
    {
        QMessageBox::information(this, "Unable to open file for read", file.errorString());
        return;
    }

    else
    {
        QTextStream in(&file);

        while(!in.atEnd())
        {
            QString line = in.readLine();
            QString trackName("O CH1");
            int pos = line.indexOf(trackName);
            if (pos >= 0)

            {

                QStringList list = line.split(' ', QString::SkipEmptyParts); // split line and get value
                QString currVal = QString::number(ui->verticalSlider->value());
                list[3] = currVal; // replace value at position 3 with slider value

            }
        }

        file.close();
    }

here I did the change in the memory.

3. Writing back the new values to the file (with contents intact).

This is something I've difficulty implement with. How do I write those modified lines back to the original file?

Answer 1

It would be best if you keep the three steps separate, so in (untested) code:

struct Model { QVector<int> values; };
// I'm assuming you call this function when you start the program.
void MyWindow::load() {
    this->model = getModelFromFile("...");
    // set up UI according to model, this is just an example
    ui->verticalSlider->value = this->model.values[0];
    QObject::connect(ui->verticalSlider, &QSlider::valueChanged,
        [=](int value) { this->model.values[0] = value; });
    QObject::connect(ui->saveButton, &QPushButton::clicked, this, &MyWindow::saveModelToFile);
}

This allows you to manipulate the values of the Model struct with (currently 1, but possibly many) slider(s). It assumes there is a save button, which calls the following method when clicked. The gist of this method is that you open the original file for reading together with a fresh file for writing, and either copy lines (if not an O CH line) or replace the value in the line otherwise. At the end you replace the original file with the newly written file.

void MyWindow::saveModelToFile() {
    QString filename = "config_keygrip";
    QString path = QCoreApplication::applicationDirPath()+"/"+filename+".txt";

    QFile originalFile(path);
    originalFile.open(QIODevice::ReadOnly | QIODevice::Text); // TODO: error handling

    QFile newFile(path+".new");
    newFile.open(QIODevice::WriteOnly | QIODevice::Text); // TODO: error handling

    while (!originalFile.atEnd()) {
        QByteArray line = originalFile.readLine();
        if (line.contains("O CH")) {
            QStringList list = QString::fromUtf8(line).split(' ', QString::SkipEmptyParts);
            int channel = list[1].mid(2).toInt(); // list[1] is "CHx"
            list[6] = QString("%1us").arg(this->model.values[channel - 1]); // actually replace the value
            line = list.join(" ").toUtf8();
        }
        // copy the line to newFile
        newFile.write(line);
    }

    // If we got this far, we can replace originalFile with newFile.
    newFile.close();
    originalFile.close();

    QFile(path+".old").remove();
    originalFile.rename(path+".old");
    newFile.rename(path);
}

A basic implementation of getModelFromFile, without error handling and untested:

Model getModelFromFile(QString path) {
    Model ret;
    QFile file(path);
    file.open(QIODevice::ReadOnly | QIODevice::Text);
    while (!file.atEnd()) {
        QByteArray line = file.readLine();
        if (line.contains("O CH")) {
            QStringList list = QString::fromUtf8(line).split(' ', QString::SkipEmptyParts);
            int value = list[6].remove("us").toInt();
            ret.values.push_back(value);
        }
    }
    return ret;
}