Qt : Write in file

Question

I'm learning how QT is working. I have this little code :

QApplication app(argc, argv);
QWidget fenetre;
fenetre.setFixedWidth(400);
fenetre.setFixedHeight(400);

QPushButton *bouton = new QPushButton("Quit", &fenetre);
bouton->setFixedHeight(50);
bouton->setFixedWidth(100);
bouton->move(170,310);


QLabel *label = new QLabel("Something", &fenetre);
label->move(30,200);
QLineEdit *line = new QLineEdit(&fenetre);
line->move(200,200);

QWidget::connect(bouton, SIGNAL(clicked()),qApp, SLOT(quit()));

fenetre.show();

I'm wondering how could I put the content of QLineEdit label in a file (.txt) continuously. The goal is to keep what the user put in the QLineEdit box in a text file when the program is finished.

Thanks

Answer 1

Use QFile and QTextStream to write to a file, when QLineEdit::textChanged signal is emitted as follows:

QObject::connect(line, &QLineEdit::textChanged, [](const QString& text) {
    QFile file("output.txt");

    if(file.open(QFile::WriteOnly | QFile::Text)) {
        QTextStream stream(&file);
        stream << text;
        file.close();
    }
});

The code above will connect a lambda expression to the QLineEdit::textChanged signal. The text argument of that lambda will be the changed content of your line . The code block inside the lambda simply rewrites the "output.txt" with the received text .

Answer 2

You can use QFile to Read/Write data in files text/binary format.

Button Press to save data:

void MainWindow::on_btnSaveData_clicked()
{
    writeDataInFile(ui->lineEdit->text());
}

Function Save Data:

void MainWindow::writeDataInFile(QString data)
{
    QString filePath = "D:/Your Path";
    QFile writeFile(filePath);
    if(!writeFile.open(QFile::Append | QFile::Text))
    {
        // Can't Open File.
    }
    else
    {
        if(data.length() > 0)
        {
            QTextStream in(&writeFile);
            in << data << "\r";
        }
    }
    writeFile.close();
}

This function gets a QString , opens a file ( filePath ) and appends data at the end of your file.

You can modify function and send QByteArray to the function or a Vector.

Answer 3

I'm wondering how could I put the content of QLineEdit label in a file (.txt) continuously . The goal is to keep what the user put in the QLineEdit box in a text file when the program is finished .

I can interpret these words as either you probably want to save QLineEdit content when your application is about to close or you want to save it "on a fly" , immidiately as user types something to QLineEdit . In both cases you can use some save() function like this:

void save(const QString &text)
{
    QFile f("out.txt");
    bool ok = f.open(QIODevice::WriteOnly);

    if(!ok) {
        qDebug() << "open file error!";
        return;
    }

    QTextStream stream(&f);
    stream << text;
    f.close();
}

and then apply one of these connect functions in your main :

// save on type
QObject::connect(line, &QLineEdit::textChanged, [line](const QString &text) {
    save(text);
});

// save on application close.
QObject::connect(&app, &QApplication::aboutToQuit, [line]() {
    save(line->text());
});

It is enough to use one of these connect s depending on your needs.

Note: &QApplication::aboutToQuit signal is emmitted when your application is closing either by pressing standard windows "Close" button or by pressing your custom "Quit" button.