Insert something into certain line and column of text file

[hajh90]

I'm newbie and using qt creator. I want to make loop to read until 11th line from beginning of my text file.
After read read until 11th line of text file, i want to the double spin box value to 11th line.
My code does not work well. If explain just like use QTextStream, then i cannot understand. I'm newbie.
Can anyone know? and explain detail to newbie?
My text file is large, and qt version is 5.13

void MainWindow::on_doubleSpinBox_6_editingFinished()
{
    QString file("D:\\my text file name");
    QFile outputFile(file);
    if (outputFile.open(QIODevice::ReadWrite | QIODevice::Text))
    {
        int i=0;
        while (true)
        {
            if(i==10)
            {
                QTextStream stream(&outputFile);
                file = stream.readLine();
                stream << QString::number(ui->doubleSpinBox_6->value());
                break;
            }
            else
            {
                i=i+1;
            }
        }
 
    }
 
    outputFile.close();

void MainWindow::on_doubleSpinBox_6_editingFinished()
{
    QString file("D:\\my text file name");
    QFile outputFile(file);
    if (outputFile.open(QIODevice::ReadWrite | QIODevice::Text))
    {
        int i=0;
        while (true)
        {
            if(i==10)
            {
                QTextStream stream(&outputFile);
                file = stream.readLine();
                stream << QString::number(ui->doubleSpinBox_6->value());
                break;
            }
            else
            {
                i=i+1;
            }
        }

    }

    outputFile.close();

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[Lesiok]

I'm newbie and using qt creator. I want to make loop to read until 11th line from beginning of my text file.
After read read until 11th line of text file, i want to the double spin box value to 11th line.
My code does not work well. If explain just like use QTextStream, then i cannot understand. I'm newbie.
Can anyone know? and explain detail to newbie?
My text file is large, and qt version is 5.13

void MainWindow::on_doubleSpinBox_6_editingFinished()
{
    QString file("D:\\my text file name");
    QFile outputFile(file);
    if (outputFile.open(QIODevice::ReadWrite | QIODevice::Text))
    {
        int i=0;
        while (true)
        {
            if(i==10)
            {
                QTextStream stream(&outputFile);
                file = stream.readLine();
                stream << QString::number(ui->doubleSpinBox_6->value());
                break;
            }
            else
            {
                i=i+1;
            }
        }
 
    }
 
    outputFile.close();

void MainWindow::on_doubleSpinBox_6_editingFinished()
{
    QString file("D:\\my text file name");
    QFile outputFile(file);
    if (outputFile.open(QIODevice::ReadWrite | QIODevice::Text))
    {
        int i=0;
        while (true)
        {
            if(i==10)
            {
                QTextStream stream(&outputFile);
                file = stream.readLine();
                stream << QString::number(ui->doubleSpinBox_6->value());
                break;
            }
            else
            {
                i=i+1;
            }
        }

    }

    outputFile.close();

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I think you must first learn the basics - C++. There is no point in using an extensive library when you do not know the basics of the language. What you want to get and the code you write are two different things.

[ChrisW67]

My code does not work well. If explain just like use QTextStream, then i cannot understand. I'm newbie.
Can anyone know? and explain detail to newbie?
My text file is large, and qt version is 5.13

I think you are missing some basic understanding that is not really anything to do with Qt.

The first blind alley you are going down is assuming that you can insert into a text file in-situ. Text files are inherently sequential files with "records" (lines) of varying length. You cannot insert bytes without rewriting every byte that follows. This is why there are two separate files, one being read and the other written, mentioned in my response to your initial post. Files open ReadWrite (as you have tried) will generally be binary data in blocks of known length that are accessed at random, allowing a block to be overwritten without affecting the block before/after.