Reading file as written by external process

[anthomas]

I have a log file that is being written asynchronously from a docker command using a tee. I want to either copy and/or parse the file up to the current point it is written. Is this possible with QFile or at all? Any advice is appreciated.

[Christian Ehrlicher]

What wrong with simply open the file and read it?

[mrjj]

Hi and welcome to the forums

Yes it will work.

You have to use a timer or similar to read it from time to time
Disclaimer. fast code. needs more love to be solid.

class Reader : QObject
{
    QFile file;
    QTextStream in;
    QTimer timer;
public:
   explicit Reader(QObject *parent) : QObject(parent)
    {
        connect(&timer, &QTimer::timeout, this, [this]() {
            while (!in.atEnd()) {
                QString line = in.readLine();
                qDebug() << line;
            }
        });
    }
    void Process(QString filename)
    {
        file.setFileName( filename);
        in.setDevice(&file);
        if ( ! file.open(QFile::ReadOnly)) {
            qDebug() << "open error" << file.errorString();
            return;
        }
        timer.start(1000);
        qDebug() << "started";
    }
};

using

 Reader *LogReader = new Reader(this);
LogReader->Process("e:/test.txt");

Note file must exist when you try.

[anthomas]

Got it working, thank you. Errors were unrelated to the program writing the file.