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.

alt text

anthomas

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