Cannot retrieve debugging output in Qt Creator

Or you may be running a version of DebugView from Sysinternals, that causes the same result.

For me, I solved the problem by simply closing the running application built with the other qt creator. So not necessary to close the other qt creator.

Well, I had two instances of QtCreator and I could not close one of them. They work together. One workaround for this problem is redirecting your application output messages using qInstallMessageHandler.

#include "mainwindow.h"

#include <QApplication>

void redirectedOutput(QtMsgType, const QMessageLogContext &, const QString &);
QMutex debugOutMutex;

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QApplication app(argc, argv);

    qInstallMessageHandler(redirectedOutput);
    
    MainWindow w;
    w.show();
    
    return app.exec();
}

void redirectedOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
    debugOutMutex.lock();
    std::cout << QDateTime::currentDateTime().toString("hh.mm.ss.zzz  ").toStdString() <<  msg.toStdString() << std::endl;
    if (type == QtFatalMsg) {
        abort();
    }
    debugOutMutex.unlock();
}

I added a QMutex too. If your application is utilizing more than one thread, debug outputs can be mixed.

For me this error message appears when I have more than one instance of my application, not of Qt Creator.