redirect qDebug() to file

[sriky27]

Hi,

How to redirect the qDebug() output to a file instead of application output

Regards,
Srikanth

[lni]

Simplest way without changing code:

your_excutable > your_file
or
your_excutable >& your_file

[sriky27]

Hi,

Thank you for your reply but I would be installing the application on the device, is there any other way please suggest

-Srikanth

[^NyAw^]

Hi,

Install a message handler using "qIntallMsgHandler" and there you can use "QTextStream" to write the message to a file.

Also, think that "qDebug" only will work when the application is compiled as debug.

[spirit]

try this

#include <QApplication>
#include <QtDebug>
#include <QFile>
#include <QTextStream>
 
void myMessageHandler(QtMsgType type, const char *msg)
{
	QString txt;
	switch (type) {
	case QtDebugMsg:
		txt = QString("Debug: %1").arg(msg);
		break;
	case QtWarningMsg:
		txt = QString("Warning: %1").arg(msg);
	break;
	case QtCriticalMsg:
		txt = QString("Critical: %1").arg(msg);
	break;
	case QtFatalMsg:
		txt = QString("Fatal: %1").arg(msg);
		abort();
	}
	QFile outFile("log");
	outFile.open(QIODevice::WriteOnly | QIODevice::Append);
	QTextStream ts(&outFile);
	ts << txt << endl;
}
 
int main( int argc, char * argv[] )
{
	QApplication app( argc, argv );
	qInstallMsgHandler(myMessageHandler);	
	...
	return app.exec();
}

#include <QApplication>
#include <QtDebug>
#include <QFile>
#include <QTextStream>

void myMessageHandler(QtMsgType type, const char *msg)
{
	QString txt;
	switch (type) {
	case QtDebugMsg:
		txt = QString("Debug: %1").arg(msg);
		break;
	case QtWarningMsg:
		txt = QString("Warning: %1").arg(msg);
	break;
	case QtCriticalMsg:
		txt = QString("Critical: %1").arg(msg);
	break;
	case QtFatalMsg:
		txt = QString("Fatal: %1").arg(msg);
		abort();
	}
	QFile outFile("log");
	outFile.open(QIODevice::WriteOnly | QIODevice::Append);
	QTextStream ts(&outFile);
	ts << txt << endl;
}

int main( int argc, char * argv[] )
{
	QApplication app( argc, argv );
	qInstallMsgHandler(myMessageHandler);	
	...
	return app.exec();
}

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[sriky27]

Thanks a lot for your suggestions I appreciate it

[fullmetalcoder]

Also it is recommended to "handle" fatal messages (using abort() or exit(-1) or something akin) because that's what the default handler does and if you don't do it you're likely to end up with segfaults instead (though not necessarily at the same place so you may have a hard time tracking the bugs...).

[spirit]

Also it is recommended to "handle" fatal messages (using abort() or exit(-1) or something akin) because that's what the default handler does and if you don't do it you're likely to end up with segfaults instead (though not necessarily at the same place so you may have a hard time tracking the bugs...).

...
     case QtFatalMsg:
        txt = QString("Fatal: %1").arg(msg);
        abort();
...

...
     case QtFatalMsg:
        txt = QString("Fatal: %1").arg(msg);
        abort();
...

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[faldzip]

Qt is using that handler in the function qt_message_output() and then it's checking if the message is QtFatalMsg and generating core dump or sth, so there is no need to implement it in addition to that. Whats more it's more complicated on Windows (with msvc) than just abort() in default implementation.

[fullmetalcoder]

...
     case QtFatalMsg:
        txt = QString("Fatal: %1").arg(msg);
        abort();
...

...
     case QtFatalMsg:
        txt = QString("Fatal: %1").arg(msg);
        abort();
...

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Sorry missed that one line, I was in a bit of a rush when I read your post...