qDebug() doesn't show messages in Qt Creator/Application Output

[jronald]

Env

arch linux
KDE Plasma 6.5.3
Qt Creator 18.0.0
Qt 6.10.1

Problem

Running in debug mode, qDebug() doesn't show messages in Qt Creator/Application Output, but when running in a terminal manually, it shows.

Codes

#include <QDebug>

int main()
{
    qDebug() << "Test123";
    qDebug() << "Test456";
    
    return 0;
}

[jronald]

It works after adding QT_ASSUME_STDERR_HAS_CONSOLE=1 in "Projects/Run Settings/Environment".
But I don't know why.

[Axel Spoerl]

Hi and welcome @jronald !
please add qInfo() << QT_VERSION_STR << QT_DEBUG and post the output here.
Cheers
Axel

[Axel Spoerl]

BTW, I have the impression that main() doesn't get called at all.
That's because of a signature mismatch, probably.
Usually the function has this signature:

int main(int argc, char *argv[])

[aha_1980]

@Axel-Spoerl In principle you are right, but I don't think thats the problem here. int main() is even the default in the C++ template in Creator and that works.

Interesting though, what happens under the hood so the linker does not complain.

Regards

[JonB]

It does not matter whether you declare main() with parameters or not. It's a C function. It gets linked/called (and caller passes parameters even if not declared as received) by its name being main(), regardless.

[Christian Ehrlicher]

I would guess there is an external logging config somewhere. Please read https://doc.qt.io/qt-6/qloggingcategory.html#configuring-categories

[JonB]

@Christian-Ehrlicher
To be fair the OP reports

Running in debug mode, qDebug() doesn't show messages in Qt Creator/Application Output, but when running a terminal manually, it shows.

Assuming the executable is compiled the same (e.g. either debug or release) whether it is run from Creator or from a terminal how would some "external logging config" allow for output to terminal in the latter case but not the former? Unless you mean the environment differs such that this logging file is picked up when running from Creator but not outside?

@jronald
You might verify that if compiled for release instead the behaviour is the same? Also if executed from Creator but as Run rather than Debug does that make any difference?

[jronald]

@Axel-Spoerl said in qDebug() doesn't show messages in Qt Creator/Application Output:

Hi and welcome @jronald !
please add qInfo() << QT_VERSION_STR << QT_DEBUG and post the output here.
Cheers
Axel

#include <QDebug>
#include <QtVersion>

int main()
{
#ifdef QT_DEBUG
    qDebug() << "Test123";
    qInfo() << QT_VERSION_STR;
#else
    qDebug() << "Test456";
    qInfo() << QT_VERSION_STR;
#endif
    return 0;
}

can't output QT_DEBUG as QT_VERSION_STR does, so do it as above.
Still no output in "Qt Creator/Application Output", but when run it in a terminal manually, it outputs as below:

Test123
6.10.1

[jronald]

@JonB said in qDebug() doesn't show messages in Qt Creator/Application Output:

You might verify that if compiled for release instead the behaviour is the same? Also if executed from Creator but as Run rather than Debug does that make any difference?

I've tried debug only.
I tried release just now, same as debug, no output in "Qt Creator/Application Output", output in a terminal.

[jronald]

If check "Projects/Run Settings/Run in terminal", it will show the messages by qDebug() and qInfo().

[jronald]

It works after adding QT_ASSUME_STDERR_HAS_CONSOLE=1 in "Projects/Run Settings/Environment".
But I don't know why.

[jronald]

https://bbs.archlinux.org/viewtopic.php?id=259035

Log from Qt Creator is redirected to systemd journal.
Maybe Arch Linux maintainers should change some build flag(s) for Qt Creator.

I've checked journalctl, the outputs are there.
It should be the cause of archlinux, not intuitive, and leaves unnecessary footprints.

[JonB]

@jronald
That looks like it to me for Arch, well found! I can only say I always have Qt from Ubuntu repo and it works, you don't need to set an environment variable.

[jronald]

@JonB said in qDebug() doesn't show messages in Qt Creator/Application Output:

I can only say I always have Qt from Ubuntu repo and it works, you don't need to set an environment variable.

It's the default behaivor of Qt to output to journelctl on linux, https://doc.qt.io/qt-6/qtlogging.html#qDebug

qDebug(const char *format, ...)
Logs debug message format to the central message handler.

I think ubuntu has changed this in a good way.