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

JonB

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

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

I do not see anything at that link or on that page which mentions journalctl or the systemd journal. I think the "central message handler" in the docs refers to Qt's own QtMessageHandler qInstallMessageHandler(QtMessageHandler handler), which is how qDebug() etc. output their messages. When I Googled for your issue and QT_ASSUME_STDERR_HAS_CONSOLE it came across that this behaviour is specifically in the Arch pre-built. We would come across a lot more questions about this if it applied widely across Linuxes.

jronald

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

this behaviour is specifically in the Arch pre-built

But the build script is clean: https://gitlab.archlinux.org/archlinux/packaging/packages/qtcreator/-/blob/main/PKGBUILD?ref_type=heads

JonB

Then for all I know other non-Arch distros compile with QT_ASSUME_STDERR_HAS_CONSOLE=1. Whatever, if you Google like I did it seems to me this is Arch but not typical Linux distro, that's all I know.

FWIW, if you don't wish to recompile Qt itself and you don't wish to have to set environment variable QT_ASSUME_STDERR_HAS_CONSOLE before running to get desired behaviour, be ware you might either:

qputenv("QT_ASSUME_STDERR_HAS_CONSOLE", "1") as the very first statement in main(), before Q[Core]Application creation; or
Use qInstallMessageHandler() to install your own message handler which does write to stderr or similar.

jronald

reported: https://qt-project.atlassian.net/browse/QTCREATORBUG-33823

aha_1980

@jronald And to add to @JonB: You can set the environment variables for a Qt Creator Kit in Edit > Preferences > Kits > Kits. It will then be used for all new projects automatically.

Regards

MHMart_asc

I have the same issue in Windows 11;
Qt Creator 18.0.0
Qt 6.10.1 (Desktop_Qt_6_10_1_MSVC2022_64bit)

I tried the solution of adding:
QT_ASSUME_STDERR_HAS_CONSOLE =1

Did so in:

projects > run settings > environment
edit > preferences > kits > (default) > environment (both)

Unfortunately, nothing is shown in the application output. Running a completely new project (Qt widget application) with the completely new project settings and only one line added:
qDebug() << "hi!";

Any thoughts?

ps. Enabling the "run in terminal" checkbox in projects > run settings does not show me any output either in the terminal.

hskoglund

Hi, maybe you have a Visual Studio instance running (behind Qt Creator) that snatches the debug output?
A telltale sign is the text "Cannot retrieve debugging output." in Qt Creator's Application Output.

MHMart_asc

@hskoglund thank you for the suggestion

No process with "visual" in the name according to the task manager.

Nothing in the application output either...

hskoglund

Just to be sure, could you rebuild Test3 in Release mode (instead of Debug mode) and check that there's no output

MHMart_asc

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

Just to be sure, could you rebuild Test3 in Release mode (instead of Debug mode) and check that there's no output

Unfortunately, no output

hskoglund

If you try the same Windows API call that Qt uses; add
#include "windows.h"
and
OutputDebugString(L"Hello there");
does that text show up in the Appliction Output?

JonB

@MHMart_asc
...And further to @hskoglund's post --- which you should try --- I believe DebugView should still work these days(?), if you download that does your output appear inside it when you run it? Not saying you will have to stick with that, just trying to track down where your messages are going....

MHMart_asc

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

If you try the same Windows API call that Qt uses; add
#include "windows.h"
and
OutputDebugString(L"Hello there");
does that text show up in the Appliction Output?

Hi @hskoglund , thanks once more for helping. Unfortunately, nope this doesn't show in the application output.

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

@MHMart_asc
...And further to @hskoglund's post --- which you should try --- I believe DebugView should still work these days(?), if you download that does your output appear inside it when you run it? Not saying you will have to stick with that, just trying to track down where your messages are going....

Thanks to you as well. Tried this, the debug is not shown there either but I do get this:

JonB

@MHMart_asc
Hmm, I don't know what that means/shows, never seen it. Might be because you are running inside debugger/VS? I don't use Windows/MSVC/VS so not sure what is going on....

One thing: that message says error in LldbEngine. Now, like I said I am not Windows/MSVC, but what is that doing here? So far as I know lldb is to do with Linux, why is it appearing in your Windows setup?

LLDB is part of the LLVM framework, and was created to work alongside of clang++, which is the LLVM C++ compiler

hskoglund

Yeah, maybe the lldb debugger is the culprit, i.e. the snatcher of the debug output

MHMart_asc

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

@MHMart_asc
Hmm, I don't know what that means/shows, never seen it. Might be because you are running inside debugger/VS? I don't use Windows/MSVC/VS so not sure what is going on....

One thing: that message says error in LldbEngine. Now, like I said I am not Windows/MSVC, but what is that doing here? So far as I know lldb is to do with Linux, why is it appearing in your Windows setup?

LLDB is part of the LLVM framework, and was created to work alongside of clang++, which is the LLVM C++ compiler

What would your suggestion be for things that I could try to test and repair?

hskoglund

Since it's probably the lldb engine inside Qt Creator that misbehaves (the call is coming from inside the house):
try disabling code models/debuggers etc. in your Qt Creator.

cristian-adam

I just tried adding a qDebug() entry and ran the program under debugger on Windows with MSVC 2022. It all worked just fine. See below:

MHMart_asc

@cristian-adam thanks for testing, one slight difference is that i'm using 6.10.1

I think i'll reinstall

cristian-adam

@MHMart_asc I've updated the screenshot to show the Debugger set for the Kit.