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

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.

MHMart_asc

Maybe I have the wrong debugger?

JonB

@MHMart_asc
As I wrote:: lldb is not normally a debugger you use with MSVC. It shows as in your Qt installation area. That probably comes from the MinGW you show you also have.

Under Windows you have to choose between two possible toolchains. The MinGW one (like gcc + gdb or lldb) or the MSVC one (MSVC compiler & linker and Visual Studio and debugger). I think you have a cross between the two. If you wish to use the MSVC C/C++ compiler, as shown in your screenshot, you should not be using an external debugger, you should be using the one which is part of MSVC. I do not know why you have lldb or what exactly you should do to correct it, but you should do whatever to sort it out.

MHMart_asc

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

@MHMart_asc
As I wrote:: lldb is not normally a debugger you use with MSVC. It shows as in your Qt installation area. That probably comes from the MinGW you show you also have.

Under Windows you have to choose between two possible toolchains. The MinGW one (like gcc + gdb or lldb) or the MSVC one (MSVC compiler & linker and Visual Studio and debugger). I think you have a cross between the two. If you wish to use the MSVC C/C++ compiler, as shown in your screenshot, you should not be using an external debugger, you should be using the one which is part of MSVC. I do not know why you have lldb or what exactly you should do to correct it, but you should do whatever to sort it out.

You were completely right! I now installed windows debugger from the maintenance tool and that helped (a bit).

I now do get output when using OutputDebugString(".."). But nothing yet when using qDebug() << "...";

I do get this error though:
onecore\windows\directx\database\helperlibrary\lib\perappusersettingsqueryimpl.cpp(159)\directxdatabasehelper.dll!00007FF96BB8FEED: (caller: 00007FF96BB8FD30) ReturnHr(5) tid(4b1c) 80070002 Het systeem kan het opgegeven bestand niet vinden.

So getting there. So dumb of me to have the wrong debugger

cristian-adam

@MHMart_asc For some reason you got lldb set as debugger.

lldb shipped with Qt Creator can debug MSVC programs, since lldb upstream can do this.

lldb can also do post mortem debugging by loading a minidump file, which Qt Creator with cdb cannot. It also might be faster than cdb.

In order to get the qDebug() calls printed, just make sure to:

Make sure to have Run in terminal checked
Set the environment variable QT_WIN_DEBUG_CONSOLE=attach

Then as seen in the picture below, things are just fine:

MHMart_asc

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

@MHMart_asc For some reason you got lldb set as debugger.

lldb shipped with Qt Creator can debug MSVC programs, since lldb upstream can do this.

lldb can also do post mortem debugging by loading a minidump file, which Qt Creator with cdb cannot. It also might be faster than cdb.

In order to get the qDebug() calls printed, just make sure to:

Make sure to have Run in terminal checked

Set the environment variable QT_WIN_DEBUG_CONSOLE=attach

Then as seen in the picture below, things are just fine:

Run in terminal now works, that is true! still strange that i'm not seeing this in application output though but anyhow this helps enough!

JonB

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

lldb shipped with Qt Creator can debug MSVC programs, since lldb upstream can do this.

As I have written, I am not a Windows/Qt user, but always interested to learn to help others in future. When we used MSVC/VS years ago we used compiler/linker/debugger from that. Are you saying that, if you choose to develop/debug in Creator rather than Visual Studio, you use the compiler/linker from MSVC --- because these can be invoked via command line from Creator/make --- but you do not use whatever debugger MSVC/VS comes with, because that is for visual use in Visual Studio only? But Creator can "drive" some lldb debugger (or cdb) under Windows like it does on gdb from Linux, so you use one of those?