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

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?

cristian-adam

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

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?

Yes. On Windows the proper debugger can only be used by Microsoft products, either Visual Studio or Visual Studio Code.

cdb is their command line debugger, part of the Windows Driver SDK, and Qt Creator has a dll extension plugin which exposes a Python interface like for gdb and lldb on Linux / macOS.

But, lldb knows how to use pdb debugger files, and can handle MSVC binaries.

This makes lldb the one of the few open source debuggers on Windows that can handle MSVC compiled debug programs!

JonB

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

Yes. On Windows the proper debugger can only be used by Microsoft products, either Visual Studio or Visual Studio Code.

So, to be 100% clear: the debugger I used for MSVC code from within VS is integrated with/cannot be separated from VS? It is not cdb (nor lldb), it is not a "standalone" debugger, it must be used from some visual VS thingie? So while they made MSVC compiler and link external tools they did not expose an "interface" to the debugger part? But gdb does allow external "driving"? Of course for me using the MS stuff all inside VS I didn't worry too much about what was what.

cristian-adam

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

So while they made MSVC compiler and link external tools they did not expose an "interface" to the debugger part? But gdb does allow external "driving"? Of course for me using the MS stuff all inside VS I didn't worry too much about what was what.

Yes. The premium debugging experience is reserved for Microsoft products, or, if you want to be a hacker, and break their EULA https://github.com/mfussenegger/nvim-dap/discussions/869

I think CLion has their own version of lldb in which they optimized some things.

gdb on Windows can only debug DWARF, cannot do PDB.

JonB

@cristian-adam
Very interesting, thank you. It turns out there is some vsdbg.exe, which I take to be the actual debugger as its own executable. Which you can "drive", if you know what to send it.

I didn't care about DWARF, PDB etc. I was interested in which debuggers allow a host to "talk" to them and vice versa, send it commands, read variables, etc. Which is what Creator will require. I know gdb can do it. I didn't know there was a standalone executable for the debugger from VS, I thought it was a built in.

cristian-adam

This topic was also present as a bug report at https://qt-project.atlassian.net/browse/QTCREATORBUG-33741

Which I've fixed, and with Qt Creator 19 things would simply just work out of the box with lldb.exe.