<![CDATA[Problem in QVariantList in Qt 5.12?]]>The following code snippet used to work fine on Qt 5.4, but on 5.12 it triggers a breakpoint inside QVariant's destructor.

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	if (true)
	{
		QVariant res;

		QVariantList list;
		list.append(QVariant(true));
		res = list;
	}
	qDebug() << "App started";

	int result = a.exec();
	return result;
}

If you change the code in order to use a QVariantMap instead of a QVariantList, it does work. Anybody can tell me why?

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	if (true)
	{
		QVariant res;

		QVariantMap map;
		map.insert("1", QVariant(true));
		res = map;

	}
	qDebug() << "App started";

	int result = a.exec();
	return result;
}

Compiled for x86 using Qt 5.12 with VS2017 on Win 10.

]]>https://forum.qt.io/topic/132407/problem-in-qvariantlist-in-qt-5-12RSS for NodeMon, 19 Oct 2026 04:28:24 GMTTue, 30 Nov 2021 12:31:55 GMT60<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Wed, 01 Dec 2021 11:13:46 GMT]]>@Christian-Ehrlicher My mistake: I could not use the right runtime library switch because I had "Ignore specific default libraries" set! Now I recompiled in debug with /MT and it works! Thanks a lot.

]]>https://forum.qt.io/post/692660https://forum.qt.io/post/692660Wed, 01 Dec 2021 11:13:46 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Wed, 01 Dec 2021 05:34:30 GMT]]>As I said above - you must not mix debug and release libraries. It may work but may break suddenly due to the different msvc rntimes used. And this may also be the problem here.

/edit: you can compile your app in debug mode and use release-only libraries but only when you use the same MSVC runtime -> /MD instead /MDd

]]>https://forum.qt.io/post/692574https://forum.qt.io/post/692574Wed, 01 Dec 2021 05:34:30 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 20:39:51 GMT]]>@Maxxximo
I agree we do not know whether this is related to your issue.

But this is not a question of .lib files. At runtime you are not supposed to have some parts of your code --- DLLs or not --- compiled for debug mixed with some for release, because they call for two incompatible versions of the MS runtime (MSVCRT/MSVCRTD.DLL). If you are able to compile/link only one or the other and see if this affects your problem it would be a good idea.

]]>https://forum.qt.io/post/692546https://forum.qt.io/post/692546Tue, 30 Nov 2021 20:39:51 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 20:31:49 GMT]]>@Christian-Ehrlicher Ok, just to make it clear: Qt is built as a dynamic library, i.e. Qt5Core.lib is the import library for Qt5Core.dll. This way I definitely can build my app in debug mode and use Qt5Core.dll compiled in release.
I can set breakpoints and step into my code and watch variables, actually I've been doing this for about 7 years on this same application.
I still don't get why it does work with QVariantMap, and doesn't with QVariantList....there must be some other reason, imho.

]]>https://forum.qt.io/post/692545https://forum.qt.io/post/692545Tue, 30 Nov 2021 20:31:49 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 19:53:10 GMT]]>@Maxxximo said in Problem in QVariantList in Qt 5.12?:

why shouldn't it be possible?

Because you must not mix debug and release libraries on windows since debug libs are using msvcrtd.dll and release ones msvcrt.dll which are not compatible.

]]>https://forum.qt.io/post/692536https://forum.qt.io/post/692536Tue, 30 Nov 2021 19:53:10 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 19:45:18 GMT]]>@Maxxximo This would work fine if you always write bug-free code and use bug-free libraries.

]]>https://forum.qt.io/post/692531https://forum.qt.io/post/692531Tue, 30 Nov 2021 19:45:18 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 19:42:48 GMT]]>@Christian-Ehrlicher said in Problem in QVariantList in Qt 5.12?:

You can't even create your own app as debug version without the Qt debug libs.

This sounds strange to me, why shouldn't it be possible? It's rather common using release libraries and the only constraint is not being able to debug them!

]]>https://forum.qt.io/post/692530https://forum.qt.io/post/692530Tue, 30 Nov 2021 19:42:48 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 18:31:24 GMT]]>@Maxxximo said in Problem in QVariantList in Qt 5.12?:

I am using a Qt version that has been supplied together with a commercial system, therefore I only have the release version of Qt.

Then ask for the debug libraries then - otherwise a useful development is imo not really possible. You can't even create your own app as debug version without the Qt debug libs.

]]>https://forum.qt.io/post/692513https://forum.qt.io/post/692513Tue, 30 Nov 2021 18:31:24 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 18:28:19 GMT]]>@Christian-Ehrlicher I am using a Qt version that has been supplied together with a commercial system, therefore I only have the release version of Qt.
I checked the dependencies, and my app depends only on Qt5Core.dll, which in turn depends on msvcp140.dll and vcruntime140.dll, so it shouldn't be a problem.

]]>https://forum.qt.io/post/692512https://forum.qt.io/post/692512Tue, 30 Nov 2021 18:28:19 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 16:52:30 GMT]]>Are you sure you don't mix binaries compiled with different MSVC versions? See e.g. here: https://bugreports.qt.io/browse/QTBUG-30009

Also compile your code in debug mode (and against Qt debug libs) to see where exactly inside Qt it is crashing.

]]>https://forum.qt.io/post/692496https://forum.qt.io/post/692496Tue, 30 Nov 2021 16:52:30 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 16:00:15 GMT]]>@mchinand Here:
Breakpoint.png

]]>https://forum.qt.io/post/692487https://forum.qt.io/post/692487Tue, 30 Nov 2021 16:00:15 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 15:49:02 GMT]]>@Maxxximo Looking at the stack trace, which line of code of yours does it break on?

]]>https://forum.qt.io/post/692484https://forum.qt.io/post/692484Tue, 30 Nov 2021 15:49:02 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 15:46:15 GMT]]>@mchinand With my configuration the code faults in both Release and Debug mode. I noticed the problem because I had to upgrade to Qt 5.12 from 5.4

]]>https://forum.qt.io/post/692483https://forum.qt.io/post/692483Tue, 30 Nov 2021 15:46:15 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 15:10:48 GMT]]>@mchinand If I remove the if block it gets properly executed both in debug and release. At any rate it works in 6.2.1.

]]>https://forum.qt.io/post/692475https://forum.qt.io/post/692475Tue, 30 Nov 2021 15:10:48 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 14:40:25 GMT]]>Is this perhaps a too simplified example of your actual code? It seems that your if(true) block will probably be removed (optimized out) entirely when compiled in Release mode.

]]>https://forum.qt.io/post/692472https://forum.qt.io/post/692472Tue, 30 Nov 2021 14:40:25 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 14:37:29 GMT]]>@Maxxximo Simple console app on macOS (Qt 6.2.1) proves it works with QVariantList:

#include <QCoreApplication>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    if (true)
    {
        QVariant res;

        QVariantList list;
        list.append(QVariant(true));
        res = list;
    }
    qDebug() << "App started";

    return a.exec();
}

3a81e78f-c420-4fd8-9089-6c89295e120a-image.png

]]>https://forum.qt.io/post/692471https://forum.qt.io/post/692471Tue, 30 Nov 2021 14:37:29 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 14:32:35 GMT]]>@JonB Yeah you're right :)

but no problem with QVariantList either.

]]>https://forum.qt.io/post/692469https://forum.qt.io/post/692469Tue, 30 Nov 2021 14:32:35 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 14:25:59 GMT]]>@mpergand
You mis-read :) OP is saying QVariantMap does work for him, but QVariantList instead does not....

]]>https://forum.qt.io/post/692467https://forum.qt.io/post/692467Tue, 30 Nov 2021 14:25:59 GMT<![CDATA[Reply to Problem in QVariantList in Qt 5.12? on Tue, 30 Nov 2021 14:22:45 GMT]]>No problem here on MacOS and Qt 5.12.10

{
QVariant res;

QVariantMap map;
map.insert("1", QVariant(true));
map.insert("2", QVariant(true));
res = map;
qDebug()<<res.value<QVariantMap>();
}

output log: QMap(("1", QVariant(bool, true))("2", QVariant(bool, true)))

]]>https://forum.qt.io/post/692466https://forum.qt.io/post/692466Tue, 30 Nov 2021 14:22:45 GMT