Trying to use QT from DLL in simple console project but it doesn't work

[Jastot]

@jsulm, hello.
FormLoader - class with pointer on QUiLoader and some another functions...nothing more and nothing interesting.

Full error looks like:
Exception thrown at 0x00007FFCD0C91AFC (ntdll.dll) in .exe: 0xC0000005: Access violation reading location 0x0000000000000024.

I read disassembled code and see that it crashes when trying to call QApplication...

[jsulm]

@Jastot I think your problem is that you're allocating qapp as a local variable inside QtUIEditorDLL. That means it only exists inside that method, as soon as it terminates qapp is deleted. If you want to use Qt signals/slots you need to start Qt event loop calling qapp.exec().

[Jastot]

@jsulm
Well. Sadly it didn't help.
So i tried to some experiments...
I found that QApplication works in dll without exec().

now QtUIEditorDLL class is QApplication.

class QTUIEDITORDLL_EXPORT QtUIEditorDLL: QApplication

In console app i have made something like that: (believe that pointer can help...)

std::shared_ptr<QtUIEditorDLL> ptrQtUIEditorDLL(new QtUIEditorDLL(argc, argv));
	QtUIEditorDLL* test = ptrQtUIEditorDLL.get();
	test->Init();

and in dll made something like that:

QtUIEditorDLL::QtUIEditorDLL(int& argc, char** argv)
	:QApplication(argc,argv) {}

void QtUIEditorDLL::Init()
{
	QtWidgetsClassTest* test = new QtWidgetsClassTest(); // QDialog initialization worked......So QApplication works
	QUiLoader quiLoader;
	QString qstr = QCoreApplication::applicationDirPath(); // All is ok. QApplication works. in qstr i can see true way to application.
	quiLoader.addPluginPath(qstr); // same error... Exception thrown at 0x00007FFCD0C91AFC (ntdll.dll) in .exe: 0xC0000005: Access violation reading location 0x0000000000000024.

So...its problem of QUiLoader...or am i not right?
Sorry for stupid questions...

[jsulm]

@Jastot said in Trying to use QT from DLL in simple console project but it doesn't work:

So...its problem of QUiLoader...or am i not right?

Since you did not post the stack trace after the crash I don't know.
Subclassing QApplication is also not needed - adding qapp as class member should be enough.

[Jastot]

@jsulm

[jsulm]

@Jastot Is it still crashing if you allocate quiLoader on the heap (just for testing)?

[Jastot]

@jsulm
Yes. Allocate it on the heap and the same error.

[Jastot]

Well, @jsulm , I am very grateful to you. Thank you.
I have found how to fix it and don't destroy logic.

[JonB]

@Jastot said in Trying to use QT from DLL in simple console project but it doesn't work:

I have found how to fix it

Wouldn't you like to share that with us, and maybe benefit future readers? :)

[Jastot]

@JonB
OPS. forget about it:D

The main problem wasn't in QApplication as I thought initially.
QUiLoader didn't want to work and showed an error that there was no access to the address.

So i created QApplication and QUiLoader in console project and then transfer pointer to library.
I still have a question why QCoreApplication::applicationDirPath(); is ok but quiLoader->addPluginPath(qstr); which calls QApplication, is not ok...

Simple Console Project:

int main(int argc, char* argv[])
{
	std::shared_ptr<QtUIEditorDLL> ptrQtUIEditorDLL(new QtUIEditorDLL(argc, argv)); // you can use it without any ptr.
	QtUIEditorDLL* test = ptrQtUIEditorDLL.get();
	QUiLoader* quiLoader = new QUiLoader(); 
// as i can see it must be created in the same tread near QApp. Jsulm said that it not important...but it doesn't work if create it in DLL.
	test->Init(quiLoader);
}

And the library:

QtUIEditorDLL::QtUIEditorDLL(int& argc, char** argv)
	:QApplication(argc,argv){}
void QtUIEditorDLL::Init(QUiLoader* quiLoader)
{
	QString qstr = QCoreApplication::applicationDirPath();
	quiLoader->addPluginPath(qstr);
        //And it works. 
}