Trying to use QT from DLL in simple console project but it doesn't work
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@hskoglund , Hi. Thank you for help.
Try to do it like you write. Now compiler says true - that it can't use QApplication or QCoreApplication.Will try to read about treads and use something like that....cuz QApplication is blocked...
But it is really interesting. i am create an QApplication on dll...and after that it writes that QAapp is blocked... But when i create all logic (not only QApp) in console project, which is calling dll - all is work.
Best regards,
Jastot.For example put some code here. If you have some ideas - i will be happy.
part 1: app init in console and call func in dll
#include <QtWidgets> #include <QApplication> #include <QtUIEditorDLL.h> int main(int argc, char* argv[]) { //QApplication QApplication qapp(argc, argv); QtUIEditorDLL* test = new QtUIEditorDLL(); - error Access violation reading location return 0; } ////////// QtUIEditorDLL::QtUIEditorDLL() { FormLoader* formLoader = new FormLoader(); formLoader->uiLoader = new QUiLoader(); formLoader->uiLoader->addPluginPath(QApplication::applicationDirPath()); - error Access violation reading location }part 2: call in dll
int main(int argc, char* argv[]) { QtUIEditorDLL* test = new QtUIEditorDLL(); - error Access violation reading location return 0; } ////////// QtUIEditorDLL::QtUIEditorDLL() { int argc = 1; char* argv[2] = { strdup("dummy"), {} }; QApplication qapp(argc, argv); FormLoader* formLoader = new FormLoader(); formLoader->uiLoader = new QUiLoader(); formLoader->uiLoader->addPluginPath(QApplication::applicationDirPath()); - error Access violation reading location }part 3: all in console project
int main(int argc, char* argv[]) { QApplication qapp(argc, argv); FormLoader* formLoader = new FormLoader(); formLoader->uiLoader = new QUiLoader(); formLoader->uiLoader->addPluginPath(QApplication::applicationDirPath()); - all is ok. it works. return 0; } -
@Jastot What is FormLoader? Please post the whole error message.
Also, did you do debugging and check the stack trace after the crash?@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...
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@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...
@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().
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@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().
@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: QApplicationIn 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
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: QApplicationIn 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...@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 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. -
J Jastot has marked this topic as solved on
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Well, @jsulm , I am very grateful to you. Thank you.
I have found how to fix it and don't destroy logic. -
@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? :)
@JonB
OPS. forget about it:DThe 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. }
