Linker error

[A Former User]

Hey, I seem to get this linker error whenever i try to use anything from qt5, including it goes fine, but as soon as i call anything it bugs.

I am using qt5 inside of a dll to handle http requests but it even happens when i just construct a QApplication. Someone mentioned it could be because I didn't link qt5 and visual studio, but i have no clue on how to solve this.
error:

1>dllmain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: __thiscall QApplication::QApplication(int &,char * *,int)" (__imp_??0QApplication@@QAE@AAHPAPADH@Z)
1>dllmain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: virtual __thiscall QApplication::~QApplication(void)" (__imp_??1QApplication@@UAE@XZ)
1>dllmain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static int __cdecl QApplication::exec(void)" (__imp_?exec@QApplication@@SAHXZ)

code:

int myLibraryExec() {
	char* appName = (char*)"Project";
	int argc = 1;
	QApplication app(argc, &appName);
	return app.exec();
}

int main() {
	auto app = myLibraryExec();
	std::cout << app << std::endl;
	return 0;
}

Thanks in advance for the help!

[koahnig]

@Mehodin

Try this here:

int myLibraryExec(int argc, char *argv[]) {
	char* appName = (char*)"Project";
	int argc = 1;
	QApplication app(argc, argv);
	return app.exec();
}

int main(int argc, char *argv[]) {
	auto app = myLibraryExec( argc, argv );
	std::cout << app << std::endl;
	return 0;
}

You seem to confuse QApplication. The parameter list of main is really old back from C, which keeps a couple of surprizes.

Check it out. Just typed brain to keyboard. Not tested and not compiled.

[A Former User]

@koahnig

gives me error saying
1>c:\users\mehodin\documents\github\project\dllmain.cpp(26): error C2082: redefinition of formal parameter 'argc'

and if i completely remove

	char* appName = (char*)"Project";
	int argc = 1;

it gives same error as original post

[koahnig]

@Mehodin

Sorry, my fault, try this:

int myLibraryExec(int argc, char *argv[]) {
	QApplication app(argc, argv);
	return app.exec();
}

int main(int argc, char *argv[]) {
	auto app = myLibraryExec( argc, argv );
	std::cout << app << std::endl;
	return 0;
}

[A Former User]

@koahnig

1>dllmain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: __thiscall QApplication::QApplication(int &,char * *,int)" (__imp_??0QApplication@@QAE@AAHPAPADH@Z)
1>dllmain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: virtual __thiscall QApplication::~QApplication(void)" (__imp_??1QApplication@@UAE@XZ)
1>dllmain.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) public: static int __cdecl QApplication::exec(void)" (__imp_?exec@QApplication@@SAHXZ)

sadly didn't solve it. Since it's a dll, will it even pass argc and argv?

int myLibraryExec(int argc, char *argv[]) {
	QApplication app(argc, argv);
	return app.exec();
}

int main(int argc, char *argv[]) {
	auto app = myLibraryExec(argc, argv);
	std::cout << app << std::endl;
	return 0;
}

BOOL APIENTRY DllMain(HMODULE hModule,
	DWORD  ul_reason_for_call,
	LPVOID lpReserved
)
{
	if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
		hThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)main, (LPVOID)hModule, 0, NULL);
		if (hThread == NULL) {
			return 0;
		}
	}
	else if (ul_reason_for_call == DLL_PROCESS_ATTACH) {
	}
	else if (ul_reason_for_call == DLL_PROCESS_DETACH) {
	}
	else if (ul_reason_for_call == DLL_THREAD_DETACH) {
	}
	return TRUE;
}

[SGaist]

Hi,

Might be a silly question but are you linking your .dll against Qt's widgets module ?