[solved]Use x64 DLL

catalin1122

Hello guys,

I want to use in Qt a DLL build in VS2012 on x64. DLL's name is TestDllToQT and it contains a class named Sum.

Sum.h

#pragma once
#define GAME_API  __declspec (dllexport)

class GAME_API Sum
{
private:
	int a;
	int b;
public:
	Sum(void);
	~Sum(void);
	void setA( int val) { a = val; }
	void setB( int val) { b = val; }
	int SumAandB();
};

Sum.cpp

#include "Sum.h"

Sum :: Sum(void)
{
}

Sum :: ~Sum(void)
{
}

int Sum :: SumAandB()
{
	return a+b;
}

SocketTest.pro


QT       += core
QT       -= gui

TARGET = SocketTest
CONFIG   += console
CONFIG   -= app_bundle

TEMPLATE = app

SOURCES += main.cpp \

win32: LIBS += -L$$PWD/Dependencies/ -lTestDllToQT

INCLUDEPATH += $$PWD/Dependencies
DEPENDPATH += $$PWD/Dependencies

win32:!win32-g++: PRE_TARGETDEPS += $$PWD/Dependencies/TestDllToQT.lib
else:win32-g++: PRE_TARGETDEPS += $$PWD/Dependencies/libTestDllToQT.a

Main.cpp

#include <QCoreApplication>
#include "myserver.h"
#include <QLibrary>
#include <Sum.h>


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

    Sum adn;

    adn.setA(5);

    adn.setB(7);

    qDebug()<<adn.SumAandB();


    return a.exec();
}

And these are the errors that i get:

main.obj : error LNK2019: unresolved external symbol "public: __thiscall Sum::Sum(void)" (??0Sum@@QAE@XZ) referenced in function _main
main.obj : error LNK2019: unresolved external symbol "public: __thiscall Sum::~Sum(void)" (??1Sum@@QAE@XZ) referenced in function _main
main.obj : error LNK2019: unresolved external symbol "public: int __thiscall Sum::SumAandB(void)" (?SumAandB@Sum@@QAEHXZ) referenced in function _main
release\SocketTest.exe : fatal error LNK1120: 3 unresolved externals

If i build the DLl on x32 it builds in Qt and everything works fine. The problem appears when i build it on x64.

What can I do to make it work?

Thank you!

SGaist

Hi,

Are you trying to link your 64bit DLL with a 32bit Qt build ?

catalin1122

@SGaist
Yes.

Franckynos

@catalin1122 said:

TestDllToQT.lib

It's impossible, you need to have your TestDllToQT.lib compile in the same architecture.

catalin1122

@Franckynos
Is there a way to make my Qt project x64 and compatible with the dll? I could compile the dll in x32 but I would prefer not to.

SGaist

Use a 64bit Qt build

Franckynos

@catalin1122
http://tver-soft.org/qt64

Here there was pre-build qt x 64 but the server not respond. :(
You need to find (or compile) qt in 64 bits

(http://sourceforge.net/projects/qt64ng/files/qt/x86-64/5.4.2/mingw-5.1/seh/)

catalin1122

I've downloaded msvc2012 from here and Qt Creator 3.5.0 x64 from here. I have installed them and changed the kit and compiler but i still get those errors.

Any ideas?

belab

Hi catalin1122,
when linking against your dll you have to import the symbols, when creating the dll the symbols have to be exported this is usually done with some macros like in the following link - http://stackoverflow.com/questions/538134/exporting-functions-from-a-dll-with-dllexport

catalin1122

@belab
Hi,
I did that, except the part extern "C".

When I import the DLL how do I do it in Qt? Now I do it statically (in *.pro) and I get those errors. The thing is that when I compile the DLL on x32 it works the way I do it. But not in x64.

SGaist

You just defined the export not import. Qt's Creating Shared Library documentation chapter explain how to do it properly

hskoglund

Hi, SGaist is correct, just want to add, to see an example how to use Q_DECL_EXPORT and Q_DECL_IMPORT, you can create a test project in Qt Creator: New File or Project, Library, C++ Library. Look in the xxx_global.h file created...

catalin1122

@SGaist @hskoglund @belab @Franckynos
Thank you for helping me!

You were right, I did not import the symbols.

I added this :

#ifdef GAME_EXPORTS
#    define  GAME_API __declspec(dllexport)
#else
#    define  GAME_API __declspec(dllimport)
#endif

to my DLL code and now everything works.

Have a nice day, you rock! :-)