Q_OBJECT macro and link errors

[pscheven]

Hello.

When I want to use the Q_OBJECT macro in one of my classes, I have link errors saying "unresolved external symbol" :


main.obj : error LNK2001: symbole externe non résolu "public: virtual struct QMetaObject const * __cdecl Recepteur::metaObject(void)const " (?metaObject@Recepteur@@UBAPBUQMetaObject@@XZ)
main.obj : error LNK2001: symbole externe non résolu "public: virtual void * __cdecl Recepteur::qt_metacast(char const *)" (?qt_metacast@Recepteur@@UAAPAXPBD@Z)
main.obj : error LNK2001: symbole externe non résolu "public: virtual int __cdecl Recepteur::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@Recepteur@@UAAHW4Call@QMetaObject@@H PAPAX@Z)

There's no error when I compile the same code without the Q_OBJECT macro.

Here's the code of my very simple class :


class Recepteur : public QObject
{
Q_OBJECT

public :

Recepteur(){};

public slots:
void ButtonPushedReceived()
{
printf("Le bouton a été poussé");
}
};

Thank you for your answers.

Patrick Schevenels

[Stukfruit]

You have to compile and link with the generated file from the meta object compiler (moc) as well.

(Q_OBJECT defines a bunch of methods for which the implementation is in that generated file, that's why you're getting linker errors)

[pscheven]

Thank you, but in Visual Studio 2005, isn't it done automatically ?

If it is not done automatically, can you tell me how to do it please ?

I've joined my very simple source code (2 classes in .h and .cpp files + 1 main) where I have the problem.

Thank you for your help.

Patrick Schevenels

[Stukfruit]

Afaik it's only done automatically with the full VS integration, but that's for commercial Qt users only.
The Eclipse plugin does it (somewhat) automatically as well.

As a non-commercial / open source user you can use qmake to generate project files for VS. If you don't want to use qmake, try to make a simple test project and look into the custom build step for a header file. That will give you enough information for executing moc as a custom build step yourself, without using qmake. Remember though, that for this to work, you will have to include the generated file (from the meta object compiler).

[jpn]

Make sure all header files are listed in .pro file and re-generate the .vcproj by running "qmake -tp vc". You must always re-run qmake after adding or removing Q_OBJECT macro. This will ensure that custom build steps for running moc are being updated properly.