[Qt-creator] make tries to link .obj file that will never be build

[Matthias Pospiech]

I am trying to work around the __dllspec Definitions in a case where I 
want to use a class in different dlls.
What I have done now is to move the class which is used in many project 
to a header file only
and include that in the project class file. This looks like this:

----------------->
#ifndef CAMERAIMAGE_H_
#define CAMERAIMAGE_H_

// for each project using this file this needs to be defined
#ifdef QSMXCAMERA_EXPORT
    #define QCAMERAIMAGEEXPORT QSMXCAMERA_EXPORT
#else
    #define QCAMERAIMAGEEXPORT
#endif

class QCAMERAIMAGEEXPORT QCameraImage : public QWidget
{
    Q_OBJECT
public:
...
};
#endif
<--------------

----------------->
#ifndef QCAMERAWIDGET_H
#define QCAMERAWIDGET_H

// this class is in the project and knows how to define QSMXCAMERA_EXPORT
#include "QCameraSMXGlobal.h"
#include "QCameraImage.h"

class QSMXCAMERA_EXPORT QCameraWidget : public QCameraImage
{
Q_OBJECT
public:
    explicit QCameraWidget(QWidget *parent = 0);

signals:

public slots:

};

#endif // QCAMERAWIDGET_H
<--------------

With this however I get the error
LINK : fatal error LNK1181: Eingabedatei "build\debug\QCameraImage.obj" 
kann nicht geöffnet werden.

However there is no QCameraImage.cpp which could be build. And I can not 
include such a file because then the header would be loaded with 
incorrect Export definitions.

Why is this happening and how can I get around it?
Concerning QtCreator - is there anything I can define within the .pro 
file to solve this?

Matthias