problem with forward declaration

[MarkoSan]

Hi to all!

I have some .h file with:

class ForwardDeclarationClass;    // forward declaration of class

class ForwardDeclarationClass;    // forward declaration of class

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In same header file there is:

class MyClass : public QGlWidget
{
    ....
    private:
        ForwardDeclarationClass* d;
}

class MyClass : public QGlWidget
{
    ....
    private:
        ForwardDeclarationClass* d;
}

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In the .cpp file I have:

...
...
...
class ForwardDeclarationClass
{
     ....
     ....
}

...
...
...
class ForwardDeclarationClass
{
     ....
     ....
}

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and after that there are defined all corresponding methods (in same .cpp file).

I try to compile this Qt project and I get following error:

forward declaration of `struct ForwardDeclarationClass'

forward declaration of `struct ForwardDeclarationClass'

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What is wrong?