COM - Query an Interface inherited from IUnknown

[Aschratt]

Hey there,

I've got a bit a strange problem. Which means I think I already know the reason, but I do not see any way around it ^^.

But let me descripe. Basicly I've got an simple interface inherting from IUnknown:

[
    object,
    ...
]
interface IMyInterface : IUnknown {
}

So far so good. Now I want to inherit many other interfaces from this interface so that a method can use different special methods of this interface later on dynamicly in the code:

[
    object,
    ...
]
interface ISpecialInterface1 : IMyInterface {
}

[
    object,
    ...
]
interface ISpecialInterface2 : IMyInterface {
}

// ...

Everything works fine, until I e.g. call QueryInterface of a special class to get an pointer to the base interface:

STDMETHODIMP ISpecialInterface2::GetInterface(/* [out, retval] */ IMyInterface** Interface)
{
    this->QueryInterface(IID_IMyInterface, reinterpret_cast<void**>(Interface));
    return S_OK;
}

Somehow I allways get an AccessViolation Exception or an InvalidCast Exeption. I guess it is because I do not implement IMyInterface so it stays abstract. But usually this is the idea behind an interface. I allways thought the methods are pointers to the real implementations of the methods, but... I don't know ^^.

Any solutions?

Thank you,
- Aschratt.

[Zaccheus]

To help you, I think we'll need a bit more detail on what you are doing.

A question:

ISpecialInterface2 should only have pure virtual member functions, why is ISpecialInterface2::GetInterface being implemented?