Re: Returning interface pointer from a COM component

"Igor Tandetnik" <>
Sat, 18 Jul 2009 20:44:21 -0400
<#W7ESoACKHA.4004@TK2MSFTNGP05.phx.gbl> wrote:

CFirstObject :: FinalContructor()
    //Here I create the encapsulated COM object
    CComObject<CLevel1>::CreateInstance( &m_objILevel1);

Be aware that CComObject::CreateInstance creates an object with initial
reference count of zero. If you want to keep the pointer long term, it's
a good idea to AddRef it. Otherwise, the object may be destroyed

STDMETHODIMP CFirstObject :: GetLevel1( ILevel1** ppL1)
     //Returning to Interface pointer: Which one is among these is
        ILevel* pLevel1;
          m_objILevel1->QueryInterface(IID_ILevel1, (void**)ppL1 );

QueryInterface already AddRef's.

         pLevel1 = (*ppL1);

What's that supposed to achieve?

         *ppL1 = (ILevel1*)m_objILevel1;

Both a) and b) would work, once you remove an extraneous AddRef in a).

    //Calling interface method from inside

Both would work if DoSomething is a method on ILevel1 interface. a) has
the advantage that you can call any method on CLevel1 class, including
those not exposed via COM.

class ATL_NO_VTABLE CLevel1 : public IDispatchImpl<ILevel1

When you were calling DoSomething above, you weren't passing any
With best wishes,
    Igor Tandetnik

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