Re: Problem with VB -> C++ interface pointer

"Igor Tandetnik" <>
Mon, 27 Nov 2006 08:40:16 -0500
"spforeman" <> wrote in message

STDMETHODIMP CFoo::ProcessSpot(ISpot *pAnalysisSpot)
 CComObject<CSpot> *pSpot = 0;
 hr = pAnalysisSpot->QueryInterface(IID_ISpot, (void **)&pSpot)

What exactly is that supposed to achieve? You query for IID_ISpot, you
get back ISpot* pointer, not CComObject<CSpot>. The net effect of this
call is the same as a simple cast:

CComObject<CSpot> *pSpot =
    reinterpret_cast<CComObject<CSpot> *>(pAnalysisSpot);

Do you see now why it won't work?

When I trace through the code I can step into the code where VB sets x
and y to be -1, but when ProcessSpot is stepped into and
QueryInterface is called pSpot has garbage in the x and y values.

pSpot pointer itself is garbage.
With best wishes,
    Igor Tandetnik

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