Re: handling QueryInterface

"Igor Tandetnik" <>
Wed, 29 Nov 2006 10:55:54 -0500
Jason S <> wrote:

What are some ways of overriding the default ATL QueryInterface?

COM_INTERFACE_ENTRY_* macros. E.g. your interface map could look like

    COM_INTERFACE_ENTRY(IUnknown) // first entry must be simple

then almost all the work of QueryInterface is delegated to

My understanding of QueryInterface is that a given object has to
provide consistent transitivity, e.g. if you can ever successfully
QueryInterface from any of interfaces in set S = (I1, I2, I3, etc.) to
another, you have to always be able to get from any one of them to any
of the others, & can't decide to return E_NOINTERFACE conditionally
based on something.

I am, however, thinking of implementing an object that offers a
different set S of interfaces depending on how the object was
initialized, which appears to be legal -- my source being "Essential
COM" chapter 4 particularly page 164.

Yes, it is legal.
With best wishes,
    Igor Tandetnik

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land, and it could be dangerous sitting under them as they fly
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