Re: CoCreateInstance inside a COM dll?

"Igor Tandetnik" <>
Fri, 24 Aug 2007 17:19:55 -0400
Donos <> wrote:

There is a small difference in what i earlier said. Please see the
inheritance list below,

interface IFirstInterface : IUnknown{};
interface ISecondInterface : IFirstInterface {};
interface IMyInterface : ISecondInterface {};

interface ITopInterface : IUnknown {};
interface IClientInterface : ITopInterface {};

Are all these interfaces implemented on the same object? In this case,
the inheritance hierarchy doesn't matter. Just list all the interfaces
in the COM map, and QueryInterface will figure it out. You can
QueryInterface from any of these interfaces to any other.

So what i am trying to do is, From inside IClientInterface, am trying
to get the interface pointer of IMyInterface.
And then i will try to pass that interface pointer as a double pointer
of ISecondInterface .

Pass where? Why as a double pointer, and not a regular pointer? You pass
a double pointer when you expect to get the interface back _from_ the
method (as in QueryInterface). You pass a regular pointer when you are
giving a valid interface _to_ the method.

What i was trying to do is typecast the IMyInterface as
ISecondInterface and then use functions of both ISecondInterface and
IMyInterface from that pointer as IMyInterface is derived from
ISecondInterface & IFirstInterface .

You don't need to cast anything. You can call methods from all of
IMyInterface, ISecondInterface, IFirstInterface and IUnknown directly on
the IMyInterface pointer.
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

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