Re: How to add new interface by extending old interface

"Igor Tandetnik" <>
Wed, 12 Mar 2008 08:37:47 -0400
"Vishal" <> wrote in message

yes its in MFC, but my query is about COM.

Not really. It's about how to implement an interface, which COM doesn't
really care much about. MFC and ATL take very different approaches to
that. I'm thoroughly familiar with ATL way, but only superficially with
MFC way (just enough to know that it's completely different from ATL's

I would like to know following things...

I have interface IA, which has some methods. Now I want to create new
interface IB, derived from IA.

interface IA{

interface IB : IA{
method1() // IS this required?
method2() // IS this required?

No, in the definition of the interface, you don't need to (in fact,
should not) repeat the declaration of inherited methods - just those
that you add above and beyond the base interface. For example, every
interface is derived from IUnknown, but you don't repeat the
declarations of QueryInterface, AddRef and Release in each interface.

In your original post, the question was stated as follows:

"Now my query is that do I need to provide the *implementation* for all
the methods in ICmdPageSite again."

Emphasis mine. So, are you asking about how to define a derived
interface, or how to implement one? The latter does depend on the
technology you use to implement COM interfaces (such as MFC or ATL).
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
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