Re: Cannot create the object

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Mon, 27 Apr 2009 13:27:23 -0400

Message-ID:

<eF$Xu11xJHA.3560@TK2MSFTNGP02.phx.gbl>

Barzo <dbarzo@gmail.com> wrote:

Only one last question, I don't understand exactly the difference
between
COM_INTERFACE_ENTRY and COM_INTERFACE_ENTRY2
In which case I have to use the second one?

Sometimes you end up deriving from an interface more than once,
indirectly:

interface ICommon {...};
interface IItf1 : public ICommon {...};
interface IItf2 : public ICommon {...};

class MyObject : public IItf1, public IItf2 {...};

In this case, the compiler needs help deciding which of the two
instances to return when queried for ICommon: note that

(ICommon*)(IItf1*)this

and

(ICommon*)(IItf2*)this

are two distinct pointers with different values. To disambiguate, you do

COM_INTERFACE_ENTRY2(ICommon, IItf1)

--
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