Re: error C2898: HRESULT IUnknown::QueryInterface(Q**p) : member function templates cannot be virtual

From:
 tom <kamildobk@poczta.onet.pl>
Newsgroups:
microsoft.public.vc.atl
Date:
Wed, 22 Aug 2007 01:44:40 -0700
Message-ID:
<1187772280.402862.131080@x35g2000prf.googlegroups.com>
On 22 Sie, 08:53, tom <kamild...@poczta.onet.pl> wrote:

On 21 Sie, 13:49, "Igor Tandetnik" <itandet...@mvps.org> wrote:

"tom" <kamild...@poczta.onet.pl> wrote in message

news:1187687316.394719.36230@w3g2000hsg.googlegroups.com

I try to move all C-based interfaces in my application to COM. I
changed

class IMyIf
{
virtual void Foo() = 0;
}

to:

#include"unknwn.h"

__interface IMyIf : IUnknown
{
virtual void Foo() = 0;
}

but when I try to compile simple console based application with this
interface I get following error

error C2898: HRESULT IUnknown::QueryInterface(Q**p) : member function
templates cannot be virtual


Just make it

struct IMyIf : public IUnknown {
    STDMETHOD(Foo)() = 0;

};

Better still, define your interfaces in an IDL file and use
MIDL-generated header.
--


Thanks Igor,
So, your advise is to give up with __interface and use just struct,
but why ? Isn't '__interface' supposed to work with COM - I thought
that this this extension is made to work with COM easier ...
On the other side,in the future, I rewrite most important interfaces
to MIDL, it probably generates struct {} so it makes a little
difference, but
I have a bigger problem- on this machine even standard ATL project
doesn't compile ( the same error as above ), but on the second one
everythng goes with no problems. The only difference is in
preprocessed unknwn.h file - it is something like that:

typedef struct IUnknown IUnknown; // ok
typedef __interface IUnknown IUnknown; // this one doesn't compile.

Both have Visual Studio 2005 on WindowsVista. I see no difference in
project configuration ... Do you know what can be a problem ?

Thanks in advance,
Kamil- Ukryj cytowany tekst -

- Poka cytowany tekst -


Sorry for bothering you. I just run 'Find and replace in files' -
replacing all my structs, and classes with __interface and Visual
replaced those words in 'unknwn.h' too :(. Now everythings works ok -
it seems that VC does some magic with those typedefs so this template
is not a problem.

Kamil

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