Re: Interface implementation

"Victor Bazarov" <>
Thu, 14 Jun 2007 14:07:21 -0400
Galian wrote:

This is my code. Task is next: I want write template class, CUnknown,
with implemented nessesary methods (Queryinterface, Release ...), to
use it for other classes.


template < class ClassType, REFIID ObjectIID >
class CUnknown : public IUnknown

What's "IUnknown"? Are we supposed to know about it? (pun intended)
I am guessing that it's the base interface you have and it's abstract.

// IUnknown methods.
virtual STDMETHODIMP QueryInterface( REFIID riid, void** ppv )
if ( ppv == NULL )
return E_POINTER;
if ( riid == *ObjectIID || riid == IID_IUnknown )
*ppv = static_cast< ClassType* >( this );
return S_OK;
*ppv = NULL;

virtual STDMETHODIMP_( ULONG ) AddRef()
return InterlockedIncrement( &m_cRef );

virtual STDMETHODIMP_( ULONG ) Release()
LSCOPE( "CMediaBuffer::Release" );
LONG lRef = InterlockedDecrement( &m_cRef );
if ( lRef == 0 )
delete this;

// m_cRef is no longer valid! Return lRef.
return lRef;

LONG m_cRef;

#include "Unknown.h"

I am guessing that's where your 'class CUnknown' is defined, or is it?

class ISMSNotificationHandler
virtual void HandleSMSMessageReceived( const CEOID messageID ) = 0;

// IMAPIAdviseSink also derived from IUnknown

class CAdviseSinc
       // This is my CUnknown,but anyway "Cannot instantiate abstract
class" error

Does it say what function prevents it from being instantiated?

public virtual CUnknown< CAdviseSinc, IID_IMAPIAdviseSink >

, public virtual IMAPIAdviseSink

ULONG OnNotify( ULONG cNotif, LPNOTIFICATION lpNotifications );

OK. Try to change the beginning of the definition of 'CUnknown' to

template < class ClassType, REFIID ObjectIID >
class CUnknown : virtual public IUnknown

Also, do the same with IMAPIAdviseSink. What you're doing is telling
the compiler that some pure virtual functions in your 'CAdviseSink'
only exist in a single base class instance and that they are happily
overridden by the corresponding functions in 'CUnknown<blah,blah>'.

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