DECLARE_IUNKNOWN

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The DECLARE_IUNKNOWN macro declares the three methods of the base interface for a new interface.

Syntax

#define DECLARE_IUNKNOWN                                        \
    STDMETHODIMP QueryInterface(REFIID riid, void **ppv) {      \
        return GetOwner()->QueryInterface(riid,ppv);            \
    };                                                          \
    STDMETHODIMP_(ULONG) AddRef() {                             \
        return GetOwner()->AddRef();                            \
    };                                                          \
    STDMETHODIMP_(ULONG) Release() {                            \
        return GetOwner()->Release();                           \
    };

Remarks

When you create a new interface, it must derive from IUnknown, which has three methods: QueryInterface, AddRef, and Release. This macro simplifies the declaration process by declaring each of these methods for the new interface.

This macro works only with classes that derive, directly or indirectly, from the CUnknown class.

Requirements

Requirement	Value
Header	Combase.h (include Streams.h)
Library	Strmbase.lib (retail builds); Strmbasd.lib (debug builds)

See also

COM Helper Functions

CUnknown::GetOwner

How to Implement IUnknown