Thursday, January 17, 2008

Error While Overriding virtual methods of Directshow Baseclasses

Error While Overriding virtual methods of Directshow Baseclasses:
---------------------------------------------------------------


while overriding some fns,
I got an error ...


class CMyTransformInputPin : public CTransformInputPin
{
public :
HRESULT Receive(IMediaSample* pSample);
};

HRESULT CMyTransformInputPin :: Receive(IMediaSample* pSample)
{
HRESULT hr = S_OK;
hr = CTransformInputPin::Receive(pSample);
return hr;
}


I got an error as follows :

error C2555: 'CTemporalInputPin::Receive' : overriding virtual function differs from 'CTransformInputPin::Receive' only by return type or calling convention
baseclasses\transfrm.h(33) : see declaration of 'CTransformInputPin'


Solution :
-------------

I modified it as follows :


class CMyTransformInputPin : public CTransformInputPin
{
public :
STDMETHODIMP Receive(IMediaSample* pSample); // Modification is Here...
};

HRESULT CMyTransformInputPin :: Receive(IMediaSample* pSample)
{
HRESULT hr = S_OK;
hr = CTransformInputPin::Receive(pSample);
return hr;
}

Now It is working.For STDMETHODIMP macro expansion is as follows :



#define STDMETHODIMP HRESULT STDMETHODCALLTYPE


For STDMETHODCALLTYPE macro defn is as follows :


#ifdef _68K_
#define STDMETHODCALLTYPE __cdecl
#else
#define STDMETHODCALLTYPE __stdcall
#endif


So it varies in calling convention, So I got an error...

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