mfc, QueryInterface for user defined interface is NULL in non MFC application

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mfc >> QueryInterface for user defined interface is NULL in non MFC application

by vijay » Tue, 02 Dec 2003 18:22:40 GMT

Platform: VC 6.0, NT4.0





I created a class ImyObject which is derived from CCmdTarget as given below



static const GUID IID_IMyObject =

{ 0xe71032e0, 0x60e9, 0x11d1, { 0xb1, 0xaa, 0x0, 0x0, 0x21, 0x85, 0x0,
0x10 } };



interface IMyObject: public IUnknown

{

virtual HRESULT STDMETHODCALLTYPE GetObjectPointer(DWORD* pdwPtr)

= 0;

};



class CStorage : public CCmdTarget

{

public:



.

BEGIN_INTERFACE_PART(PersistStreamObj, IPersistStream)


...

END_INTERFACE_PART(PersistStreamObj)



BEGIN_INTERFACE_PART(MyObject, IMyObject)

STDMETHOD_(HRESULT,GetObjectPointer)(DWORD* pdwPtr);

END_INTERFACE_PART(IMyObject)

.



};





IMPLEMENT_SERIAL(CStorage, CCmdTarget, 0)



BEGIN_INTERFACE_MAP(CStorage, CCmdTarget)

INTERFACE_PART(CStorage, IID_IPersistStream, PersistStreamObj)

INTERFACE_PART(CStorage, IID_IMyObject, MyObject)

END_INTERFACE_MAP()



STATSTG memstat;

IPersistStream* pPersistStm = NULL;

CoCreateInstance(statstg.clsid, NULL, CLSCTX_ALL, IID_IPersistStream,

(void**)&pPersistStm);



IMyObject* pMyObject;

HRESULT h;

h = pPersistStm->QueryInterface(IID_IMyObject,(void**)&pMyObject);



Above code is reside in a DLL and it is being executed through global
function. My problem is that



1.. QueryInterface for IID_IMyObject is NULL i.e pMyObject is NULL when
call global function from non MFC application.
2.. It works fine when call function from MFC application


May I know the reason for that problem? Is there any initialization required
before to execute above code in non-MFC application?



Thanks in advance.



Regards

Vijay



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mfc >> QueryInterface for user defined interface is NULL in non MFC application

by Trevor » Tue, 02 Dec 2003 21:47:05 GMT





below
required

Vijay,
Yes, you need to call CoInitialize(Ex), CoUninitialize.




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