Creating a File-Handler Instance in a DLL

When an application specifies your file-handler DLL or stream handler, the system looks it up in the registry by its class identifier and loaded. The system then calls the DllGetClassObject function of the DLL to create an instance of the file or stream handler. The following example (written in C++) shows how a file handler creates an instance.

// Main DLL entry point.

STDAPI DllGetClassObject(const CLSID FAR& rclsid,

const IID FAR& riid, void FAR* FAR* ppv)

{

HRESULT hresult;

hresult = CAVIFileCF::Create(rclsid, riid, ppv);

return hresult;

}

HRESULT CAVIFileCF::Create(const CLSID FAR& rclsid,

const IID FAR& riid, void FAR* FAR* ppv)

{

// The following is the class factory creation and not an

// actual PAVIFile.

CAVIFileCF FAR* pAVIFileCF;

IUnknown FAR* pUnknown;

HRESULT hresult;

// Create the instance.

pAVIFileCF = new FAR CAVIFileCF(rclsid, &pUnknown);

if (pAVIFileCF == NULL)

return ResultFromScode(E_OUTOFMEMORY);

// Set the interface pointer.

hresult = pUnknown->QueryInterface(riid, ppv);

if (FAILED(GetScode(hresult)))

delete pAVIFileCF;

return hresult;

}

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