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 DllGetClassObject55NO_PZ 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;

}