How does COM select how to marshal an interface?

Question

As I get it there\'re three ways to implement marshalling in COM:

• typelib marshalling
• proxy/stub marshalling
• implementing IMarshal by the obj

Answer 1

I am a bit rusty at this, but do you have a function named blindquery in your project ? (its usually declared by the wizard if you created a C++ ATL project). Breakpoint inside the function. The function is generated by the wizard often has problems with queryinterface returning E_NOINTERFACE due to buggy code.

edit (found sample code) from my old project _blindquery

class ATL_NO_VTABLE CChildEvents :
    public CComObjectRootEx ,
    public CComCoClass,
    public IDispatchImpl
{
public:
    CChildEvents(void) :
    m_pItfMgr(0)
    {
    }

    /* called from internalQI to tear off a new blind interface */
    static HRESULT WINAPI   _BlindQuery(void *pvThis, REFIID riid, void **ppv, DWORD dw);

    DECLARE_REGISTRY_RESOURCEID(IDR_CHILDEVENTS)
    DECLARE_PROTECT_FINAL_CONSTRUCT()

    BEGIN_COM_MAP(CChildEvents)
        COM_INTERFACE_ENTRY(IChildEvents)
        COM_INTERFACE_ENTRY(IDispatch)
        COM_INTERFACE_ENTRY_FUNC_BLIND(0, _BlindQuery)
    END_COM_MAP()
};


HRESULT WINAPI CChildEvents::_BlindQuery(void *pvThis, REFIID riid, void **ppv, DWORD /* dw */ )
{
    HRESULT hr = E_NOINTERFACE;
    USES_CONVERSION;

    try
    {
        if(pvThis == NULL)
        {
            ATLASSERT(FALSE);
        }
        else
        {
            /*
            * cast the pvThis pointer to the actual class £
            * so we can use it here £
            * reinterpret_cast should be safe since we're calling ourself
            */
            CChildEvents    *pThis = reinterpret_cast < CChildEvents * > (pvThis);
            if(pThis == NULL)
            {
                ATLASSERT(FALSE);
            }
            else
            {

                    /* check to see if it matches on of our children's DIID */
                                    if(memcmp(&riid,&l_someotherguid,sizeof(GUID)) == 0) {

                        /* if so cast to a IDispatch -- the standard for event interfaces */
                        *ppv = reinterpret_cast < IDispatch * > (pvThis);

                        /* addref */
                        pThis->AddRef();

                        /* reply */
                        hr = S_OK;

                }
            }
        }
    }
    catch(...)
    {
        ATLASSERT(FALSE);
    }

    /* must not be in our map - tell them to GO FISH */
    return(hr);
}