Re: How to return parameters in an ATL COM component event function?

Christian Berczely <>
Tue, 3 Jun 2008 12:49:33 -0700 (PDT)
In the following code, I was able to also get back a BSTR from the
Client in the event.
The problem is that someone needs to allocate the BSTR. So, if the
allocation is done in the server and it is bigger than what the client
wants to pass back everything is ok, but if the allocation in the
server is smaller than what the client needs, then there is an

So, how can I make the client allocate the BSTR?

HRESULT Fire_Continue(VARIANT_BOOL * pContinue, long * pNumb, BSTR *
    T* pT = static_cast<T*>(this);
    int nConnectionIndex;
    int nConnections = m_vec.GetSize();

    CComVariant varResult;
    CComVariant* pvars = new CComVariant[3];

    // you can pass in a parameter in case it needs to be processed here
    VARIANT_BOOL vntbContinue = *pContinue;
    long lNumb = *pNumb;
    CComBSTR bsTxt;

    for (nConnectionIndex = 0; nConnectionIndex < nConnections;
        CComPtr<IUnknown> sp = m_vec.GetAt(nConnectionIndex);
        IDispatch* pDispatch = reinterpret_cast<IDispatch*>(sp.p);
        if (pDispatch != NULL)


            V_VT(&pvars[2]) = VT_BYREF | VT_BOOL;
            V_BOOLREF(&pvars[2]) = &vntbContinue;

            V_VT(&pvars[1]) = VT_BYREF | VT_I4;
            V_I4REF(&pvars[1]) = &lNumb;

            V_VT(&pvars[0]) = VT_BYREF | VT_BSTR;
            V_BSTRREF(&pvars[0]) = &bsTxt;

            DISPPARAMS disp = { pvars, NULL, 3, 0 };
            pDispatch->Invoke(0x1, IID_NULL, LOCALE_USER_DEFAULT,
DISPATCH_METHOD, &disp, &varResult, NULL, NULL);
    *pContinue = vntbContinue;
    *pNumb = lNumb;
    *pTxt = bsTxt;


    return varResult.scode;

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