RE: MIDL2039: interface does not conform to [oleautomation] attribute

A BSTR is defined as: OLECHAR __RPC_FAR *, so what your interface states is
to accept/return a pointer to a pointer to a OLECHAR pointer.

Remove one level of indirection in your MIDL, header and implementation files
and it should work. Not sure what type m_sDataReceived is from your code...
I just usually construct a CComBSTR from a TCHAR array like this.

STDMETHODIMP CZone::get_ZoneName(BSTR *pVal)
{
if (m_pIAreIZon != NULL)
{
CComBSTR bstr(m_pIAreIZon->ZoneIName); // TCHAR Array
*pVal = bstr.Copy();
} else {
CComBSTR bstr;
*pVal = bstr.Copy();
}
return S_OK;
}


"TxITGuy" wrote:

> Hello,
>
> I am having a curious (and mildly frustrating) problem with a COM component
> I am writing in C++. Every method and event works flawlessly in both the
> ActiveX Control Test container and in a Visual Basic application. I just
> tried to add my first property (get, read-only) to the class, though, and
> can't figure out how to get Visual Basic to accept it.
>
> Here are the declaration and definition statements from C++:
>
> IDL:
> [propget, id(6), helpstring("Contains the data returned by the most recent
> HTTP request.")] HRESULT Data([out, retval] BSTR* *pVal);
>
> Declaration:
> STDMETHOD(get_Data)(/*[out, retval]*/ BSTR* *pVal);
>
> definition:
> STDMETHODIMP CHTTP::get_Data(BSTR **pVal)
> {
> CComBSTR bsData;
> bsData = m_sDataReceived.c_str(); //convert string to BSTR
> **pVal = bsData.Copy(); //I read on
> //
> "http://www.roblocher.com/
> //
> whitepapers/oletypes.aspx"
> //that
> this was the way to get a
> //OLE
> compatible BSTR pointer.
> //Any
> other ideas are welcome.
> return S_OK;
> }
>
> When compiled, the IDL declaration produces the following warning:
>
> MIDL2039 : interface does not conform to [oleautomation] attribute : [
> Parameter 'pVal' of Procedure 'get_Data' ( Interface 'IHTTP' ) ]
>
> It finishes the build process normally, though, without any other errors or
> warnings.
>
> When I attempt to use the control on a Visual Basic form (with early
> binding), however, I receive the following error if I try to read the Data
> property:
>
> "Function or interface marked as restricted, or the function uses an
> automation type not supported in Visual Basic."
>
> The Visual Basic object browser lists this property as returning a String,
> though, which is what I wanted and expected ... and supposedly is supported
> by Visual Basic.
>
> The only difference between this BSTR and the other BSTRings in the
> component is that this one is passed as a pointer. I tried changing the
> declaration to to eliminate the pointers, but C++ really didn't like that at
> all.
>
> There doesn't seem to be much documentation on OLE data type requirements
> around, at least not that I've been able to locate. Does anyone know how to
> create a BSTR property that Visual Basic will accept?
>
> Thanks,
> Ben
.

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