Re: Newbee Question: How to return an void* in a VARIANT parameter?

"Alexander Nickolov" <>
Thu, 19 Apr 2007 11:41:11 -0700
Well, let's say you have the following C API (void* strongly
suggests C instead of C++):

void* GetHandle(whatever);
void UseHandle(void* handle, whatever);

Then you expose this like:

// in original interface
HRESULT GetHandle(wahtever, [out, retval] IDispatch** handler);

// handler interface
{ uuid(...), dual]
interface IHandler : IDispatch {
    HRESULT UseHandle(whatever);

class CHandler : public IDispatchImpl<IHandler, ...>, ...
    void Init(void* handle) { m_handle = handle; }
    STDMETHOD(UseHandle)(whatever) {
        ::UseHandle(m_handle, whatever);
        return S_OK;
    void* m_handle;

STDMETHODIMP class::GetHandle(whatever, IDispatch** ppDisp) {
    void* handle = ::GetHandle(whatever);

    CComObject<CHandler> *pObj = NULL;
    HRESULT hr = CComObject<CHandler>::CreateInstance(&pObj);
    if (FAILED(hr)) {
        return E_MEMORY;
    return pObj->GetUnknown()->QueryInterface(ppDisp);

Alexander Nickolov
Microsoft MVP [VC], MCSD

"Valmir" <> wrote in message
Thanks Alexander, but since I'm a newbee in C++, VC, ATL, etc, I
think it will be a little hard for me to implement.

Would you mind if I ask you to post a quick sample or some directions
on how to do that?

On 18 abr, 16:21, "Alexander Nickolov" <> wrote:

Then do as Igor said. Note this is not portable for 64-bit (in case
you care) - you want LONG_PTR for that purpose, which
maps to LONG in 32-bit and __int64 for 64-bit compilation.

Of course the better solution is to wrap all operations associated
with that void pointer and present them as a separate object
which you return to VB6. This object contains the original void
pointer internally and makes all the calls on VB6's behalf. Then
you return IDispatch* of the wrapper object.

Alexander Nickolov
Microsoft MVP [VC], MCSD

"Valmir" <> wrote in message
On 18 abr, 14:07, "Igor Tandetnik" <> wrote:

Valmir <> wrote:

Hi. I was told to develop an activeX to wrapper function calls to an
c+ + dll, in order to make this dll useful to VB 6 applications.

This another dll has some functions that return void* like the

void* OpenConfiguration(const char* tpCtrl, const char* tpPersist,
const char* tpFormat, const char* tpCripto, const char* flags, int*

How can I convert a void* which is returned by the function to a
VARIANT var that will be the parameter that VB?will pass to my

Just return it as long. I assume the only way VB program can use this
value is to pass it back to some other method of your component.
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

Exactly. This value will be passed back to the activex to call other


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