Re: out parameter in COM method

You can, but using a trick. For example, using a local/call_as
pair of methods and some code you write for the P/S DLL:

[local]
HRESULT GetStruct([out] TestStructType** ppStruct);

[call_as(GetStruct)]]
HRESULT GetStruct_remote([out] long* psz, [out, size_is(*psz)] BYTE**
ppStruct);

You need to manually code the conversion routines for
your interface and compile and link them in the P/S DLL
(note this is in C, not C++):

#define COBJINTERFACES
#include "MIDL_header.h"

HRESULT STDMETHODCALLTYPE IFace_GetStruct_Proxy(LPVOID pThis, struct
TestStructType** ppStruct)
{
    long sz;
    return IFace_GetStruct_remote_Proxy(pThis, &sz, (BYTE**)ppStruct);
}

HRESULT STDMETHODCALLTYPE IFace_GetStruct_Stub(LPVOID pThis, long* psz,
BYTE** ppStruct)
{
    HRESULT hr = IFace_GetStruct(pThis, (struct TestStructType**)ppStruct);
    if (SUCCEEDED(hr)) {
        *psz = ?; // From the struct data
    } else {
        *psz = 0;
    }
    return hr;
}

Note I typed this based on the MIDL documentation after correcting
glaring errors, but I haven't actually compiled it.

Also note, I assumed the struct doesn't have embedded pointers.
If it does, you need to serailize it at the stub and then recreate it
at the proxy making this a true excersize in marshaling :)...

I leave the excersize in passing the struct as an [in] parameter
to you. It shouldn't be very different, but you'd be passing the
data in the opposite direction.

You'd probably quickly realize that writing a pair of methods
and the associated code each time you want to transmit a struct
quickly gets old. MIDL has more advanced mechanisms, but
I haven't used them myself, so can't provide you with snippets.
Look at the following MIDL attributes: transmit_as, represent_as,
wire_marshal, user_marshal. I'd suggest [wire_marshal] based
on the MIDL description.

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://www.mvps.org/vcfaq
=====================================

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