Re: Unusual usage of IUknown

"Gingko" <Gingko@nospam.nospam>
Wed, 2 Sep 2009 08:54:35 +0200
"Scot T Brennecke" <> a ?crit dans le message de
news: OaTBH%233KKHA.4608@TK2MSFTNGP02.phx.gbl...

All your examples do not exhibit any aggregation. I think you understand
the potential problem if you had

class V
     char * szData;
     ULONG m_cRef;
     V() : szData("V") {}
     VIRTUAL ~V() {}
     ULONG STDMETHODCALLTYPE CUnknownStub::Release()
        if (--m_cRef == 0) {
            delete this;
            return 0;
        return m_cRef;

 class W
     V v;
     char * szData;
     W() : szData("W") {}
     VIRTUAL ~W() {}

This is completely against the underlying idea of my "CUnknownStub" class
(see 6 messages earlier in this thread), and that's exactly why I wrote :

Of course I will never declare such objects as flat members of other
objects (if needed, I'll use pointers to these objects, likely protected
by CComPtr).

If I had to build it that way, I'd write something like :

class W
     CComPtr<V> v;
     char * szData;
      W() :
        v(new V),
     VIRTUAL ~W() {}

.... although, thinking to it better, even if I write it like you did, this
should actually not raise any problem :

As no member of my initial "CUnknownStub" class are implied in its
constructor nor in its destructor, these members (including "Release" and
its "delete" instruction) would be simply ignored if I aggregate it, leaving
only possible class duplication problems, if ever this can be a problem, and
the fact that nobody should try to call its "Release" member from the
outside, but who would ever think to do that ? :-)

And of course, I would never try to use "delete" on the "this" member of the
"v" aggregate, as well as I would never try to use "delete" on any object
not created by "new".

Anyway, the idea of the "CUnknownStub" class is to emulate the reference
count feature of the COM objects, so normally it is expected to not be

Normal "COM" objects are expected to not be aggregated as well.

So I still don't understand why this question has even been raised ...


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