Re: CComPtr strange behaviour

"Igor Tandetnik" <>
Mon, 27 Jul 2009 08:56:31 -0400
Alexander Lamaison wrote:

else if (riid == __uuidof(IExtractIconW))
assert(cpidl == 1);
if (cpidl == 1)
object = extract_icon_w(hwnd, apidl[0]).p;

The program still crashes. If I put the .p back, it doesn't!

Any more ideas?

What happens to the pointer _after_ folder_item_object returns? I bet
the caller just casts it to the expected interface type, without using

Ah, indeed:

CFolder::GetUIObjectOf(..., REFIID riid, void** ppv) {
    CComPtr<IUnknown> object;
    object = folder_item_object(..., riid);
    *ppv = object.Detach();

GetUIObjectOf takes an IUnknown* pointer it got from folder_item_object,
and tells the caller that it's really a pointer of type riid (which
amounts to a downcast). Due to a happy coincidence of implementation
details, this does happen to be the case when you use ".p" form in
folder_item_object, but not when you use assignment without ".p".
With best wishes,
    Igor Tandetnik

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