Why are COM pointer arguments cast as void instead of IUnknown?
See the question and my original answer on StackOverflowIn "get-type" interface methods (like IObjectWithSite::QueryInterface
, IObjectWithSite::GetSite
, IMoniker::BindToObject
, etc...), because it wouldn't change anything, you'd have to cast anyway, except when you do require an IUnknown*
reference, but you already have it because ... you're using it (the IUknown*
reference is always the same pointer per COM rules).
IObjectWithSite::SetSite
is a "set-type" method, so it makes more sense to give you an IUnknown*
reference.
It's probably more arguable in some static methods like CoCreateInstance or CoGetObject I think they could have put IUnknown**
there instead of void**
but then, they would have two different styles. And you wouldn't be able to use the old IID_PPV_ARGS macro that's so practical to use, and recommended as a coding practice to avoid type cast errors.
I suggest you get a copy of the authoritative "Essential COM" from Don Box, and read up to page 60 (at least :-).