Re: stroustrup, void*, and reinterpret_cast
I believe you need more than the Standard guarantees for this to work.
A more conformant way would be
if (/* co-create succeeded */)
ISomeInterface* isi = static_cast<ISomeInterface*>(out_param);
// code using isi here
It also means you can't accidentally forget the & operator.
Internally a lot of hocus-pocus happens and the API ends up calling an
implementation of a standard IUnknown method called QueryInterface that
returns a pointer to ISomeInterface like so:
class SomeInterfaceImpl : public ISomeInterface
void QueryInterface(REFIID riid, void** ppv)
*ppv = static_cast<ISomeInterface*>(this);
// remaining implementations elided for clarity
Don't all interfaces inherit IUnknown? If so, the reinterpret_cast
isn't needed at all (or a static_cast could be used just in case AddRef
has been hidden by ISomeInterface).
What I've said only addresses the casts used in a COM-like system. If I
remember correctly, to create real COM classes in C++, the compiler
needs to lay out the objects in a particular way. I've mostly seen
C-style casts in COM code; these work because of the extra requirements
COM places on the compiler's ABI. (You can create COM classes on other
compilers, but COM features won't map to C++ features. For example,
you'd have to create your own v-tables - that's how you write COM
classes in C).
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