Quote:
Originally Posted by stax76
That sounded weird as I thought that after casting to different interfaces it will be a different address for each interface, just tried it in the debugger and it is as you say always the same address.
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Keep in mind that in C/C++ pointers are just numbers – the memory address where a certain object is located.
Consequently, doing a simple
type-cast on a
pointer type does
not change the value of the pointer (memory address) at all! All a type-cast from type
X* to type
Y* really does is, it tells the compiler to
assume that the object located at that memory address is of type Y rather than of type X – which can make sense or not. The C/C++ compiler does what you asked for, even if it results in
undefined behavior.
On the other hand, which pointer (memory address) is returned by the
QueryInterface() function
totally depends on the implementation of that function! It is possible that
QueryInterface(__uuidof(Y), ...) is implemented simply as "(Y*)this", in which case it would be equivalent to a simple type-cast – but you really can (should)
not rely on that. After all, it is just as well possible that
p->QueryInterface() returns a pointer (memory address) different from
p.