Re: class memory layout in vc 6.0
On Tue, 18 Sep 2007 18:53:21 +0200, "Sigurd Lerstad" <email@example.com>
Thanks for the answers, but unfortunately none of them helped me.
I've come up with a few examples that are problematic:
#define _PACKING 8
#define offsetofclass(base, derived) \
class Derived1 : public Object, public EmptyClass
class Derived2 : public Object, public SmallClass
class Derived3 : public EmptyClass
sizeof(Object) = 4
sizeof(Derived1) = 8
offsetofclass(EmptyClass, Derived1) = 5 ??? (This one I really don't
sizeof(Derived2) = 8
offsetofclass(SmallClass, Derived2) = 4
sizeof(Derived3) = 4
offsetofclass(SmallClass, Derived3) = 4
Also, why are Derived1 sizeof 8 while Derived3 is 4 (the empty-class
optimization doesn't always apply)
Does anybody know the exact rules ?
VC++ only does the empty base class optimization for single inheritance.
The best reference for the VC object model I know of remains Jan Gray's old
I don't recall if it talks about this optimization, but it does answer a
lot of other questions.
Visual C++ MVP
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