Re: class memory layout in vc 6.0

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) \
      ((DWORD)(static_cast<base*>((derived*)_PACKING))-_PACKING)

class Object
{
public:
   virtual ~Object();
};

class EmptyClass
{
};

class SmallClass
{
char member;
};

class Object
{
virtual ~Object();
};

class Derived1 : public Object, public EmptyClass
{
};

class Derived2 : public Object, public SmallClass
{
};

class Derived3 : public EmptyClass
{
public:
virtual ~Derived3()
{
}
};

sizeof(Object) = 4

sizeof(Derived1) = 8
offsetofclass(EmptyClass, Derived1) = 5 ??? (This one I really don't
understand)

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 ?