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[Anders Logg <logg@xxxxxxxxx>]

Thanks. Sounds reasonable.

--
Anders


On Mon, Nov 09, 2009 at 07:25:58AM -0600, Matthew Knepley wrote:
> I believe that the cast causes it to offset into the object structure. Everyone
> still
> points to the same virtual function table, but the full object structure
> consists of
> a concatenation of the individual parts for superclasses. This makes it easy to
> do casts. I had to do this when I wrote my own classes for SIDL.
>
>   Matt
>
> On Mon, Nov 9, 2009 at 7:12 AM, Anders Logg <logg@xxxxxxxxx> wrote:
>
>     I'm struggling with some problems in the implementation of automatic
>     update/interpolation during mesh refinement.
>
>     I've narrowed one of the problems down to the following simple
>     example. Say that a class C inherits from both A and B (which both
>     have member variables - this is important). Then I would expect an
>     object c of class C to have the same address/pointer as seen from all
>     three classes. But what happens is that A and C (if C inherits from A
>     first) agree on the address, but not B.
>
>     Try the following simple code:
>
>     #include <iostream>
>     using namespace std;
>
>     class A
>     {
>     public:
>      A() { cout << "A pointer: " << this << endl; }
>      int avar;
>     };
>
>     class B
>     {
>     public:
>      B() { cout << "B pointer: " << this << endl; }
>      int bvar;
>     };
>
>     class C : public A, public B
>     {
>     public:
>      C() { cout << "C pointer: " << this << endl; }
>     };
>
>     int main()
>     {
>      C c;
>
>      A* a = &c;
>      B* b = &c;
>
>      cout << "&a = " << a << endl;
>      cout << "&b = " << b << endl;
>      cout << "&c = " << &c << endl;
>
>      return 0;
>     }
>
>     The output when running the program is something like this:
>
>     A pointer: 0x7fff89a97a50
>     B pointer: 0x7fff89a97a54
>     C pointer: 0x7fff89a97a50
>     &a = 0x7fff89a97a50
>     &b = 0x7fff89a97a54
>     &c = 0x7fff89a97a50
>
>     Any ideas why this happens?
>
>
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>
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>
>
>
>

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