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Section 5.2.6 paragraph 7 of the April 95 WP states, that for
polymorphic types, the result of a dynamic_cast<void*>(v) "is a
pointer to the complete object (12.6.2) pointed to by v". Now 
section 12.6.2 does not define the term "complete object", which
actually happens in section 1.4 paragraph 2, but the term 
"most derived class". This makes a differnce, if we pass a pointer
to a data member subobject (and not a base class subobject) to
dynamic_cast. According to 12.6.2, we would get the address of that
data member, according to 1.4, the address of the containing 
object of that data member.

Please note, that the term "complete object (12.6.2)" is also used 
in section 5.2.7, where the typeid expression is defined. Therefore 
I suppose, that in 5.2.6 and 5.2.7 "most derived object" is meant 
instead of "complete object" in both sections. Is this correct?

Example:

#include <typeinfo>
#include <iostream>

class foo1{
public:
  foo1(){};
  virtual ~foo1(){}
};

class foo2{
public:
  foo2(){};
  virtual ~foo2(){}
};

class bar:public foo1, public foo2{
public:
  foo1 f1m;
  foo2 f2m;
  bar(){};
  virtual ~bar(){}
};

int main()
{
  bar    b;
  foo1 & f1=b;
  foo2 & f2=b;
  foo1 & f1m=b.f1m;
  foo2 & f2m=b.f2m;

  cout << "  &b == " << &b   
    << "  dynamic_cast<void*>(  &b) == " << dynamic_cast<void*>(&b) << endl;
  cout << " &f1 == " << &f1
    << "  dynamic_cast<void*>( &f1) == " << dynamic_cast<void*>(&f1) << endl;
  cout << " &f2 == " << &f2
    << "  dynamic_cast<void*>( &f2) == " << dynamic_cast<void*>(&f2) << endl;
  cout << "&f1m == " << &f1m
    << "  dynamic_cast<void*>(&f1m) == " << dynamic_cast<void*>(&f1m) << endl;
  cout << "&f2m == " << &f2m
    << "  dynamic_cast<void*>(&f2m) == " << dynamic_cast<void*>(&f2m) << endl;
  return 0;
}
  

Interpreting 5.2.6 in the sense of "most derived object" would yield 
something like (at least gcc 2.7.0 does it in this way)

  &b == 0xbffffaa8  dynamic_cast<void*>(  &b) == 0xbffffaa8
 &f1 == 0xbffffaa8  dynamic_cast<void*>( &f1) == 0xbffffaa8
 &f2 == 0xbffffaac  dynamic_cast<void*>( &f2) == 0xbffffaa8
&f1m == 0xbffffab0  dynamic_cast<void*>(&f1m) == 0xbffffab0
&f2m == 0xbffffab4  dynamic_cast<void*>(&f2m) == 0xbffffab4

where "complete object" should result in

  &b == 0xbffffaa8  dynamic_cast<void*>(  &b) == 0xbffffaa8
 &f1 == 0xbffffaa8  dynamic_cast<void*>( &f1) == 0xbffffaa8
 &f2 == 0xbffffaac  dynamic_cast<void*>( &f2) == 0xbffffaa8
&f1m == 0xbffffab0  dynamic_cast<void*>(&f1m) == 0xbffffaa8
&f2m == 0xbffffab4  dynamic_cast<void*>(&f2m) == 0xbffffaa8

-- 
Bernd Anhaeupl			Tel.:  +49 9131 857787
LATE - Uni Erlangen			
Cauerstr. 7			Email: anhaeupl@late.e-technik.uni-erlangen.de
91058 Erlangen
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