Question

Possible Duplicate:
Printing derived class name in base class

I am using GCC, and the following code output something unexpected

#include <iostream>
#include <typeinfo>
using namespace std;

class B {
  public:
  B ( B * ptr) { cout<< typeid(*ptr).name()<<endl;}
};

class  D : public B {
  public:
  D() : B(this) { cout<<typeid(this).name()<<endl;}
};

int main()
{
    D d;
    return 0;
}

output:

1B
P1D

Can anyone please explain to me why here the base class cannot tell the type of the derived class correctly?
Many thanks

Answer 1

Two reasons:

1. The object (*ptr) hasn’t been fully constructed yet.
2. Your classes are not polymorphic (no virtual member functions), so no dynamic type information exists.