Question

If I create a static const in the base class of my hierarchy, can I redefine its value in a derived class?

edit:

#include <iostream>

class Base
{
public:
  static const int i = 1;
};

class Derived : public Base
{
public:
  static const int i = 2;
};

int main()
{
  std::cout << "Base::i == " << Base::i << std::endl;
  std::cout << "Derived::i == " << Derived::i << std::endl;  

  Base * ptr;

  ptr= new Derived;

  std::cout<< "ptr=" << ptr->i << std::endl;

  return 0;
}

…ptr refers to Base::i, which is undesirable.

Answer 1

Access via ptr to static members is via its declared type Base * and not its runtime type (sometimes Base *, sometimes Derived *). You can see this with the following trivial extension of your program:

#include <iostream>

class Base
{
public:
    static const int i = 1;
};

class Derived : public Base
{
public:
    static const int i = 2;
};

int main()
{
    std::cout << "Base::i == " << Base::i << std::endl;
    std::cout << "Derived::i == " << Derived::i << std::endl;  

    Base *b_ptr = new Derived;
    std::cout<< "b_ptr=" << b_ptr->i << std::endl;

    Derived *d_ptr = new Derived;
    std::cout<< "d_ptr=" << d_ptr->i << std::endl;

    return 0;
}

Output:

Base::i == 1
Derived::i == 2
b_ptr=1
d_ptr=2