why can a base pointer point to derived object only under public inheritance?

Question

I think its because the base class data members and methods wont be accessible , but I\'d like some more clarity on this. Also, is this the reason why polymorphism (using vi

Answer 1

Actually, a pointer to base can point to a derived class even if the base is private. The thing is that such a conversion is impossible from outside the class. However, it's still possible to perfrom such a conversion in a context where the base is accessible.

Example:

#include 
using namespace std;

struct Base
{
    void foo() const {
        cout << "Base::foo()\n";
    }
};

struct Derived : private Base
{
    const Base* get() const {
        return this; // This is fine
    }
};

int main()
{
    Derived d;
    const Base *b = &d; // This is illegal
    const Base *b = d.get(); //This is fine
    b->foo();
}

Live example

Live example with virtual call