Question

From an answer on Inheritance: why is there a difference in behaviour between inherited and supplied variables?, I understand that the below code prints 0 because there is only one copy of x.

#include<iostream>
using namespace std;

class A {
    public:
        int x;
        A() { x = 10; }
};

class B : public A {
    public:
        B() { x = 0; }
};

int main() {
    A* ab = new B;
    cout << ab->x << endl; // prints 0
}

But does this not go against the very meaning of inheritance?

I coded class B to interit publicly from class A, and I expected it to inherit a copy of member variable x, which should have resulted in ab->x printing value 10.

What am I missing here? I am finding it too difficult to understand why this prints 0 despite inheritance.

Answer 1

Here is a simple figure that briefly explains inheritance in terms of member variables:

When the ChildClass is created, the BaseClass is created and exists inside the ChildClass. Variables a, b and c can be accessed from both ChildClass and Baseclass (depending on access modifiers such as public, private and protected). They’re shared, not copied.