Thread: How actually is a derived class implementation on inheritance ?

How actually is a derived class implementation on inheritance, as class is just abstract.
E.g.

Code:

class A {public: int x;};
class B : public A {int y;};

Does a B object instantly "realize" having A member.

Code:

int main()    {

A a;
B b;
a.x =7;
b.x += 3;   // How is inheritance supposed to be?
                 // how will be b.x =10?

}