Question

class A
{
protected:
    int m_a;
    int m_b;
};

class B: public A
{
};

In class B i want to make m_a private.
Does the following the correct way to do it

class B:public A
{    
private:
    int m_a;
};

Won’t this result in 2 copies of m_a ?

Answer 1

The m_a in class B shadows that of class A. It is a different data member, so class B actually has three ints: A::m_a, A::m_b and B::m_a. The way to get private access to m_a in B is to “use” A::m_a privately in class B:

class A {
  int m_a;
};

class B:  public A {    
    using A::m_a;
};

class C : public B {
  void foo() { 
    m_a++; // ERROR!
  }
};