Accessing protected members in a derived class

Question

I ran into an error yesterday and, while it\'s easy to get around, I wanted to make sure that I\'m understanding C++ right.

I have a base class with a protected memb

Answer 1

protected members can be accessed:

• through this pointer
• or to the same type protected members even if declared in base
• or from friend classes, functions

To solve your case you can use one of last two options.

Accept Derived in Derived::DoSomething or declare Derived friend to Base:

class Derived;

class Base
{
  friend class Derived;
  protected:
    int b;
  public:
    void DoSomething(const Base& that)
    {
      b+=that.b;
    }
};

class Derived : public Base
{
  protected:
    int d;
  public:
    void DoSomething(const Base& that)
    {
      b+=that.b;
      d=0;
    }
};

You may also consider public getters in some cases.