one1

#include <iostream>
using std::cout;
using std::endl;
using std::string;

class Ancestor
{
  public:
  Ancestor(): var("ancestor")
  {
  }

  protected:
  string var;
};

class Child1 : public Ancestor
{
  public:
  Child1()
  {
    this->var="child1";
  }
};
class Child2 : public Ancestor
{
  public:
  void output(Ancestor &subject)
  {
    cout << subject.var << endl;
  }
};

int main()
{
  Child1 child1;
  Child2 child2;

  child2.output(child1);

return 0;
}

//$ g++ one1.cpp
//one1.cpp: В функции-члене ‘void Child2::output(Ancestor&)’:
//one1.cpp:14:10: ошибка: ‘std::string Ancestor::var’ is protected