one0

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

class MyClass
{
  public:
  MyClass(string val="default")
  {
    this->val=val;
  }

  void output(MyClass &subject)
  {
    cout << subject.val << endl;
  }

  protected:
  string val;
};

int main()
{
  MyClass obj1;
  MyClass obj2("hello world");

  obj1.output(obj2);

return 0;
}

//$ ./a.out
//hello world