Exceptional C++ Style 40 New Engineering Puzzles, Programming Problems, and Solutions

Chapter 15. Uses and Abuses of Access Rights

Difficulty: 6

Who really has access to your class's internals? This Item is about forgers, cheats, pickpockets, and thieves and how to recognize and avoid them.

JG Question

1. What code can access the following parts of a class?

   1. public

   2. protected

   3. private

Guru Question

1. Consider the following header file:

   // File x.h
   //
   class X {
   public:
    X() : private_(1) { /*...*/ }
   
    template<class T>
    void f(const T& t) { /*...*/ }
   
    int Value() { return private_; }
   
    // …
   
   private:
    int private_;
   };
   

   Demonstrate:

   1. a non-standards-conforming and non-portable hack; and

   2. a fully standards-conforming and portable technique

   for any calling code to get direct access to this class's private_ member.

1. Is this a hole in C++'s access control mechanism, ...