An example of legally getting access to private members in C++

private-members-access.cpp

// The code below demonstrates how to access private members without changing
// the class.  It's useful for e.g. debugging when you for some reason can't
// change a library class, but need to have some private values printed.
// Original idea by litb, see
// http://bloglitb.blogspot.com/2010/07/access-to-private-members-thats-easy.html

template<typename Pointer>
struct RobberyResult
{
    static Pointer ptr;
};
template<typename Pointer> Pointer RobberyResult<Pointer>::ptr;

template<typename Pointer, Pointer p>
struct Rob : RobberyResult<Pointer>
{
    struct Filler
    {
        Filler()
        {
            RobberyResult<Pointer>::ptr=p;
        }
    };
    static Filler filler;
};
template<typename Pointer, Pointer p> typename Rob<Pointer,p>::Filler Rob<Pointer,p>::filler;

#define STEAL_CLASS_MEMBER(member) template class Rob<decltype(&member), &member>

// ---------------- usage below ------------------------------------
#include <iostream>

class Victim
{
    int treasure=7;
    double privilegedAction(int x) { return treasure*0.14+x; }
};

STEAL_CLASS_MEMBER(Victim::treasure);
STEAL_CLASS_MEMBER(Victim::privilegedAction);
int main()
{
    Victim victim;
    std::cout << "treasure: " << victim.*RobberyResult<int Victim::*>::ptr << "\n";
    std::cout << "privileged result: " << (victim.*RobberyResult<double (Victim::*)(int)>::ptr)(23) << "\n";
}