C++ accessing memory class and changing private variable

Question

My friend made this code that will access the memory of class and change the value of a private variable.

#include <iostream>

using namespace std;

class has_private_variable
{
private:
    const int member1;
public:
    has_private_variable()
    : member1(5) //initializer list. In case you haven't seen that before
    {
    }
    int getMember1()
    {
        return member1;
    }
};

int main()
{
    has_private_variable hpv;
    int tmp = hpv.getMember1();
    cout << hpv.getMember1() << endl;
    char* ptr = (char*)&hpv; //Yeah this will generate all types of warnings hopefully
    //find the actual address of the member
    while (*(int*)ptr != tmp)
        ptr++;
    int* ptr_int = (int*)ptr;
    *ptr_int = 3;
    cout << hpv.getMember1() << endl;
    //There's a joke in here about hpv.vaccinate(), but I can't be bothered to find it
    return 0;
}

The ability to do this seems like it destroy the entire point of having a private variable. Is there some method to stop a programmer from being able to access a private variable like so?

Edit:

From the comments I'm getting, my friend is invoking undefined behavior of C++. But is there someway to it so that a programmer may not be able to do this?

Answer 1

It could be possible using a dedicated template class, the template class makes a private member and allocates it statically in an hidden memory location:

template<typename type>
class true_private
{
public:
    ~true_private()
    {
       type local;
       get_set(-1, local);
    }

    true_private(type value)
    {
       type local = value;
       get_set(0, local);
    }

    void get_set(int op, type& value)
    {
        static type* var = 0;

        if( var == 0)
            var = new type();

        if( op == 0 ) // set
            *var = value;

        else if(op == 1) // get
            value = *var;
        else  // delete
            delete var;
    }

    type Get()
    {
        type local;
        get_set(1, local);
        return local;
    }

    void Set(type value)
    {
       type local = value;
       get_set(0, local);
    }
};

class has_private_variable
{
private:
     true_private<int> member1;
public:
    has_private_variable()
    :member1(5) //initializer list. In case you haven't seen that before
    {
    }
    int getMember1()
    {
        return member1.Get();
    }
};

This is just an exercise to show the power of template class :)