Access to private members and methods in C++

How to use it

Copy privablic.h into your project and #include "privablic.h", and for easy reading, add:

using namespace privablic;

Now, suppose you know the implementation of a class (or a struct) like that:

class Sheep 
{
public:
    Sheep(std::string name_) : name{ std::move(name_) } {}
    
private:
    // Data
    std::string name;
    static int TOTAL;

    // Functions
    void baa() { std::cout << name << ": Baa! Baa!\n"; };
    
    static void FlockCount() 
    {
      std::cout << "sheperd actually counted " << TOTAL << " sheep\n";
    }
};

int Sheep::TOTAL = 42;

You only have to map some stubs according to types of members and/or methods signatures:

Instance Member

struct Sheep_name { typedef string (Sheep::*type); };
template class private_member<Sheep_name, &Sheep::name>;

Instance Method

struct Sheep_baa { typedef void(Sheep::*type)(); };
template class private_method<Sheep_baa, &Sheep::baa>;

Static Instance Member

struct Sheep_TOTAL { typedef int *type; };
template class private_member<Sheep_TOTAL, &Sheep::TOTAL>;

Static Instance Method

struct Sheep_FlockCount { typedef void(*type)(); };
template class private_method<Sheep_FlockCount, &Sheep::FlockCount>;

Then, using an instance of Sheep, you can access the private members like this:

Sheep dolly = Sheep("Dolly");

// now we have a sheep under our complete control:

// - change dolly's identity
dolly.*member<Sheep_name>::value = "Lilly";

// - make dolly baa
(&dolly->*func<Sheep_baa>::ptr)();

// - steal dolly
int flockCount = *member<Sheep_TOTAL>::value -= 1;

// - let the sheperd realize it
(*func<Sheep_FlockCount>::ptr)();

Output:

Lilly: Baa! Baa!
sheperd actually counted 41 sheeps

Tested compilers which works with

clang

Works under OSX

gcc

GCC 7.x (at least!)

msvc

Tested successfully for accessing protected members in Unreal Engine 5 in derived classes under Windows 11

Credits

• Johannes Schaub (litb)
• Dave Abrahams
• Christof Warlich

License

Copyright 2017 Michelangelo Altamore. It may be redistributed under the terms specified in the LICENSE file.