Question

Inside main.cpp

class vivek
{
    int i;
    float d;
public:
    vivek()
    {
        i = 4;
        d = 4.44;
    }
    ~vivek()
    {
        cout << "destructor" << i;
    }
    int get()
    {
        return i;
    }
};

int main()
{
    vivek *viku = new vivek;
    vivek *p;

    p = viku;
    cout << (*(int*) (p));
    getchar();

    return 0;
}

Through above code i can able to access variable i , but i want to know how can i access the variable d .

I know this concept shall not be advisable since it violates encapsulation .. But i just want to know how we can do this ?

Answer 1

While it’s extremely hacky, it is possible, because vivek is a standard-layout struct. This means you can do this:

#include <iostream>

// copied from original
class vivek {
  int i;
  float d;
public:
  vivek() {i = 4; d = 4.44; }
  ~vivek() { cout<<"destructor"<<i; }
  int get() { return i; }
};

struct vivek_sneaky_accessor {
  int i;
  float d;
};

int main() {
  vivek v;
  vivek_sneaky_accessor *acc = reinterpret_cast<vivek_sneaky_accessor*>(&v);
  std::cout << acc->d;
  return 0;
}

This relies on [class] points 7 and 8 (definition of standard-layout struct) and on [class.mem] points 17 and 20 (layout-compatibility of standard-layout structs).

Disclaimer I am in no way advocating this as a reasonable thing to do. I am just saying that it is actually possible.