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Can we access private data members of a class without using a member or a friend function?

  • Difficulty Level : Medium
  • Last Updated : 11 May, 2020

The idea of Encapsulation is to bundle data and methods (that work on the data) together and restrict access of private data members outside the class. In C++, a friend function or friend class can also access private data members.

Is it possible to access private members outside a class without friend?
Yes, it is possible using pointers. See the following program as an example.

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#include <iostream>
using namespace std;
  
class Test {
private:
    int data;
  
public:
    Test() { data = 0; }
    int getData() { return data; }
};
  
int main()
{
    Test t;
    int* ptr = (int*)&t;
    *ptr = 10;
    cout << t.getData();
    return 0;
}
Output:
10

Example 2:






/*Program to initialize the private members and 
display them without using member functions.*/
  
#include <bits/stdc++.h>
using namespace std;
  
class A {
private:
    int x;
    int y;
};
  
int main()
{
    A a;
    int* p = (int*)&a;
    *p = 3;
    p++;
    *p = 9;
    p--;
    cout << endl
         << "x = " << *p;
    p++;
    cout << endl
         << "y = " << *p;
}
Output:
x = 3
y = 9

Explanation:
In the above program, a is an object of class A. The address of the object is assigned to integer pointer p by applying typecasting. The pointer p points to private member x. Integer value is assigned to *p, that is, x. Address of object a is increased and by accessing the memory location value 9 is assigned to y. The p– statement sets the memory location of x. Using the cout statement contains of x is displayed.

Example 3:




/*Program to initialize and display
private members using pointers.*/
#include <bits/stdc++.h>
using namespace std;
  
class A {
private:
    int x;
    int y;
};
  
class B : public A {
public:
    int z;
  
    void show(int* k)
    {
        cout << "x = " << *k << " y = " 
            << *(k + 1) << " z = " << *(k + 2);
    }
};
  
int main()
{
    B b; // object declaration
    int* p; // pointer declaration
    p = &b.z; // address of z is assigned to p
    *p = 3; // initialization of z
    p--; // points to previous location
    *p = 4; // initialization of y
    p--; // points to previous location
    *p = 5; // initialization of x
    b.show(p); // passing address of x to function show()
  
    return 0;
}
Output:
x = 5 y = 4 z = 3

/*This code is contributed by Shubham Sharma.*/

Note that the above way of accessing private data members is not at all a recommended way of accessing members and should never be used. Also, it doesn’t mean that the encapsulation doesn’t work in C++. The idea of making private members is to avoid accidental changes. The above change to data is not accidental. It’s an intentionally written code to fool the compiler.

This article is contributed by Ashish Kumar. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above




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