Can We Access Private Data Members of a Class without using a Member or a Friend Function in C++?

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. 
So, is it possible to access private members outside a class without friend? Yes, it is possible using pointers. Although it’s a loophole in C++, yes it’s possible through pointers.

Example 1:

CPP

// CPP Program to initialize the private members and display
// them without using member functions

#include <bits/stdc++.h>
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:

CPP

// CPP 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;
};

// Driver Code
int main()
{
    A a;
    int* p = (int*)&a;
    *p = 3;
    p++;
    *p = 9;
    p--;
    cout << endl << "x = " << *p;
    p++;
    cout << endl << "y = " << *p;
    return 0;
}

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. The 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:

CPP

// CPP 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()
{
    // object declaration
    B b;

    // pointer declaration
    int* p;

    // address of z is assigned to p
    p = &b.z;

    // initialization of z
    *p = 3;

    // points to previous location
    p--;

    // initialization of y
    *p = 4;

    // points to previous location
    p--;

    // initialization of x
    *p = 5;

    // passing address of x to function show()
    b.show(p);

    return 0;
}

Output:

x = 5 y = 4 z = 3

Note: In 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.

Time Complexity : O(1)

Auxiliary Space: O(1)