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; } |
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; } |
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; } |
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)
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