private

C++: Simplified version of ‘Friends with benefits’ demonstrating friend classes

 in C++ / Funny  tagged friend / friend class / private by

A friend class in C++ can access the private and protected members of the class in which it is declared as a friend.

Friendship may allow a class to be better encapsulated by granting per-class access to parts of its API that would otherwise have to be public.[2] This increased encapsulation comes at the cost of tighter coupling due to interdependency between the classes.

Properties

  • Friendships are not symmetric – if class A is a friend of class B, class B is not automatically a friend of class A.
  • Friendships are not transitive – if class A is a friend of class B, and class B is a friend of class C, class A is not automatically a friend of class C.
  • Friendships are not inherited – if class Base is a friend of class X, subclass Derived is not automatically a friend of class X; and if class X is a friend of class Base, class X is not automatically a friend of subclass Derived.

From Wikipedia: https://en.wikipedia.org/wiki/Friend_class

In the following example we assign both the Man to be a friend of the Woman and the Woman to be a friend of the Man in order to allow both parties to access the private members of the other.

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#include <iostream>
using namespace std;
 
class Man;
 
class Woman {
  friend class Man;
 
public:
  void touch(Man man);
private:
  void * body;
};
 
class Man {
  friend class Woman;
 
public:
  void touch(Woman woman);
private:
  void * body;
};
 
void Woman::touch(Man man) {
  void * other = man.body;
}
 
void Man::touch(Woman woman) {
  void * other = woman.body;
}
 
int main() {
  Man man;
  Woman woman;
 
  man.touch(woman);
  woman.touch(man);
  return 0;
}