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Tip of the Day
Home » Tip Bank » C++
Language: C++
Expertise: Beginner
Jul 18, 1997



Application Security Testing: An Integral Part of DevOps

Friend class and function

I need to know what the class or function called "friend" is. My teacher explained it in class, but I don't quite understand how to call it and declare it.

A friend function is allowed to access all the protected and private members of a class, just like any other member function. If the whole class is declared as a friend, any member function of that class can access the private and public members of the original class.

Here is an example:

class X
   X ();

class A
   A ();
   friend class B; // friend class declaration
   friend void foo (); // friend function
   friend X::X (); // friend member function of another class
   int i; // private member.

void bar () // non-friend
   A a;
   a.i = 10; // **error** A::i is private

void foo ()
   A a;
   a.i = 10; // **OKAY*** foo is a friend
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