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

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Friend class and function

Question:
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.

Answer:
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
{
public:
   A ();
   friend class B; // friend class declaration
   friend void foo (); // friend function
   friend X::X (); // friend member function of another class
private:
   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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