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In [[object-oriented programming]], a '''friend function''', that is a "friend" of a given [[class (computer science)|class]], is a function that is given the same access as methods to private and protected [[data]].<ref>{{cite book|last=Holzner|first=Steven|title=C++ : Black Book|year=2001|publisher=Coriolis Group|___location=Scottsdale, Ariz.|isbn=1-57610-777-9|page=397|quote=When you declare a function a friend of a class, that function has access to the internal data members of that object (that is, its protected, and private data members.)}}
</ref>
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==Use cases==
This approach may be used in friendly function when a function needs to access private data in objects from two different classes.
This may be accomplished in two similar ways:
*
*
<syntaxhighlight lang=
// C++ implementation of friend functions.
#include <iostream>
using namespace std;
class Foo; // Forward declaration of class Foo in order for example to compile.
class Bar {
private:
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public:
void show(Bar& x, Foo& y);
friend void show(Bar& x, Foo& y); // declaration of global function as friend
};
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int b = 6;
public:
friend void show(Bar& x, Foo& y); // declaration of global function as friend
friend void Bar::show(Bar& x, Foo& y); // declaration of friend from other class
};
// Definition of a
void Bar::show(Bar& x, Foo& y) {
cout << "Show via function member of Bar" << endl;
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==External links==
*[http://www.codersource.net/c/ctutorials/ctutorialfriend.aspx C++ friend function tutorial] at CoderSource.net
[[Category:Method (computer programming)]]
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