Friend function: Difference between revisions

Revision as of 04:55, 26 September 2021

Revision as of 12:41, 4 July 2023

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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>{{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.)}}

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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:

*aA function of global or [[namespace]] scope may be declared as friend of both classes.

*aA member function of one class may be declared as friend of another one.

<syntaxhighlight lang=Cpp"cpp">

// 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: