What is Friend Function in C++?

[addisoncave]

Guys,
I seriously never understood why C++ provide the friends function to access the private member of parent class? But, there is nothing like this in Java and PHP? why we use friend function? what is concept behind the use of friend function?

[arianagrand]

A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.

[hemaweb]

C++ Friend Functions. Advertisements. A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.

[Olivia Brown]

A friend function in C++ can be a function, function template, or member function, or a class or class template, in which case the entire class and all of its members are friends.

[hemaweb]

C++ Friend Functions. Advertisements. A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.

[hillajax]

A friend function is the member class of derived class which can access to the private member function of parent class without actually including them time of inheritance. We just need to use friend keyword to make them friend

[james014]

A friend function of a class which can access all the private and public member outside the class.

Some ex:
#include <iostream>

using namespace std;

class Box
{
double width;
public:
friend void printWidth( Box box );
void setWidth( double wid );
};

// Member function definition
void Box::setWidth( double wid )
{
width = wid;
}

// Note: printWidth() is not a member function of any class.
void printWidth( Box box )
{
/* Because printWidth() is a friend of Box, it can
directly access any member of this class */
cout << "Width of box : " << box.width <<endl;
}

// Main function for the program
int main( )
{
Box box;

// set box width with member function
box.setWidth(10.0);

// Use friend function to print the wdith.
printWidth( box );

return 0;
}

Result:
Width of box : 10

[SD Group Kolkata]

A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.

[Krishnabangla]

Thanks for posting.
A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.

[educaindia358]

A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class.
For more details visit Indian online education forum

[jacks]

In object-oriented programming, a friend function, that is a "friend" of a given class, is a function that is given the same access as methods to private and protected data.

[ziya.pathan]

Afriend function is the member class of derived class which can accessto the private member function of parent class without actuallyincluding them ofinheritance. We just need to use friend keyword to make them friend.

[luffy268]

A friend function of a class is defined outside that class' scope but it has the right to access all private and protected members of the class. Even though the prototypes for friend functions appear in the class definition, friends are not member functions.


A friend can be a function, function template, or member function, or a class or class template, in which case the entire class and all of its members are friends.