C++ Class:14
Friend Function
Friend Class
Friend
Functions and Friend Class
Friend Function:
A friend function can access
the private and protected data of a class. We declare a friend
function using the friend keyword inside the body of the class.
class className {
... .. ...
friend returnType
functionName(arguments);
... .. ...
}
Similar to friend class, this function can access the private and protected
members of another class. A global function can also be declared as friend as
shown in the example below:
Friend Function Example
#include <iostream>
using namespace std;
class XYZ {
private:
int num=100;
char ch='Z';
friend void disp(XYZ obj);
};
void disp(XYZ obj){
cout<<obj.num<<endl;
cout<<obj.ch<<endl;
}
int main() {
XYZ obj;
disp(obj);
return 0;
}
Output:
100
Z
1. The Friend Functions are used to access the member
variables of the class indirectly.
2. It is a not a member function of a class. It is a friend function of the class.
3. We define the friend function outside the class.
4. it can be declared either in public or private.
5. It has object as an argument.
6. It can access the member variables with the use of
the objects of that class.
Friend Class:
A friend class is a class that can access the private and
protected members of a class in which it is declared as friend.
This is needed when we want to allow a particular class to access the private
and protected members of a class.
we can also use a friend Class in
C++ using the friend keyword. For example,
class ClassB;
class ClassA {
// ClassB is a
friend class of ClassA
friend class
ClassB;
... .. ...
}
class ClassB {
... .. ...
}
When a class is declared a friend
class, all the member functions of the friend class become friend functions.
Since ClassB is a friend class, we
can access all members of ClassA from inside ClassB.
However, we cannot access members of
ClassB from inside ClassA. It is because friend relation in C++ is only
granted, not taken.
Friend Class Example
#include <iostream>
using namespace std;
class classA {
private:
char ch='A';
int num = 11;
public:
/* This
statement would make class classB
* a friend
class of classA, this means that
* classB can
access the private and protected
* members of
classA class.
*/
friend class
classB;
};
class classB {
public:
void
disp(classA objA){
cout<<objA.ch<<endl;
cout<<objA.num<<endl;
}
};
int main() {
classA objA;
classB objB;
objB.disp(objA);
return 0;
}
Output:
A11
