Study of Friend Function in C++ with examples

Friend Function in C++
Mrs. J P Jankar-Tamkhade

friend Function
2
 A function outside the class can be made friend of class
 It can access private and protected members of the class in
which it is declared as friend
 It is declared inside the class as
friend ret_type function_name(parameters);
 Examples
1.Time
2. Complex numbers
3. Matrices

3
friend Function
#include <iostream>
using namespace std;
class Shape
{
double width;
public:
friend void print( Shape S1 );
void set( double wid );
};
// Member function definition
void Shape::set( double wid )
{
width = wid;
}
void print( Shape S )
{
cout << "Width of box : " << S.width ;
}
// Main function for the program
int main( )
{
Shape S1;
S1.set(10.0);
// Use friend function to print the wdith.
print( S1);
return 0;
}

Example of friend Function
4
#include<iostream>
class B
{
int val1,val2;
public:
void get()
{
cout<<"Enter two values:";
cin>>val1>>val2;
}
friend float mean(B ob);
};

5
float mean(B ob)
{
return float(ob.val1+ob.val2)/2;
}
int main()
{
B obj;
obj.get();
cout<<"n Mean value is : "<<mean(obj);
return 0;
}

6
#include <iostream>
class ONE;
class TWO
{
public:
void print(ONE& x);
};
class ONE
{
int a, b;
friend voidTWO::print(ONE& x);
public:
void getdata()
{
cin>>a>>b;
}
};

7
voidTWO::print(ONE& x)
{
cout << "a is " << x.a << endl;
cout << "b is " << x.b << endl;
}
int main()
{
ONE xobj;
TWO yobj;
xobj.getdata();
yobj.print(xobj);
return 0;
}

Friend Class
8
 Friend Class can access the private and protected
members of the class for which it is friend ,it is done by a
declaring prototype of this external function within the
class, and with the keyword friend.
 Friend class is used in C++ to gain access to protected
members exclusively by the friend class

9
Example of Friend Class
#include<iostream>
class getdata
{
float num1,num2;
public:
void read()
{
cout<<"nnEnter the First Number : ";
cin>>num1;
cout<<"nnEnter the Second Number : ";
cin>>num2;
}
friend class add;
};

10
class add
{
public:
float c;
void add1(getdata G)
{
c=G.num1+G.num2;
cout<<"nnSum="<<c;
}
};
int main()
{
int cont;
getdata G1;
add A;
do {
G1.read();
A.add1(G1);
cout<<"nnDo you want to continue?
(1-YES,0-NO)";
cin>>cont;
}while(cont==1);
return 0;
}

Study of Friend Function in C++ with examples

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