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Friend function in c++

                                                             
   FRIEND FUNCTION

We know that private member cannot be access from out side the class.That is a non member function cannot have an access to the private data of a class,but there may be some situation where we would like two classes to share a particular function.In such situation c++ allows the common function to be made friendly with both the classes,that allows to have access to the private data of these classes.Such a function need not be a function of any of these classes.
To declear a friend function the function decided by  the keyword friend.the definition does not used the keyword friend or the scope resulation operator(::) .A function can be decleare as a friend in any number of classes.All the a friend function of class is a but it has full access to the private members of class.

Charaterstatices of friends function :-

   ·       A friend function is not the scope of class to his it has been decleare as friend.
   ·      Since it is not in the scope of the class, it cannot be called using the object of class it can be called like a normal function without the help of any function
   ·      It cannot access data members directly and has to used an object and dot membership operator with each member name.
   ·      Friend function either in the public or private part of th class without effecting its meaning.
   ·      Usually it has the object as arguments.

Friend function with single class

#include<iostream.h>
#include<conio.h>
Class test
{
Int a,b;
Public:
Void getdata()
{
Cout<<”enter two values”;
Cin>>a>>b;
}
Friend float mean(test t);
};
Float mean(test t)
{
Float x;
X=(t.a+t.b)/2;
Return x;
}
Void main()
{
Test t;
t.getdata();
cout<<”\n mean value=”<<mean(t);
getch();
}

Friend function double class :-

#include<iostream.h>
#include<conio.h>
Class test2 ;
Class test1
{
Int x;
Public:
Void getdata()
{
Cout<<”enter any value”;
Cin>>x;
}
Friend void sum( test1, test2);
};
Class test2
{
Int y;
Public:
Void getdata()
{
Cout<<”\n enter any value”;
Cin>>y;
}
Friend void sum( test1, test2);
};
Void sum(test1 t1, test2 t2)
{
Int total;
total=t1.x + t2.y;
cout<<”\n sum=”<,total;
}
Void main()
{
Test t1;
Test2 t2;
T1.getdata();
T2.getdata();
Sum(t1,t2);
Getch();
}



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