Friends to a Class
The concepts of encapsulation and data hiding dictate that non-member functions should not be able to access an object's private or protected data. Any attempt by a non-member function to directly access these data members ( via object ) will result in a compile-time error.
There are situations in which a class may grant friendship:
1) To a non-member function.
2) To a particular member function of another class.
3) To another class ( all member functions of that class are friend functions ).
Since a friend is a non-member of a class, it is not affected by the public, protected or private section in which they are declared within the class body.
For example,
class A
{
friend class B ;
private :
int v1 ;
int v2 ;
} ;
class B
{
public :
void myfunc ( A & obj )
{
v1 + + ; // error
obj.v1+ +; // ok
+ +( obj.v2 ) ; // ok
}
} ;
A friend class ( and function ) has the right to access the data members through the object only, and not directly.
