Q. What is friend function in C++? What are the risks associated with the use of friend function?
Ans.
As we know that the private members of the class cannot be assessed from outside the class, a non member function cannot have access to the private data of that class. Though there could be a condition where we would like two classes to distribute a particular function.
For instance:
Consider a case where two classes' manager and employee have defined. We could like to use a function to operate on the both objects of both classes. In such situation C++ allows the common function to be made friendly with both the classes, thereby allowing the function to be access to the private data of these classes. Such members need not be members of these classes. A member function of one class can be friend function of another class in such a case. They are defining using the case scope resolution operator.
Syntax: Friend return _ type class name : : function name (args) we can also declare all the members functions of one classes as the friend function of another class, in such class the class is called a friend class.
Syntax: Friend class name: A friend function has certain special characteristics:
1. It is not in scope of the class, it cannot be called by the object of that class.
2. As it is not in the scope of the class, it cannot be called with the object of that class.
3. It can be invoked as a normal function without the help of some object.
4. Unlike member functions, it cannot be access the member names directly and has to be used an object name and dot membership operator with each member name.
5. It can be stated either in the public or private part of a class without disturbing its sense.
6. Usually it has the objects as the arguments.
Example
Class X, Y, Z;
Int n;
Public :
Void value (Int s)
{
Int x;
X = s;
}
Friend void max (X, Y, Z; ABC);
};
Class ABC
{
Int a;
Public :
Void value (Int s)
{
a = s;
}
Friend void max (XYZ, ABC);
};
Void max (XYZ m, ABC n)
{
If (m. X. > = n. a)
Cout << m. x.;
else
cout << n. a.;
}
Int main ();
{
A, B, C a, b, c;
A, b, c value (1);
X, Y, Z x, y, z;
X, y, z; value (20);
}
Max (X, Y, Z; a, b, c);
Return 0;