Friend function part 1 | very very easy

-
Friend function:
  1. Friend function is not a member function of a class to which it is a friend.
  2. Friend function is declared inside the class with friend keyword.
  3. It must be defined outside the class to which it is friend.
  4. Friend function can access any member of the class to which it is a friend.
  5. Friend function can not access the members of the class directly.
  6. Friend function can not access members of the class directly because it has no caller object.
  7. It should not be defined with membership label.
Let's consider a simple example to implement all above points:

#include<iostream>
using namespace std;
       class Complex{
    private:
           int a, b;
    public:
           void setData(int x, int y){
           a=x;
           b=y;
}
           void showData(){
           cout<<a<<" "<<b<<endl;
}
          friend void add( Complex );   // 2. friend function declared inside the class
};
//1. and 7. As friend function is not a member function so it is not defined using member ship label or scope resolution operator.
void add( Complex c ){         // 3. friend function defined outside the class
     cout<<"Sum is:"<<endl<<c.a+c.b<<endl;     
}
int main(){
     // creating object of class Complex
       Complex c1;
       c1.setData( 42, 87 );  // here c1 is the caller object
//4. 5. 6. as our friend function does not have a caller object it is called directly
         add(c1); // but to access the members of the class we have to pass the object to the 
// friend function so the compiler can determine whose members to be used.
return 0;
}

Output:
Sum is:
129

Friend function as friend of more than one classes:
     
Friend function can be the friend of more than one classes.

Let us consider a simple example to understand this:

#include<iostream>
using namespace std;
   class B; //without the previous declaration of class B compiler will 
            // not be able to decide what is B inside friend function
   class A{
    private:
    int a;
    public:  // a friend function can be made either public or private 
    // during class declaration
    friend void fun( A, B );
    A(){   // to set value of a
    a=23;
   }
   };
   class B{
    private:
    int b;
    public:
    friend void fun( A, B );
    B(){   // to set value of b
    b=54;
   }
   };
   void fun(A o1, B o2){   // friend function as friend of class A and B
    cout<<"Sum is:"<<endl<<o1.a+o2.b<<endl;
   }
int main(){
A obj1;
B obj2;
fun(obj1,obj2);
return 0;
}

Output:
Sum is:
77
  

Comments

Post a Comment

Popular posts from this blog

Virtual function in c++

-
Virtual Function: Virtual means existing in effect but not in reality. A type of function that appears to exist in some part of the program but does not exist really is called a virtual function. Virtual functions are used to implement polymorphism. They enable the user to execute completely different functions by the same function call. A virtual function is defined in the parent class and is overridden in child classes. It is defined by the keyword virtual. If you want to call a virtual function in C++ and execute the redefined version of the member function, you can achieve this task using a pointer or a reference ( -> ) by referring a derived class object to the base class. A base class pointer has the capability to point to the objects of the base class and the derived class. But it's converse is not true. An example of using virtual function with reference: #include<iostream> using namespace std; class Animal {     public:         virtual ...
Read more

Multiple, Multilevel, Hybrid and Hierarchical inheritance

-
Image
Multiple inheritance:                          Multiple inheritance is a type of inheritance in c++ in which a class can be inherited from more than one classes. In this case the inherited class has more than one parent class. Multiple inheritance example:         #include <iostream> using namespace   std; class Animal { public:    Animal(){ cout<<" Animal's constructor "<<endl;} }; class Mammal { public:    Mammal(){cout<<" Mammal's constructor "<<endl;} }; class Bat : public Animal,public Mammal { public:   Bat(){ cout<<" Bat's constructor "<<endl;} }; int main(){     Bat bat1;    return 0; } Output: Animal's constructor Mammal's constructor Bat's constructor Multilevel inheritance:            In multilevel inheritance a class can be derived from another class who is already def...
Read more

Practice problem classes and objects.

-
        Creating classes and objects in C++ Problem:        Create a class named ClassRoom  that has 6 private  member variables named t otalChairs, totalTables, classGrade, teacherName, totalStudents and  classRep. Your class must have 2  public member functions named as input and  output. These two input and output functions will work as getter and setter. You must also create a constructor that initializes the values of all the private member variables to null or 0. Remember: We can use any name for our getter and setter function. Now for our main method create an object of our class ClassRoom named Class1. Input values from the user by calling the Input function of the object Class1. Then output all the values. All the above conditions must be fulfilled. Visit here for reference about classes and objects: C++ classes and objects
Read more