Overloading [] Operator in a class to access data within the class by indexing method.

In the previous article Overloading [] Operator, we overloaded the [] operator in a class to access data within the class by indexing method.

The operator [] function was defined as below:

  int myclass::operator[](int index)

 {

   // if not out of bound

   if(index     return a[index];

 }

As you can see, the above operator function is returning values, hence it could only be used on the right hand side of a statement. It’s a limitation!

You very well know that a statement like below is very common with respect to arrays:

a[1]=10;

But as I said, the way we overloaded the [] operator, statement like the one above is not possible. The good news is, it is very easy to achieve this.

For this we need to overload the [] operator like this:

  int &myclass::operator[](int index)

 {

   // if not out of bound

   if(index     return a[index];

 }

By returning a reference to the particular element, it is possible to use the index expression on the left hand side of the statement too.

The following program illustrates this:

 // Example Program illustrating

 // the overloading of [] operator

 // ----

 // now the index expression can be

 // used on the left side too

 #include 



 class myclass

 {

   // stores the number of element

   int num;

   // stores the elements

   int a[10];



 public:

   myclass(int num);



   int &operator[](int);

 };



 // takes the number of element

 // to be entered.(<=10)

 myclass::myclass(int n)

 {

   num=n;

   for(int i=0;i   {

     cout<<"Enter value for element "<1<<":";

     cin>>a[i];

   }

 }



 // returns a reference

 int &myclass::operator[](int index)

 {

   // if not out of bound

   if(index     return a[index];

 }



 void main()

 {

   myclass a(2);



   cout<0]<   cout<1]<

   // indexing expression on the

   // left-hand side

   a[1]=21;

   cout<1];

 }