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C++ - Subscript Operator Overloading



Subscript operator [ ], like the function-call operator, is considered a binary operator. The declaration is identical to any binary operator, with the following exception:

  • It can not be declared as a non-member function. It must be a non-static member function.
  • It should take a single argument. The argument can be of any type and designates the desired array subscript.

Example: overloading subscript operator

In the example below, assignment operator (=) is overloaded. It is used to return a reference to the element at the specified position of the vector class.

#include <iostream>
using namespace std;
 
class vector {
  private:
    int size;
    int *Elements;
  public:

    //class constructor
    vector(int i) {
      Elements = new int[i];
      size = i;
    }

    //function for overloading []
    int& operator[] (int index) {
      if(index >= 0 && index < size){
        return Elements[index];
      } else {
        cout<<"IndexOutOfBounds\n";
        exit(0);
      }
    }         
};

int main (){
  vector myVec(10);
  
  for(int i = 0; i < 10; i++) {
    myVec[i] = (i+1)*10;
  }
 
  for(int i = 0; i < 12; i++) {
    cout<<"myVec["<<i<<"] = "<<myVec[i]<<"\n";
  }  
  return 0;
}

The output of the above code will be:

myVec[0] = 10
myVec[1] = 20
myVec[2] = 30
myVec[3] = 40
myVec[4] = 50
myVec[5] = 60
myVec[6] = 70
myVec[7] = 80
myVec[8] = 90
myVec[9] = 100
myVec[10] = IndexOutOfBounds

❮ C++ - Operator Overloading

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