C++ overloading array operator

Question

I'm creating a Heap, like this:

struct Heap {
    int H[100];
    int operator [] (int i) { return H[i]; }
    //...    
};

When I try to print elements from it I do like this:

Heap h;
// add some elements...
printf("%d\n", h[3]); // instead of h.H[3]

If, instead of accessing I want to set them, like this:

for (int i = 0; i < 10; i++) h[i] = i;

How can I do?

Answer 1

It is idiomatic to provide couple of overloads of the operator[] function - one for const objects and one for non- const objects. The return type of the const member function can be a const& or just a value depending on the object being returned while the return type of the non- const member function is usually a reference.

struct Heap{
    int H[100];
    int operator [] (int i) const {return H[i];}
    int& operator [] (int i) {return H[i];}
};

This allows you to modify a non- const object using the array operator.

Heap h1;
h1[0] = 10;

while still allowing you to access const objects.

Heap const h2 = h1;
int val = h2[0];

Answer 2

You can return references to what should be set. Add & to the return type.

int& operator [] (int i){return H[i];}

Answer 3

You should return by reference. With your current version you are taking a copy and editing this copy which will not affect the original array. You have to change your operator overloading to this:

int& operator [] (int i){return H[i];}