How to make a function to adress doubly linked list node?

Question

I made an inmplementation of doubly linked list as class in C++

In main.cpp I'm pushing objects of other class into this list like this

list.insertBack(ClassA(name, description));

But after that I need to change a certain field of this object, for example perform a method that changes population. For that I need to somehow adress this object from the list like I would do with a regular array (smth like a[i]). For that I need a special method/function in my List class. How can I implement this?

Answer 1

You just need to provide a operator[] for your class:

template<class T>
class List {

    // your private interface

public:

    // your other public interface 

    T& operator[](unsigned int i)
    {
        Node* n = this->head;
        for (; i>0; --i)
        {
            n = n->next;
        }
        return n->data;
    }
};

In your main you can then simply use it like

int main() {
    List<double> l;
    l.insertBack(0.0);
    l.insertBack(1.0);
    l.insertBack(2.0);
    l.insertBack(3.0);

    std::cout <<  l[2] << std::endl;
}

Note that you might also want a const version of this function. Here is a demo.

Note: As pointed out by @Botje, you might also want do some sanity checks on the input. If i is equal or larger than the number of existing nodes, my code snippet dereferences a nullptr and you get undefined behavior.