Question

I am working on a program in which I practice using template classes to write a linked list, with a list container behind the scenes doing most of the operations:

template <typename T>
class LinkedList
{
public:                                                                                                                                                       
    void add(const T& t) {
        q.push_front(t);
    }

    T pop() {
        T t = q.front();
        q.pop_front();
        return t;
    }

    T& operator[](int i);

private:
    list<T> q;
};

Now I want to implement the [] operator such that I can create a LinkedList object and then do operations such as:

list1[0] = 1;

Currently, I have:

template <typename T>
T& LinkedList<T>::operator[](int i)
{
    LinkedList<T> tempList;
    int j;
    T* getNode;

    for(j = 0; j < (i + 1); j++) {
        T* currentNode = pop();
        tempList.add(currentNode);

        if(j == i) {
            getNode = currentNode;
        }
    }

    while(tempList.isEmpty == false) {
        add(tempList.pop());
    }

    return *getNode;
}

This is clearly not working and it is because I am somehow messing up getting the reference of the particular element I want and returning it, but I am new to C++ and I do not exactly know what the best way of approaching this problem is.

Answer 1

As far as I can tell, your code is attempting to do a simple thing in an amazingly complicated way. What is wrong with just:

template <typename T>
T& LinkedList<T>::operator[](int i)
{
    assert(i >= 0 && i < q.size());
    typename list<T>::iterator it(q.begin());
    std::advance(it, i);
    return *it;
}

However – I do not understand why you would want this operation. This operation has a time complexity of O(N) (where N is the size of the list). If you want random access to the elements of a list, a resizable array would be a far better data-structure.