Does a standard implementation of a Circular List exist for C++?

Question

I want to use a circular list.

Short of implementing my own (like this person did) what are my options?

Specifically what I want to do is iterate over a list of objects. When my iterator reaches the end of the list, it should automatically return to the beginning. (Yes, I realize this could be dangerous.)

See Vladimir's definition of a circular_iterator: "A circular_iterator will never be equal with CircularList::end(), thus you can always dereference this iterator."

Answer 1

There's no standard circular list.

However, there is a circular buffer in Boost, which might be helpful.

If you don't need anything fancy, you might consider just using a vector and accessing the elements with an index. You can just mod your index with the size of the vector to achieve much the same thing as a circular list.

Answer 2

If you want something looking like an iterator you can roll your own, looking something like

template <class baseIter>
class circularIterator {
    private:
        baseIter cur;
        baseIter begin;
        baseIter end;
    public:
        circularIterator(baseIter b, baseIter e, baseIter c=b)
            :cur(i), begin(b), end(e) {}
        baseIter & operator ++(void) {++cur; if(cur == end) {cur = begin;}}
};

(Other iterator operations left as exercise to reader).

Answer 3

list<int>::iterator circularNext(list<int> &l, list<int>::iterator &it)
{
    return std::next(it) == l.end() ? l.begin() : std::next(it);
}

Answer 4

In addition to @captain-segfault and @mahmoud-khaled's iterator-focused answers, you can also use std::list as a circular list by altering what you do to retrieve elements from it. Use splice to move one end of the list to the other end as you process it.

template <typename T>
T & circularFront(std::list<T> & l)
{
  l.splice(l.end(), l, l.begin());
  return l.back();
}
template <typename T>
T & circularBack(std::list<T> & l)
{
  l.splice(l.begin(), l, l.rbegin());
  return l.front();
}