reverseiterator

Reverse_iterator is an iterator adapter in the C++ Standard Template Library that provides a view of a container in reverse order by wrapping another iterator, called the base iterator. It allows traversal of a sequence from end to beginning without copying or restructuring the data.

The reverse_iterator stores a base iterator and defines its operations in reverse relation to that base. Dereferencing a reverse_iterator yields the element preceding the base iterator’s position, while incrementing the reverse_iterator moves toward the beginning of the sequence by decrementing the base iterator. The base() member returns the underlying forward iterator. Containers commonly expose reverse iterators through rbegin() and rend(), where rbegin() points to the last element and rend() is positioned before the first.

In practice, reverse_iterator is used via reverse iterators or range-based constructs. Typical loops look like for (auto it = v.rbegin(); it != v.rend(); ++it) { /* use *it */ }. Many standard algorithms also accept reverse iterators to operate on ranges in reverse, such as std::copy(v.rbegin(), v.rend(), out.begin()) or std::sort(v.rbegin(), v.rend()) for reverse-order sorting. The reverse_iterator abstraction is defined generically as std::reverse_iterator<Iterator> and can adapt any bidirectional iterator, or a random-access iterator, depending on the container’s capabilities.

Common considerations include understanding how base() relates to the element accessed by the reverse_iterator, and ensuring compatibility with algorithms that expect forward iterators. Reverse iterators are provided by standard containers, and they enable concise, efficient reverse traversal without manual index arithmetic or temporary copies.