constreverseiterator

A const_reverse_iterator is a read-only reverse iterator used to traverse a container in reverse order. It is the const version of a reverse iterator, meaning that dereferencing yields a const reference to the element and the element cannot be modified through the iterator. This type is provided by the C++ standard library for standard containers such as vector, deque, list, set, and map, typically as a nested typedef named const_reverse_iterator.

In most containers, const_reverse_iterator is defined as reverse_iterator<const_iterator>, where const_iterator is the container’s iterator type that yields a const reference to the element. The reverse iterator adapts a bidirectional iterator and traverses the container from end to beginning. Dereferencing it yields a const reference to the element, and operator-> yields a pointer to const T. Incrementing a const_reverse_iterator moves toward the beginning of the container (i.e., it advances the reverse traversal), while decrementing moves toward the end, opposite to the direction of a forward iterator.

The base() member function returns the corresponding underlying iterator, typically a const_iterator, pointing to the element that would be visited next by a forward iteration. This allows one to translate between reverse and forward views when needed.

Since const_reverse_iterator enforces constness, it is commonly obtained via crbegin and crend (introduced in C++17) to perform read-only reverse traversal. This is useful when iterating const containers or when read-only access is required while walking elements from end to start.

Overall, const_reverse_iterator provides a standard, read-only means to traverse containers in reverse, complementing reverse_iterator and const_iterator in the C++ iterator toolbox.