Standard Template Library Programmer's Guide

Reversible Container, reverse_bidirectional_iterator, Random Access Iterator, iterator tags, Iterator Overview

Categories: iterators, adaptors

Component type: type

Reverse_bidirectional_iterator is an iterator adaptor that enables backwards traversal of a range. Operator++ applied to an object of class reverse_bidirectional_iterator means the same thing as operator-- applied to an object of class BidirectionalIterator . There are two different reverse iterator adaptors: the class reverse_bidirectional_iterator has a template argument that is a Bidirectional Iterator, and the class reverse_iterator has a template argument that is a Random Access Iterator. [1]

template

void forw(const list & L) {

list::iterator first = L.begin();

list::iterator last = L.end();

while (first != last) cout << *first++ << endl;

}

template

void rev(const list & L) {

typedef reverse_bidirectional_iterator::iterator, T, list::reference_type, list::difference_type> reverse_iterator; [2]

reverse_iterator rfirst(L.end());

reverse_iterator rlast(L.begin());

while (rfirst != rlast) cout << *rfirst++ << endl;

}

In the function forw , the elements are printed in the order *first , *(first+1) , …, *(last-1) . In the function rev , they are printed in the order *(last – 1) , *(last - 2) , …, *first . [3]

Defined in the standard header iterator, and in the nonstandard backward-compatibility header iterator.h. This class is no longer part of the C++ standard, but it was present in early drafts, and it is retained in this implementation for backward compatibility.

Bidirectional Iterator.

The base iterator type (that is, the template parameter BidirectionalIterator ) must be a Bidirectional Iterator . The reverse_bidirectional_iterator 's value type, reference type, and distance type (that is, the template parameters T , Reference , and Distance , respectively) must be the same as the base iterator's value type, reference type, and distance type.

None.

These members are not defined in the Bidirectional Iterator requirements, but are specific to reverse_bidirectional_iterator .

[1] There isn't really any good reason to have two separate classes: this separation is purely because of a technical limitation in some of today's C++ compilers. If the two classes were combined into one, then there would be no way to declare the return types of the iterator tag functions iterator_category , distance_type and value_type correctly. The iterator traits class solves this problem: it addresses the same issues as the iterator tag functions, but in a cleaner and more flexible manner. Iterator traits, however, rely on partial specialization , and many C++ compilers do not yet implement partial specialization. Once compilers that support partial specialization become more common, these two different reverse iterator classes will be combined into a single class.