C++ Cookbook

11.13. Implementing a Stride Iterator

Problem

You have a contiguous series of numbers and you want to iterate through the elements n at a time.

Solution

Example 11-24 presents a stride iterator class as a separate header file.

Example 11-24. stride_iter.hpp

#ifndef STRIDE_ITER_HPP #define STRIDE_ITER_HPP #include <iterator> #include <cassert> template<class Iter_T> class stride_iter { public: // public typedefs typedef typename std::iterator_traits<Iter_T>::value_type value_type; typedef typename std::iterator_traits<Iter_T>::reference reference; typedef typename std::iterator_traits<Iter_T>::difference_type difference_type; typedef typename std::iterator_traits<Iter_T>::pointer pointer; typedef std::random_access_iterator_tag iterator_category; typedef stride_iter self; // constructors stride_iter() : m(NULL), step(0) { }; stride_iter(const self& x) : m(x.m), step(x.step) { } stride_iter(Iter_T x, difference_type n) : m(x), step(n) { } // operators self& operator++() { m += step; return *this; } self operator++(int) { self tmp = *this; m += step; return tmp; } self& operator+=(difference_type x) { m += x * step; return *this; } self& operator--() { m -= step; return *this; } self operator--(int) { self tmp = *this; m -= step; return tmp; } self& operator-=(difference_type x) { m -= x * step; return *this; } reference operator[](difference_type n) { return m[n * step]; } reference operator*() { return *m; } // friend operators friend bool operator==(const self& x, const self& y) { ...