reverse_iterator

Module:  Standard C++ Library   Library:  Iterators

Does not inherit

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An iterator adaptor that traverses a collection backwards.

#include <iterator>

namespace std {
  template <class Iterator>
  class reverse_iterator;
}

The class template reverse_iterator adapts any random access iterator or bidirectional_iterator to facilitate the traversal of collections in the opposite direction. The fundamental relationship between a reverse iterator and its corresponding iterator i is established by the identity:

        
&*(reverse_iterator(i)) == &*(i - 1);

This mapping is necessary because, while an iterator past the end of a sequence is still valid but not dereferenceable, there might not be a valid iterator before its beginning.

namespace std {

  template <class Iterator>
  class reverse_iterator
    : public iterator
       <typename iterator_traits<iterator>::iterator_category,
       <typename iterator_traits<iterator>::value_type,
       <typename iterator_traits<iterator>::difference_type,
       <typename iterator_traits<iterator>::pointer,
       <typename iterator_traits<iterator>::reference>
  {

    public:
      typedef Iterator iterator_type;

      reverse_iterator();
      explicit reverse_iterator(iterator_type);

      iterator_type base();

      reference operator*();

      reverse_iterator& operator++();
      reverse_iterator  operator++(int);
      reverse_iterator& operator--();
      reverse_iterator  operator--(int);

      reverse_iterator  operator+  (difference_type) const;
      reverse_iterator& operator+= (difference_type);
      reverse_iterator operator-   (difference_type) const;
      reverse_iterator& operator-= (difference_type);

      reference operator[] (difference_type) const;
  };

  // Nonmember Operators

  template <class Iterator> 
  bool operator== (const reverse_iterator<Iterator>&,
                   const reverse_iterator<Iterator>&);

  template <class Iterator> 
  bool operator!= (const reverse_iterator<Iterator>&,
                   const reverse_iterator<Iterator>&);

  template <class Iterator> 
  bool operator< (const reverse_iterator<Iterator>&,
                  const reverse_iterator<Iterator>&);

  template <class Iterator> 
  bool operator> (const reverse_iterator<Iterator>&,
                  const reverse_iterator<Iterator>&);

  template <class Iterator> 
  bool operator<= (const reverse_iterator<Iterator>&,
                   const reverse_iterator<Iterator>&);

  template <class Iterator> 
  bool operator>= (const reverse_iterator<Iterator>&,
                   const reverse_iterator<Iterator>&);

  template <class Iterator> 
  typename reverse_iterator<Iterator>::difference_type
  operator- (const reverse_iterator<Iterator>&,
             const reverse_iterator<Iterator>&);

  template <class Iterator> 
  reverse_iterator<Iterator>
  operator+ (
      typename reverse_iterator<Iterator>::difference_type,
      const reverse_iterator<Iterator>&);
}

//
//  rev_itr.cpp
//

#include <iostream>   // for cout, endl
#include <vector>     // for vector


int main ()
{
    typedef std::vector<int, std::allocator<int> > Vector;

    // Initialize a vector using an array.
    const Vector::value_type arr[] = { 3, 4, 7, 8 };
    const Vector v (arr + 0, arr + sizeof arr / sizeof *arr);

    // Output the original vector.
    std::cout << "Traversing vector with iterator: \n     ";
    for (Vector::const_iterator i = v.begin (); 
         i != v.end (); ++i)
        std::cout << *i << " ";

    // Output the vector backwards.
    std::cout << "\n\nSame vector, same loop, "
              << "reverse_iterator: \n     ";
    for (Vector::const_reverse_iterator j (v.end ());
         j != Vector::const_reverse_iterator (v.begin ());
         ++j)
        std::cout << *j << " ";

    std::cout << std::endl;

    return 0;
}


Program Output:

Traversing vector with iterator: 
     3 4 7 8 

Same vector, same loop, reverse_iterator: 
     8 7 4 3 

All iterator operations are required to take at most amortized constant time.

Iterators

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 24.4.1.1

Copyright (c) 1994-2006 Rogue Wave Software, a Quovadx Division.
Licensed under the Apache License, Version 2.0.
Contact Rogue Wave about documentation or support issues. You can also seek help from other developers through the Apache stdcxx community (see below).