iterator/doc/quickbook/reverse_iterator.qbk

[section:reverse Reverse Iterator]

The reverse iterator adaptor iterates through the adapted iterator
range in the opposite direction.

[h2 Example]

The following example prints an array of characters in reverse order
using `reverse_iterator`.

    char letters_[] = "hello world!";
    const int N = sizeof(letters_)/sizeof(char) - 1;
    typedef char* base_iterator;
    base_iterator letters(letters_);
    std::cout << "original sequence of letters:\t\t\t" << letters_ << std::endl;

    boost::reverse_iterator<base_iterator>
      reverse_letters_first(letters + N),
      reverse_letters_last(letters);

    std::cout << "sequence in reverse order:\t\t\t";
    std::copy(reverse_letters_first, reverse_letters_last,
              std::ostream_iterator<char>(std::cout));
    std::cout << std::endl;

    std::cout << "sequence in double-reversed (normal) order:\t";
    std::copy(boost::make_reverse_iterator(reverse_letters_last),
              boost::make_reverse_iterator(reverse_letters_first),
              std::ostream_iterator<char>(std::cout));
    std::cout << std::endl;



The output is:

[pre
original sequence of letters:                   hello world!
sequence in reverse order:                      !dlrow olleh
sequence in double-reversed (normal) order:     hello world!
]

The source code for this example can be found
[example_link reverse_iterator_example.cpp..here].

[h2 Reference]

[h3 Synopsis]

  template <class Iterator>
  class reverse_iterator
  {
  public:
    typedef iterator_traits<Iterator>::value_type value_type;
    typedef iterator_traits<Iterator>::reference reference;
    typedef iterator_traits<Iterator>::pointer pointer;
    typedef iterator_traits<Iterator>::difference_type difference_type;
    typedef /* see below */ iterator_category;

    reverse_iterator() {}
    explicit reverse_iterator(Iterator x) ;

    template<class OtherIterator>
    reverse_iterator(
        reverse_iterator<OtherIterator> const& r
      , typename enable_if_convertible<OtherIterator, Iterator>::type* = 0 // exposition
    );
    Iterator const& base() const;
    reference operator*() const;
    reverse_iterator& operator++();
    reverse_iterator& operator--();
  private:
    Iterator m_iterator; // exposition
  };


If `Iterator` models Random Access Traversal Iterator and Readable
Lvalue Iterator, then `iterator_category` is convertible to
`random_access_iterator_tag`. Otherwise, if
`Iterator` models Bidirectional Traversal Iterator and Readable
Lvalue Iterator, then `iterator_category` is convertible to
`bidirectional_iterator_tag`. Otherwise, `iterator_category` is
convertible to `input_iterator_tag`.

[h3 Requirements]

`Iterator` must be a model of Bidirectional Traversal Iterator.  The
type `iterator_traits<Iterator>::reference` must be the type of
`*i`, where `i` is an object of type `Iterator`.

[h3 Concepts]

A specialization of `reverse_iterator` models the same iterator
traversal and iterator access concepts modeled by its `Iterator`
argument.  In addition, it may model old iterator concepts
specified in the following table:

[table Categories
  [[If `I` models                 ][then `reverse_iterator<I>` models]]
  [[Readable Lvalue Iterator, Bidirectional Traversal Iterator][Bidirectional Iterator]]
  [[Writable Lvalue Iterator, Bidirectional Traversal Iterator][Mutable Bidirectional Iterator]]
  [[Readable Lvalue Iterator, Random Access Traversal Iterator][Random Access Iterator]]
  [[Writable Lvalue Iterator, Random Access Traversal Iterator][Mutable Random Access Iterator]]
]

`reverse_iterator<X>` is interoperable with
`reverse_iterator<Y>` if and only if `X` is interoperable with
`Y`.

[h3 Operations]

In addition to the operations required by the concepts modeled by
`reverse_iterator`, `reverse_iterator` provides the following
operations.

  reverse_iterator();

[*Requires: ] `Iterator` must be Default Constructible.[br]
[*Effects: ] Constructs an instance of `reverse_iterator` with `m_iterator`
  default constructed.

  explicit reverse_iterator(Iterator x);

[*Effects: ] Constructs an instance of `reverse_iterator` with
    `m_iterator` copy constructed from `x`.


    template<class OtherIterator>
    reverse_iterator(
        reverse_iterator<OtherIterator> const& r
      , typename enable_if_convertible<OtherIterator, Iterator>::type* = 0 // exposition
    );

[*Requires: ] `OtherIterator` is implicitly convertible to `Iterator`.[br]
[*Effects: ] Constructs instance of `reverse_iterator` whose
    `m_iterator` subobject is constructed from `y.base()`.



  Iterator const& base() const;

[*Returns: ] `m_iterator`


  reference operator*() const;

[*Effects: ]  Iterator tmp = m_iterator; return *--tmp;


  reverse_iterator& operator++();

[*Effects: ] `--m_iterator`[br]
[*Returns: ] `*this`

  reverse_iterator& operator--();

[*Effects: ] `++m_iterator`[br]
[*Returns: ] `*this`

[endsect]