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[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]
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