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The reverse iterator adaptor iterates through the adapted iterator range in the opposite direction.
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:
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 here.
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.
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.
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 1.15. Categories
|
If |
then |
|---|---|
|
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.
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.
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.
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
Returns:
*this
reverse_iterator& operator--();
Effects: ++m_iterator
Returns:
*this