std::ranges::views::reverse, std::ranges::reverse_view
Defined in header <ranges>
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||
template< ranges::view V > requires ranges::bidirectional_range<V> |
(1) | (since C++20) |
namespace views { inline constexpr /* unspecified */ reverse = /* unspecified */; |
(2) | (since C++20) |
Call signature |
||
template< ranges::viewable_range R > requires /* see below */ |
(since C++20) | |
view
with reversed order.- e.base(), if the type of
e
is a (possibly cv-qualified) specialization ofreverse_view
; - otherwise, if the type of e is (possibly cv-qualified) ranges::subrange<std::reverse_iterator<I>, std::reverse_iterator<I>, K> for some iterator type
I
and valueK
of typeranges::subrange_kind
:
- ranges::subrange<I, I, K>(e.end().base(), e.begin().base(), e.size()), if
K
isranges::subrange_kind::sized
; - otherwise ranges::subrange<I, I, K>(e.end().base(), e.begin().base());
- ranges::subrange<I, I, K>(e.end().base(), e.begin().base(), e.size()), if
- otherwise ranges::reverse_view{e}.
views::reverse
unwraps reversed views if possible.A reverse_view
always models bidirectional_range
and common_range
, and it models borrowed_range
, sized_range
, or random_access_range
if the underlying view type V
models the corresponding concept.
Contents |
[edit] Data members
Member name | Definition |
base_ (private)
|
The underlying view of type V .(exposition-only member object*) |
cached_end_ (private)
|
An optional-like cache object that holds either no value or the end iterator/position of the underlying view, which exists only if the underlying view type V does not model common_range .(exposition-only member object*) |
[edit] Member functions
constructs a reverse_view (public member function) | |
returns the underlying view V (public member function) | |
returns the beginning iterator of the reverse_view (public member function) | |
returns the end iterator of the reverse_view (public member function) | |
returns the size of the view if it is bounded (public member function) | |
Inherited from std::ranges::view_interface | |
returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range . (public member function of std::ranges::view_interface<D> )
| |
(C++23) |
returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D> )
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(C++23) |
returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D> )
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returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D> )
| |
returns the first element in the derived view. Provided if it satisfies forward_range . (public member function of std::ranges::view_interface<D> )
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returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range . (public member function of std::ranges::view_interface<D> )
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returns the n th element in the derived view. Provided if it satisfies random_access_range . (public member function of std::ranges::view_interface<D> )
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std::ranges::reverse_view::reverse_view
reverse_view() requires std::default_initializable<V> = default; |
(1) | (since C++20) |
constexpr reverse_view( V r ); |
(2) | (since C++20) |
base_
via its default member initializer (= V()).base_
with std::move(r).Parameters
r | - | range to reverse |
std::ranges::reverse_view::base
constexpr V base() const& requires std::copy_constructible<V>; |
(1) | (since C++20) |
constexpr V base() &&; |
(2) | (since C++20) |
Returns the underlying view.
std::ranges::reverse_view::begin
constexpr std::reverse_iterator<ranges::iterator_t<V>> begin(); |
(1) | (since C++20) |
constexpr std::reverse_iterator<ranges::iterator_t<V>> begin() requires ranges::common_range<V>; |
(2) | (since C++20) |
constexpr auto begin() const requires ranges::common_range<const V>; |
(3) | (since C++20) |
range
concept, this function caches the result within the cache object for use on subsequent calls.
std::ranges::reverse_view::end
constexpr std::reverse_iterator<ranges::iterator_t<V>> end(); |
(1) | (since C++20) |
constexpr auto end() const requires ranges::common_range<const V>; |
(2) | (since C++20) |
Equivalent to return std::make_reverse_iterator(ranges::begin(base_));.
std::ranges::reverse_view::size
constexpr auto size() requires ranges::sized_range<V>; |
(1) | (since C++20) |
constexpr auto size() const requires ranges::sized_range<const V>; |
(2) | (since C++20) |
Returns the size of the view if the view is bounded.
[edit] Deduction guides
template< class R > reverse_view( R&& ) -> reverse_view<views::all_t<R>>; |
(since C++20) | |
[edit] Helper templates
template< class T > constexpr bool enable_borrowed_range<std::ranges::reverse_view<T>> = |
(since C++20) | |
This specialization of std::ranges::enable_borrowed_range makes reverse_view
satisfy borrowed_range
when the underlying view satisfies it.
[edit] Example
#include <iostream> #include <ranges> int main() { static constexpr auto il = {3, 1, 4, 1, 5, 9}; std::ranges::reverse_view rv{il}; for (int i : rv) std::cout << i << ' '; std::cout << '\n'; for (int i : il | std::views::reverse) std::cout << i << ' '; std::cout << '\n'; // operator[] is inherited from std::view_interface for (auto i{0U}; i != rv.size(); ++i) std::cout << rv[i] << ' '; std::cout << '\n'; }
Output:
9 5 1 4 1 3 9 5 1 4 1 3 9 5 1 4 1 3
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
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LWG 3494 | C++20 | reverse_view was never a borrowed_range
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it is a borrowed_range if its underlying view is
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[edit] See also
iterator adaptor for reverse-order traversal (class template) | |
(C++20) |
reverses the order of elements in a range (algorithm function object) |
(C++20) |
creates a copy of a range that is reversed (algorithm function object) |