std::ranges::views::reverse, std::ranges::reverse_view - cppreference.com (original) (raw)

1. A range adaptor that represents a view of underlying view with reversed order.

2. RangeAdaptorObject. The expression views::reverse(e) is expression-equivalent to one of the following expressions, except that e is evaluated only once:

• e.base(), if the type of e is a (possibly cv-qualified) specialization of reverse_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 value K of type ranges::subrange_kind:

• ranges::subrange<I, I, K>(e.end().base(), e.begin().base(), e.size()), if K is ranges::subrange_kind::sized;

• otherwise ranges::subrange<I, I, K>(e.end().base(), e.begin().base());

• otherwise ranges::reverse_view{e}.

In other words, 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

• 1 Data members
• 2 Member functions
  • 2.1 Inherited from std::ranges::view_interface
• 3 std::ranges::reverse_view::reverse_view
  • 3.1 Parameters
• 4 std::ranges::reverse_view::base
• 5 std::ranges::reverse_view::begin
• 6 std::ranges::reverse_view::end
• 7 std::ranges::reverse_view::size
• 8 std::ranges::as_rvalue_view::reserve_hint
  • 8.1 Deduction guides
  • 8.2 Helper templates
  • 8.3 Notes
  • 8.4 Example
  • 8.5 Defect reports
  • 8.6 See also

[edit] Data members

[edit] Member functions

std::ranges::reverse_view::reverse_view

| | (1) | (since C++20) | | | ------------------------------- | ------------- | ------------- | | constexpr reverse_view( V r ); | (2) | (since C++20) |

1. Value-initializes _[base](reverse%5Fview.html#base)_ via its default member initializer (= V()).

2. Initializes _[base](reverse%5Fview.html#base)_ with std::move(r).

Parameters

std::ranges::reverse_view::base

| | (1) | (since C++20) | | | ---------------------- | ------------- | ------------- | | constexpr V base() &&; | (2) | (since C++20) |

Returns the underlying view.

1. Copy-constructs the result from the underlying view. Equivalent to return _[base](reverse%5Fview.html#base)_ ;.

2. Move-constructs the result from the underlying view. Equivalent to return std::move(_[base](reverse%5Fview.html#base)_ );.

std::ranges::reverse_view::size

Returns the size of the view if the view is bounded. Equivalent to return ranges::size(_[base](reverse%5Fview.html#base)_ );.

std::ranges::as_rvalue_view::reserve_hint

Returns ranges::reserve_hint(_[base](reverse%5Fview.html#base)_ ).

[edit] Deduction guides

| template< class R >reverse_view( R&& ) -> reverse_view<views::all_t<R>>; | | (since C++20) | | -------------------------------------------------------------------------------------------------- | | ------------- |

[edit] Helper templates

This specialization of std::ranges::enable_borrowed_range makes reverse_view satisfy borrowed_range when the underlying view satisfies it.

[edit] Notes

[edit] Example

#include #include   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.

[edit] See also