std::ranges::reverse
From cppreference.com
Defined in header <algorithm>
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Call signature |
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template< std::bidirectional_iterator I, std::sentinel_for<I> S > requires std::permutable<I> |
(1) | (since C++20) |
template< ranges::bidirectional_range R > requires std::permutable<ranges::iterator_t<R>> |
(2) | (since C++20) |
1) Reverses the order of the elements in the range
[
first,
last)
. Behaves as if applying ranges::iter_swap to every pair of iterators first + i, last - i - 1 for each integer
i
, where 0 ≤ i < (last - first) / 2.2) Same as (1), but uses r as the range, as if using ranges::begin(r) as first and ranges::end(r) as last.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
[edit] Parameters
first, last | - | the range of elements to reverse |
r | - | the range of elements to reverse |
[edit] Return value
An iterator equal to last.
[edit] Complexity
Exactly (last - first) / 2 swaps.
[edit] Notes
Implementations (e.g. MSVC STL) may enable vectorization when the iterator type models contiguous_iterator
and swapping its value type calls neither non-trivial special member function nor ADL-found swap
.
[edit] Possible implementation
See also implementations in libstdc++ and MSVC STL.
struct reverse_fn { template<std::bidirectional_iterator I, std::sentinel_for<I> S> requires std::permutable<I> constexpr I operator()(I first, S last) const { auto last2 {ranges::next(first, last)}; for (auto tail {last2}; !(first == tail or first == --tail); ++first) ranges::iter_swap(first, tail); return last2; } template<ranges::bidirectional_range R> requires std::permutable<ranges::iterator_t<R>> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r) const { return (*this)(ranges::begin(r), ranges::end(r)); } }; inline constexpr reverse_fn reverse {}; |
[edit] Example
Run this code
#include <algorithm> #include <array> #include <iostream> #include <string> int main() { std::string s {"ABCDEF"}; std::cout << s << " → "; std::ranges::reverse(s.begin(), s.end()); std::cout << s << " → "; std::ranges::reverse(s); std::cout << s << " │ "; std::array a {1, 2, 3, 4, 5}; for (auto e : a) std::cout << e << ' '; std::cout << "→ "; std::ranges::reverse(a); for (auto e : a) std::cout << e << ' '; std::cout << '\n'; }
Output:
ABCDEF → FEDCBA → ABCDEF │ 1 2 3 4 5 → 5 4 3 2 1
[edit] See also
(C++20) |
creates a copy of a range that is reversed (niebloid) |
a view that iterates over the elements of another bidirectional view in reverse order(class template) (range adaptor object) | |
reverses the order of elements in a range (function template) |