Difference between revisions of "cpp/algorithm/ranges/reverse"
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Revision as of 11:02, 27 January 2021
| 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 |
Parameters
| first, last | - | the range of elements to reverse |
| r | - | the range of elements to reverse |
Return value
An iterator equal to last.
Complexity
Exactly (last - first)/2 swaps.
Possible implementation
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{}; |
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
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) |
