std::ranges::reverse - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| Call signature | ||
| template< std::bidirectional_iterator I, std::sentinel_for<I> S > requires std::permutable<I> constexpr I reverse( I first, S last ); | (1) | (since C++20) |
| template< ranges::bidirectional_range R > requires std::permutable<ranges::iterator_t<R>> constexpr ranges::borrowed_iterator_t<R> reverse( R&& r ); | (2) | (since C++20) |
- 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.
- 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 algorithm function objects (informally known as 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.
Contents
[edit] Parameters
| first, last | - | the iterator-sentinel pair defining 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.
[edit] Example
#include #include #include #include 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