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>
constexpr I reverse( I first, S last );
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(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 );
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(2) | (since C++20) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S >
requires std::permutable<I>
I reverse( Ep&& policy, I first, S last );
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(3) | (since C++26) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R >
requires std::permutable<ranges::iterator_t<R>>
ranges::borrowed_iterator_t<R> reverse( Ep&& policy, R&& r );
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(4) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
1,2) Reverses the order of the elements in the target range
[first, last) or r by swapping each pair of corresponding elements using std::iter_swap.3,4) Same as (1,2), but executed according to
policy.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.
Parameters
| first, last | - | the iterator-sentinel pair defining the target range |
| r | - | the target range |
| policy | - | the execution policy to use |
Return value
The past-the-end iterator of the target range.
Complexity
Given \(\scriptsize N\)N as ranges::distance(first, last) or ranges::distance(r):
Exceptions
3,4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
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.
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::next(ranges::begin(r), ranges::end(r)));
}
};
inline constexpr reverse_fn reverse{};
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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
| reverses the order of elements in a range (function template) | |
(C++20) |
creates a copy of a range that is reversed (algorithm function object) |
| a view that iterates over the elements of another bidirectional view in reverse order (class template) (range adaptor object) |