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std::ranges::reverse

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
(C++11)
(C++11)
(C++17)

 
Constrained algorithms
All names in this menu belong to namespace std::ranges
       
       
    
     
         
       
       
(C++23)
(C++23)  
(C++23)
(C++23)  
(C++23)            
 
Defined in header <algorithm>
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)
1) Reverses the order of the elements in the range [firstlast).
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 algorithm function objects (informally known as niebloids), that is:

[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.

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

creates a copy of a range that is reversed
(algorithm function object)[edit]
a view that iterates over the elements of another bidirectional view in reverse order
(class template) (range adaptor object)[edit]
reverses the order of elements in a range
(function template) [edit]
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