Std::reverse (3) Linux Manual Page

std::reverse – std::reverse

Synopsis

Defined in header<algorithm>

    template <class BidirIt>
    (until C++ 20)

        void reverse(BidirIt first, BidirIt last);

template <class BidirIt>
(1)(since C++ 20)

    constexpr void reverse(BidirIt first, BidirIt last);

template <class ExecutionPolicy, class BidirIt>
(2)(since C++ 17)

    void reverse(ExecutionPolicy &&policy, BidirIt first, BidirIt last);

1) Reverses the order of the elements in the range [first, last)
Behaves as if applying std::iter_swap to every pair of iterators first+i, (last-i) – 1 for each non-negative i < (last-first)/2
2) Same as (1), but executed according to policy. This overload does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last – the range of elements to reverse
policy – the execution policy to use. See execution_policy for details.

Type requirements

–
BidirIt must meet the requirements of ValueSwappable and LegacyBidirectionalIterator.

Return value

(none)

Exceptions

The overload with a template parameter named ExecutionPolicy reports errors as follows:

* If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard_policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

See also the implementations in libstdc++ and libc++.

  template<class BidirIt>
  void reverse(BidirIt first, BidirIt last)
  {
      while ((first != last) && (first != –last)) {
          std::iter_swap(first++, last);
      }
  }

Complexity

Exactly (last – first)/2 swaps.

Example

// Run this code

#include <vector>

#include <iostream>

#include <iterator>

#include <algorithm>
int main()

{
    std::vector<int> v{1, 2, 3};
    std::reverse(std::begin(v), std::end(v));
    for (auto e : v)
        std::cout << e;
    std::cout << '\n';
    int a[] = {4, 5, 6, 7};
    std::reverse(std::begin(a), std::end(a));
    for (auto e : a)
        std::cout << e;
}

Output:

321
7654

std::reverse (3) Linux Manual Page