std::reverse (3) - Linux Manuals

std::reverse: std::reverse

NAME

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