Difference between revisions of "cpp/algorithm/reverse"
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===Possible implementation=== | ===Possible implementation=== | ||
| − | See also the implementations in [https://github.com/gcc-mirror/gcc/blob/ | + | Some implementations enables vectorization when {{tt|I}} is a {{named req|ContiguousIterator}} and swapping its value type does not call any non-trivial function. See also the implementations in [https://github.com/gcc-mirror/gcc/blob/14d8a5ae472ca5743016f37da2dd4770d83dea21/libstdc%2B%2B-v3/include/bits/stl_algo.h#L1087-L1152 libstdc++], [https://github.com/llvm/llvm-project/blob/6adbc83ee9e46b476e0f75d5671c3a21f675a936/libcxx/include/__algorithm/reverse.h libc++], and [https://github.com/microsoft/STL/blob/472161105d596192194d4715ccad307c6c163b4a/stl/inc/xutility#L5335-L5370 MSVC STL]. |
{{eq fun | 1= | {{eq fun | 1= | ||
template<class BidirIt> | template<class BidirIt> | ||
Revision as of 09:01, 10 August 2021
| Defined in header <algorithm>
|
||
| (1) | ||
template< class BidirIt > void reverse( BidirIt first, BidirIt last ); |
(until C++20) | |
| template< class BidirIt > constexpr void reverse( BidirIt first, BidirIt last ); |
(since C++20) | |
| template< class ExecutionPolicy, class BidirIt > void reverse( ExecutionPolicy&& policy, BidirIt first, BidirIt last ); |
(2) | (since C++17) |
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 participates in overload resolution only if |
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. |
(until C++20) |
|
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. |
(since C++20) |
Contents |
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)
Complexity
Exactly (last - first)/2 swaps.
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
ExecutionPolicyis one of the standard policies, std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Possible implementation
Some implementations enables vectorization when I is a LegacyContiguousIterator and swapping its value type does not call any non-trivial function. See also the implementations in libstdc++, libc++, and MSVC STL.
template<class BidirIt> void reverse(BidirIt first, BidirIt last) { while ((first != last) && (first != --last)) { std::iter_swap(first++, last); } } |
Example
Run this code
#include <vector> #include <iostream> #include <iterator> #include <algorithm> int main() { std::vector<int> v{1, 2, 3}; std::reverse(v.begin(), v.end()); 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
See also
| creates a copy of a range that is reversed (function template) | |
| (C++20) |
reverses the order of elements in a range (niebloid) |
