std::swap_ranges

 

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Defined in header <algorithm>
template<class ForwardIt1, class ForwardIt2 > ForwardIt2 swap_ranges( ForwardIt1 first1, ForwardIt1 last1,                         ForwardIt2 first2 );	(1)	(constexpr since C++20)
template<class ExecutionPolicy,           class ForwardIt1, class ForwardIt2 > ForwardIt2 swap_ranges( ExecutionPolicy&& policy,                         ForwardIt1 first1, ForwardIt1 last1,                         ForwardIt2 first2 );	(2)	(since C++17)

1) Exchanges elements between range [first1, last1) and another range of std::distance(first1, last1) elements starting at first2.

2) Same as (1), but executed according to policy.

This overload participates in overload resolution only if all following conditions are satisfied:

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)

If any of the following conditions is satisfied, the behavior is undefined:

• The two ranges overlap.
• There exists a pair of corresponding iterators iter1 and iter2 in the two ranges such that *iter1 is not Swappable with *iter2.

Parameters

first1, last1	-	the pair of iterators defining the range of elements to swap
first2	-	beginning of the second range of elements to swap
policy	-	the execution policy to use
Type requirements
- ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.

Return value

Iterator to the element past the last element exchanged in the range beginning with first2.

Complexity

Exactly std::distance(first1, last1) 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 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.

Notes

Implementations (e.g. MSVC STL) may enable vectorization when the iterator type satisfies LegacyContiguousIterator and swapping its value type calls neither non-trivial special member function nor ADL-found swap.

Possible implementation

template<class ForwardIt1, class ForwardIt2>constexpr//< since C++20 ForwardIt2 swap_ranges(ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2){for(; first1 != last1;++first1, ++first2)std::iter_swap(first1, first2);   return first2;}

Example

Demonstrates swapping of subranges from different containers.

Run this code

#include <algorithm>#include <iostream>#include <list>#include <vector>   auto print =[](auto comment, autoconst& seq){std::cout<< comment;for(constauto& e : seq)std::cout<< e <<' ';std::cout<<'\n';};   int main(){std::vector<char> v{'a', 'b', 'c', 'd', 'e'};std::list<char> l{'1', '2', '3', '4', '5'};   print("Before swap_ranges:\n""v: ", v); print("l: ", l);   std::swap_ranges(v.begin(), v.begin()+3, l.begin());   print("After swap_ranges:\n""v: ", v); print("l: ", l);}

Output:

Before swap_ranges: v: a b c d e l: 1 2 3 4 5 After swap_ranges: v: 1 2 3 d e l: a b c 4 5

See also

iter_swap	swaps the elements pointed to by two iterators (function template)
swap	swaps the values of two objects (function template)
ranges::swap_ranges (C++20)	swaps two ranges of elements (algorithm function object)