NAME¶

std::swap_ranges - std::swap_ranges

Synopsis¶

Defined in header <algorithm>
template< class ForwardIt1, class ForwardIt2 >

ForwardIt2 swap_ranges( ForwardIt1 first1, ForwardIt1 last1, (until C++20)

ForwardIt2 first2 );
template< class ForwardIt1, class ForwardIt2 >

constexpr ForwardIt2 swap_ranges( ForwardIt1 first1, (since C++20)
ForwardIt1 last1, (1)

ForwardIt2 first2 );
template< class ExecutionPolicy, class ForwardIt1, class
ForwardIt2 >
(2) (since C++17)
ForwardIt2 swap_ranges( ExecutionPolicy&& policy,

ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2 );

1) Exchanges elements between range [first1, last1) and another range starting at
first2.
Precondition: the two ranges [first1, last1) and [first2, last2) do not overlap,
where last2 = std::next(first2, std::distance(first1, last1)).
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>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.

Parameters¶

first1, last1 - the first range of elements to swap
first2 - beginning of the second range of elements to swap
policy - the execution policy to use. See execution policy for
details.

Type requirements¶

-
ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
The types of dereferenced ForwardIt1 and ForwardIt2 must meet the requirements of
Swappable

Return value¶

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

Complexity¶

linear in the distance between first1 and last1.

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 ForwardIt2 swap_ranges(ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2)
{
while (first1 != last1) {
std::iter_swap(first1++, first2++);
}
return first2;
}

Example¶

Demonstrates swapping of subranges from different containers.

// Run this code

#include <list>
#include <vector>
#include <iostream>
#include <algorithm>

auto print = [](auto comment, auto const& seq) {
std::cout << comment;
for (const auto& 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 swaps two ranges of elements
(C++20) (niebloid)