NAME¶

std::swap_ranges - std::swap_ranges

Synopsis¶

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

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

ForwardIt2 first2 );
template< class ExecutionPolicy,

class ForwardIt1, class ForwardIt2 >
ForwardIt2 swap_ranges( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt1 first1, ForwardIt1
last1,

ForwardIt2 first2 );

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

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 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.

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, 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)