std::swap_ranges

template< class ForwardIt1, class ForwardIt2 >
ForwardIt2 swap_ranges( ForwardIt1 first1, ForwardIt1 last1,
                        ForwardIt2 first2 );

template< class ExecutionPolicy,
          class ForwardIt1, class ForwardIt2 >
ForwardIt2 swap_ranges( ExecutionPolicy&& policy,
                        ForwardIt1 first1, ForwardIt1 last1,
                        ForwardIt2 first2 );

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

Return value

The past-the-end iterator of the second range.

Complexity

Exactly std::distance(first1, last1) swaps.

Exceptions

• If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
• If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).

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

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

auto print = [](auto comment, const auto& 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);
}

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