NAME¶

std::unordered_multiset::swap - std::unordered_multiset::swap

Synopsis¶

void swap( unordered_multiset& other ); (since C++11)
(until C++17)
void swap( unordered_multiset& other ) noexcept(/* see below */); (since C++17)

Exchanges the contents of the container with those of other. Does not invoke any
move, copy, or swap operations on individual elements.

All iterators and references remain valid. The past-the-end iterator is invalidated.

The Hash and KeyEqual objects must be Swappable, and they are exchanged using
unqualified calls to non-member swap.

If std::allocator_traits<allocator_type>::propagate_on_container_swap::value
is true, then the allocators are exchanged using an unqualified call to (since
non-member swap. Otherwise, they are not swapped (and if get_allocator() != C++11)
other.get_allocator(), the behavior is undefined).

Parameters¶

other - container to exchange the contents with

Return value¶

(none)

Exceptions¶

Any exception thrown by the swap of the Hash or KeyEqual objects. (until C++17)
noexcept specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::value
(since C++17)
&& std::is_nothrow_swappable<Hash>::value

&& std::is_nothrow_swappable<key_equal>::value)

Complexity¶

Constant.

Example¶

// Run this code

#include <iostream>
#include <unordered_set>

template<class Os, class Co> Os& operator<<(Os& os, const Co& co) {
os << "{";
for (auto const& i : co) { os << ' ' << i; }
return os << " } ";
}

int main()
{
std::unordered_multiset<int> a1{3, 1, 3, 2}, a2{5, 4, 5};

auto it1 = std::next(a1.begin());
auto it2 = std::next(a2.begin());

const int& ref1 = *(a1.begin());
const int& ref2 = *(a2.begin());

std::cout << a1 << a2 << *it1 << ' ' << *it2 << ' ' << ref1 << ' ' << ref2 << '\n';
a1.swap(a2);
std::cout << a1 << a2 << *it1 << ' ' << *it2 << ' ' << ref1 << ' ' << ref2 << '\n';

// Note that every iterator referring to an element in one container before the swap
// refers to the same element in the other container after the swap. Same is true
// for references.
}

Possible output:¶

{ 2 3 3 1 } { 4 5 5 } 3 5 2 4
{ 4 5 5 } { 2 3 3 1 } 3 5 2 4

See also¶

std::swap(std::unordered_multiset) specializes the std::swap algorithm
(C++11) (function template)