# std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::swap

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< cpp‎ | container‎ | unordered multiset

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 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 non-member `swap`. Otherwise, they are not swapped (and if get_allocator() != other.get_allocator(), the behavior is undefined). | (since C++11)

### 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 && std::is_nothrow_swappable<Hash>::value && std::is_nothrow_swappable<key_equal>::value) | (since C++17)

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

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