std::unordered_set<Key,Hash,KeyEqual,Allocator>:: swap

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. Hash and KeyEqual must be Swappable , and objects of these types 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).

Parameters

Exceptions

Complexity

Constant.

Example

#include <iostream>
#include <unordered_set>
template<class Os, class Co> Os& operator<<(Os& os, const Co& co)
{
    os << '{';
    for (const auto& i : co)
        os << ' ' << i;
    return os << " } ";
}
int main()
{
    std::unordered_set<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.
}

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

See also