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

From cppreference.com

 
C++
 
Containers library
Sequence
(C++11)
(C++11)
Associative
Unordered associative
(C++11)
(C++11)
(C++11)
(C++11)
Adaptors
Views
(C++20)
 
std::unordered_set
Member functions
Iterators
Capacity
Modifiers
unordered_set::swap
(C++17)
(C++17)
Lookup
(C++20)
Bucket interface
Hash policy
Observers
Non-member functions
(until C++20)
(C++20)
Deduction guides(C++17)
 
void swap( unordered_set& other );
 (since C++11)
(until C++17)
void swap( unordered_set& 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 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_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.
}

Possible output: 

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

See also

(C++11)
 specializes the std::swap algorithm
(function template)
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/container/unordered_set/swap&oldid=121443"