Namespaces
Variants
Actions

std::swap(std::unordered_map)

From cppreference.com

[edit template]
 
C++
 
Containers library
 
std::unordered_map
Member types
Member functions
Non-member functions
(until C++20)
std::swap(std::unordered_map)
(C++20)
Deduction guides(C++17)
 
Defined in header <unordered_map>
template< class Key, class T, class Hash, class KeyEqual, class Alloc >

void swap( std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& lhs,

           std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& rhs );
 (since C++11)
(until C++17)
template< class Key, class T, class Hash, class KeyEqual, class Alloc >

void swap( std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& lhs,
           std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& rhs )

    noexcept(/* see below */);
 (since C++17)
(constexpr since C++26)

Specializes the std::swap algorithm for std::unordered_map. Swaps the contents of lhs and rhs. Calls lhs.swap(rhs).

Contents

[edit] Parameters

lhs, rhs - containers whose contents to swap

[edit] Complexity

Constant.

Exceptions

noexcept specification:  
noexcept(noexcept(lhs.swap(rhs)))
 (since C++17)

[edit] Example

Run this code
#include <algorithm>
#include <iostream>
#include <unordered_map>
 
int main()
{
    std::unordered_map<int, char> alice{{1, 'a'}, {2, 'b'}, {3, 'c'}};
    std::unordered_map<int, char> bob{{7, 'Z'}, {8, 'Y'}, {9, 'X'}, {10, 'W'}};
 
    auto print = [](std::pair<const int, char>& n)
    {
        std::cout << ' ' << n.first << ':' << n.second;
    };
 
    // Print state before swap
    std::cout << "Alice:";
    std::for_each(alice.begin(), alice.end(), print);
    std::cout << "\nBobby:";
    std::for_each(bob.begin(), bob.end(), print);
    std::cout << '\n';
 
    std::cout << "-- SWAP\n";
    std::swap(alice, bob);
 
    // Print state after swap
    std::cout << "Alice:";
    std::for_each(alice.begin(), alice.end(), print);
    std::cout << "\nBobby:";
    std::for_each(bob.begin(), bob.end(), print);
    std::cout << '\n';
}

Possible output: 

Alice: 1:a 2:b 3:c
Bobby: 7:Z 8:Y 9:X 10:W
-- SWAP
Alice: 7:Z 8:Y 9:X 10:W
Bobby: 1:a 2:b 3:c

[