NAME¶

std::swap(std::unordered_map) - std::swap(std::unordered_map)

Synopsis¶

Defined in header <unordered_map>
template< class Key, class T, class Hash, class KeyEqual, class Alloc
>
(since C++11)
void swap( std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& lhs, (until C++17)

std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& rhs );
template< class Key, class T, class Hash, class KeyEqual, class Alloc
>

void swap( std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& lhs, (since C++17)

std::unordered_map<Key,T,Hash,KeyEqual,Alloc>& rhs ) noexcept(/* see
below */);

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

Parameters¶

lhs, rhs - containers whose contents to swap

Return value¶

(none)

Complexity¶

Constant.

Exceptions¶

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

Notes¶

Although the overloads of std::swap for container adaptors are introduced in C++11,
container adaptors can already be swapped by std::swap in C++98. Such calls to
std::swap usually have linear time complexity, but better complexity may be
provided.

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 << "\n" "bob :";
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 << "\n" "bob :";
std::for_each(bob.begin(), bob.end(), print);
std::cout << '\n';
}

Possible output:¶

alice: 1(a) 2(b) 3(c)
bob : 7(Z) 8(Y) 9(X) 10(W)
-- SWAP
alice: 7(Z) 8(Y) 9(X) 10(W)
bob : 1(a) 2(b) 3(c)

See also¶

swap swaps the contents
(C++11) (public member function)