std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::merge

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

Tables

Iterator invalidation

Member function table

Non-member function table

 

std::unordered_multiset

Member types
Member functions
unordered_multiset::unordered_multiset unordered_multiset::~unordered_multiset    unordered_multiset::operator= unordered_multiset::get_allocator Iterators unordered_multiset::beginunordered_multiset::cbegin unordered_multiset::endunordered_multiset::cend Capacity unordered_multiset::size unordered_multiset::max_size unordered_multiset::empty Modifiers unordered_multiset::clear unordered_multiset::insert unordered_multiset::insert_range (C++23) unordered_multiset::emplace unordered_multiset::emplace_hint unordered_multiset::erase unordered_multiset::swap unordered_multiset::extract (C++17) unordered_multiset::merge (C++17)	Lookup unordered_multiset::count unordered_multiset::find unordered_multiset::contains (C++20) unordered_multiset::equal_range Bucket interface unordered_multiset::begin(size_type)unordered_multiset::cbegin(size_type) unordered_multiset::end(size_type)unordered_multiset::cend(size_type) unordered_multiset::bucket_count unordered_multiset::max_bucket_count unordered_multiset::bucket_size unordered_multiset::bucket Hash policy unordered_multiset::load_factor unordered_multiset::max_load_factor unordered_multiset::rehash unordered_multiset::reserve Observers unordered_multiset::hash_function unordered_multiset::key_eq
Non-member functions
operator==operator!= (until C++20)	std::swap(std::unordered_multiset) erase_if(std::unordered_multiset) (C++20)
Deduction guides (C++17)

 

template< class H2, class P2 > void merge( std::unordered_set<Key, H2, P2, Allocator>& source );	(1)	(since C++17)
template< class H2, class P2 > void merge( std::unordered_set<Key, H2, P2, Allocator>&& source );	(2)	(since C++17)
template< class H2, class P2 > void merge( std::unordered_multiset<Key, H2, P2, Allocator>& source );	(3)	(since C++17)
template< class H2, class P2 > void merge( std::unordered_multiset<Key, H2, P2, Allocator>&& source );	(4)	(since C++17)

Attempts to extract ("splice") each element in source and insert it into *this using the hash function and key equality predicate of *this.

No elements are copied or moved, only the internal pointers of the container nodes are repointed. All pointers and references to the transferred elements remain valid, but now refer into *this, not into source. Iterators referring to the transferred elements and all iterators referring to *this are invalidated.

The behavior is undefined if get_allocator() != source.get_allocator().

Parameters

source

-

compatible container to transfer the nodes from

Return value

(none)

Complexity

Average case O(N), worst case O(N * size() + N), where N is source.size().

Example

Run this code

#include <iostream>
#include <unordered_set>
 
// print out a container
template<class Os, class K>
Os& operator<<(Os& os, const std::unordered_multiset<K>& v)
{
    os << '[' << v.size() << "] {";
    bool o{};
    for (const auto& e : v)
        os << (o ? ", " : (o = 1, " ")) << e;
    return os << " }\n";
}
 
int main()
{
    std::unordered_multiset<char>
        p{'C', 'B', 'B', 'A'}, 
        q{'E', 'D', 'E', 'C'};
 
    std::cout << "p: " << p << "q: " << q;
 
    p.merge(q);
 
    std::cout << "p.merge(q);\n" << "p: " << p << "q: " << q;
}

Possible output:

p: [4] { A, B, B, C }
q: [4] { C, D, E, E }
p.merge(q);
p: [8] { E, E, D, A, B, B, C, C }
q: [0] { }

See also

extract (C++17)	extracts nodes from the container (public member function)
insert	inserts elements or nodes(since C++17) (public member function)