std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::merge

 

C++

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Feature test macros(C++20)

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Symbols index

External libraries

 

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node-handle (C++17)

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multimap

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unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

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std::unordered_multimap

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

 

template<class H2, class P2 > void merge(std::unordered_map<Key, T, H2, P2, Allocator>& source );	(1)	(since C++17)
template<class H2, class P2 > void merge(std::unordered_map<Key, T, H2, P2, Allocator>&& source );	(2)	(since C++17)
template<class H2, class P2 > void merge(std::unordered_multimap<Key, T, H2, P2, Allocator>& source );	(3)	(since C++17)
template<class H2, class P2 > void merge(std::unordered_multimap<Key, T, 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 <string>#include <unordered_map>#include <utility>   // print out a std::pairtemplate<class Os, class U, class V> Os& operator<<(Os& os, conststd::pair<U,V>& p){return os <<'{'<< p.first<<", "<< p.second<<'}';}   // print out an associative containertemplate<class Os, class K, class V> Os& operator<<(Os& os, conststd::unordered_multimap<K, V>& v){ os <<'['<< v.size()<<"] {";bool o{};for(constauto& e : v) os <<(o ?", ":(o =1, ""))<< e;return os <<"}\n";}   int main(){std::unordered_multimap<std::string, int> p{{"C", 3}, {"B", 2}, {"A", 1}, {"A", 0}}, q{{"E", 6}, {"E", 7}, {"D", 5}, {"A", 4}};   std::cout<<"p: "<< p <<"q: "<< q;   p.merge(q);   std::cout<<"p.merge(q);\n"<<"p: "<< p <<"q: "<< q;}

Possible output:

p: [4] {{A, 1}, {A, 0}, {B, 2}, {C, 3}} q: [4] {{A, 4}, {D, 5}, {E, 6}, {E, 7}} p.merge(q); p: [8] {{E, 6}, {E, 7}, {C, 3}, {A, 1}, {A, 0}, {A, 4}, {D, 5}, {B, 2}} 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)