std::map<Key,T,Compare,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)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

Symbols index

External libraries

 

Containers library

node-handle (C++17)

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

hive (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::map

Member functions

map::map map::~map               map::operator= map::get_allocator

Element access map::at map::operator[] Iterators map::beginmap::cbegin (C++11) map::endmap::cend (C++11) map::rbeginmap::crbegin (C++11)      map::rendmap::crend (C++11) Capacity map::size map::max_size map::empty Observers map::key_comp map::value_comp Modifiers map::clear map::insert map::erase map::swap map::extract (C++17) map::merge (C++17) map::insert_range (C++23) map::insert_or_assign (C++17) map::emplace (C++11) map::emplace_hint (C++11) map::try_emplace (C++17) Lookup map::count map::find map::contains (C++20) map::equal_range map::lower_bound map::upper_bound

Non-member functions

operator==operator<=> (C++20) std::swap(std::map) erase_if(std::map) (C++20)   operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)

Deduction guides (C++17)

 

template< class C2 > void merge( std::map<Key, T, C2, Allocator>& source );	(1)	(since C++17) (constexpr since C++26)
template< class C2 > void merge( std::map<Key, T, C2, Allocator>&& source );	(2)	(since C++17) (constexpr since C++26)
template< class C2 > void merge( std::multimap<Key, T, C2, Allocator>& source );	(3)	(since C++17) (constexpr since C++26)
template< class C2 > void merge( std::multimap<Key, T, C2, Allocator>&& source );	(4)	(since C++17) (constexpr since C++26)

Attempts to extract (“splice”) each element in source and insert it into *this using the comparison object of *this. If there is an element in *this with key equivalent to the key of an element from source, then that element is not extracted from source. If get_allocator() == source.get_allocator() is false, the behavior is undefined.

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.

Parameters

source

-

compatible container to transfer the nodes from

Exceptions

Does not throw unless comparison throws.

Complexity

Given \(\scriptsize S\)S as size() and \(\scriptsize N\)N as source.size():

1-4) \(\scriptsize S \cdot \log(S + N)\)S·log(S+N)

Example

Run this code

#include <iostream>
#include <map>
#include <string>
 
int main()
{
    std::map<int, std::string> ma{{1, "apple"}, {5, "pear"}, {10, "banana"};
    std::map<int, std::string> mb{{2, "zorro"}, {4, "batman"}, {5, "X"}, {8, "alpaca"};
    std::map<int, std::string> u;
    u.merge(ma);
    std::cout << "ma.size(): " << ma.size() << '\n';
    u.merge(mb);
    std::cout << "mb.size(): " << mb.size() << '\n';
    std::cout << "mb.at(5): " << mb.at(5) << '\n';
    for (const auto& kv : u)
        std::cout << kv.first << ", " << kv.second << '\n';
}

Output:

ma.size(): 0
mb.size(): 1
mb.at(5): X
1, apple
2, zorro
4, batman
5, pear
8, alpaca
10, banana

See also

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

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