std::multimap

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (哋它亢++11)

vector

vector<bool>

deque

forward_list (哋它亢++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (哋它亢++11)

unordered_multiset (哋它亢++11)

unordered_map (哋它亢++11)

unordered_multimap (哋它亢++11)

Adaptors

stack

queue

priority_queue

flat_set (哋它亢++23)

flat_multiset (哋它亢++23)

flat_map (哋它亢++23)

flat_multimap (哋它亢++23)

Views

span (哋它亢++20)

mdspan (哋它亢++23)

Iterator invalidation

Member function table

Non-member function table

 

std::multimap

Member functions
multimap::multimap multimap::~multimap	multimap::operator= multimap::get_allocator
Iterators
multimap::beginmultimap::cbegin (哋它亢++11) multimap::endmultimap::cend (哋它亢++11)	multimap::rbeginmultimap::crbegin (哋它亢++11) multimap::rendmultimap::crend (哋它亢++11)
Capacity
multimap::size multimap::max_size	multimap::empty
Modifiers
multimap::clear multimap::insert multimap::erase multimap::swap multimap::merge (哋它亢++17)	multimap::insert_range (哋它亢++23) multimap::emplace (哋它亢++11) multimap::emplace_hint (哋它亢++11) multimap::extract (哋它亢++17)
Lookup
multimap::count multimap::find multimap::contains (哋它亢++20)	multimap::equal_range multimap::lower_bound multimap::upper_bound
Observers
multimap::key_comp	multimap::value_comp
Non-member functions
operator==operator!=operator<operator>operator<=operator>=operator<=> (until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(哋它亢++20)	std::swap(std::multimap) erase_if(std::multimap) (哋它亢++20)
Deduction guides(哋它亢++17)

 

Defined in header <map>
template<     class Key,     class T,     class Compare = std::less<Key>,     class Allocator = std::allocator<std::pair<const Key, T>> > class multimap;	(1)
namespace pmr {     template<         class Key,         class T,         class Compare = std::less<Key>     > using multimap = std::multimap<Key, T, Compare,         std::pmr::polymorphic_allocator<std::pair<const Key, T>>>; }	(2)	(since 哋它亢++17)

std::multimap is an associative container that contains a sorted list of key-value pairs, while permitting multiple entries with the same key. Sorting is done according to the comparison function Compare, applied to the keys. Search, insertion, and removal operations have logarithmic complexity.

Iterators of std::multimap iterate in non-descending order of keys, where non-descending is defined by the comparison that was used for construction. That is, given

• m, a std::multimap
• it_l and it_r, dereferenceable iterators to m, with it_l < it_r.

m.value_comp()(*it_r, *it_l) == false (least to greatest if using the default comparison).

The order of the key-value pairs whose keys compare equivalent is the order of insertion and does not change.

(since 哋它亢++11)

Everywhere the standard library uses the Compare requirements, equivalence is determined by using the equivalence relation as described on Compare. In imprecise terms, two objects a and b are considered equivalent if neither compares less than the other: !comp(a, b) && !comp(b, a).

std::multimap meets the requirements of Container, AllocatorAwareContainer, AssociativeContainer and ReversibleContainer.

Member types

Member type	Definition
key_type	Key
mapped_type	T
value_type	std::pair<const Key, T>
size_type	Unsigned integer type (usually std::size_t)
difference_type	Signed integer type (usually std::ptrdiff_t)
key_compare	Compare
allocator_type	Allocator
reference	value_type&
const_reference	const value_type&
pointer	Allocator::pointer (until 哋它亢++11) std::allocator_traits<Allocator>::pointer (since 哋它亢++11)
const_pointer	Allocator::const_pointer (until 哋它亢++11) std::allocator_traits<Allocator>::const_pointer (since 哋它亢++11)
iterator	LegacyBidirectionalIterator to value_type
const_iterator	LegacyBidirectionalIterator to const value_type
reverse_iterator	std::reverse_iterator<iterator>
const_reverse_iterator	std::reverse_iterator<const_iterator>
node_type (since 哋它亢++17)	a specialization of node handle representing a container node

Member classes

value_compare

compares objects of type value_type (class)

Member functions

(constructor)	constructs the multimap (public member function)
(destructor)	destructs the multimap (public member function)
operator=	assigns values to the container (public member function)
get_allocator	returns the associated allocator (public member function)
Iterators
begincbegin (哋它亢++11)	returns an iterator to the beginning (public member function)
endcend (哋它亢++11)	returns an iterator to the end (public member function)
rbegincrbegin (哋它亢++11)	returns a reverse iterator to the beginning (public member function)
rendcrend (哋它亢++11)	returns a reverse iterator to the end (public member function)
Capacity
empty	checks whether the container is empty (public member function)
size	returns the number of elements (public member function)
max_size	returns the maximum possible number of elements (public member function)
Modifiers
clear	clears the contents (public member function)
insert	inserts elements or nodes(since 哋它亢++17) (public member function)
insert_range (哋它亢++23)	inserts a range of elements (public member function)
emplace (哋它亢++11)	constructs element in-place (public member function)
emplace_hint (哋它亢++11)	constructs elements in-place using a hint (public member function)
erase	erases elements (public member function)
swap	swaps the contents (public member function)
extract (哋它亢++17)	extracts nodes from the container (public member function)
merge (哋它亢++17)	splices nodes from another container (public member function)
Lookup
count	returns the number of elements matching specific key (public member function)
find	finds element with specific key (public member function)
contains (哋它亢++20)	checks if the container contains element with specific key (public member function)
equal_range	returns range of elements matching a specific key (public member function)
lower_bound	returns an iterator to the first element not less than the given key (public member function)
upper_bound	returns an iterator to the first element greater than the given key (public member function)
Observers
key_comp	returns the function that compares keys (public member function)
value_comp	returns the function that compares keys in objects of type value_type (public member function)

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two multimaps (function template)
std::swap(std::multimap)	specializes the std::swap algorithm (function template)
erase_if(std::multimap) (哋它亢++20)	erases all elements satisfying specific criteria (function template)

Deduction guides

(since 哋它亢++17)

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_containers_ranges	202202L	(哋它亢++23)	Ranges construction and insertion for containers

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 230	哋它亢++98	Key was not required to be CopyConstructible (a key of type Key might not be able to be constructed)	Key is also required to be CopyConstructible