From cppreference.com
Defined in header
template<classKey,classT,classCompare=std::less<Key>,classAllocator=std::allocator<std::pair<constKey,T>>>classmultimap; (1) namespacepmr{template<classKey,classT,classCompare=std::less<Key>>usingmultimap=std::multimap<Key,T,Compare,std::pmr::polymorphic_allocator<std::pair<constKey,T>>>;} (2) (since C++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 C++11)Everywhere the standard library uses the
requirements, equivalence is determined by using the equivalence relation as described on
. 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
,
,
and
.
All member functions of std::multimap are constexpr: it is possible to create and use std::multimap objects in the evaluation of a constant expression.
However, defining a constexprstd::multimap variable is generally an error, because constant evaluation requires any dynamically allocated storage to be released in the same evaluation, which is usually not the case with std::multimap's initializer.
(since C++26)Template parameters
Member types
Member classes
Member functions
constructs the multimap
(public member function)
destructs the multimap
(public member function)
assigns values to the container
(public member function)
returns the associated allocator
(public member function)
Iterators
(C++11)
returns an iterator to the beginning
(public member function)
(C++11)
returns an iterator to the end
(public member function)
(C++11)
returns a reverse iterator to the beginning
(public member function)
(C++11)
returns a reverse iterator to the end
(public member function)
Capacity
checks whether the container is empty
(public member function)
returns the number of elements
(public member function)
returns the maximum possible number of elements
(public member function)
Modifiers
clears the contents
(public member function)
inserts elements or nodes(since C++17)
(public member function)
(C++23)
inserts a range of elements
(public member function)
(C++11)
constructs element in-place
(public member function)
(C++11)
constructs elements in-place using a hint
(public member function)
erases elements
(public member function)
swaps the contents
(public member function)
(C++17)
extracts nodes from the container
(public member function)
(C++17)
splices nodes from another container
(public member function)
Lookup
returns the number of elements matching specific key
(public member function)
finds element with specific key
(public member function)
(C++20)
checks if the container contains element with specific key
(public member function)
returns range of elements matching a specific key
(public member function)
returns an iterator to the first element not less than the given key
(public member function)
returns an iterator to the first element greater than the given key
(public member function)
Observers
returns the function that compares keys
(public member function)
returns the function that compares keys in objects of type value_type
(public member function)
Non-member functions
Notes
macro ValueStdFeature
(C++23)Ranges construction and insertion for containers
(C++26)Constexpr std::multimapExample
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 Key was not required to be
(a key of type Key might not be able to be constructed) Key is also required to
be
See also
collection of key-value pairs, sorted by keys, keys are unique
(class template)
(C++11)
collection of key-value pairs, hashed by keys
(class template)
(C++23)
adapts two containers to provide a collection of key-value pairs, sorted by keys
(class template)