NAME¶

std::multimap - std::multimap

Synopsis¶

Defined in header <map>
template<

class Key,
class T, (1)
class Compare = std::less<Key>,
class Allocator = std::allocator<std::pair<const Key, T> >

> class multimap;
namespace pmr {

template <class Key, class T, class Compare = std::less<Key>>
using multimap = std::multimap<Key, T, Compare, (2) (since C++17)
std::pmr::polymorphic_allocator<std::pair<const Key,T>>>;

}

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.

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 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 C++11)
std::allocator_traits<Allocator>::pointer (since C++11)
Allocator::const_pointer (until
const_pointer C++11)
std::allocator_traits<Allocator>::const_pointer (since
C++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 C++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¶

begin returns an iterator to the beginning
cbegin (public member function)
(C++11)
end returns an iterator to the end
cend (public member function)
(C++11)
rbegin returns a reverse iterator to the beginning
crbegin (public member function)
(C++11)
rend returns a reverse iterator to the end
crend (public member function)
(C++11)

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)
inserts elements
insert or nodes
(since C++17)
(public member function)
emplace constructs element in-place
(C++11) (public member function)
emplace_hint constructs elements in-place using a hint
(C++11) (public member function)
erase erases elements
(public member function)
swap swaps the contents
(public member function)
extract extracts nodes from the container
(C++17) (public member function)
merge splices nodes from another container
(C++17) (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 checks if the container contains element with specific key
(C++20) (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>= lexicographically compares the values in the multimap
operator<=> (function template)
(removed in C++20)
(removed in C++20)
(removed in C++20)
(removed in C++20)
(removed in C++20)
(C++20)
std::swap(std::multimap) specializes the std::swap algorithm
(function template)
erase_if(std::multimap) Erases all elements satisfying specific criteria
(C++20) (function template)

Deduction guides(since C++17)