std::multimap
Defined in header <map>
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template< class Key, |
(1) | |
namespace pmr { template< |
(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 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.
Contents |
[edit] Template parameters
This section is incomplete Reason: Add descriptions of the template parameters. |
[edit] Member types
Member type | Definition | ||||
key_type
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Key
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mapped_type
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T
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value_type
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std::pair<const Key, T> | ||||
size_type
|
Unsigned integer type (usually std::size_t) | ||||
difference_type
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Signed integer type (usually std::ptrdiff_t) | ||||
key_compare
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Compare
| ||||
allocator_type
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Allocator
| ||||
reference
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value_type& | ||||
const_reference
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const value_type& | ||||
pointer
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| ||||
const_pointer
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| ||||
iterator
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LegacyBidirectionalIterator to value_type
| ||||
const_iterator
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LegacyBidirectionalIterator to const value_type | ||||
reverse_iterator
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std::reverse_iterator<iterator> | ||||
const_reverse_iterator
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std::reverse_iterator<const_iterator> | ||||
node_type (since C++17)
|
a specialization of node handle representing a container node |
[edit] Member classes
compares objects of type value_type (class) |
[edit] 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) |
[edit] Non-member functions
(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20) |
lexicographically compares the values of two multimap s (function template) |
specializes the std::swap algorithm (function template) | |
(C++20) |
erases all elements satisfying specific criteria (function template) |
Deduction guides |
(since C++17) |
[edit] Notes
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_containers_ranges |
202202L | (C++23) | Ranges construction and insertion for containers |
[edit] Example
This section is incomplete Reason: no example |
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 230 | C++98 | Key was not required to be CopyConstructible(a key of type Key might not be able to be constructed)
|
Key is also required tobe CopyConstructible |
[edit] 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) |