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Difference between revisions of "cpp/container/unordered multimap"

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< cpp‎ | container
m (→‎Member types: ~Type)
 
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{{cpp/title|unordered_multimap}}
 
{{cpp/title|unordered_multimap}}
 
{{cpp/container/unordered_multimap/navbar}}
 
{{cpp/container/unordered_multimap/navbar}}
−
{{ddcl | header=unordered_map | since=c++11 |
+
{{dcl begin}}
 +
{{dcl header|unordered_map}}
 +
{{dcl|num=1|since=c++11|1=
 
template<
 
template<
 
     class Key,
 
     class Key,
 
     class T,
 
     class T,
−
     class Hash {{=}} std::hash<Key>,
+
     class Hash = std::hash<Key>,
−
     class KeyEqual {{=}} std::equal_to<Key>,
+
     class KeyEqual = std::equal_to<Key>,
−
     class Allocator {{=}} std::allocator< std::pair<const Key, T> >
+
     class Allocator = std::allocator<std::pair<const Key, T>>
 
> class unordered_multimap;
 
> class unordered_multimap;
−
}}  
+
}}
 +
{{dcl|num=2|since=c++17|1=
 +
namespace pmr {
 +
    template<
 +
        class Key,
 +
        class T,
 +
        class Hash = std::hash<Key>,
 +
        class Pred = std::equal_to<Key>
 +
    > using unordered_multimap =
 +
          std::unordered_multimap<Key, T, Hash, Pred,
 +
              std::pmr::polymorphic_allocator<std::pair<const Key, T>>>;
 +
}
 +
}}
 +
{{dcl end}}
  
−
Unordered multimap is an unordered associative container that supports equivalent keys (an unordered_multimap may contain multiple copies of each key value) and that associates values of another type with the keys. The unordered_multimap class supports forward iterators. Search, insertion, and removal have average constant-time complexity.
+
{{tt|std::unordered_multimap}} is an unordered associative container that supports equivalent keys (an unordered_multimap may contain multiple copies of each key value) and that associates values of another type with the keys. The unordered_multimap class supports forward iterators. Search, insertion, and removal have average constant-time complexity.
  
−
Internally, the elements are not sorted in any particular order, but organized into buckets. Which bucket an element is placed into depends entirely on the hash of its key. This allows fast access to individual elements, since once hash is computed, it refers to the exact bucket the element is placed into.
+
Internally, the elements are not sorted in any particular order, but organized into buckets. Which bucket an element is placed into depends entirely on the hash of its key. This allows fast access to individual elements, since once the hash is computed, it refers to the exact bucket the element is placed into.
  
−
{{tt|std::unordered_multimap}} meets the requirements of {{concept|Container}}, {{concept|AllocatorAwareContainer}}, {{concept|UnorderedAssociativeContainer}}.
+
The iteration order of this container is not required to be stable (so, for example, {{lc|std::equal}} cannot be used to compare two {{tt|std::unordered_multimap}}s), except that every group of elements whose keys compare ''equivalent'' (compare equal with {{lc|key_eq()}} as the comparator) forms a contiguous subrange in the iteration order, also accessible with {{lc|std::unordered_multimap::equal_range|equal_range()}}.
 +
 
 +
{{tt|std::unordered_multimap}} meets the requirements of {{named req|Container}}, {{named req|AllocatorAwareContainer}}, {{named req|UnorderedAssociativeContainer}}.
 +
 
 +
===Template parameters===
 +
{{todo|Add descriptions of the template parameters.}}
  
 
===Member types===
 
===Member types===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc hitem | Member type | Definition}}
+
{{dsc hitem|Type|Definition}}
−
{{dsc inc | cpp/container/dsc key_type | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc key_type|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc mapped_type | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc mapped_type|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc value_type | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc value_type|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc size_type | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc size_type|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc difference_type | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc difference_type|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc hasher | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc hasher|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc key_equal | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc key_equal|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc allocator_type | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc allocator_type|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc reference | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc reference|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc const_reference | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc const_reference|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc pointer | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc pointer|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc const_pointer | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc const_pointer|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc iterator | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc iterator|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc const_iterator | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc const_iterator|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc local_iterator | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc local_iterator|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc const_local_iterator | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc const_local_iterator|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc node_type|unordered_multimap}}
 
{{dsc end}}
 
{{dsc end}}
  
 
===Member functions===
 
===Member functions===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/container/dsc constructor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc constructor|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc destructor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc destructor|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc operator{{=}} | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc operator{{=}}|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc get_allocator | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc get_allocator|unordered_multimap}}
  
−
{{dsc h2 | Iterators}}
+
{{dsc h2|Iterators}}
−
{{dsc inc | cpp/container/dsc begin | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc begin|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc end | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc end|unordered_multimap}}
  
−
{{dsc h2 | Capacity}}
+
{{dsc h2|Capacity}}
−
{{dsc inc | cpp/container/dsc empty | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc empty|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc size | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc size|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc max_size | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc max_size|unordered_multimap}}
  
−
{{dsc h2 | Modifiers}}
+
{{dsc h2|Modifiers}}
−
{{dsc inc | cpp/container/dsc clear | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc clear|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc insert | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc insert|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc emplace | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc insert_range|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc emplace_hint | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc emplace|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc erase | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc emplace_hint|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc swap | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc erase|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc swap|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc extract|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc merge|unordered_multimap}}
  
−
{{dsc h2 | Lookup}}
+
{{dsc h2|Lookup}}
−
{{dsc inc | cpp/container/dsc count | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc count|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc find | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc find|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc equal_range | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc contains|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc equal_range|unordered_multimap}}
  
−
{{dsc h2 | Bucket interface}}
+
{{dsc h2|Bucket interface}}
−
{{dsc inc | cpp/container/dsc begin(int) | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc begin(int)|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc end(int) | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc end(int)|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc bucket_count | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc bucket_count|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc max_bucket_count | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc max_bucket_count|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc bucket_size | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc bucket_size|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc bucket | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc bucket|unordered_multimap}}
  
−
{{dsc h2 | Hash policy}}
+
{{dsc h2|Hash policy}}
−
{{dsc inc | cpp/container/dsc load_factor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc load_factor|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc max_load_factor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc max_load_factor|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc rehash | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc rehash|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc reserve | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc reserve|unordered_multimap}}
  
−
{{dsc h2 | Observers}}
+
{{dsc h2|Observers}}
−
{{dsc inc | cpp/container/dsc hash_function | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc hash_function|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc key_eq | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc key_eq|unordered_multimap}}
 
{{dsc end}}
 
{{dsc end}}
  
 
===Non-member functions===
 
===Non-member functions===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/container/dsc operator_cmp_unord | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc operator_cmp_unord|unordered_multimap}}
−
{{dsc inc | cpp/container/dsc swap2 | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc swap2|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc erase_if|unordered_multimap}}
 +
{{dsc end}}
 +
 
 +
{{rrev|since=c++17|
 +
==={{rl|deduction guides|Deduction guides}}===
 +
}}
 +
 
 +
===Notes===
 +
{{ftm begin|std=1|comment=1}}
 +
{{ftm|__cpp_lib_containers_ranges|value=202202L|std=C++23|Ranges construction and insertion for containers}}
 +
{{ftm end}}
 +
 
 +
===Example===
 +
{{example}}
 +
 
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=2050|std=C++11|before=the definitions of {{tt|reference}}, {{tt|const_reference}}, {{tt|pointer}}<br>and {{tt|const_pointer}} were based on {{tt|allocator_type}}|after=based on {{tt|value_type}} and<br>{{lc|std::allocator_traits}}}}
 +
{{dr list end}}
 +
 
 +
===See also===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/container/dsc unordered_map}}
 +
{{dsc inc|cpp/container/dsc multimap}}
 +
{{dsc inc|cpp/container/dsc flat_multimap}}
 
{{dsc end}}
 
{{dsc end}}
  
−
[[de:cpp/container/unordered multimap]]
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
−
[[es:cpp/container/unordered multimap]]
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[[fr:cpp/container/unordered multimap]]
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[[it:cpp/container/unordered multimap]]
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[[ja:cpp/container/unordered multimap]]
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[[pt:cpp/container/unordered multimap]]
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[[ru:cpp/container/unordered multimap]]
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[[zh:cpp/container/unordered multimap]]
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Latest revision as of 15:46, 1 November 2024

 
C++
 
Containers library
 
std::unordered_multimap
Member types
Member functions
Non-member functions
(until C++20)
Deduction guides (C++17)
 
Defined in header <unordered_map>
template<

    class Key,
    class T,
    class Hash = std::hash<Key>,
    class KeyEqual = std::equal_to<Key>,
    class Allocator = std::allocator<std::pair<const Key, T>>

> class unordered_multimap;
 (1) (since C++11)
namespace pmr {

    template<
        class Key,
        class T,
        class Hash = std::hash<Key>,
        class Pred = std::equal_to<Key>
    > using unordered_multimap =
          std::unordered_multimap<Key, T, Hash, Pred,
              std::pmr::polymorphic_allocator<std::pair<const Key, T>>>;

}
 (2) (since C++17)

std::unordered_multimap is an unordered associative container that supports equivalent keys (an unordered_multimap may contain multiple copies of each key value) and that associates values of another type with the keys. The unordered_multimap class supports forward iterators. Search, insertion, and removal have average constant-time complexity.

Internally, the elements are not sorted in any particular order, but organized into buckets. Which bucket an element is placed into depends entirely on the hash of its key. This allows fast access to individual elements, since once the hash is computed, it refers to the exact bucket the element is placed into.

The iteration order of this container is not required to be stable (so, for example, std::equal cannot be used to compare two std::unordered_multimaps), except that every group of elements whose keys compare equivalent (compare equal with key_eq() as the comparator) forms a contiguous subrange in the iteration order, also accessible with equal_range().

std::unordered_multimap meets the requirements of Container, AllocatorAwareContainer, UnorderedAssociativeContainer.

Contents

[edit] Template parameters

This section is incomplete
Reason: Add descriptions of the template parameters.

[edit] Member types

Type Definition
key_type Key[edit]
mapped_type T[edit]
value_type std::pair<const Key, T>[edit]
size_type Unsigned integer type (usually std::size_t)[edit]
difference_type Signed integer type (usually std::ptrdiff_t)[edit]
hasher Hash[edit]
key_equal KeyEqual[edit]
allocator_type Allocator[edit]
reference value_type&[edit]
const_reference const value_type&[edit]
pointer std::allocator_traits<Allocator>::pointer[edit]
const_pointer std::allocator_traits<Allocator>::const_pointer[edit]
iterator LegacyForwardIterator to value_type[edit]
const_iterator LegacyForwardIterator to const value_type[edit]
local_iterator An iterator type whose category, value, difference, pointer and
reference types are the same as iterator. This iterator
can be used to iterate through a single bucket but not across buckets[edit]
const_local_iterator An iterator type whose category, value, difference, pointer and
reference types are the same as const_iterator. This iterator
can be used to iterate through a single bucket but not across buckets[edit]
node_type (since C++17) a specialization of node handle representing a container node[edit]

[edit] Member functions

 constructs the unordered_multimap
(public member function) [edit]
destructs the unordered_multimap
(public member function) [edit]
assigns values to the container
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Iterators
returns an iterator to the beginning
(public member function) [edit]
returns an iterator to the end
(public member function) [edit]
Capacity
checks whether the container is empty
(public member function) [edit]
returns the number of elements
(public member function) [edit]
returns the maximum possible number of elements
(public member function) [edit]
Modifiers
clears the contents
(public member function) [edit]
inserts elements or nodes(since C++17)
(public member function) [edit]
(C++23)
 inserts a range of elements
(public member function) [edit]
constructs element in-place
(public member function) [edit]
constructs elements in-place using a hint
(public member function) [edit]
erases elements
(public member function) [edit]
swaps the contents
(public member function) [edit]
(C++17)
 extracts nodes from the container
(public member function) [edit]
(C++17)
 splices nodes from another container
(public member function) [edit]
Lookup
returns the number of elements matching specific key
(public member function) [edit]
finds element with specific key
(public member function) [edit]
(C++20)
 checks if the container contains element with specific key
(public member function) [edit]
returns range of elements matching a specific key
(public member function) [edit]
Bucket interface
returns an iterator to the beginning of the specified bucket
(public member function) [edit]
returns an iterator to the end of the specified bucket
(public member function) [edit]
returns the number of buckets
(public member function) [edit]
returns the maximum number of buckets
(public member function) [edit]
returns the number of elements in specific bucket
(public member function) [edit]
returns the bucket for specific key
(public member function) [edit]
Hash policy
returns average number of elements per bucket
(public member function) [edit]
manages maximum average number of elements per bucket
(public member function) [edit]
reserves at least the specified number of buckets and regenerates the hash table
(public member function) [edit]
reserves space for at least the specified number of elements and regenerates the hash table
(public member function) [edit]
Observers
returns function used to hash the keys
(public member function) [edit]
returns the function used to compare keys for equality
(public member function) [edit]

[edit] Non-member functions

(C++11)(C++11)(removed in C++20)
 compares the values in the unordered_multimap
(function template) [edit]
(C++11)
 specializes the std::swap algorithm
(function template) [edit]
(C++20)
 erases all elements satisfying specific criteria
(function template) [edit]

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 2050 C++11 the definitions of reference, const_reference, pointer
and const_pointer were based on allocator_type 		based on value_type and
std::allocator_traits

[edit] See also

(C++11)
 collection of key-value pairs, hashed by keys, keys are unique
(class template) [edit]
collection of key-value pairs, sorted by keys
(class template) [edit]
(C++23)
 adapts two containers to provide a collection of key-value pairs, sorted by keys
(class template) [edit]
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