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

From cppreference.com
< cpp‎ | container
(Undo revision 9452 by 64.222.253.193 (talk) unordered_multimap is defined in <unordered_map>)
m (→‎Member types: ~Type)
 
(40 intermediate revisions by 14 users not shown)
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{{cpp/title|unordered_multimap}}
 
{{cpp/title|unordered_multimap}}
−
{{cpp/container/unordered_multimap/sidebar}}
+
{{cpp/container/unordered_multimap/navbar}}
−
{{ddcl | header=unordered_map | notes={{mark c++11 feature}} |
+
{{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.
+
{{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.
  
−
===Member types===
+
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.
−
{{tdcl list begin}}
+
−
{{tdcl list hitem | Member type | Definition}}
+
−
{{tdcl list template | cpp/container/tdcl list key_type | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list mapped_type | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list value_type | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list size_type | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list difference_type | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list hasher | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list key_equal | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list allocator_type | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list reference | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_reference | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list pointer | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_pointer | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list iterator | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_iterator | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list local_iterator | unordered_multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_local_iterator | unordered_multimap}}
+
−
{{tdcl list end}}
+
  
 +
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===
 +
{{dsc begin}}
 +
{{dsc hitem|Type|Definition}}
 +
{{dsc inc|cpp/container/dsc key_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 size_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 key_equal|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc allocator_type|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc 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 const_pointer|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc 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 const_local_iterator|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc node_type|unordered_multimap}}
 +
{{dsc end}}
  
 
===Member functions===
 
===Member functions===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/container/dcl list constructor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc constructor|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list destructor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc destructor|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list operator{{=}} | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc operator{{=}}|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list get_allocator | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc get_allocator|unordered_multimap}}
  
−
{{dcl list h2 | Iterators}}
+
{{dsc h2|Iterators}}
−
{{dcl list template | cpp/container/dcl list begin | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc begin|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list end | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc end|unordered_multimap}}
  
−
{{dcl list h2 | Capacity}}
+
{{dsc h2|Capacity}}
−
{{dcl list template | cpp/container/dcl list empty | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc empty|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list size | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc size|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list max_size | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc max_size|unordered_multimap}}
  
−
{{dcl list h2 | Modifiers}}
+
{{dsc h2|Modifiers}}
−
{{dcl list template | cpp/container/dcl list clear | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc clear|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list insert | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc insert|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list emplace | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc insert_range|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list emplace_hint | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc emplace|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list erase | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc emplace_hint|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list 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}}
  
−
{{dcl list h2 | Lookup}}
+
{{dsc h2|Lookup}}
−
{{dcl list template | cpp/container/dcl list count | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc count|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list find | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc find|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list equal_range | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc contains|unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc equal_range|unordered_multimap}}
  
−
{{dcl list h2 | Bucket interface}}
+
{{dsc h2|Bucket interface}}
−
{{dcl list template | cpp/container/dcl list begin(int) | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc begin(int)|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list end(int) | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc end(int)|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list bucket_count | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc bucket_count|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list max_bucket_count | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc max_bucket_count|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list bucket_size | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc bucket_size|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list bucket | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc bucket|unordered_multimap}}
  
−
{{dcl list h2 | Hash policy}}
+
{{dsc h2|Hash policy}}
−
{{dcl list template | cpp/container/dcl list load_factor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc load_factor|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list max_load_factor | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc max_load_factor|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list rehash | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc rehash|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list reserve | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc reserve|unordered_multimap}}
  
−
{{dcl list h2 | Observers}}
+
{{dsc h2|Observers}}
−
{{dcl list template | cpp/container/dcl list hash_function | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc hash_function|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list key_eq | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc key_eq|unordered_multimap}}
−
{{dcl list end}}
+
{{dsc end}}
  
 
===Non-member functions===
 
===Non-member functions===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/container/dcl list operator_comp_unord | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc operator_cmp_unord|unordered_multimap}}
−
{{dcl list template | cpp/container/dcl list std_swap | unordered_multimap}}
+
{{dsc inc|cpp/container/dsc swap2|unordered_multimap}}
−
{{dcl list end}}
+
{{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}}
 +
 
 +
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

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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