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Difference between revisions of "cpp/container/multimap"

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{{cpp/title|multimap}}
 
{{cpp/title|multimap}}
−
{{cpp/container/multimap/sidebar}}
+
{{cpp/container/multimap/navbar}}
−
{{ddcl | header=map |
+
{{dcl begin}}
 +
{{dcl header|map}}
 +
{{dcl|num=1|1=
 
template<
 
template<
 
     class Key,
 
     class Key,
 
     class T,
 
     class T,
−
     class Compare {{=}} std::less<Key>,
+
     class Compare = std::less<Key>,
−
     class Allocator {{=}} std::allocator<std::pair<const Key, T> >
+
     class Allocator = std::allocator<std::pair<const Key, T>>
 
> class multimap;
 
> class multimap;
−
}}  
+
}}
 +
{{dcl|num=2|since=c++17|1=
 +
namespace pmr {
 +
    template<
 +
        class Key,
 +
        class T,
 +
        class Compare = std::less<Key>
 +
    > using multimap = std::multimap<Key, T, Compare,
 +
        std::pmr::polymorphic_allocator<std::pair<const Key, T>>>;
 +
}
 +
}}
 +
{{dcl end}}
  
−
Multimap is an associative container that contains a sorted list of key-value pairs. That list is sorted according keys of the elements.  
+
{{tt|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 {{tt|Compare}}, applied to the keys. Search, insertion, and removal operations have logarithmic complexity.
  
−
{{tdcl list begin}}
+
Iterators of {{tt|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
−
{{tdcl list h1 | Member types}}
+
* {{c|m}}, a {{tt|std::multimap}}
−
{{tdcl list hitem | Member type | Definition}}
+
* {{c|it_l}} and {{c|it_r}}, dereferenceable iterators to {{c|m}}, with {{c|it_l < it_r}}.
−
{{tdcl list template | cpp/container/tdcl list key_type | multimap}}
+
{{c|1=m.value_comp()(*it_r, *it_l) == false}} (least to greatest if using the default comparison).
−
{{tdcl list template | cpp/container/tdcl list mapped_type | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list value_type | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list size_type | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list difference_type | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list key_compare | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list allocator_type | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list reference | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_reference | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list pointer | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_pointer | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list iterator | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_iterator | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list reverse_iterator | multimap}}
+
−
{{tdcl list template | cpp/container/tdcl list const_reverse_iterator | multimap}}
+
−
{{tdcl list end}}
+
  
 +
{{rrev|since=c++11|
 +
The order of the key-value pairs whose keys compare equivalent is the order of insertion and does not change.
 +
}}
  
 +
Everywhere the standard library uses the {{named req|Compare}} requirements, equivalence is determined by using the equivalence relation as described on {{named req|Compare}}. In imprecise terms, two objects {{c|a}} and {{c|b}} are considered equivalent if neither compares less than the other: {{c|!comp(a, b) && !comp(b, a)}}.
  
−
{{dcl list begin}}
+
{{tt|std::multimap}} meets the requirements of {{named req|Container}}, {{named req|AllocatorAwareContainer}}, {{named req|AssociativeContainer}} and {{named req|ReversibleContainer}}.
−
{{dcl list h1 | Member functions}}
+
−
{{dcl list template | cpp/container/dcl list constructor | multimap}}
+
−
{{dcl list template | cpp/container/dcl list destructor | multimap}}
+
−
{{dcl list template | cpp/container/dcl list operator{{=}} | multimap}}
+
−
{{dcl list template | cpp/container/dcl list get_allocator | multimap}}
+
  
−
{{dcl list h2 | Iterators}}
+
===Template parameters===
−
{{dcl list template | cpp/container/dcl list begin | multimap}}
+
{{todo|Add descriptions of the template parameters.}}
−
{{dcl list template | cpp/container/dcl list end | multimap}}
+
−
{{dcl list template | cpp/container/dcl list rbegin | multimap}}
+
−
{{dcl list template | cpp/container/dcl list rend | multimap}}
+
  
−
{{dcl list h2 | Capacity}}
+
===Member types===
−
{{dcl list template | cpp/container/dcl list empty | multimap}}
+
{{dsc begin}}
−
{{dcl list template | cpp/container/dcl list size | multimap}}
+
{{dsc hitem|Type|Definition}}
−
{{dcl list template | cpp/container/dcl list max_size | multimap}}
+
{{dsc inc|cpp/container/dsc key_type|multimap}}
 +
{{dsc inc|cpp/container/dsc mapped_type|multimap}}
 +
{{dsc inc|cpp/container/dsc value_type|multimap}}
 +
{{dsc inc|cpp/container/dsc size_type|multimap}}
 +
{{dsc inc|cpp/container/dsc difference_type|multimap}}
 +
{{dsc inc|cpp/container/dsc key_compare|multimap}}
 +
{{dsc inc|cpp/container/dsc allocator_type|multimap}}
 +
{{dsc inc|cpp/container/dsc reference|multimap}}
 +
{{dsc inc|cpp/container/dsc const_reference|multimap}}
 +
{{dsc inc|cpp/container/dsc pointer|multimap}}
 +
{{dsc inc|cpp/container/dsc const_pointer|multimap}}
 +
{{dsc inc|cpp/container/dsc iterator|multimap}}
 +
{{dsc inc|cpp/container/dsc const_iterator|multimap}}
 +
{{dsc inc|cpp/container/dsc reverse_iterator|multimap}}
 +
{{dsc inc|cpp/container/dsc const_reverse_iterator|multimap}}
 +
{{dsc inc|cpp/container/dsc node_type|multimap}}
 +
{{dsc end}}
  
−
{{dcl list h2 | Modifiers}}
+
===Member classes===
−
{{dcl list template | cpp/container/dcl list clear | multimap}}
+
{{dsc begin}}
−
{{dcl list template | cpp/container/dcl list insert | multimap}}
+
{{dsc inc|cpp/container/dsc value_compare|multimap}}
−
{{dcl list template | cpp/container/dcl list emplace | multimap}}
+
{{dsc end}}
−
{{dcl list template | cpp/container/dcl list emplace_hint | multimap}}
+
−
{{dcl list template | cpp/container/dcl list erase | multimap}}
+
−
{{dcl list template | cpp/container/dcl list swap | multimap}}
+
  
−
{{dcl list h2 | Lookup}}
+
===Member functions===
−
{{dcl list template | cpp/container/dcl list count | multimap}}
+
{{dsc begin}}
−
{{dcl list template | cpp/container/dcl list find | multimap}}
+
{{dsc inc|cpp/container/dsc constructor|multimap}}
−
{{dcl list template | cpp/container/dcl list equal_range | multimap}}
+
{{dsc inc|cpp/container/dsc destructor|multimap}}
−
{{dcl list template | cpp/container/dcl list lower_bound | multimap}}
+
{{dsc inc|cpp/container/dsc operator{{=}}|multimap}}
−
{{dcl list template | cpp/container/dcl list upper_bound | multimap}}
+
{{dsc inc|cpp/container/dsc get_allocator|multimap}}
  
−
{{dcl list h2 | Observers}}
+
{{dsc h2|Iterators}}
−
{{dcl list template | cpp/container/dcl list key_comp | multimap}}
+
{{dsc inc|cpp/container/dsc begin|multimap}}
−
{{dcl list template | cpp/container/dcl list value_comp | multimap}}
+
{{dsc inc|cpp/container/dsc end|multimap}}
−
{{dcl list end}}
+
{{dsc inc|cpp/container/dsc rbegin|multimap}}
 +
{{dsc inc|cpp/container/dsc rend|multimap}}
 +
 
 +
{{dsc h2|Capacity}}
 +
{{dsc inc|cpp/container/dsc empty|multimap}}
 +
{{dsc inc|cpp/container/dsc size|multimap}}
 +
{{dsc inc|cpp/container/dsc max_size|multimap}}
 +
 
 +
{{dsc h2|Modifiers}}
 +
{{dsc inc|cpp/container/dsc clear|multimap}}
 +
{{dsc inc|cpp/container/dsc insert|multimap}}
 +
{{dsc inc|cpp/container/dsc insert_range|multimap}}
 +
{{dsc inc|cpp/container/dsc emplace|multimap}}
 +
{{dsc inc|cpp/container/dsc emplace_hint|multimap}}
 +
{{dsc inc|cpp/container/dsc erase|multimap}}
 +
{{dsc inc|cpp/container/dsc swap|multimap}}
 +
{{dsc inc|cpp/container/dsc extract|multimap}}
 +
{{dsc inc|cpp/container/dsc merge|multimap}}
 +
 
 +
{{dsc h2|Lookup}}
 +
{{dsc inc|cpp/container/dsc count|multimap}}
 +
{{dsc inc|cpp/container/dsc find|multimap}}
 +
{{dsc inc|cpp/container/dsc contains|multimap}}
 +
{{dsc inc|cpp/container/dsc equal_range|multimap}}
 +
{{dsc inc|cpp/container/dsc lower_bound|multimap}}
 +
{{dsc inc|cpp/container/dsc upper_bound|multimap}}
 +
 
 +
{{dsc h2|Observers}}
 +
{{dsc inc|cpp/container/dsc key_comp|multimap}}
 +
{{dsc inc|cpp/container/dsc value_comp|multimap}}
 +
{{dsc end}}
 +
 
 +
===Non-member functions===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/container/dsc operator_cmp|multimap}}
 +
{{dsc inc|cpp/container/dsc swap2|multimap}}
 +
{{dsc inc|cpp/container/dsc erase_if|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=230|std=C++98|before={{tt|Key}} was not required to be {{named req|CopyConstructible}}<br>(a key of type {{tt|Key}} might not be able to be constructed)|after={{tt|Key}} is also required to<br>be {{named req|CopyConstructible}}}}
 +
{{dr list end}}
 +
 
 +
===See also===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/container/dsc map}}
 +
{{dsc inc|cpp/container/dsc unordered_multimap}}
 +
{{dsc inc|cpp/container/dsc flat_multimap}}
 +
{{dsc end}}
 +
 
 +
{{langlinks|de|es|fr|it|ja||pl|pt|ru|zh}}

Latest revision as of 15:49, 1 November 2024

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

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

> class multimap;
 (1)
namespace pmr {

    template<
        class Key,
        class T,
        class Compare = std::less<Key>
    > using multimap = std::multimap<Key, T, Compare,
        std::pmr::polymorphic_allocator<std::pair<const Key, 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 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

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]
key_compare Compare[edit]
allocator_type Allocator[edit]
reference value_type&[edit]
const_reference const value_type&[edit]
pointer

Allocator::pointer

(until C++11)

std::allocator_traits<Allocator>::pointer

(since C++11)
[edit]
const_pointer

Allocator::const_pointer

(until C++11)

std::allocator_traits<Allocator>::const_pointer

(since C++11)
[edit]
iterator LegacyBidirectionalIterator to value_type[edit]
const_iterator LegacyBidirectionalIterator to const value_type[edit]
reverse_iterator std::reverse_iterator<iterator>[edit]
const_reverse_iterator std::reverse_iterator<const_iterator>[edit]
node_type (since C++17) a specialization of node handle representing a container node[edit]

[edit] Member classes

 compares objects of type value_type
(class) [edit]

[edit] Member functions

 constructs the multimap
(public member function) [edit]
destructs the multimap
(public member function) [edit]
assigns values to the container
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Iterators
(C++11)
 returns an iterator to the beginning
(public member function) [edit]
(C++11)
 returns an iterator to the end
(public member function) [edit]
(C++11)
 returns a reverse iterator to the beginning
(public member function) [edit]
(C++11)
 returns a reverse 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]
(C++11)
 constructs element in-place
(public member function) [edit]
(C++11)
 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]
returns an iterator to the first element not less than the given key
(public member function) [edit]
returns an iterator to the first element greater than the given key
(public member function) [edit]
Observers
returns the function that compares keys
(public member function) [edit]
returns the function that compares keys in objects of type value_type
(public member function) [edit]

[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 multimaps
(function template) [edit]
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 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 to
be CopyConstructible

[edit] See also

 collection of key-value pairs, sorted by keys, keys are unique
(class template) [edit]
(C++11)
 collection of key-value pairs, hashed 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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