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Difference between revisions of "cpp/container/multimap"

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(+value_compare)
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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. Sorting is done according to the comparison function {{tt|Compare}}, applied to the keys. Search, insertion, and removal operations have logarithmic complexity.
+
{{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.
  
−
The order of the key-value pairs whose keys compare equivalent is the order of insertion and does not change. {{mark c++11 feature}}
+
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
 +
* {{c|m}}, a {{tt|std::multimap}}
 +
* {{c|it_l}} and {{c|it_r}}, dereferenceable iterators to {{c|m}}, with {{c|it_l < it_r}}.
 +
{{c|1=m.value_comp()(*it_r, *it_l) == false}} (least to greatest if using the default comparison).
 +
 
 +
{{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)}}.
 +
 
 +
{{tt|std::multimap}} meets the requirements of {{named req|Container}}, {{named req|AllocatorAwareContainer}}, {{named req|AssociativeContainer}} and {{named req|ReversibleContainer}}.
 +
 
 +
===Template parameters===
 +
{{todo|Add descriptions of the template parameters.}}
  
 
===Member types===
 
===Member types===
−
{{tdcl list begin}}
+
{{dsc begin}}
−
{{tdcl list hitem | Member type | Definition}}
+
{{dsc hitem|Type|Definition}}
−
{{tdcl list template | cpp/container/tdcl list key_type | multimap}}
+
{{dsc inc|cpp/container/dsc key_type|multimap}}
−
{{tdcl list template | cpp/container/tdcl list mapped_type | multimap}}
+
{{dsc inc|cpp/container/dsc mapped_type|multimap}}
−
{{tdcl list template | cpp/container/tdcl list value_type | multimap}}
+
{{dsc inc|cpp/container/dsc value_type|multimap}}
−
{{tdcl list template | cpp/container/tdcl list size_type | multimap}}
+
{{dsc inc|cpp/container/dsc size_type|multimap}}
−
{{tdcl list template | cpp/container/tdcl list difference_type | multimap}}
+
{{dsc inc|cpp/container/dsc difference_type|multimap}}
−
{{tdcl list template | cpp/container/tdcl list key_compare | multimap}}
+
{{dsc inc|cpp/container/dsc key_compare|multimap}}
−
{{tdcl list template | cpp/container/tdcl list allocator_type | multimap}}
+
{{dsc inc|cpp/container/dsc allocator_type|multimap}}
−
{{tdcl list template | cpp/container/tdcl list reference | multimap}}
+
{{dsc inc|cpp/container/dsc reference|multimap}}
−
{{tdcl list template | cpp/container/tdcl list const_reference | multimap}}
+
{{dsc inc|cpp/container/dsc const_reference|multimap}}
−
{{tdcl list template | cpp/container/tdcl list pointer | multimap}}
+
{{dsc inc|cpp/container/dsc pointer|multimap}}
−
{{tdcl list template | cpp/container/tdcl list const_pointer | multimap}}
+
{{dsc inc|cpp/container/dsc const_pointer|multimap}}
−
{{tdcl list template | cpp/container/tdcl list iterator | multimap}}
+
{{dsc inc|cpp/container/dsc iterator|multimap}}
−
{{tdcl list template | cpp/container/tdcl list const_iterator | multimap}}
+
{{dsc inc|cpp/container/dsc const_iterator|multimap}}
−
{{tdcl list template | cpp/container/tdcl list reverse_iterator | multimap}}
+
{{dsc inc|cpp/container/dsc reverse_iterator|multimap}}
−
{{tdcl list template | cpp/container/tdcl list const_reverse_iterator | multimap}}
+
{{dsc inc|cpp/container/dsc const_reverse_iterator|multimap}}
−
{{tdcl list end}}
+
{{dsc inc|cpp/container/dsc node_type|multimap}}
 +
{{dsc end}}
  
 
===Member classes===
 
===Member classes===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/container/dcl list value_compare | multimap}}
+
{{dsc inc|cpp/container/dsc value_compare|multimap}}
−
{{dcl list end}}
+
{{dsc end}}
  
 
===Member functions===
 
===Member functions===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/container/dcl list constructor | multimap}}
+
{{dsc inc|cpp/container/dsc constructor|multimap}}
−
{{dcl list template | cpp/container/dcl list destructor | multimap}}
+
{{dsc inc|cpp/container/dsc destructor|multimap}}
−
{{dcl list template | cpp/container/dcl list operator{{=}} | multimap}}
+
{{dsc inc|cpp/container/dsc operator{{=}}|multimap}}
−
{{dcl list template | cpp/container/dcl list get_allocator | multimap}}
+
{{dsc inc|cpp/container/dsc get_allocator|multimap}}
  
−
{{dcl list h2 | Iterators}}
+
{{dsc h2|Iterators}}
−
{{dcl list template | cpp/container/dcl list begin | multimap}}
+
{{dsc inc|cpp/container/dsc begin|multimap}}
−
{{dcl list template | cpp/container/dcl list end | multimap}}
+
{{dsc inc|cpp/container/dsc end|multimap}}
−
{{dcl list template | cpp/container/dcl list rbegin | multimap}}
+
{{dsc inc|cpp/container/dsc rbegin|multimap}}
−
{{dcl list template | cpp/container/dcl list rend | multimap}}
+
{{dsc inc|cpp/container/dsc rend|multimap}}
  
−
{{dcl list h2 | Capacity}}
+
{{dsc h2|Capacity}}
−
{{dcl list template | cpp/container/dcl list empty | multimap}}
+
{{dsc inc|cpp/container/dsc empty|multimap}}
−
{{dcl list template | cpp/container/dcl list size | multimap}}
+
{{dsc inc|cpp/container/dsc size|multimap}}
−
{{dcl list template | cpp/container/dcl list max_size | multimap}}
+
{{dsc inc|cpp/container/dsc max_size|multimap}}
  
−
{{dcl list h2 | Modifiers}}
+
{{dsc h2|Modifiers}}
−
{{dcl list template | cpp/container/dcl list clear | multimap}}
+
{{dsc inc|cpp/container/dsc clear|multimap}}
−
{{dcl list template | cpp/container/dcl list insert | multimap}}
+
{{dsc inc|cpp/container/dsc insert|multimap}}
−
{{dcl list template | cpp/container/dcl list emplace | multimap}}
+
{{dsc inc|cpp/container/dsc insert_range|multimap}}
−
{{dcl list template | cpp/container/dcl list emplace_hint | multimap}}
+
{{dsc inc|cpp/container/dsc emplace|multimap}}
−
{{dcl list template | cpp/container/dcl list erase | multimap}}
+
{{dsc inc|cpp/container/dsc emplace_hint|multimap}}
−
{{dcl list template | cpp/container/dcl list swap | 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}}
  
−
{{dcl list h2 | Lookup}}
+
{{dsc h2|Lookup}}
−
{{dcl list template | cpp/container/dcl list count | multimap}}
+
{{dsc inc|cpp/container/dsc count|multimap}}
−
{{dcl list template | cpp/container/dcl list find | multimap}}
+
{{dsc inc|cpp/container/dsc find|multimap}}
−
{{dcl list template | cpp/container/dcl list equal_range | multimap}}
+
{{dsc inc|cpp/container/dsc contains|multimap}}
−
{{dcl list template | cpp/container/dcl list lower_bound | multimap}}
+
{{dsc inc|cpp/container/dsc equal_range|multimap}}
−
{{dcl list template | cpp/container/dcl list upper_bound | multimap}}
+
{{dsc inc|cpp/container/dsc lower_bound|multimap}}
 +
{{dsc inc|cpp/container/dsc upper_bound|multimap}}
  
−
{{dcl list h2 | Observers}}
+
{{dsc h2|Observers}}
−
{{dcl list template | cpp/container/dcl list key_comp | multimap}}
+
{{dsc inc|cpp/container/dsc key_comp|multimap}}
−
{{dcl list template | cpp/container/dcl list value_comp | multimap}}
+
{{dsc inc|cpp/container/dsc value_comp|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 | multimap}}
+
{{dsc inc|cpp/container/dsc operator_cmp|multimap}}
−
{{dcl list template | cpp/container/dcl list swap2 | multimap}}
+
{{dsc inc|cpp/container/dsc swap2|multimap}}
−
{{dcl list end}}
+
{{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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