Difference between revisions of "cpp/container/multiset"
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{{tt|std::multiset}} is an associative container that contains a sorted set of objects of type Key. Unlike set, multiple keys with equivalent values are allowed. Sorting is done using the key comparison function Compare. Search, insertion, and removal operations have logarithmic complexity. | {{tt|std::multiset}} is an associative container that contains a sorted set of objects of type Key. Unlike set, multiple keys with equivalent values are allowed. Sorting is done using the key comparison function Compare. Search, insertion, and removal operations have logarithmic complexity. | ||
| − | Everywhere the standard library uses the {{ | + | Everywhere the standard library uses the {{named req|Compare}} concept, equivalence is determined by using the equivalence relation as described on {{named req|Compare}}. In imprecise terms, two objects {{tt|a}} and {{tt|b}} are considered equivalent if neither compares less than the other: {{tt|!comp(a, b) && !comp(b, a)}}. |
The order of the elements that compare equivalent is the order of insertion and does not change. {{mark since c++11}} | The order of the elements that compare equivalent is the order of insertion and does not change. {{mark since c++11}} | ||
| − | {{tt|std::multiset}} meets the requirements of {{ | + | {{tt|std::multiset}} meets the requirements of {{named req|Container}}, {{named req|AllocatorAwareContainer}}, {{named req|AssociativeContainer}} and {{named req|ReversibleContainer}}. |
===Member types=== | ===Member types=== | ||
Revision as of 14:41, 15 June 2018
| Defined in header <set>
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| template< class Key, |
(1) | |
| namespace pmr { template <class Key, class Compare = std::less<Key>> |
(2) | (since C++17) |
std::multiset is an associative container that contains a sorted set of objects of type Key. Unlike set, multiple keys with equivalent values are allowed. Sorting is done using the key comparison function Compare. Search, insertion, and removal operations have logarithmic complexity.
Everywhere the standard library uses the Compare concept, 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).
The order of the elements that compare equivalent is the order of insertion and does not change. (since C++11)
std::multiset meets the requirements of Container, AllocatorAwareContainer, AssociativeContainer and ReversibleContainer.
Contents |
Member types
| Member type | Definition | ||||
key_type
|
Key
| ||||
value_type
|
Key
| ||||
size_type
|
Unsigned integer type (usually std::size_t) | ||||
difference_type
|
Signed integer type (usually std::ptrdiff_t) | ||||
key_compare
|
Compare
| ||||
value_compare
|
Compare
| ||||
allocator_type
|
Allocator
| ||||
reference
|
value_type& | ||||
const_reference
|
const value_type& | ||||
pointer
|
| ||||
const_pointer
|
| ||||
iterator
|
Constant LegacyBidirectionalIterator to value_type
| ||||
const_iterator
|
LegacyBidirectionalIterator to const value_type | ||||
reverse_iterator
|
std::reverse_iterator<iterator> | ||||
const_reverse_iterator
|
std::reverse_iterator<const_iterator> | ||||
node_type (since C++17)
|
a specialization of node handle representing a container node |
Member functions
constructs the multiset (public member function) | |
destructs the multiset (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++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) | |
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 multisets (function template) |
| specializes the std::swap algorithm (function template) |
Deduction guides(since C++17)
Notes
The member types iterator and const_iterator may be aliases to the same type. This means defining a pair of function overloads using the two types as parameter types may violate the One Definition Rule. Since iterator is convertible to const_iterator, a single function with a const_iterator as parameter type will work instead.
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 103 | C++98 | iterator allows modification of keys | iterator made constant |
