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std::flat_map(3) C++ Standard Libary std::flat_map(3) NAME std::flat_map - std::flat_map Synopsis Defined in header <flat_map> template< class Key, class T, class Compare = std::less<Key>, (since C++23) class KeyContainer = std::vector<Key>, class MappedContainer = std::vector<T> > class flat_map; The flat map is a container adaptor that gives the functionality of an associative container that contains key-value pairs with unique keys. Keys are sorted by using the comparison function Compare. The class template flat_map acts as a wrapper to the two underlying containers, passed as objects of type KeyContainer and MappedContainer respec- tively. The first container is sorted, and for each key its corresponding value is in the second container at the same index (offset). The number of elements in both containers is the same. Everywhere the standard library uses the Compare requirements, uniqueness is determined by using the equivalence relation. Informally, two ob- jects a and b are considered equivalent if neither compares less than the other: !comp(a, b) && !comp(b, a). std::flat_map meets the requirements of Container, ReversibleCon- tainer, optional container requirements, and all requirements of AssociativeContainer (including logarithmic search complexity), except that: * requirements related to nodes are not applicable, * iterator invalidation requirements differ, * the complexity of insertion and erasure operations is linear. A flat map supports most AssociativeContainer's operations that use unique keys. Template parameters Key - The type of the keys. The program is ill-formed if Key is not the same type as KeyContainer::value_type. T - The type of mapped values. The program is ill- formed if T is not the same type as MappedContainer::value_type. Compare - A Compare type providing a strict weak ordering. The types of the underlying SequenceContainer to store keys and mapped values correspondingly. The iterators of such containers should satisfy LegacyRandomAccessIterator or model KeyContainer - random_access_iterator. Invocations of their mem- ber functions size MappedContainer and max_size should not exit via an exception. The standard containers std::vector and std::deque satisfy these requirements. Member types Member type Definition key_container_type KeyContainer mapped_container_type MappedContainer key_type Key mapped_type T value_type std::pair<key_type, mapped_type> key_compare Compare reference std::pair<const key_type&, mapped_type&> const_reference std::pair<const key_type&, const mapped_type&> size_type std::size_t difference_type std::ptrdiff_t iterator implementation-defined LegacyInputIterator and random_access_iterator to value_type const_iterator implementation-defined LegacyInputIterator and random_access_iterator to const value_type reverse_iterator std::reverse_iterator<iterator> const_reverse_iterator std::reverse_iterator<const_iterator> type describing the underlying containers struct containers containers { key_container_type keys; mapped_container_type values; }; Member classes value_compare compares objects of type value_type (class) Member objects Member name Definition c (private) the object of type containers (exposition-only member object*) compare (private) the comparison function object of type key_compare (exposition-only member object*) Member functions constructor constructs the flat_map (public member function) destructor destroys every element of the container adap- tor (implicitly declared) (public member function) operator= assigns values to the container adaptor (public member function) Element access at access specified element with bounds checking (public member function) operator[] access or insert specified element (public member function) Iterators begin returns an iterator to the beginning cbegin (public member function) end returns an iterator to the end cend (public member function) rbegin returns a reverse iterator to the beginning crbegin (public member function) rend returns a reverse iterator to the end crend (public member function) Capacity empty checks whether the container adaptor is empty (public member function) size returns the number of elements (public member function) max_size returns the maximum possible number of ele- ments (public member function) Modifiers emplace constructs element in-place (public member function) emplace_hint constructs elements in-place using a hint (public member function) inserts in-place if the key does not exist, does nothing if try_emplace the key exists (public member function) insert inserts elements (public member function) insert_range inserts a range of elements (public member function) inserts an element or assigns to the current element if the insert_or_assign key already exists (public member function) extract extracts the underlying containers (public member function) replace replaces the underlying containers (public member function) erase erases elements (public member function) swap swaps the contents (public member function) clear clears the contents (public member function) Lookup find finds element with specific key (public member function) count returns the number of elements matching spe- cific key (public member function) contains checks if the container contains element with specific key (public member function) returns an iterator to the first element not less than the lower_bound given key (public member function) returns an iterator to the first element greater than the upper_bound given key (public member function) equal_range returns range of elements matching a specific key (public member function) Observers key_comp returns the function that compares keys (public member function) returns the function that compares keys in ob- jects of type value_comp value_type (public member function) keys direct access to the underlying keys container (public member function) values direct access to the underlying values con- tainer (public member function) Non-member functions operator== lexicographically compares the values of two flat_maps operator<=> (function template) (C++23) std::swap(std::flat_map) specializes the std::swap algorithm (C++23) (function template) erase_if(std::flat_map) erases all elements satisfying specific criteria (C++23) (function template) Helper classes std::uses_allocator<std::flat_map> specializes the std::uses_alloca- tor type trait (C++23) (class template specialization) Tags sorted_unique indicates that elements of a range are sorted and unique sorted_unique_t (tag) (C++23) Deduction guides 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. Feature-test macro Value Std Feature __cpp_lib_flat_map 202207L (C++23) std::flat_map and std::flat_mul- timap Example This section is incomplete Reason: no example See also flat_multimap adapts two containers to provide a collection of key- value pairs, (C++23) sorted by keys (class template) map collection of key-value pairs, sorted by keys, keys are unique (class template) unordered_map collection of key-value pairs, hashed by keys, keys are unique (C++11) (class template) Categories: * Todo without reason * Todo no example http://cppreference.com 2024.06.10 std::flat_map(3)
NAME | Synopsis | Template parameters | Member types | Member classes | Member objects | Member functions | Element access | Iterators | Capacity | Modifiers | Lookup | Observers | Non-member functions | Helper classes | Notes | Example | See also | Categories:
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