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std::flat_set(3) C++ Standard Libary std::flat_set(3) NAME std::flat_set - std::flat_set Synopsis Defined in header <flat_set> template< class Key, class Compare = std::less<Key>, (since C++23) class KeyContainer = std::vector<Key> > class flat_set; The flat set is a container adaptor that gives the functionality of an associative container that stores a sorted set of unique objects of type Key. Sorting is done using the key comparison function Compare. The class template flat_set acts as a wrapper to the underlying sorted container passed as object of type KeyContainer. 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_set 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 set supports most AssociativeContainer's operations that use unique keys. Template parameters Key - The type of the stored elements. The program is ill- formed if Key is not the same type as KeyContainer::value_type. Compare - A Compare type providing a strict weak ordering. The type of the underlying SequenceContainer to store the elements. The iterators of such container should satisfy KeyContainer - LegacyRandomAccessIterator or model random_access_it- erator. The standard containers std::vector and std::deque satisfy these requirements. Member types Member type Definition container_type KeyContainer key_type Key value_type Key key_compare Compare value_compare Compare reference value_type& const_reference const value_type& size_type typename KeyContainer::size_type difference_type typename KeyContainer::difference_type iterator implementation-defined LegacyRandomAccessIt- erator and random_access_iterator to value_type const_iterator implementation-defined LegacyRandomAccessIt- erator and random_access_iterator to const value_type reverse_iterator std::reverse_iterator<iterator> const_reverse_iterator std::reverse_iterator<const_iterator> Member objects Member name Definition c (private) the underlying container of container_type (exposition-only member object*) compare (private) the comparison function object of type key_compare (exposition-only member object*) Member functions constructor constructs the flat_set (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) 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) insert inserts elements (public member function) insert_range inserts a range of elements (public member function) extract extracts the underlying container (public member function) replace replaces the underlying container (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) Non-member functions operator== lexicographically compares the values of two flat_sets operator<=> (function template) (C++23) std::swap(std::flat_set) specializes the std::swap algorithm (C++23) (function template) erase_if(std::flat_set) erases all elements satisfying specific criteria (C++23) (function template) Helper classes std::uses_allocator<std::flat_set> 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. Some advantages of flat set over other standard container adaptors are: * Potentially faster lookup (even though search operations have logarithmic complexity). * Much faster iteration: random access iterators instead of bidi- rectional iterators. * Less memory consumption for small objects (and for big objects if KeyContainer::shrink_to_fit() is available). * Better cache performance (depending on KeyContainer, keys are stored in a contiguous block(s) of memory). Some disadvantages of flat set are: * Non-stable iterators (iterators are invalidated when inserting and erasing elements). * Non-copyable and non-movable type values can not be stored. * Weaker exception safety (copy/move constructors can throw when shifting values in erasures and insertions). * Slower (i.e. linear) insertion and erasure, especially for non- movable types. Feature-test macro Value Std Feature __cpp_lib_flat_set 202207L (C++23) std::flat_set and std::flat_mul- tiset Example This section is incomplete Reason: no example See also flat_multiset adapts a container to provide a collection of keys, sorted by keys (C++23) (class template) set collection of unique keys, sorted by keys (class template) unordered_set collection of unique keys, hashed by keys (C++11) (class template) Categories: * Todo without reason * Todo no example http://cppreference.com 2024.06.10 std::flat_set(3)
NAME | Synopsis | Template parameters | Member types | Member objects | Member functions | Iterators | Capacity | Modifiers | Lookup | Observers | Non-member functions | Helper classes | Notes | Example | See also | Categories:
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