(C++17) | ||||
| Sequence | ||||
(C++11) | ||||
(C++26) | ||||
(C++26) | ||||
(C++11) | ||||
| Associative | ||||
| Unordered associative | ||||
(C++11) | ||||
(C++11) | ||||
(C++11) | ||||
(C++11) | ||||
| Adaptors | ||||
flat_set (C++23) | ||||
(C++23) | ||||
(C++23) | ||||
(C++23) | ||||
| Views | ||||
(C++20) | ||||
(C++23) | ||||
| Tables | ||||
| Iterator invalidation | ||||
| Member function table | ||||
| Non-member function table |
Defined in header <flat_set> | ||
template< class Key, | (since C++23) | |
The flat set is acontainer adaptor that gives the functionality of an associative container that stores a sorted set of unique objects of typeKey. Sorting is done using the key comparison functionCompare.
The class templateflat_set acts as a wrapper to the underlying sorted container passed as object of typeKeyContainer.
Everywhere the standard library uses theCompare requirements, uniqueness is determined by using the equivalence relation. Informally, two objectsa andb are considered equivalent if neither compares less than the other:!comp(a, b)&&!comp(b, a).
std::flat_set meets the requirements ofContainer,ReversibleContainer,optional container requirements, and all requirements ofAssociativeContainer (including logarithmic search complexity), except that:
A flat set supports mostAssociativeContainer's operations that use unique keys.
All member functions ofstd::flat_set areconstexpr: it is possible to create and usestd::flat_set objects in the evaluation of a constant expression.However, | (since C++26) |
Contents |
| This section is incomplete |
| Key | - | The type of the stored elements. The program is ill-formed ifKey is not the same type asKeyContainer::value_type. |
| Compare | - | ACompare type providing a strict weak ordering. |
| KeyContainer | - | The type of the underlyingSequenceContainer to store the elements. The iterators of such container should satisfyLegacyRandomAccessIterator or modelrandom_access_iterator.The standard containersstd::vector andstd::deque satisfy these requirements. |
| Type | Definition |
container_type | KeyContainer[edit] |
key_type | Key[edit] |
value_type | Key[edit] |
key_compare | Compare[edit] |
value_compare | Compare[edit] |
reference | value_type&[edit] |
const_reference | const value_type&[edit] |
size_type | typename KeyContainer::size_type[edit] |
difference_type | typename KeyContainer::difference_type[edit] |
iterator | implementation-definedLegacyRandomAccessIterator,ConstexprIterator(since C++26) andrandom_access_iterator tovalue_type[edit] |
const_iterator | implementation-definedLegacyRandomAccessIterator,ConstexprIterator(since C++26) andrandom_access_iterator toconst value_type[edit] |
reverse_iterator | std::reverse_iterator<iterator>[edit] |
const_reverse_iterator | std::reverse_iterator<const_iterator>[edit] |
| Member | Description |
container_typec(private) | the adapted container (exposition-only member object*) |
key_comparecompare(private) | the comparison function object (exposition-only member object*) |
constructs theflat_set(public member function)[edit] | |
(destructor) (implicitly declared) | destroys every element of the container adaptor (public member function) |
| assigns values to the container adaptor (public member function)[edit] | |
Iterators | |
| returns an iterator to the beginning (public member function)[edit] | |
| returns an iterator to the end (public member function)[edit] | |
| returns a reverse iterator to the beginning (public member function)[edit] | |
| returns a reverse iterator to the end (public member function)[edit] | |
Capacity | |
| checks whether the container adaptor 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 | |
| constructs element in-place (public member function)[edit] | |
| constructs elements in-place using a hint (public member function)[edit] | |
| inserts elements (public member function)[edit] | |
| inserts a range of elements (public member function)[edit] | |
| extracts the underlying container (public member function)[edit] | |
| replaces the underlying container (public member function)[edit] | |
| erases elements (public member function)[edit] | |
| swaps the contents (public member function)[edit] | |
| clears the contents (public member function)[edit] | |
Lookup | |
| finds element with specific key (public member function)[edit] | |
| returns the number of elements matching specific key (public member function)[edit] | |
| checks if the container contains element with specific key (public member function)[edit] | |
| returns an iterator to the first elementnot less than the given key (public member function)[edit] | |
| returns an iterator to the first elementgreater than the given key (public member function)[edit] | |
| returns range of elements matching a specific 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 typevalue_type(public member function)[edit] | |
(C++23) | lexicographically compares the values of twoflat_sets(function template)[edit] |
(C++23) | specializes thestd::swap algorithm (function template)[edit] |
(C++23) | erases all elements satisfying specific criteria (function template)[edit] |
| specializes thestd::uses_allocator type trait (class template specialization)[edit] |
(C++23) | indicates that elements of a range are sorted and unique (tag)[edit] |
The member typesiterator andconst_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 theOne Definition Rule. Sinceiterator is convertible toconst_iterator, a single function with aconst_iterator as parameter type will work instead.
Some advantages of flat set over other standardcontainer adaptors are:
KeyContainer, keys are stored in a contiguous block(s) of memory).Some disadvantages of flat set are:
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_flat_set | 202207L | (C++23) | std::flat_set andstd::flat_multiset |
__cpp_lib_constexpr_flat_set | 202502L | (C++26) | constexprstd::flat_set |
| This section is incomplete Reason: no example |
(C++23) | adapts a container to provide a collection of keys, sorted by keys (class template)[edit] |
| collection of unique keys, sorted by keys (class template)[edit] | |
(C++11) | collection of unique keys, hashed by keys (class template)[edit] |
