std::set

Defined in header `<set>`
template< class Key, class Compare = std::less<Key>, class Allocator = std::allocator<Key> > class set;	(1)
namespace pmr { template <class Key, class Compare = std::less<Key>> using set = std::set<Key, Compare, std::pmr::polymorphic_allocator<Key>>; }	(2)	(since C++17)

std::set is an associative container that contains a sorted set of unique objects of type Key. Sorting is done using the key comparison function Compare. Search, removal, and insertion operations have logarithmic complexity. Sets are usually implemented as red-black trees.

Everywhere the standard library uses the Compare requirements, uniqueness is determined by using the equivalence relation. 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::set meets the requirements of Container, AllocatorAwareContainer, AssociativeContainer and ReversibleContainer.

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

`Allocator::reference`	(until C++11)
`value_type&`	(since C++11)

const_reference

`Allocator::const_reference`	(until C++11)
`const value_type&`	(since C++11)

pointer

`Allocator::pointer`	(until C++11)
std::allocator_traits<Allocator>::pointer	(since C++11)

const_pointer

`Allocator::const_pointer`	(until C++11)
std::allocator_traits<Allocator>::const_pointer	(since C++11)

iterator Constant LegacyBidirectionalIterator

const_iterator Constant LegacyBidirectionalIterator

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

insert_return_type(since C++17)

type describing the result of inserting a node_type, a specialization of

template <class Iter, class NodeType> struct /*unspecified*/ {
    Iter     position;
    bool     inserted;
    NodeType node;
};

instantiated with template arguments iterator and node_type.

Member functions

(constructor)	constructs the `set` (public member function)
(destructor)	destructs the `set` (public member function)
operator=	assigns values to the container (public member function)
get_allocator	returns the associated allocator (public member function)
Iterators
begin cbegin	returns an iterator to the beginning (public member function)
end cend	returns an iterator to the end (public member function)
rbegin crbegin	returns a reverse iterator to the beginning (public member function)
rend crend	returns a reverse iterator to the end (public member function)
Capacity
empty	checks whether the container is empty (public member function)
size	returns the number of elements (public member function)
max_size	returns the maximum possible number of elements (public member function)
Modifiers
clear	clears the contents (public member function)
insert	inserts elements or nodes (since C++17) (public member function)
emplace (C++11)	constructs element in-place (public member function)
emplace_hint (C++11)	constructs elements in-place using a hint (public member function)
erase	erases elements (public member function)
swap	swaps the contents (public member function)
extract (C++17)	extracts nodes from the container (public member function)
merge (C++17)	splices nodes from another container (public member function)
Lookup
count	returns the number of elements matching specific key (public member function)
find	finds element with specific key (public member function)
contains (C++20)	checks if the container contains element with specific key (public member function)
equal_range	returns range of elements matching a specific key (public member function)
lower_bound	returns an iterator to the first element not less than the given key (public member function)
upper_bound	returns an iterator to the first element greater than the given key (public member function)
Observers
key_comp	returns the function that compares keys (public member function)
value_comp	returns the function that compares keys in objects of type value_type (public member function)

Non-member functions

operator==operator!=operator<operator<=operator>operator>=	lexicographically compares the values in the set (function template)
std::swap(std::set)	specializes the std::swap algorithm (function template)
erase_if(std::set) (C++20)	Erases all elements satisfying specific criteria (function template)

Deduction guides(since C++17)

Notes

The member types iterator and const_iterator may be aliases to the same type. Since iterator is convertible to const_iterator, const_iterator should be used in function parameter lists to avoid violations of the One Definition Rule.

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

Language
Standard Library Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

array (C++11)
vector
deque
forward_list (C++11)
list
set
multiset
map
multimap
unordered_set (C++11)
unordered_multiset (C++11)
unordered_map (C++11)
unordered_multimap (C++11)
stack
queue
priority_queue
span (C++20)

Member functions
set::set
set::~set
set::operator=
set::get_allocator
Iterators
set::beginset::cbegin (C++11)
set::endset::cend (C++11)
set::rbeginset::crbegin (C++11)
set::rendset::crend (C++11)
Capacity
set::empty
set::size
set::max_size
Modifiers
set::clear
set::insert
set::emplace (C++11)
set::emplace_hint (C++11)
set::erase
set::swap
set::extract (C++17)
set::merge (C++17)
Lookup
set::count
set::find
set::contains (C++20)
set::equal_range
set::lower_bound
set::upper_bound
Observers
set::key_comp
set::value_comp
Deduction guides(C++17)

std::set

Member types

Member functions

Iterators

Capacity

Modifiers

Lookup

Observers

Non-member functions

Deduction guides(since C++17)

Notes

Defect Reports