std::set (3) - Linux Manuals

std::set: std::set


std::set - std::set


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

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

                                  template <class Iter, class NodeType> struct /*unspecified*/ {
                                      Iter position;
insert_return_type(since C++17) bool inserted;
                                      NodeType node;

                                instantiated with template arguments iterator and node_type.

Member functions

              constructs the set
constructor (public member function)
              destructs the set
destructor (public member function)
              assigns values to the container
operator= (public member function)
              returns the associated allocator
get_allocator (public member function)


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)


              checks whether the container is empty
empty (public member function)
              returns the number of elements
size (public member function)
              returns the maximum possible number of elements
max_size (public member function)


              clears the contents
clear (public member function)
              inserts elements
              or nodes
insert (since C++17)
              (public member function)

emplace constructs element in-place
              (public member function)

emplace_hint constructs elements in-place using a hint
              (public member function)
              erases elements
erase (public member function)
              swaps the contents
swap (public member function)

extract extracts nodes from the container
              (public member function)

merge splices nodes from another container
              (public member function)


              returns the number of elements matching specific key
count (public member function)
              finds element with specific key
find (public member function)

contains checks if the container contains element with specific key
              (public member function)
              returns range of elements matching a specific key
equal_range (public member function)
              returns an iterator to the first element not less than the given key
lower_bound (public member function)
              returns an iterator to the first element greater than the given key
upper_bound (public member function)


              returns the function that compares keys
key_comp (public member function)
              returns the function that compares keys in objects of type value_type
value_comp (public member function)

Non-member functions

operator!= lexicographically compares the values in the set
operator< (function template)
                    specializes the std::swap algorithm
std::swap(std::set) (function template)

erase_if(std::set) Erases all elements satisfying specific criteria
                    (function template)

Deduction_guides(since C++17)


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