constexpr containers and adaptors
This paper proposes marking all containers and adaptors constexpr. This will make compile time programming much easier by making normal C++ and constexpr C++ more similar.
Introduction and motivation
All necessary constexpr functionality required by the containers to be changed is supported by the language. There is no reason for them not to be constexpr, and the standard library should support these in order for them to properly serve as vocabulary types.
The following table shows what this paper proposes, and the status quo:
| container / adapter | before | after | note |
|---|---|---|---|
std::array | ✔︎ | ✔︎ | since C++11/14 |
std::deque | x | ✔︎ | |
std::forward_list | x | ✔︎ | |
std::list | x | ✔︎ | |
std::vector | ✔︎ | ✔︎ | since C++20 🍫 |
std::map | x | ✔︎ | using node_handle::key() is UB (CWG-2514) |
std::multimap | x | ✔︎ | using node_handle::key() is UB (CWG-2514) |
std::set | x | ✔︎ | |
std::multiset | x | ✔︎ | |
std::unordered_map | x | ✔︎ | using node_handle::key() is UB (CWG-2514) |
std::unordered_multimap | x | ✔︎ | using node_handle::key() is UB (CWG-2514) |
std::unordered_set | x | ✔︎ | |
std::unordered_multiset | x | ✔︎ | |
std::queue | x | ✔︎ | |
std::priority_queue | x | ✔︎ | |
std::stack | x | ✔︎ | |
std::flat_map | x | ✔︎ | new adapter in C++23, originally proposed for C++20 |
std::flat_multimap | x | ✔︎ | new adapter in C++23, originally proposed for C++20 |
std::flat_set | x | ✔︎ | new adapter in C++23, originally proposed for C++20 |
std::flat_multiset | x | ✔︎ | new adapter in C++23, originally proposed for C++20 |
std::span | ✔︎ | ✔︎ | |
std::mdspan | ✔︎ | ✔︎ | |
std::basic_string | ✔︎ | ✔︎ | since C++20 🍫 |
std::basic_string_view | ✔︎ | ✔︎ | since C++17 |
Implementation experience
I implemented the proposal in a personal fork of libc++ by marking all functions and member functions associated with containers with constexpr. Containers deque, forward_list, list, and all adaptors (note: libc++ doesn't have flat_map and flat_set yet) were modified without any problem.
When marking set, map, unordered_set, and unordered_map I ran into problems with UB in the construction of nodes, where the node is allocated but not constructed and only its subobject with value is constructed. Another UB I ran into was type-punning via union and static_cast from size_t into unsigned char when calculating hash; both these issues were fixed by using std::bit_cast instead. This is actually a good argument for constexpr ALL the things as proper testing during constant evaluation can easily catch such problems.
Another problem with unordered_set and unordered_map was the absence of constexpr ceilf(float) function, a prime calculation function in hash.cpp, and a non-constexpr std::hash type template.
Here are examples with iterators and here are examples with normal operations.
std::hash
One remaining UB needs to be solved in order to make std::hash<T *> constexpr: converting pointer to a number. For my implementation I did it by extending std::bit_cast to convert constexpr symbolic address to an integer.
This approach has the problem of returning an inconsistent result for constant evaluated hash in comparison to runtime computation. Same thing already applies to comparing pointers with std::less<T*>.
Personally I would just allow std::bit_cast from (but not to) pointer. Another alternative implementation would be a single purpose builtin __builtin_ptr_to_hash.
key & node_handle::key()
Another problem I ran into is the already existing CWG-2514 where node_handle::key() returns non-const reference to key which is const inside node_type. I don't think this is a problem with constexpr; more with the general specification of map and unordered_map and when fixed it will allow using this functionality in constexpr too.
non-transient allocations
This change does not allow non-transient allocation, so no allocation done during constant evaluation can survive to runtime. This is currently an unsolved problem and is not specific to the proposed change. This is also an argument to allow constexpr std::hash<T *> as we can see constexpr pointers and runtime pointers as two different address spaces.
Impact on existing code
None, this is purely an API extension as the previous API wasn't usable in constexpr, and all types are templates and must be available in headers already.
Intention for wording changes
Mechanically mark all functionality in [container] constexpr. Also make sure all iterator types are constexpr.
Proposed changes to wording
24 Containers library [containers]
24.2.5 Node handles [container.node]
24.2.5.1 Overview [container.node.overview]
A node handle is an object that accepts ownership of a single element
from an associative container ([associative.reqmts]) or an unordered
associative container ([unord.req]).
It may be used to transfer that
ownership to another container with compatible nodes.
Containers with
compatible nodes have the same node handle type.
Table 86: Container types with compatible nodes [tab:container.node.compat]
map<K, T, C1, A> | map<K, T, C2, A> | |
map<K, T, C1, A> | multimap<K, T, C2, A> | |
set<K, C1, A> | set<K, C2, A> | |
set<K, C1, A> | multiset<K, C2, A> | |
unordered_map<K, T, H1, E1, A> | unordered_map<K, T, H2, E2, A> | |
unordered_map<K, T, H1, E1, A> | unordered_multimap<K, T, H2, E2, A> | |
unordered_set<K, H1, E1, A> | unordered_set<K, H2, E2, A> | |
unordered_set<K, H1, E1, A> | unordered_multiset<K, H2, E2, A> |
If a user-defined specialization of pair exists for
pair<const Key, T> or pair<Key, T>, where Key is the
container's key_type and T is the container's
mapped_type, the behavior of operations involving node handles is
undefined.
template<unspecified>
class node-handle {
public:
// These type declarations are described in [associative.reqmts] and [unord.req].
using value_type = see below; // not present for map containers
using key_type = see below; // not present for set containers
using mapped_type = see below; // not present for set containers
using allocator_type = see below;
private:
using container_node_type = unspecified; // exposition only
using ator_traits = allocator_traits<allocator_type>; // exposition only
typename ator_traits::template
rebind_traits<container_node_type>::pointer ptr_; // exposition only
optional<allocator_type> alloc_; // exposition only
public:
// [container.node.cons], constructors, copy, and assignment
constexpr node-handle() noexcept : ptr_(), alloc_() {}
constexpr node-handle(node-handle&&) noexcept;
constexpr node-handle& operator=(node-handle&&);
// [container.node.dtor], destructor
constexpr ~node-handle();
// [container.node.observers], observers
constexpr value_type& value() const; // not present for map containers
constexpr key_type& key() const; // not present for set containers
constexpr mapped_type& mapped() const; // not present for set containers
constexpr allocator_type get_allocator() const;
constexpr explicit operator bool() const noexcept;
constexpr bool empty() const noexcept;
// [container.node.modifiers], modifiers
constexpr void swap(node-handle&)
noexcept(ator_traits::propagate_on_container_swap::value ||
ator_traits::is_always_equal::value);
constexpr friend void swap(node-handle& x, node-handle& y) noexcept(noexcept(x.swap(y))) {
x.swap(y);
}
};
24.2.5.2 Constructors, copy, and assignment [container.node.cons]
constexpr node-handle(node-handle&& nh) noexcept;
constexpr node-handle& operator=(node-handle&& nh);
Effects:
- If ptr_ != nullptr, destroys the value_type subobject in the container_node_type object pointed to by ptr_ by calling ator_traits::destroy, then deallocates ptr_ by calling ator_traits::template rebind_traits<container_node_type>::deallocate.
- If !alloc_ or ator_traits::propagate_on_container_move_assignment::value is true, move assigns nh.alloc_ to alloc_.
24.2.5.3 Destructor [container.node.dtor]
constexpr ~node-handle();
24.2.5.4 Observers [container.node.observers]
constexpr value_type& value() const;
constexpr key_type& key() const;
constexpr mapped_type& mapped() const;
constexpr allocator_type get_allocator() const;
constexpr explicit operator bool() const noexcept;
constexpr bool empty() const noexcept;
24.2.5.5 Modifiers [container.node.modifiers]
constexpr void swap(node-handle& nh)
noexcept(ator_traits::propagate_on_container_swap::value ||
ator_traits::is_always_equal::value);
24.3.3 Header <deque> synopsis [deque.syn]
#include <compare> // see [compare.syn]
#include <initializer_list> // see [initializer.list.syn]
namespace std {
// [deque], class template deque
template<class T, class Allocator = allocator<T>> class deque;
template<class T, class Allocator>
constexpr bool operator==(const deque<T, Allocator>& x, const deque<T, Allocator>& y);
template<class T, class Allocator>
constexpr synth-three-way-result<T> operator<=>(const deque<T, Allocator>& x,
const deque<T, Allocator>& y);
template<class T, class Allocator>
constexpr void swap(deque<T, Allocator>& x, deque<T, Allocator>& y)
noexcept(noexcept(x.swap(y)));
// [deque.erasure], erasure
template<class T, class Allocator, class U = T>
constexpr typename deque<T, Allocator>::size_type
erase(deque<T, Allocator>& c, const U& value);
template<class T, class Allocator, class Predicate>
constexpr typename deque<T, Allocator>::size_type
erase_if(deque<T, Allocator>& c, Predicate pred);
namespace pmr {
template<class T>
using deque = std::deque<T, polymorphic_allocator<T>>;
}
}
24.3.4 Header <forward_list> synopsis [forward.list.syn]
#include <compare> // see [compare.syn]
#include <initializer_list> // see [initializer.list.syn]
namespace std {
// [forward.list], class template forward_list
template<class T, class Allocator = allocator<T>> class forward_list;
template<class T, class Allocator>
constexpr bool operator==(const forward_list<T, Allocator>& x, const forward_list<T, Allocator>& y);
template<class T, class Allocator>
constexpr synth-three-way-result<T> operator<=>(const forward_list<T, Allocator>& x,
const forward_list<T, Allocator>& y);
template<class T, class Allocator>
constexpr void swap(forward_list<T, Allocator>& x, forward_list<T, Allocator>& y)
noexcept(noexcept(x.swap(y)));
// [forward.list.erasure], erasure
template<class T, class Allocator, class U = T>
constexpr typename forward_list<T, Allocator>::size_type
erase(forward_list<T, Allocator>& c, const U& value);
template<class T, class Allocator, class Predicate>
constexpr typename forward_list<T, Allocator>::size_type
erase_if(forward_list<T, Allocator>& c, Predicate pred);
namespace pmr {
template<class T>
using forward_list = std::forward_list<T, polymorphic_allocator<T>>;
}
}
24.3.5 Header <list> synopsis [list.syn]
#include <compare> // see [compare.syn]
#include <initializer_list> // see [initializer.list.syn]
namespace std {
// [list], class template list
template<class T, class Allocator = allocator<T>> class list;
template<class T, class Allocator>
constexpr bool operator==(const list<T, Allocator>& x, const list<T, Allocator>& y);
template<class T, class Allocator>
constexpr synth-three-way-result<T> operator<=>(const list<T, Allocator>& x,
const list<T, Allocator>& y);
template<class T, class Allocator>
constexpr void swap(list<T, Allocator>& x, list<T, Allocator>& y)
noexcept(noexcept(x.swap(y)));
// [list.erasure], erasure
template<class T, class Allocator, class U = T>
constexpr typename list<T, Allocator>::size_type
erase(list<T, Allocator>& c, const U& value);
template<class T, class Allocator, class Predicate>
constexpr typename list<T, Allocator>::size_type
erase_if(list<T, Allocator>& c, Predicate pred);
namespace pmr {
template<class T>
using list = std::list<T, polymorphic_allocator<T>>;
}
}
24.3.9 Class template deque [deque]
24.3.9.1 Overview [deque.overview]
A deque meets all of the requirements
of a container ([container.reqmts]),
of a reversible container ([container.rev.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]), and
of a sequence container,
including the optional sequence container requirements ([sequence.reqmts]).
Descriptions are provided here only for operations on
deque
that are not described in one of these tables
or for operations where there is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class T, class Allocator = allocator<T>>
class deque {
public:
// types
using value_type = T;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
// [deque.cons], construct/copy/destroy
constexpr deque() : deque(Allocator()) { }
constexpr explicit deque(const Allocator&);
constexpr explicit deque(size_type n, const Allocator& = Allocator());
constexpr deque(size_type n, const T& value, const Allocator& = Allocator());
template<class InputIterator>
constexpr deque(InputIterator first, InputIterator last, const Allocator& = Allocator());
template<container-compatible-range<T> R>
constexpr deque(from_range_t, R&& rg, const Allocator& = Allocator());
constexpr deque(const deque& x);
constexpr deque(deque&&);
constexpr deque(const deque&, const type_identity_t<Allocator>&);
constexpr deque(deque&&, const type_identity_t<Allocator>&);
constexpr deque(initializer_list<T>, const Allocator& = Allocator());
constexpr ~deque();
constexpr deque& operator=(const deque& x);
constexpr deque& operator=(deque&& x)
noexcept(allocator_traits<Allocator>::is_always_equal::value);
constexpr deque& operator=(initializer_list<T>);
template<class InputIterator>
constexpr void assign(InputIterator first, InputIterator last);
template<container-compatible-range<T> R>
constexpr void assign_range(R&& rg);
constexpr void assign(size_type n, const T& t);
constexpr void assign(initializer_list<T>);
constexpr allocator_type get_allocator() const noexcept;
// iterators
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr reverse_iterator rbegin() noexcept;
constexpr const_reverse_iterator rbegin() const noexcept;
constexpr reverse_iterator rend() noexcept;
constexpr const_reverse_iterator rend() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cend() const noexcept;
constexpr const_reverse_iterator crbegin() const noexcept;
constexpr const_reverse_iterator crend() const noexcept;
// [deque.capacity], capacity
constexpr bool empty() const noexcept;
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
constexpr void resize(size_type sz);
constexpr void resize(size_type sz, const T& c);
constexpr void shrink_to_fit();
// element access
constexpr reference operator[](size_type n);
constexpr const_reference operator[](size_type n) const;
constexpr reference at(size_type n);
constexpr const_reference at(size_type n) const;
constexpr reference front();
constexpr const_reference front() const;
constexpr reference back();
constexpr const_reference back() const;
// [deque.modifiers], modifiers
template<class... Args> constexpr reference emplace_front(Args&&... args);
template<class... Args> constexpr reference emplace_back(Args&&... args);
template<class... Args> constexpr iterator emplace(const_iterator position, Args&&... args);
constexpr void push_front(const T& x);
constexpr void push_front(T&& x);
template<container-compatible-range<T> R>
constexpr void prepend_range(R&& rg);
constexpr void push_back(const T& x);
constexpr void push_back(T&& x);
template<container-compatible-range<T> R>
constexpr void append_range(R&& rg);
constexpr iterator insert(const_iterator position, const T& x);
constexpr iterator insert(const_iterator position, T&& x);
constexpr iterator insert(const_iterator position, size_type n, const T& x);
template<class InputIterator>
constexpr iterator insert(const_iterator position, InputIterator first, InputIterator last);
template<container-compatible-range<T> R>
constexpr iterator insert_range(const_iterator position, R&& rg);
constexpr iterator insert(const_iterator position, initializer_list<T>);
constexpr void pop_front();
constexpr void pop_back();
constexpr iterator erase(const_iterator position);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void swap(deque&)
noexcept(allocator_traits<Allocator>::is_always_equal::value);
constexpr void clear() noexcept;
};
template<class InputIterator, class Allocator = allocator<iter-value-type<InputIterator>>>
deque(InputIterator, InputIterator, Allocator = Allocator())
-> deque<iter-value-type<InputIterator>, Allocator>;
template<ranges::input_range R, class Allocator = allocator<ranges::range_value_t<R>>>
deque(from_range_t, R&&, Allocator = Allocator())
-> deque<ranges::range_value_t<R>, Allocator>;
}
24.3.9.2 Constructors, copy, and assignment [deque.cons]
constexpr explicit deque(const Allocator&);
constexpr explicit deque(size_type n, const Allocator& = Allocator());
constexpr deque(size_type n, const T& value, const Allocator& = Allocator());
template<class InputIterator>
constexpr deque(InputIterator first, InputIterator last, const Allocator& = Allocator());
template<container-compatible-range<T> R>
constexpr deque(from_range_t, R&& rg, const Allocator& = Allocator());
24.3.9.3 Capacity [deque.capacity]
constexpr void resize(size_type sz);
constexpr void resize(size_type sz, const T& c);
constexpr void shrink_to_fit();
24.3.9.4 Modifiers [deque.modifiers]
constexpr iterator insert(const_iterator position, const T& x);
constexpr iterator insert(const_iterator position, T&& x);
constexpr iterator insert(const_iterator position, size_type n, const T& x);
template<class InputIterator>
constexpr iterator insert(const_iterator position,
InputIterator first, InputIterator last);
template<container-compatible-range<T> R>
constexpr iterator insert_range(const_iterator position, R&& rg);
constexpr iterator insert(const_iterator position, initializer_list<T>);
template<class... Args> constexpr reference emplace_front(Args&&... args);
template<class... Args> constexpr reference emplace_back(Args&&... args);
template<class... Args> constexpr iterator emplace(const_iterator position, Args&&... args);
constexpr void push_front(const T& x);
constexpr void push_front(T&& x);
template<container-compatible-range<T> R>
constexpr void prepend_range(R&& rg);
constexpr void push_back(const T& x);
constexpr void push_back(T&& x);
template<container-compatible-range<T> R>
constexpr void append_range(R&& rg);
Remarks: If an exception is thrown other than by the
copy constructor, move constructor,
assignment operator, or move assignment operator of
T
there are no effects.
If an exception is thrown while inserting a single element at either end,
there are no effects.
Otherwise, if an exception is thrown by the move constructor of a
non-Cpp17CopyInsertable
T, the effects are unspecified.
constexpr iterator erase(const_iterator position);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void pop_front();
constexpr void pop_back();
Effects: An erase operation that erases the last element of a deque invalidates only the past-the-end iterator
and all iterators and references to the erased elements.
An erase operation that erases the first
element of a deque but not the last element invalidates only iterators
and references to the erased elements.
An erase operation
that erases neither the first element nor the last element of a deque invalidates the past-the-end
iterator and all iterators and references to all the elements of the deque.
24.3.9.5 Erasure [deque.erasure]
template<class T, class Allocator, class U = T>
constexpr typename deque<T, Allocator>::size_type
erase(deque<T, Allocator>& c, const U& value);
Effects: Equivalent to:
auto it = remove(c.begin(), c.end(), value);
auto r = distance(it, c.end());
c.erase(it, c.end());
return r;
template<class T, class Allocator, class Predicate>
constexpr typename deque<T, Allocator>::size_type
erase_if(deque<T, Allocator>& c, Predicate pred);
24.3.10 Class template forward_list [forward.list]
24.3.10.1 Overview [forward.list.overview]
A forward_list meets all of the requirements
of a container ([container.reqmts]),
except that the size() member function is not provided and
operator== has linear complexity,
A forward_list also meets all of the requirements
for an allocator-aware container ([container.alloc.reqmts]).
In addition, a forward_list
provides the assign member functions and
several of the optional sequence container requirements ([sequence.reqmts]).
Descriptions are provided here only for operations on
forward_list that are not described in that table or for operations where there
is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class T, class Allocator = allocator<T>>
class forward_list {
public:
// types
using value_type = T;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
// [forward.list.cons], construct/copy/destroy
constexpr forward_list() : forward_list(Allocator()) { }
constexpr explicit forward_list(const Allocator&);
constexpr explicit forward_list(size_type n, const Allocator& = Allocator());
constexpr forward_list(size_type n, const T& value, const Allocator& = Allocator());
template<class InputIterator>
constexpr forward_list(InputIterator first, InputIterator last, const Allocator& = Allocator());
template<container-compatible-range<T> R>
constexpr forward_list(from_range_t, R&& rg, const Allocator& = Allocator());
constexpr forward_list(const forward_list& x);
constexpr forward_list(forward_list&& x);
constexpr forward_list(const forward_list& x, const type_identity_t<Allocator>&);
constexpr forward_list(forward_list&& x, const type_identity_t<Allocator>&);
constexpr forward_list(initializer_list<T>, const Allocator& = Allocator());
constexpr ~forward_list();
constexpr forward_list& operator=(const forward_list& x);
constexpr forward_list& operator=(forward_list&& x)
noexcept(allocator_traits<Allocator>::is_always_equal::value);
constexpr forward_list& operator=(initializer_list<T>);
template<class InputIterator>
constexpr void assign(InputIterator first, InputIterator last);
template<container-compatible-range<T> R>
constexpr void assign_range(R&& rg);
constexpr void assign(size_type n, const T& t);
constexpr void assign(initializer_list<T>);
constexpr allocator_type get_allocator() const noexcept;
// [forward.list.iter], iterators
constexpr iterator before_begin() noexcept;
constexpr const_iterator before_begin() const noexcept;
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cbefore_begin() const noexcept;
constexpr const_iterator cend() const noexcept;
// capacity
constexpr bool empty() const noexcept;
constexpr size_type max_size() const noexcept;
// [forward.list.access], element access
constexpr reference front();
constexpr const_reference front() const;
// [forward.list.modifiers], modifiers
template<class... Args> constexpr reference emplace_front(Args&&... args);
constexpr void push_front(const T& x);
constexpr void push_front(T&& x);
template<container-compatible-range<T> R>
constexpr void prepend_range(R&& rg);
constexpr void pop_front();
template<class... Args> constexpr iterator emplace_after(const_iterator position, Args&&... args);
constexpr iterator insert_after(const_iterator position, const T& x);
constexpr iterator insert_after(const_iterator position, T&& x);
constexpr iterator insert_after(const_iterator position, size_type n, const T& x);
template<class InputIterator>
constexpr iterator insert_after(const_iterator position, InputIterator first, InputIterator last);
constexpr iterator insert_after(const_iterator position, initializer_list<T> il);
template<container-compatible-range<T> R>
constexpr iterator insert_range_after(const_iterator position, R&& rg);
constexpr iterator erase_after(const_iterator position);
constexpr iterator erase_after(const_iterator position, const_iterator last);
constexpr void swap(forward_list&)
noexcept(allocator_traits<Allocator>::is_always_equal::value);
constexpr void resize(size_type sz);
constexpr void resize(size_type sz, const value_type& c);
constexpr void clear() noexcept;
// [forward.list.ops], forward_list operations
constexpr void splice_after(const_iterator position, forward_list& x);
constexpr void splice_after(const_iterator position, forward_list&& x);
constexpr void splice_after(const_iterator position, forward_list& x, const_iterator i);
constexpr void splice_after(const_iterator position, forward_list&& x, const_iterator i);
constexpr void splice_after(const_iterator position, forward_list& x,
const_iterator first, const_iterator last);
constexpr void splice_after(const_iterator position, forward_list&& x,
const_iterator first, const_iterator last);
constexpr size_type remove(const T& value);
template<class Predicate> constexpr size_type remove_if(Predicate pred);
constexpr size_type unique();
template<class BinaryPredicate> constexpr size_type unique(BinaryPredicate binary_pred);
constexpr void merge(forward_list& x);
constexpr void merge(forward_list&& x);
template<class Compare> constexpr void merge(forward_list& x, Compare comp);
template<class Compare> constexpr void merge(forward_list&& x, Compare comp);
constexpr void sort();
template<class Compare> constexpr void sort(Compare comp);
constexpr void reverse() noexcept;
};
template<class InputIterator, class Allocator = allocator<iter-value-type<InputIterator>>>
forward_list(InputIterator, InputIterator, Allocator = Allocator())
-> forward_list<iter-value-type<InputIterator>, Allocator>;
template<ranges::input_range R, class Allocator = allocator<ranges::range_value_t<R>>>
forward_list(from_range_t, R&&, Allocator = Allocator())
-> forward_list<ranges::range_value_t<R>, Allocator>;
}
An incomplete type T may be used when instantiating forward_list
if the allocator meets the
allocator completeness requirements.
T shall be complete before any member of the resulting specialization
of forward_list is referenced.
24.3.10.2 Constructors, copy, and assignment [forward.list.cons]
constexpr explicit forward_list(const Allocator&);
constexpr explicit forward_list(size_type n, const Allocator& = Allocator());
constexpr forward_list(size_type n, const T& value, const Allocator& = Allocator());
template<class InputIterator>
constexpr forward_list(InputIterator first, InputIterator last, const Allocator& = Allocator());
template<container-compatible-range<T> R>
constexpr forward_list(from_range_t, R&& rg, const Allocator& = Allocator());
24.3.10.3 Iterators [forward.list.iter]
constexpr iterator before_begin() noexcept;
constexpr const_iterator before_begin() const noexcept;
constexpr const_iterator cbefore_begin() const noexcept;
24.3.10.4 Element access [forward.list.access]
constexpr reference front();
constexpr const_reference front() const;
24.3.10.5 Modifiers [forward.list.modifiers]
None of the overloads of insert_after shall affect the validity of iterators and
references, and erase_after shall invalidate only iterators and references to
the erased elements.
If an exception is thrown during insert_after there shall
be no effect.
Inserting n elements into a forward_list is linear in
n, and the number of calls to the copy or move constructor of T is
exactly equal to n.
Erasing n elements from a forward_list is
linear in n and the number of calls to the destructor of type T is
exactly equal to n.
template<class... Args> constexpr reference emplace_front(Args&&... args);
constexpr void push_front(const T& x);
constexpr void push_front(T&& x);
template<container-compatible-range<T> R>
constexpr void prepend_range(R&& rg);
constexpr void pop_front();
constexpr iterator insert_after(const_iterator position, const T& x);
constexpr iterator insert_after(const_iterator position, T&& x);
constexpr iterator insert_after(const_iterator position, size_type n, const T& x);
template<class InputIterator>
constexpr iterator insert_after(const_iterator position, InputIterator first, InputIterator last);
template<container-compatible-range<T> R>
constexpr iterator insert_range_after(const_iterator position, R&& rg);
constexpr iterator insert_after(const_iterator position, initializer_list<T> il);
template<class... Args>
constexpr iterator emplace_after(const_iterator position, Args&&... args);
constexpr iterator erase_after(const_iterator position);
constexpr iterator erase_after(const_iterator position, const_iterator last);
constexpr void resize(size_type sz);
constexpr void resize(size_type sz, const value_type& c);
constexpr void clear() noexcept;
24.3.10.6 Operations [forward.list.ops]
In this subclause,
arguments for a template parameter
named Predicate or BinaryPredicate
shall meet the corresponding requirements in [algorithms.requirements].
The semantics of i + n,
where i is an iterator into the list and n is an integer,
are the same as those of next(i, n).
The expression i - n,
where i is an iterator into the list and n is an integer,
means an iterator j such that j + n == i is true.
constexpr void splice_after(const_iterator position, forward_list& x);
constexpr void splice_after(const_iterator position, forward_list&& x);
constexpr void splice_after(const_iterator position, forward_list& x, const_iterator i);
constexpr void splice_after(const_iterator position, forward_list&& x, const_iterator i);
Iterators to *++i continue to refer to
the same element, but now behave as iterators into *this, not into x.
constexpr void splice_after(const_iterator position, forward_list& x,
const_iterator first, const_iterator last);
constexpr void splice_after(const_iterator position, forward_list&& x,
const_iterator first, const_iterator last);
Effects: Inserts elements in the range (first, last) after position and
removes the elements from x.
Pointers and references to the moved elements of
x now refer to those same elements but as members of *this.
Iterators
referring to the moved elements will continue to refer to their elements, but they now
behave as iterators into *this, not into x.
constexpr size_type remove(const T& value);
template<class Predicate> constexpr size_type remove_if(Predicate pred);
constexpr size_type unique();
template<class BinaryPredicate> constexpr size_type unique(BinaryPredicate binary_pred);
Effects: Erases all but the first element from every consecutive
group of equivalent elements.
That is, for a nonempty list, erases all elements referred to
by the iterator i in the range [begin() + 1, end())
for which binary_pred(*i, *(i - 1)) is true.
Invalidates only the iterators and references to the erased elements.
constexpr void merge(forward_list& x);
constexpr void merge(forward_list&& x);
template<class Compare> constexpr void merge(forward_list& x, Compare comp);
template<class Compare> constexpr void merge(forward_list&& x, Compare comp);
Effects: If addressof(x) == this, there are no effects.
The result is a range
that is sorted with respect to the comparator comp.
Pointers and references to the moved elements of x now refer to those same elements
but as members of *this.
Iterators referring to the moved elements will continue to
refer to their elements, but they now behave as iterators into *this, not into
x.
constexpr void sort();
template<class Compare> constexpr void sort(Compare comp);
constexpr void reverse() noexcept;
24.3.10.7 Erasure [forward.list.erasure]
template<class T, class Allocator, class U = T>
constexpr typename forward_list<T, Allocator>::size_type
erase(forward_list<T, Allocator>& c, const U& value);
template<class T, class Allocator, class Predicate>
constexpr typename forward_list<T, Allocator>::size_type
erase_if(forward_list<T, Allocator>& c, Predicate pred);
24.3.11 Class template list [list]
24.3.11.1 Overview [list.overview]
A
list
is a sequence container that supports
bidirectional iterators and allows constant time insert and erase
operations anywhere within the sequence, with storage management handled
automatically.
A list meets all of the requirements
of a container ([container.reqmts]),
of a reversible container ([container.rev.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]), and
of a sequence container,
including most of the optional sequence container
requirements ([sequence.reqmts]).
Descriptions are provided here only for operations on
list
that are not described in one of these tables
or for operations where there is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class T, class Allocator = allocator<T>>
class list {
public:
// types
using value_type = T;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
// [list.cons], construct/copy/destroy
constexpr list() : list(Allocator()) { }
constexpr explicit list(const Allocator&);
constexpr explicit list(size_type n, const Allocator& = Allocator());
constexpr list(size_type n, const T& value, const Allocator& = Allocator());
template<class InputIterator>
constexpr list(InputIterator first, InputIterator last, const Allocator& = Allocator());
template<container-compatible-range<T> R>
constexpr list(from_range_t, R&& rg, const Allocator& = Allocator());
constexpr list(const list& x);
constexpr list(list&& x);
constexpr list(const list&, const type_identity_t<Allocator>&);
constexpr list(list&&, const type_identity_t<Allocator>&);
constexpr list(initializer_list<T>, const Allocator& = Allocator());
constexpr ~list();
constexpr list& operator=(const list& x);
constexpr list& operator=(list&& x)
noexcept(allocator_traits<Allocator>::is_always_equal::value);
constexpr list& operator=(initializer_list<T>);
template<class InputIterator>
constexpr void assign(InputIterator first, InputIterator last);
template<container-compatible-range<T> R>
constexpr void assign_range(R&& rg);
constexpr void assign(size_type n, const T& t);
constexpr void assign(initializer_list<T>);
constexpr allocator_type get_allocator() const noexcept;
// iterators
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr reverse_iterator rbegin() noexcept;
constexpr const_reverse_iterator rbegin() const noexcept;
constexpr reverse_iterator rend() noexcept;
constexpr const_reverse_iterator rend() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cend() const noexcept;
constexpr const_reverse_iterator crbegin() const noexcept;
constexpr const_reverse_iterator crend() const noexcept;
// [list.capacity], capacity
constexpr bool empty() const noexcept;
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
constexpr void resize(size_type sz);
constexpr void resize(size_type sz, const T& c);
// element access
constexpr reference front();
constexpr const_reference front() const;
constexpr reference back();
constexpr const_reference back() const;
// [list.modifiers], modifiers
template<class... Args> constexpr reference emplace_front(Args&&... args);
template<class... Args> constexpr reference emplace_back(Args&&... args);
constexpr void push_front(const T& x);
constexpr void push_front(T&& x);
template<container-compatible-range<T> R>
constexpr void prepend_range(R&& rg);
constexpr void pop_front();
constexpr void push_back(const T& x);
constexpr void push_back(T&& x);
template<container-compatible-range<T> R>
constexpr void append_range(R&& rg);
constexpr void pop_back();
template<class... Args> iterator emplace(const_iterator position, Args&&... args);
constexpr iterator insert(const_iterator position, const T& x);
constexpr iterator insert(const_iterator position, T&& x);
constexpr iterator insert(const_iterator position, size_type n, const T& x);
template<class InputIterator>
constexpr iterator insert(const_iterator position, InputIterator first, InputIterator last);
template<container-compatible-range<T> R>
constexpr iterator insert_range(const_iterator position, R&& rg);
constexpr iterator insert(const_iterator position, initializer_list<T> il);
constexpr iterator erase(const_iterator position);
constexpr iterator erase(const_iterator position, const_iterator last);
constexpr void swap(list&) noexcept(allocator_traits<Allocator>::is_always_equal::value);
constexpr void clear() noexcept;
// [list.ops], list operations
constexpr void splice(const_iterator position, list& x);
constexpr void splice(const_iterator position, list&& x);
constexpr void splice(const_iterator position, list& x, const_iterator i);
constexpr void splice(const_iterator position, list&& x, const_iterator i);
constexpr void splice(const_iterator position, list& x, const_iterator first, const_iterator last);
constexpr void splice(const_iterator position, list&& x, const_iterator first, const_iterator last);
constexpr size_type remove(const T& value);
template<class Predicate> constexpr size_type remove_if(Predicate pred);
constexpr size_type unique();
template<class BinaryPredicate>
constexpr size_type unique(BinaryPredicate binary_pred);
constexpr void merge(list& x);
constexpr void merge(list&& x);
template<class Compare> constexpr void merge(list& x, Compare comp);
template<class Compare> constexpr void merge(list&& x, Compare comp);
constexpr void sort();
template<class Compare> constexpr void sort(Compare comp);
constexpr void reverse() noexcept;
};
template<class InputIterator, class Allocator = allocator<iter-value-type<InputIterator>>>
list(InputIterator, InputIterator, Allocator = Allocator())
-> list<iter-value-type<InputIterator>, Allocator>;
template<ranges::input_range R, class Allocator = allocator<ranges::range_value_t<R>>>
list(from_range_t, R&&, Allocator = Allocator())
-> list<ranges::range_value_t<R>, Allocator>;
}
An incomplete type T may be used when instantiating list
if the allocator meets the
allocator completeness requirements.
24.3.11.2 Constructors, copy, and assignment [list.cons]
constexpr explicit list(const Allocator&);
constexpr explicit list(size_type n, const Allocator& = Allocator());
constexpr list(size_type n, const T& value, const Allocator& = Allocator());
template<class InputIterator>
constexpr list(InputIterator first, InputIterator last, const Allocator& = Allocator());
template<container-compatible-range<T> R>
constexpr list(from_range_t, R&& rg, const Allocator& = Allocator());
24.3.11.3 Capacity [list.capacity]
constexpr void resize(size_type sz);
constexpr void resize(size_type sz, const T& c);
24.3.11.4 Modifiers [list.modifiers]
constexpr iterator insert(const_iterator position, const T& x);
constexpr iterator insert(const_iterator position, T&& x);
constexpr iterator insert(const_iterator position, size_type n, const T& x);
template<class InputIterator>
constexpr iterator insert(const_iterator position, InputIterator first,
InputIterator last);
template<container-compatible-range<T> R>
constexpr iterator insert_range(const_iterator position, R&& rg);
constexpr iterator insert(const_iterator position, initializer_list<T>);
template<class... Args> constexpr reference emplace_front(Args&&... args);
template<class... Args> constexpr reference emplace_back(Args&&... args);
template<class... Args> constexpr iterator emplace(const_iterator position, Args&&... args);
constexpr void push_front(const T& x);
constexpr void push_front(T&& x);
template<container-compatible-range<T> R>
constexpr void prepend_range(R&& rg);
constexpr void push_back(const T& x);
constexpr void push_back(T&& x);
template<container-compatible-range<T> R>
constexpr void append_range(R&& rg);
Complexity: Insertion of a single element into a list takes constant time and
exactly one call to a constructor of
T.
Insertion of multiple elements into a list is linear in the
number of elements inserted, and the number of calls to the copy
constructor or move constructor of T is exactly equal
to the number of elements inserted.
constexpr iterator erase(const_iterator position);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void pop_front();
constexpr void pop_back();
constexpr void clear() noexcept;
24.3.11.5 Operations [list.ops]
Since lists allow fast insertion and erasing from the middle of a list, certain
operations are provided specifically for them.205
In this subclause,
arguments for a template parameter
named Predicate or BinaryPredicate
shall meet the corresponding requirements in [algorithms.requirements].
The semantics of i + n and i - n,
where i is an iterator into the list and n is an integer,
are the same as those of next(i, n) and prev(i, n),
respectively.
constexpr void splice(const_iterator position, list& x);
constexpr void splice(const_iterator position, list&& x);
constexpr void splice(const_iterator position, list& x, const_iterator i);
constexpr void splice(const_iterator position, list&& x, const_iterator i);
constexpr void splice(const_iterator position, list& x, const_iterator first,
const_iterator last);
constexpr void splice(const_iterator position, list&& x, const_iterator first,
const_iterator last);
Effects: Inserts elements in the range
[first, last)
before
position
and removes the elements from
x.
Pointers and references to the moved elements of
x
now refer to those same elements but as members of
*this.
Iterators referring to the moved elements will continue to refer to their
elements, but they now behave as iterators into
*this,
not into
x.
constexpr size_type remove(const T& value);
template<class Predicate> constexpr size_type remove_if(Predicate pred);
constexpr size_type unique();
template<class BinaryPredicate> constexpr size_type unique(BinaryPredicate binary_pred);
Effects: Erases all but the first element from every
consecutive group of equivalent elements.
That is, for a nonempty list, erases all elements referred to
by the iterator i in the range [begin() + 1, end())
for which binary_pred(*i, *(i - 1)) is true.
Invalidates only the iterators and references to the erased elements.
constexpr void merge(list& x);
constexpr void merge(list&& x);
template<class Compare> constexpr void merge(list& x, Compare comp);
template<class Compare> constexpr void merge(list&& x, Compare comp);
Effects: If addressof(x) == this, there are no effects.
The result is a range
that is sorted with respect to the comparator comp.
Pointers and references to the moved elements of x now refer to those same elements
but as members of *this.
Iterators referring to the moved elements will continue to
refer to their elements, but they now behave as iterators into *this, not into
x.
constexpr void reverse() noexcept;
constexpr void sort();
template<class Compare> constexpr void sort(Compare comp);
205)205)
As specified
in [allocator.requirements], the requirements in this Clause apply only to
lists whose allocators compare equal.
24.3.11.6 Erasure [list.erasure]
template<class T, class Allocator, class U = T>
constexpr typename list<T, Allocator>::size_type
erase(list<T, Allocator>& c, const U& value);
template<class T, class Allocator, class Predicate>
constexpr typename list<T, Allocator>::size_type
erase_if(list<T, Allocator>& c, Predicate pred);
24.4 Associative containers [associative]
24.4.1 General [associative.general]
The following exposition-only alias templates may appear in deduction guides for associative containers:
template<class InputIterator>
using iter-value-type =
typename iterator_traits<InputIterator>::value_type; // exposition only
template<class InputIterator>
using iter-key-type = remove_const_t<
tuple_element_t<0, iter-value-type<InputIterator>>>; // exposition only
template<class InputIterator>
using iter-mapped-type =
tuple_element_t<1, iter-value-type<InputIterator>>; // exposition only
template<class InputIterator>
using iter-to-alloc-type = pair<
add_const_t<tuple_element_t<0, iter-value-type<InputIterator>>>,
tuple_element_t<1, iter-value-type<InputIterator>>>; // exposition only
template<ranges::input_range Range>
using range-key-type =
remove_const_t<typename ranges::range_value_t<Range>::first_type>; // exposition only
template<ranges::input_range Range>
using range-mapped-type = typename ranges::range_value_t<Range>::second_type; // exposition only
template<ranges::input_range Range>
using range-to-alloc-type =
pair<add_const_t<typename ranges::range_value_t<Range>::first_type>,
typename ranges::range_value_t<Range>::second_type>; // exposition only
24.4.2 Header <map> synopsis [associative.map.syn]
#include <compare> // see [compare.syn]
#include <initializer_list> // see [initializer.list.syn]
namespace std {
// [map], class template map
template<class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T>>>
class map;
template<class Key, class T, class Compare, class Allocator>
constexpr bool operator==(const map<Key, T, Compare, Allocator>& x,
const map<Key, T, Compare, Allocator>& y);
template<class Key, class T, class Compare, class Allocator>
constexpr synth-three-way-result<pair<const Key, T>>
operator<=>(const map<Key, T, Compare, Allocator>& x,
const map<Key, T, Compare, Allocator>& y);
template<class Key, class T, class Compare, class Allocator>
constexpr void swap(map<Key, T, Compare, Allocator>& x,
map<Key, T, Compare, Allocator>& y)
noexcept(noexcept(x.swap(y)));
// [map.erasure], erasure for map
template<class Key, class T, class Compare, class Allocator, class Predicate>
constexpr typename map<Key, T, Compare, Allocator>::size_type
erase_if(map<Key, T, Compare, Allocator>& c, Predicate pred);
// [multimap], class template multimap
template<class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T>>>
class multimap;
template<class Key, class T, class Compare, class Allocator>
constexpr bool operator==(const multimap<Key, T, Compare, Allocator>& x,
const multimap<Key, T, Compare, Allocator>& y);
template<class Key, class T, class Compare, class Allocator>
constexpr synth-three-way-result<pair<const Key, T>>
operator<=>(const multimap<Key, T, Compare, Allocator>& x,
const multimap<Key, T, Compare, Allocator>& y);
template<class Key, class T, class Compare, class Allocator>
constexpr void swap(multimap<Key, T, Compare, Allocator>& x,
multimap<Key, T, Compare, Allocator>& y)
noexcept(noexcept(x.swap(y)));
// [multimap.erasure], erasure for multimap
template<class Key, class T, class Compare, class Allocator, class Predicate>
constexpr typename multimap<Key, T, Compare, Allocator>::size_type
erase_if(multimap<Key, T, Compare, Allocator>& c, Predicate pred);
namespace pmr {
template<class Key, class T, class Compare = less<Key>>
using map = std::map<Key, T, Compare,
polymorphic_allocator<pair<const Key, T>>>;
template<class Key, class T, class Compare = less<Key>>
using multimap = std::multimap<Key, T, Compare,
polymorphic_allocator<pair<const Key, T>>>;
}
}
24.4.3 Header <set> synopsis [associative.set.syn]
#include <compare> // see [compare.syn]
#include <initializer_list> // see [initializer.list.syn]
namespace std {
// [set], class template set
template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
class set;
template<class Key, class Compare, class Allocator>
constexpr bool operator==(const set<Key, Compare, Allocator>& x,
const set<Key, Compare, Allocator>& y);
template<class Key, class Compare, class Allocator>
constexpr synth-three-way-result<Key> operator<=>(const set<Key, Compare, Allocator>& x,
const set<Key, Compare, Allocator>& y);
template<class Key, class Compare, class Allocator>
constexpr void swap(set<Key, Compare, Allocator>& x,
set<Key, Compare, Allocator>& y)
noexcept(noexcept(x.swap(y)));
// [set.erasure], erasure for set
template<class Key, class Compare, class Allocator, class Predicate>
constexpr typename set<Key, Compare, Allocator>::size_type
erase_if(set<Key, Compare, Allocator>& c, Predicate pred);
// [multiset], class template multiset
template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
class multiset;
template<class Key, class Compare, class Allocator>
constexpr bool operator==(const multiset<Key, Compare, Allocator>& x,
const multiset<Key, Compare, Allocator>& y);
template<class Key, class Compare, class Allocator>
constexpr synth-three-way-result<Key> operator<=>(const multiset<Key, Compare, Allocator>& x,
const multiset<Key, Compare, Allocator>& y);
template<class Key, class Compare, class Allocator>
constexpr void swap(multiset<Key, Compare, Allocator>& x,
multiset<Key, Compare, Allocator>& y)
noexcept(noexcept(x.swap(y)));
// [multiset.erasure], erasure for multiset
template<class Key, class Compare, class Allocator, class Predicate>
constexpr typename multiset<Key, Compare, Allocator>::size_type
erase_if(multiset<Key, Compare, Allocator>& c, Predicate pred);
namespace pmr {
template<class Key, class Compare = less<Key>>
using set = std::set<Key, Compare, polymorphic_allocator<Key>>;
template<class Key, class Compare = less<Key>>
using multiset = std::multiset<Key, Compare, polymorphic_allocator<Key>>;
}
}
24.4.4 Class template map [map]
24.4.4.1 Overview [map.overview]
A map meets all of the requirements of
a container ([container.reqmts]),
of a reversible container ([container.rev.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]).
and
of an associative container ([associative.reqmts]).
This means that a
map
supports the
a_uniq
operations in [associative.reqmts]
but not the
a_eq
operations.
Descriptions are provided here only for operations on
map
that are not described in one of those tables
or for operations where there is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T>>>
class map {
public:
// types
using key_type = Key;
using mapped_type = T;
using value_type = pair<const Key, T>;
using key_compare = Compare;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
using node_type = unspecified;
using insert_return_type = insert-return-type<iterator, node_type>;
class value_compare {
friend class map;
protected:
Compare comp;
constexpr value_compare(Compare c) : comp(c) {}
public:
constexpr bool operator()(const value_type& x, const value_type& y) const {
return comp(x.first, y.first);
}
};
// [map.cons], construct/copy/destroy
constexpr map() : map(Compare()) { }
constexpr explicit map(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr map(InputIterator first, InputIterator last,
const Compare& comp = Compare(), const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr map(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator());
constexpr map(const map& x);
constexpr map(map&& x);
explicit map(const Allocator&);
constexpr map(const map&, const type_identity_t<Allocator>&);
constexpr map(map&&, const type_identity_t<Allocator>&);
constexpr map(initializer_list<value_type>,
const Compare& = Compare(),
const Allocator& = Allocator());
template<class InputIterator>
constexpr map(InputIterator first, InputIterator last, const Allocator& a)
: map(first, last, Compare(), a) { }
template<container-compatible-range<value_type> R>
constexpr map(from_range_t, R&& rg, const Allocator& a))
: map(from_range, std::forward<R>(rg), Compare(), a) { }
constexpr map(initializer_list<value_type> il, const Allocator& a)
: map(il, Compare(), a) { }
constexpr ~map();
constexpr map& operator=(const map& x);
constexpr map& operator=(map&& x)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_move_assignable_v<Compare>);
constexpr map& operator=(initializer_list<value_type>);
constexpr allocator_type get_allocator() const noexcept;
// iterators
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr reverse_iterator rbegin() noexcept;
constexpr const_reverse_iterator rbegin() const noexcept;
constexpr reverse_iterator rend() noexcept;
constexpr const_reverse_iterator rend() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cend() const noexcept;
constexpr const_reverse_iterator crbegin() const noexcept;
constexpr const_reverse_iterator crend() const noexcept;
// capacity
constexpr bool empty() const noexcept;
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
// [map.access], element access
constexpr mapped_type& operator[](const key_type& x);
constexpr mapped_type& operator[](key_type&& x);
template<class K> constexpr mapped_type& operator[](K&& x);
constexpr mapped_type& at(const key_type& x);
constexpr const mapped_type& at(const key_type& x) const;
template<class K> constexpr mapped_type& at(const K& x);
template<class K> constexpr const mapped_type& at(const K& x) const;
// [map.modifiers], modifiers
template<class... Args> constexpr pair<iterator, bool> emplace(Args&&... args);
template<class... Args> constexpr iterator emplace_hint(const_iterator position, Args&&... args);
pair<iterator, bool> constexpr insert(const value_type& x);
pair<iterator, bool> constexpr insert(value_type&& x);
template<class P> constexpr pair<iterator, bool> insert(P&& x);
constexpr iterator insert(const_iterator position, const value_type& x);
constexpr iterator insert(const_iterator position, value_type&& x);
template<class P>
constexpr iterator insert(const_iterator position, P&&);
template<class InputIterator>
constexpr void insert(InputIterator first, InputIterator last);
template<container-compatible-range<value_type> R>
constexpr void insert_range(R&& rg);
constexpr void insert(initializer_list<value_type>);
constexpr node_type extract(const_iterator position);
constexpr node_type extract(const key_type& x);
template<class K> constexpr node_type extract(K&& x);
constexpr insert_return_type insert(node_type&& nh);
constexpr iterator insert(const_iterator hint, node_type&& nh);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
template<class K, class... Args>
constexpr pair<iterator, bool> try_emplace(K&& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
template<class K, class... Args>
constexpr iterator try_emplace(const_iterator hint, K&& k, Args&&... args);
template<class M>
constexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
template<class M>
constexpr pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
template<class K, class M>
constexpr pair<iterator, bool> insert_or_assign(K&& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
template<class K, class M>
constexpr iterator insert_or_assign(const_iterator hint, K&& k, M&& obj);
constexpr iterator erase(iterator position);
constexpr iterator erase(const_iterator position);
constexpr size_type erase(const key_type& x);
template<class K> constexpr size_type erase(K&& x);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void swap(map&)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_swappable_v<Compare>);
constexpr void clear() noexcept;
template<class C2>
constexpr void merge(map<Key, T, C2, Allocator>& source);
template<class C2>
constexpr void merge(map<Key, T, C2, Allocator>&& source);
template<class C2>
constexpr void merge(multimap<Key, T, C2, Allocator>& source);
template<class C2>
constexpr void merge(multimap<Key, T, C2, Allocator>&& source);
// observers
constexpr key_compare key_comp() const;
constexpr value_compare value_comp() const;
// map operations
constexpr iterator find(const key_type& x);
constexpr const_iterator find(const key_type& x) const;
template<class K> constexpr iterator find(const K& x);
template<class K> constexpr const_iterator find(const K& x) const;
constexpr size_type count(const key_type& x) const;
template<class K> constexpr size_type count(const K& x) const;
constexpr bool contains(const key_type& x) const;
template<class K> constexpr bool contains(const K& x) const;
constexpr iterator lower_bound(const key_type& x);
constexpr const_iterator lower_bound(const key_type& x) const;
template<class K> constexpr iterator lower_bound(const K& x);
template<class K> constexpr const_iterator lower_bound(const K& x) const;
constexpr iterator upper_bound(const key_type& x);
constexpr const_iterator upper_bound(const key_type& x) const;
template<class K> constexpr iterator upper_bound(const K& x);
template<class K> constexpr const_iterator upper_bound(const K& x) const;
constexpr pair<iterator, iterator> equal_range(const key_type& x);
constexpr pair<const_iterator, const_iterator> equal_range(const key_type& x) const;
template<class K>
constexpr pair<iterator, iterator> equal_range(const K& x);
template<class K>
constexpr pair<const_iterator, const_iterator> equal_range(const K& x) const;
};
template<class InputIterator, class Compare = less<iter-key-type<InputIterator>>,
class Allocator = allocator<iter-to-alloc-type<InputIterator>>>
map(InputIterator, InputIterator, Compare = Compare(), Allocator = Allocator())
-> map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>, Compare, Allocator>;
template<ranges::input_range R, class Compare = less<range-key-type<R>,
class Allocator = allocator<range-to-alloc-type<R>>>
map(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
-> map<range-key-type<R>, range-mapped-type<R>, Compare, Allocator>;
template<class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T>>>
map(initializer_list<pair<Key, T>>, Compare = Compare(), Allocator = Allocator())
-> map<Key, T, Compare, Allocator>;
template<class InputIterator, class Allocator>
map(InputIterator, InputIterator, Allocator)
-> map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>,
less<iter-key-type<InputIterator>>, Allocator>;
template<ranges::input_range R, class Allocator>
map(from_range_t, R&&, Allocator)
-> map<range-key-type<R>, range-mapped-type<R>, less<range-key-type<R>>, Allocator>;
template<class Key, class T, class Allocator>
map(initializer_list<pair<Key, T>>, Allocator) -> map<Key, T, less<Key>, Allocator>;
}
24.4.4.2 Constructors, copy, and assignment [map.cons]
constexpr explicit map(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr map(InputIterator first, InputIterator last,
const Compare& comp = Compare(), const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr map(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator());
24.4.4.3 Element access [map.access]
constexpr mapped_type& operator[](const key_type& x);
constexpr mapped_type& operator[](key_type&& x);
template<class K> constexpr mapped_type& operator[](K&& x);
constexpr mapped_type& at(const key_type& x);
constexpr const mapped_type& at(const key_type& x) const;
template<class K> constexpr mapped_type& at(const K& x);
template<class K> constexpr const mapped_type& at(const K& x) const;
24.4.4.4 Modifiers [map.modifiers]
template<class P>
constexpr pair<iterator, bool> insert(P&& x);
template<class P>
constexpr iterator insert(const_iterator position, P&& x);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
template<class K, class... Args>
constexpr pair<iterator, bool> try_emplace(K&& k, Args&&... args);
template<class K, class... Args>
constexpr iterator try_emplace(const_iterator hint, K&& k, Args&&... args);
For the first overload,
is_convertible_v<K&&, const_iterator> and
is_convertible_v<K&&, iterator>
are both false.
template<class M>
constexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
template<class M>
constexpr pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
template<class K, class M>
constexpr pair<iterator, bool> insert_or_assign(K&& k, M&& obj);
template<class K, class M>
constexpr iterator insert_or_assign(const_iterator hint, K&& k, M&& obj);
Effects: If the map already contains an element e
whose key is equivalent to k,
assigns std::forward<M>
(obj) to e.second.
(obj) to e.second.
24.4.4.5 Erasure [map.erasure]
template<class Key, class T, class Compare, class Allocator, class Predicate>
constexpr typename map<Key, T, Compare, Allocator>::size_type
erase_if(map<Key, T, Compare, Allocator>& c, Predicate pred);
24.4.5 Class template multimap [multimap]
24.4.5.1 Overview [multimap.overview]
A multimap meets all of the requirements
of a container ([container.reqmts]),
of a reversible container ([container.rev.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]), and
of an associative container ([associative.reqmts]).
This means that a
multimap
supports the
a_eq
operations in [associative.reqmts]
but not the
a_uniq
operations.
Descriptions are provided here only for operations on
multimap
that are not described in one of those tables
or for operations where there is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T>>>
class multimap {
public:
// types
using key_type = Key;
using mapped_type = T;
using value_type = pair<const Key, T>;
using key_compare = Compare;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
using node_type = unspecified;
class value_compare {
friend class multimap;
protected:
Compare comp;
constexpr value_compare(Compare c) : comp(c) { }
public:
constexpr bool operator()(const value_type& x, const value_type& y) const {
return comp(x.first, y.first);
}
};
// [multimap.cons], construct/copy/destroy
constexpr multimap() : multimap(Compare()) { }
constexpr explicit multimap(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr multimap(InputIterator first, InputIterator last,
const Compare& comp = Compare(),
const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr multimap(from_range_t, R&& rg,
const Compare& comp = Compare(), const Allocator& = Allocator());
constexpr multimap(const multimap& x);
constexpr multimap(multimap&& x);
constexpr explicit multimap(const Allocator&);
constexpr multimap(const multimap&, const type_identity_t<Allocator>&);
constexpr multimap(multimap&&, const type_identity_t<Allocator>&);
constexpr multimap(initializer_list<value_type>,
const Compare& = Compare(),
const Allocator& = Allocator());
template<class InputIterator>
constexpr multimap(InputIterator first, InputIterator last, const Allocator& a)
: multimap(first, last, Compare(), a) { }
template<container-compatible-range<value_type> R>
constexpr multimap(from_range_t, R&& rg, const Allocator& a))
: multimap(from_range, std::forward<R>(rg), Compare(), a) { }
constexpr multimap(initializer_list<value_type> il, const Allocator& a)
: multimap(il, Compare(), a) { }
constexpr ~multimap();
constexpr multimap& operator=(const multimap& x);
constexpr multimap& operator=(multimap&& x)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_move_assignable_v<Compare>);
constexpr multimap& operator=(initializer_list<value_type>);
constexpr allocator_type get_allocator() const noexcept;
// iterators
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr reverse_iterator rbegin() noexcept;
constexpr const_reverse_iterator rbegin() const noexcept;
constexpr reverse_iterator rend() noexcept;
constexpr const_reverse_iterator rend() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cend() const noexcept;
constexpr const_reverse_iterator crbegin() const noexcept;
constexpr const_reverse_iterator crend() const noexcept;
// capacity
constexpr bool empty() const noexcept;
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
// [multimap.modifiers], modifiers
template<class... Args> constexpr iterator emplace(Args&&... args);
template<class... Args> constexpr iterator emplace_hint(const_iterator position, Args&&... args);
constexpr iterator insert(const value_type& x);
constexpr iterator insert(value_type&& x);
template<class P> constexpr iterator insert(P&& x);
constexpr iterator insert(const_iterator position, const value_type& x);
constexpr iterator insert(const_iterator position, value_type&& x);
template<class P> constexpr iterator insert(const_iterator position, P&& x);
template<class InputIterator>
constexpr void insert(InputIterator first, InputIterator last);
template<container-compatible-range<value_type> R>
constexpr void insert_range(R&& rg);
constexpr void insert(initializer_list<value_type>);
constexpr node_type extract(const_iterator position);
constexpr node_type extract(const key_type& x);
template<class K> constexpr node_type extract(K&& x);
constexpr iterator insert(node_type&& nh);
constexpr iterator insert(const_iterator hint, node_type&& nh);
constexpr iterator erase(iterator position);
constexpr iterator erase(const_iterator position);
constexpr size_type erase(const key_type& x);
template<class K> constexpr size_type erase(K&& x);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void swap(multimap&)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_swappable_v<Compare>);
constexpr void clear() noexcept;
template<class C2>
constexpr void merge(multimap<Key, T, C2, Allocator>& source);
template<class C2>
constexpr void merge(multimap<Key, T, C2, Allocator>&& source);
template<class C2>
constexpr void merge(map<Key, T, C2, Allocator>& source);
template<class C2>
constexpr void merge(map<Key, T, C2, Allocator>&& source);
// observers
constexpr key_compare key_comp() const;
constexpr value_compare value_comp() const;
// map operations
constexpr iterator find(const key_type& x);
constexpr const_iterator find(const key_type& x) const;
template<class K> constexpr iterator find(const K& x);
template<class K> constexpr const_iterator find(const K& x) const;
constexpr size_type count(const key_type& x) const;
template<class K> constexpr size_type count(const K& x) const;
constexpr bool contains(const key_type& x) const;
template<class K> constexpr bool contains(const K& x) const;
constexpr iterator lower_bound(const key_type& x);
constexpr const_iterator lower_bound(const key_type& x) const;
template<class K> constexpr iterator lower_bound(const K& x);
template<class K> constexpr const_iterator lower_bound(const K& x) const;
constexpr iterator upper_bound(const key_type& x);
constexpr const_iterator upper_bound(const key_type& x) const;
template<class K> constexpr iterator upper_bound(const K& x);
template<class K> constexpr const_iterator upper_bound(const K& x) const;
constexpr pair<iterator, iterator> equal_range(const key_type& x);
constexpr pair<const_iterator, const_iterator> equal_range(const key_type& x) const;
template<class K>
constexpr pair<iterator, iterator> equal_range(const K& x);
template<class K>
constexpr pair<const_iterator, const_iterator> equal_range(const K& x) const;
};
template<class InputIterator, class Compare = less<iter-key-type<InputIterator>>,
class Allocator = allocator<iter-to-alloc-type<InputIterator>>>
multimap(InputIterator, InputIterator, Compare = Compare(), Allocator = Allocator())
-> multimap<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>,
Compare, Allocator>;
template<ranges::input_range R, class Compare = less<range-key-type<R>>,
class Allocator = allocator<range-to-alloc-type<R>>>
multimap(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
-> multimap<range-key-type<R>, range-mapped-type<R>, Compare, Allocator>;
template<class Key, class T, class Compare = less<Key>,
class Allocator = allocator<pair<const Key, T>>>
multimap(initializer_list<pair<Key, T>>, Compare = Compare(), Allocator = Allocator())
-> multimap<Key, T, Compare, Allocator>;
template<class InputIterator, class Allocator>
multimap(InputIterator, InputIterator, Allocator)
-> multimap<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>,
less<iter-key-type<InputIterator>>, Allocator>;
template<ranges::input_range R, class Allocator>
multimap(from_range_t, R&&, Allocator)
-> multimap<range-key-type<R>, range-mapped-type<R>, less<range-key-type<R>>, Allocator>;
template<class Key, class T, class Allocator>
multimap(initializer_list<pair<Key, T>>, Allocator)
-> multimap<Key, T, less<Key>, Allocator>;
}
24.4.5.2 Constructors [multimap.cons]
constexpr explicit multimap(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr multimap(InputIterator first, InputIterator last,
const Compare& comp = Compare(),
const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr multimap(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator());
24.4.5.3 Modifiers [multimap.modifiers]
template<class P> constexpr iterator insert(P&& x);
template<class P> constexpr iterator insert(const_iterator position, P&& x);
24.4.5.4 Erasure [multimap.erasure]
template<class Key, class T, class Compare, class Allocator, class Predicate>
constexpr typename multimap<Key, T, Compare, Allocator>::size_type
erase_if(multimap<Key, T, Compare, Allocator>& c, Predicate pred);
24.4.6 Class template set [set]
24.4.6.1 Overview [set.overview]
A set meets all of the requirements
of a container ([container.reqmts]),
of a reversible container ([container.rev.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]).
and
of an associative container ([associative.reqmts]).
This means that a
set
supports the
a_uniq
operations in [associative.reqmts]
but not the
a_eq
operations.
Descriptions are provided here only for operations on
set
that are not described in one of these tables
and for operations where there is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class Key, class Compare = less<Key>,
class Allocator = allocator<Key>>
class set {
public:
// types
using key_type = Key;
using key_compare = Compare;
using value_type = Key;
using value_compare = Compare;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
using node_type = unspecified;
using insert_return_type = insert-return-type<iterator, node_type>;
// [set.cons], construct/copy/destroy
constexpr set() : set(Compare()) { }
constexpr explicit set(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr set(InputIterator first, InputIterator last,
const Compare& comp = Compare(), const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr set(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator());
constexpr set(const set& x);
constexpr set(set&& x);
constexpr explicit set(const Allocator&);
constexpr set(const set&, const type_identity_t<Allocator>&);
constexpr set(set&&, const type_identity_t<Allocator>&);
constexpr set(initializer_list<value_type>, const Compare& = Compare(),
const Allocator& = Allocator());
template<class InputIterator>
constexpr set(InputIterator first, InputIterator last, const Allocator& a)
: set(first, last, Compare(), a) { }
template<container-compatible-range<value_type> R>
constexpr set(from_range_t, R&& rg, const Allocator& a))
: set(from_range, std::forward<R>(rg), Compare(), a) { }
constexpr set(initializer_list<value_type> il, const Allocator& a)
: set(il, Compare(), a) { }
constexpr ~set();
constexpr set& operator=(const set& x);
constexpr set& operator=(set&& x)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_move_assignable_v<Compare>);
constexpr set& operator=(initializer_list<value_type>);
constexpr allocator_type get_allocator() const noexcept;
// iterators
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr reverse_iterator rbegin() noexcept;
constexpr const_reverse_iterator rbegin() const noexcept;
constexpr reverse_iterator rend() noexcept;
constexpr const_reverse_iterator rend() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cend() const noexcept;
constexpr const_reverse_iterator crbegin() const noexcept;
constexpr const_reverse_iterator crend() const noexcept;
// capacity
constexpr bool empty() const noexcept;
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
// [set.modifiers], modifiers
template<class... Args> constexpr pair<iterator, bool> emplace(Args&&... args);
template<class... Args> constexpr iterator emplace_hint(const_iterator position, Args&&... args);
constexpr pair<iterator,bool> insert(const value_type& x);
constexpr pair<iterator,bool> insert(value_type&& x);
template<class K> constexpr pair<iterator, bool> insert(K&& x);
constexpr iterator insert(const_iterator position, const value_type& x);
constexpr iterator insert(const_iterator position, value_type&& x);
template<class K> constexpr iterator insert(const_iterator position, K&& x);
template<class InputIterator>
constexpr void insert(InputIterator first, InputIterator last);
template<container-compatible-range<value_type> R>
constexpr void insert_range(R&& rg);
constexpr void insert(initializer_list<value_type>);
constexpr node_type extract(const_iterator position);
constexpr node_type extract(const key_type& x);
template<class K> constexpr node_type extract(K&& x);
constexpr insert_return_type insert(node_type&& nh);
constexpr iterator insert(const_iterator hint, node_type&& nh);
constexpr iterator erase(iterator position)
requires (!same_as<iterator, const_iterator>);
constexpr iterator erase(const_iterator position);
constexpr size_type erase(const key_type& x);
template<class K> constexpr size_type erase(K&& x);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void swap(set&)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_swappable_v<Compare>);
constexpr void clear() noexcept;
template<class C2>
constexpr void merge(set<Key, C2, Allocator>& source);
template<class C2>
constexpr void merge(set<Key, C2, Allocator>&& source);
template<class C2>
constexpr void merge(multiset<Key, C2, Allocator>& source);
template<class C2>
constexpr void merge(multiset<Key, C2, Allocator>&& source);
// observers
constexpr key_compare key_comp() const;
constexpr value_compare value_comp() const;
// set operations
constexpr iterator find(const key_type& x);
constexpr const_iterator find(const key_type& x) const;
template<class K> constexpr iterator find(const K& x);
template<class K> constexpr const_iterator find(const K& x) const;
constexpr size_type count(const key_type& x) const;
template<class K> constexpr size_type count(const K& x) const;
constexpr bool contains(const key_type& x) const;
template<class K> constexpr bool contains(const K& x) const;
constexpr iterator lower_bound(const key_type& x);
constexpr const_iterator lower_bound(const key_type& x) const;
template<class K> constexpr iterator lower_bound(const K& x);
template<class K> constexpr const_iterator lower_bound(const K& x) const;
constexpr iterator upper_bound(const key_type& x);
constexpr const_iterator upper_bound(const key_type& x) const;
template<class K> constexpr iterator upper_bound(const K& x);
template<class K> constexpr const_iterator upper_bound(const K& x) const;
constexpr pair<iterator, iterator> equal_range(const key_type& x);
constexpr pair<const_iterator, const_iterator> equal_range(const key_type& x) const;
template<class K>
constexpr pair<iterator, iterator> equal_range(const K& x);
template<class K>
constexpr pair<const_iterator, const_iterator> equal_range(const K& x) const;
};
template<class InputIterator,
class Compare = less<iter-value-type<InputIterator>>,
class Allocator = allocator<iter-value-type<InputIterator>>>
set(InputIterator, InputIterator,
Compare = Compare(), Allocator = Allocator())
-> set<iter-value-type<InputIterator>, Compare, Allocator>;
template<ranges::input_range R, class Compare = less<ranges::range_value_t<R>>,
class Allocator = allocator<ranges::range_value_t<R>>>
set(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
-> set<ranges::range_value_t<R>, Compare, Allocator>;
template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
set(initializer_list<Key>, Compare = Compare(), Allocator = Allocator())
-> set<Key, Compare, Allocator>;
template<class InputIterator, class Allocator>
set(InputIterator, InputIterator, Allocator)
-> set<iter-value-type<InputIterator>,
less<iter-value-type<InputIterator>>, Allocator>;
template<ranges::input_range R, class Allocator>
set(from_range_t, R&&, Allocator)
-> set<ranges::range_value_t<R>, less<ranges::range_value_t<R>>, Allocator>;
template<class Key, class Allocator>
set(initializer_list<Key>, Allocator) -> set<Key, less<Key>, Allocator>;
}
24.4.6.2 Constructors, copy, and assignment [set.cons]
constexpr explicit set(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr set(InputIterator first, InputIterator last,
const Compare& comp = Compare(), const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr set(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator());
24.4.6.3 Erasure [set.erasure]
template<class Key, class Compare, class Allocator, class Predicate>
constexpr typename set<Key, Compare, Allocator>::size_type
erase_if(set<Key, Compare, Allocator>& c, Predicate pred);
24.4.6.4 Modifiers [set.modifiers]
template<class K> constexpr pair<iterator, bool> insert(K&& x);
template<class K> constexpr iterator insert(const_iterator hint, K&& x);
For the second overload,
is_convertible_v<K&&, const_iterator> and
is_convertible_v<K&&, iterator> are both false.
24.4.7 Class template multiset [multiset]
24.4.7.1 Overview [multiset.overview]
A multiset meets all of the requirements
of a container ([container.reqmts]),
of a reversible container ([container.rev.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]),
of an associative container ([associative.reqmts]).
This means that a
multiset
supports the
a_eq
operations in [associative.reqmts]
but not the
a_uniq
operations.
Descriptions are provided here only for operations on
multiset
that are not described in one of these tables
and for operations where there is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class Key, class Compare = less<Key>,
class Allocator = allocator<Key>>
class multiset {
public:
// types
using key_type = Key;
using key_compare = Compare;
using value_type = Key;
using value_compare = Compare;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
using node_type = unspecified;
// [multiset.cons], construct/copy/destroy
constexpr multiset() : multiset(Compare()) { }
constexpr explicit multiset(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr multiset(InputIterator first, InputIterator last,
const Compare& comp = Compare(), const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr multiset(from_range_t, R&& rg,
const Compare& comp = Compare(), const Allocator& = Allocator());
constexpr multiset(const multiset& x);
constexpr multiset(multiset&& x);
constexpr explicit multiset(const Allocator&);
constexpr multiset(const multiset&, const type_identity_t<Allocator>&);
constexpr multiset(multiset&&, const type_identity_t<Allocator>&);
constexpr multiset(initializer_list<value_type>, const Compare& = Compare(),
const Allocator& = Allocator());
template<class InputIterator>
constexpr multiset(InputIterator first, InputIterator last, const Allocator& a)
: multiset(first, last, Compare(), a) { }
template<container-compatible-range<value_type> R>
constexpr multiset(from_range_t, R&& rg, const Allocator& a))
: multiset(from_range, std::forward<R>(rg), Compare(), a) { }
constexpr multiset(initializer_list<value_type> il, const Allocator& a)
: multiset(il, Compare(), a) { }
constexpr ~multiset();
constexpr multiset& operator=(const multiset& x);
constexpr multiset& operator=(multiset&& x)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_move_assignable_v<Compare>);
constexpr multiset& operator=(initializer_list<value_type>);
constexpr allocator_type get_allocator() const noexcept;
// iterators
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr reverse_iterator rbegin() noexcept;
constexpr const_reverse_iterator rbegin() const noexcept;
constexpr reverse_iterator rend() noexcept;
constexpr const_reverse_iterator rend() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cend() const noexcept;
constexpr const_reverse_iterator crbegin() const noexcept;
constexpr const_reverse_iterator crend() const noexcept;
// capacity
constexpr bool empty() const noexcept;
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
// modifiers
template<class... Args> constexpr iterator emplace(Args&&... args);
template<class... Args> constexpr iterator emplace_hint(const_iterator position, Args&&... args);
constexpr iterator insert(const value_type& x);
constexpr iterator insert(value_type&& x);
constexpr iterator insert(const_iterator position, const value_type& x);
constexpr iterator insert(const_iterator position, value_type&& x);
template<class InputIterator>
constexpr void insert(InputIterator first, InputIterator last);
template<container-compatible-range<value_type> R>
constexpr void insert_range(R&& rg);
constexpr void insert(initializer_list<value_type>);
constexpr node_type extract(const_iterator position);
constexpr node_type extract(const key_type& x);
template<class K> constexpr node_type extract(K&& x);
constexpr iterator insert(node_type&& nh);
constexpr iterator insert(const_iterator hint, node_type&& nh);
constexpr iterator erase(iterator position)
requires (!same_as<iterator, const_iterator>);
constexpr iterator erase(const_iterator position);
constexpr size_type erase(const key_type& x);
template<class K> constexpr size_type erase(K&& x);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void swap(multiset&)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_swappable_v<Compare>);
constexpr void clear() noexcept;
template<class C2>
constexpr void merge(multiset<Key, C2, Allocator>& source);
template<class C2>
constexpr void merge(multiset<Key, C2, Allocator>&& source);
template<class C2>
constexpr void merge(set<Key, C2, Allocator>& source);
template<class C2>
constexpr void merge(set<Key, C2, Allocator>&& source);
// observers
constexpr key_compare key_comp() const;
constexpr value_compare value_comp() const;
// set operations
constexpr iterator find(const key_type& x);
constexpr const_iterator find(const key_type& x) const;
template<class K> constexpr iterator find(const K& x);
template<class K> constexpr const_iterator find(const K& x) const;
constexpr size_type count(const key_type& x) const;
template<class K> constexpr size_type count(const K& x) const;
constexpr bool contains(const key_type& x) const;
template<class K> constexpr bool contains(const K& x) const;
constexpr iterator lower_bound(const key_type& x);
constexpr const_iterator lower_bound(const key_type& x) const;
template<class K> constexpr iterator lower_bound(const K& x);
template<class K> constexpr const_iterator lower_bound(const K& x) const;
constexpr iterator upper_bound(const key_type& x);
constexpr const_iterator upper_bound(const key_type& x) const;
template<class K> constexpr iterator upper_bound(const K& x);
template<class K> constexpr const_iterator upper_bound(const K& x) const;
constexpr pair<iterator, iterator> equal_range(const key_type& x);
constexpr pair<const_iterator, const_iterator> equal_range(const key_type& x) const;
template<class K>
constexpr pair<iterator, iterator> equal_range(const K& x);
template<class K>
constexpr pair<const_iterator, const_iterator> equal_range(const K& x) const;
};
template<class InputIterator,
class Compare = less<iter-value-type<InputIterator>>,
class Allocator = allocator<iter-value-type<InputIterator>>>
multiset(InputIterator, InputIterator,
Compare = Compare(), Allocator = Allocator())
-> multiset<iter-value-type<InputIterator>, Compare, Allocator>;
template<ranges::input_range R, class Compare = less<ranges::range_value_t<R>>,
class Allocator = allocator<ranges::range_value_t<R>>>
multiset(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
-> multiset<ranges::range_value_t<R>, Compare, Allocator>;
template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
multiset(initializer_list<Key>, Compare = Compare(), Allocator = Allocator())
-> multiset<Key, Compare, Allocator>;
template<class InputIterator, class Allocator>
multiset(InputIterator, InputIterator, Allocator)
-> multiset<iter-value-type<InputIterator>,
less<iter-value-type<InputIterator>>, Allocator>;
template<ranges::input_range R, class Allocator>
multiset(from_range_t, R&&, Allocator)
-> multiset<ranges::range_value_t<R>, less<ranges::range_value_t<R>>, Allocator>;
template<class Key, class Allocator>
multiset(initializer_list<Key>, Allocator) -> multiset<Key, less<Key>, Allocator>;
}
24.4.7.2 Constructors [multiset.cons]
constexpr explicit multiset(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
constexpr multiset(InputIterator first, InputIterator last,
const Compare& comp = Compare(), const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
constexpr multiset(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator());
24.4.7.3 Erasure [multiset.erasure]
template<class Key, class Compare, class Allocator, class Predicate>
constexpr typename multiset<Key, Compare, Allocator>::size_type
erase_if(multiset<Key, Compare, Allocator>& c, Predicate pred);
24.5 Unordered associative containers [unord]
24.5.1 General [unord.general]
The header <unordered_map> defines the class
templates unordered_map and unordered_multimap;
the header <unordered_set> defines the class
templates unordered_set and unordered_multiset.
The exposition-only alias templates
iter-value-type, iter-key-type,
iter-mapped-type, iter-to-alloc-type,
range-key-type, range-mapped-type,
and range-to-alloc-type
defined in [associative.general] may appear in deduction guides for unordered containers.
24.5.2 Header <unordered_map> synopsis [unord.map.syn]
#include <compare> // see [compare.syn]
#include <initializer_list> // see [initializer.list.syn]
namespace std {
// [unord.map], class template unordered_map
template<class Key,
class T,
class Hash = hash<Key>,
class Pred = equal_to<Key>,
class Alloc = allocator<pair<const Key, T>>>
class unordered_map;
// [unord.multimap], class template unordered_multimap
template<class Key,
class T,
class Hash = hash<Key>,
class Pred = equal_to<Key>,
class Alloc = allocator<pair<const Key, T>>>
class unordered_multimap;
template<class Key, class T, class Hash, class Pred, class Alloc>
constexpr bool operator==(const unordered_map<Key, T, Hash, Pred, Alloc>& a,
const unordered_map<Key, T, Hash, Pred, Alloc>& b);
template<class Key, class T, class Hash, class Pred, class Alloc>
constexpr bool operator==(const unordered_multimap<Key, T, Hash, Pred, Alloc>& a,
const unordered_multimap<Key, T, Hash, Pred, Alloc>& b);
template<class Key, class T, class Hash, class Pred, class Alloc>
constexpr void swap(unordered_map<Key, T, Hash, Pred, Alloc>& x,
unordered_map<Key, T, Hash, Pred, Alloc>& y)
noexcept(noexcept(x.swap(y)));
template<class Key, class T, class Hash, class Pred, class Alloc>
constexpr void swap(unordered_multimap<Key, T, Hash, Pred, Alloc>& x,
unordered_multimap<Key, T, Hash, Pred, Alloc>& y)
noexcept(noexcept(x.swap(y)));
// [unord.map.erasure], erasure for unordered_map
template<class K, class T, class H, class P, class A, class Predicate>
constexpr typename unordered_map<K, T, H, P, A>::size_type
erase_if(unordered_map<K, T, H, P, A>& c, Predicate pred);
// [unord.multimap.erasure], erasure for unordered_multimap
template<class K, class T, class H, class P, class A, class Predicate>
constexpr typename unordered_multimap<K, T, H, P, A>::size_type
erase_if(unordered_multimap<K, T, H, P, A>& c, Predicate pred);
namespace pmr {
template<class Key,
class T,
class Hash = hash<Key>,
class Pred = equal_to<Key>>
using unordered_map =
std::unordered_map<Key, T, Hash, Pred,
polymorphic_allocator<pair<const Key, T>>>;
template<class Key,
class T,
class Hash = hash<Key>,
class Pred = equal_to<Key>>
using unordered_multimap =
std::unordered_multimap<Key, T, Hash, Pred,
polymorphic_allocator<pair<const Key, T>>>;
}
}
24.5.3 Header <unordered_set> synopsis [unord.set.syn]
#include <compare> // see [compare.syn]
#include <initializer_list> // see [initializer.list.syn]
namespace std {
// [unord.set], class template unordered_set
template<class Key,
class Hash = hash<Key>,
class Pred = equal_to<Key>,
class Alloc = allocator<Key>>
class unordered_set;
// [unord.multiset], class template unordered_multiset
template<class Key,
class Hash = hash<Key>,
class Pred = equal_to<Key>,
class Alloc = allocator<Key>>
class unordered_multiset;
template<class Key, class Hash, class Pred, class Alloc>
constexpr bool operator==(const unordered_set<Key, Hash, Pred, Alloc>& a,
const unordered_set<Key, Hash, Pred, Alloc>& b);
template<class Key, class Hash, class Pred, class Alloc>
constexpr bool operator==(const unordered_multiset<Key, Hash, Pred, Alloc>& a,
const unordered_multiset<Key, Hash, Pred, Alloc>& b);
template<class Key, class Hash, class Pred, class Alloc>
constexpr void swap(unordered_set<Key, Hash, Pred, Alloc>& x,
unordered_set<Key, Hash, Pred, Alloc>& y)
noexcept(noexcept(x.swap(y)));
template<class Key, class Hash, class Pred, class Alloc>
constexpr void swap(unordered_multiset<Key, Hash, Pred, Alloc>& x,
unordered_multiset<Key, Hash, Pred, Alloc>& y)
noexcept(noexcept(x.swap(y)));
// [unord.set.erasure], erasure for unordered_set
template<class K, class H, class P, class A, class Predicate>
constexpr typename unordered_set<K, H, P, A>::size_type
erase_if(unordered_set<K, H, P, A>& c, Predicate pred);
// [unord.multiset.erasure], erasure for unordered_multiset
template<class K, class H, class P, class A, class Predicate>
constexpr typename unordered_multiset<K, H, P, A>::size_type
erase_if(unordered_multiset<K, H, P, A>& c, Predicate pred);
namespace pmr {
template<class Key,
class Hash = hash<Key>,
class Pred = equal_to<Key>>
using unordered_set = std::unordered_set<Key, Hash, Pred,
polymorphic_allocator<Key>>;
template<class Key,
class Hash = hash<Key>,
class Pred = equal_to<Key>>
using unordered_multiset = std::unordered_multiset<Key, Hash, Pred,
polymorphic_allocator<Key>>;
}
}
24.5.4 Class template unordered_map [unord.map]
24.5.4.1 Overview [unord.map.overview]
An unordered_map meets all of the requirements
of a container ([container.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]), and
of an unordered associative container ([unord.req]).
It provides the operations described in the preceding requirements table for unique keys;
that is, an unordered_map supports the a_uniq operations in that table,
not the a_eq operations.
For an unordered_map<Key, T> the key_type is Key,
the mapped_type is T,
and the value_type is pair<const Key, T>.
Subclause [unord.map] only describes operations on unordered_map that
are not described in one of the requirement tables, or for which there
is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class Key,
class T,
class Hash = hash<Key>,
class Pred = equal_to<Key>,
class Allocator = allocator<pair<const Key, T>>>
class unordered_map {
public:
// types
using key_type = Key;
using mapped_type = T;
using value_type = pair<const Key, T>;
using hasher = Hash;
using key_equal = Pred;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using local_iterator = implementation-defined; // see [container.requirements]
using const_local_iterator = implementation-defined; // see [container.requirements]
using node_type = unspecified;
using insert_return_type = insert-return-type<iterator, node_type>;
// [unord.map.cnstr], construct/copy/destroy
constexpr unordered_map();
constexpr explicit unordered_map(size_type n,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
template<class InputIterator>
constexpr unordered_map(InputIterator f, InputIterator l,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
template<container-compatible-range<value_type> R>
constexpr unordered_map(from_range_t, R&& rg, size_type n = see below,
const hasher& hf = hasher(), const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
constexpr unordered_map(const unordered_map&);
constexpr unordered_map(unordered_map&&);
constexpr explicit unordered_map(const Allocator&);
constexpr unordered_map(const unordered_map&, const type_identity_t<Allocator>&);
constexpr unordered_map(unordered_map&&, const type_identity_t<Allocator>&);
constexpr unordered_map(initializer_list<value_type> il,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
constexpr unordered_map(size_type n, const allocator_type& a)
: unordered_map(n, hasher(), key_equal(), a) { }
constexpr unordered_map(size_type n, const hasher& hf, const allocator_type& a)
: unordered_map(n, hf, key_equal(), a) { }
template<class InputIterator>
constexpr unordered_map(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
: unordered_map(f, l, n, hasher(), key_equal(), a) { }
template<class InputIterator>
constexpr unordered_map(InputIterator f, InputIterator l, size_type n, const hasher& hf,
const allocator_type& a)
: unordered_map(f, l, n, hf, key_equal(), a) { }
template<container-compatible-range<value_type> R>
constexpr unordered_map(from_range_t, R&& rg, size_type n, const allocator_type& a)
: unordered_map(from_range, std::forward<R>(rg), n, hasher(), key_equal(), a) { }
template<container-compatible-range<value_type> R>
constexpr unordered_map(from_range_t, R&& rg, size_type n, const hasher& hf, const allocator_type& a)
: unordered_map(from_range, std::forward<R>(rg), n, hf, key_equal(), a) { }
constexpr unordered_map(initializer_list<value_type> il, size_type n, const allocator_type& a)
: unordered_map(il, n, hasher(), key_equal(), a) { }
constexpr unordered_map(initializer_list<value_type> il, size_type n, const hasher& hf,
const allocator_type& a)
: unordered_map(il, n, hf, key_equal(), a) { }
constexpr ~unordered_map();
constexpr unordered_map& operator=(const unordered_map&);
constexpr unordered_map& operator=(unordered_map&&)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_move_assignable_v<Hash> &&
is_nothrow_move_assignable_v<Pred>);
constexpr unordered_map& operator=(initializer_list<value_type>);
constexpr allocator_type get_allocator() const noexcept;
// iterators
constexpr iterator begin() noexcept;
constexpr const_iterator begin() const noexcept;
constexpr iterator end() noexcept;
constexpr const_iterator end() const noexcept;
constexpr const_iterator cbegin() const noexcept;
constexpr const_iterator cend() const noexcept;
// capacity
constexpr bool empty() const noexcept;
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
// [unord.map.modifiers], modifiers
template<class... Args> constexpr pair<iterator, bool> emplace(Args&&... args);
template<class... Args> constexpr iterator emplace_hint(const_iterator position, Args&&... args);
constexpr pair<iterator, bool> insert(const value_type& obj);
constexpr pair<iterator, bool> insert(value_type&& obj);
template<class P> constexpr pair<iterator, bool> insert(P&& obj);
constexpr iterator insert(const_iterator hint, const value_type& obj);
constexpr iterator insert(const_iterator hint, value_type&& obj);
template<class P> constexpr iterator insert(const_iterator hint, P&& obj);
template<class InputIterator> constexpr void insert(InputIterator first, InputIterator last);
template<container-compatible-range<value_type> R>
constexpr void insert_range(R&& rg);
constexpr void insert(initializer_list<value_type>);
constexpr node_type extract(const_iterator position);
constexpr node_type extract(const key_type& x);
template<class K> constexpr node_type extract(K&& x);
constexpr insert_return_type insert(node_type&& nh);
constexpr iterator insert(const_iterator hint, node_type&& nh);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
template<class K, class... Args>
constexpr pair<iterator, bool> try_emplace(K&& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
template<class K, class... Args>
constexpr iterator try_emplace(const_iterator hint, K&& k, Args&&... args);
template<class M>
constexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
template<class M>
constexpr pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
template<class K, class M>
constexpr pair<iterator, bool> insert_or_assign(K&& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
template<class K, class M>
constexpr iterator insert_or_assign(const_iterator hint, K&& k, M&& obj);
constexpr iterator erase(iterator position);
constexpr iterator erase(const_iterator position);
constexpr size_type erase(const key_type& k);
template<class K> constexpr size_type erase(K&& x);
constexpr iterator erase(const_iterator first, const_iterator last);
constexpr void swap(unordered_map&)
noexcept(allocator_traits<Allocator>::is_always_equal::value &&
is_nothrow_swappable_v<Hash> &&
is_nothrow_swappable_v<Pred>);
constexpr void clear() noexcept;
template<class H2, class P2>
constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>& source);
template<class H2, class P2>
constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>&& source);
template<class H2, class P2>
constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source);
template<class H2, class P2>
constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source);
// observers
constexpr hasher hash_function() const;
constexpr key_equal key_eq() const;
// map operations
constexpr iterator find(const key_type& k);
constexpr const_iterator find(const key_type& k) const;
template<class K>
constexpr iterator find(const K& k);
template<class K>
constexpr const_iterator find(const K& k) const;
constexpr size_type count(const key_type& k) const;
template<class K>
constexpr size_type count(const K& k) const;
constexpr bool contains(const key_type& k) const;
template<class K>
constexpr bool contains(const K& k) const;
constexpr pair<iterator, iterator> equal_range(const key_type& k);
constexpr pair<const_iterator, const_iterator> equal_range(const key_type& k) const;
template<class K>
constexpr pair<iterator, iterator> equal_range(const K& k);
template<class K>
constexpr pair<const_iterator, const_iterator> equal_range(const K& k) const;
// [unord.map.elem], element access
constexpr mapped_type& operator[](const key_type& k);
constexpr mapped_type& operator[](key_type&& k);
template<class K> constexpr mapped_type& operator[](K&& k);
constexpr mapped_type& at(const key_type& k);
constexpr const mapped_type& at(const key_type& k) const;
template<class K> constexpr mapped_type& at(const K& k);
template<class K> constexpr const mapped_type& at(const K& k) const;
// bucket interface
constexpr size_type bucket_count() const noexcept;
constexpr size_type max_bucket_count() const noexcept;
constexpr size_type bucket_size(size_type n) const;
constexpr size_type bucket(const key_type& k) const;
template<class K> constexpr size_type bucket(const K& k) const;
constexpr local_iterator begin(size_type n);
constexpr const_local_iterator begin(size_type n) const;
constexpr local_iterator end(size_type n);
constexpr const_local_iterator end(size_type n) const;
constexpr const_local_iterator cbegin(size_type n) const;
constexpr const_local_iterator cend(size_type n) const;
// hash policy
constexpr float load_factor() const noexcept;
constexpr float max_load_factor() const noexcept;
constexpr void max_load_factor(float z);
constexpr void rehash(size_type n);
constexpr void reserve(size_type n);
};
template<class InputIterator,
class Hash = hash<iter-key-type<InputIterator>>,
class Pred = equal_to<iter-key-type<InputIterator>>,
class Allocator = allocator<iter-to-alloc-type<InputIterator>>>
unordered_map(InputIterator, InputIterator, typename see below::size_type = see below,
Hash = Hash(), Pred = Pred(), Allocator = Allocator())
-> unordered_map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>, Hash, Pred,
Allocator>;
template<ranges::input_range R, class Hash = hash<range-key-type<R>>,
class Pred = equal_to<range-key-type<R>>,
class Allocator = allocator<range-to-alloc-type<R>>>
unordered_map(from_range_t, R&&, typename see below::size_type = see below,
Hash = Hash(), Pred = Pred(), Allocator = Allocator())
-> unordered_map<range-key-type<R>, range-mapped-type<R>, Hash, Pred, Allocator>;
template<class Key, class T, class Hash = hash<Key>,
class Pred = equal_to<Key>, class Allocator = allocator<pair<const Key, T>>>
unordered_map(initializer_list<pair<Key, T>>,
typename see below::size_type = see below, Hash = Hash(),
Pred = Pred(), Allocator = Allocator())
-> unordered_map<Key, T, Hash, Pred, Allocator>;
template<class InputIterator, class Allocator>
unordered_map(InputIterator, InputIterator, typename see below::size_type, Allocator)
-> unordered_map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>,
hash<iter-key-type<InputIterator>>,
equal_to<iter-key-type<InputIterator>>, Allocator>;
template<class InputIterator, class Allocator>
unordered_map(InputIterator, InputIterator, Allocator)
-> unordered_map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>,
hash<iter-key-type<InputIterator>>,
equal_to<iter-key-type<InputIterator>>, Allocator>;
template<class InputIterator, class Hash, class Allocator>
unordered_map(InputIterator, InputIterator, typename see below::size_type, Hash, Allocator)
-> unordered_map<iter-key-type<InputIterator>, iter-mapped-type<InputIterator>, Hash,
equal_to<iter-key-type<InputIterator>>, Allocator>;
template<ranges::input_range R, class Allocator>
unordered_map(from_range_t, R&&, typename see below::size_type, Allocator)
-> unordered_map<range-key-type<R>, range-mapped-type<R>, hash<range-key-type<R>>,
equal_to<range-key-type<R>>, Allocator>;
template<ranges::input_range R, class Allocator>
unordered_map(from_range_t, R&&, Allocator)
-> unordered_map<range-key-type<R>, range-mapped-type<R>, hash<range-key-type<R>>,
equal_to<range-key-type<R>>, Allocator>;
template<ranges::input_range R, class Hash, class Allocator>
unordered_map(from_range_t, R&&, typename see below::size_type, Hash, Allocator)
-> unordered_map<range-key-type<R>, range-mapped-type<R>, Hash,
equal_to<range-key-type<R>>, Allocator>;
template<class Key, class T, class Allocator>
unordered_map(initializer_list<pair<Key, T>>, typename see below::size_type,
Allocator)
-> unordered_map<Key, T, hash<Key>, equal_to<Key>, Allocator>;
template<class Key, class T, class Allocator>
unordered_map(initializer_list<pair<Key, T>>, Allocator)
-> unordered_map<Key, T, hash<Key>, equal_to<Key>, Allocator>;
template<class Key, class T, class Hash, class Allocator>
unordered_map(initializer_list<pair<Key, T>>, typename see below::size_type, Hash,
Allocator)
-> unordered_map<Key, T, Hash, equal_to<Key>, Allocator>;
}
24.5.4.2 Constructors [unord.map.cnstr]
constexpr unordered_map() : unordered_map(size_type(see below)) { }
constexpr explicit unordered_map(size_type n,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
template<class InputIterator>
constexpr unordered_map(InputIterator f, InputIterator l,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
template<container-compatible-range<value_type> R>
constexpr unordered_map(from_range_t, R&& rg,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
constexpr unordered_map(initializer_list<value_type> il,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
Effects: Constructs an empty unordered_map using the
specified hash function, key equality predicate, and allocator, and
using at least n buckets.
24.5.4.3 Element access [unord.map.elem]
constexpr mapped_type& operator[](const key_type& k);
constexpr mapped_type& operator[](key_type&& k);
template<class K> constexpr mapped_type& operator[](K&& k);
Constraints: The qualified-ids Hash::is_transparent and
Pred::is_transparent are valid and denote types.
constexpr mapped_type& at(const key_type& k);
constexpr const mapped_type& at(const key_type& k) const;
template<class K> constexpr mapped_type& at(const K& k);
template<class K> constexpr const mapped_type& at(const K& k) const;
Constraints: The qualified-ids Hash::is_transparent and
Pred::is_transparent are valid and denote types.
24.5.4.4 Modifiers [unord.map.modifiers]
template<class P>
constexpr pair<iterator, bool> insert(P&& obj);
template<class P>
constexpr iterator insert(const_iterator hint, P&& obj);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(const key_type& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args);
template<class... Args>
constexpr pair<iterator, bool> try_emplace(key_type&& k, Args&&... args);
template<class... Args>
constexpr iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args);
template<class K, class... Args>
constexpr pair<iterator, bool> try_emplace(K&& k, Args&&... args);
template<class K, class... Args>
constexpr iterator try_emplace(const_iterator hint, K&& k, Args&&... args);
Constraints: The qualified-ids Hash::is_transparent and
Pred::is_transparent are valid and denote types.
For the first overload,
is_convertible_v<K&&, const_iterator> and
is_convertible_v<K&&, iterator> are both false.
template<class M>
constexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj);
template<class M>
constexpr pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj);
template<class M>
constexpr iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj);
template<class K, class M>
constexpr pair<iterator, bool> insert_or_assign(K&& k, M&& obj);
template<class K, class M>
constexpr iterator insert_or_assign(const_iterator hint, K&& k, M&& obj);
Constraints: The qualified-ids Hash::is_transparent and
Pred::is_transparent are valid and denote types.
Effects: If the map already contains an element e
whose key is equivalent to k,
assigns std::forward<M>
(obj) to e.second.
(obj) to e.second.
24.5.4.5 Erasure [unord.map.erasure]
template<class K, class T, class H, class P, class A, class Predicate>
constexpr typename unordered_map<K, T, H, P, A>::size_type
erase_if(unordered_map<K, T, H, P, A>& c, Predicate pred);
24.5.5 Class template unordered_multimap [unord.multimap]
24.5.5.1 Overview [unord.multimap.overview]
An unordered_multimap meets all of the requirements
of a container ([container.reqmts]),
of an allocator-aware container ([container.alloc.reqmts]), and
of an unordered associative container ([unord.req]).
It provides the operations described in the
preceding requirements table for equivalent keys; that is, an unordered_multimap
supports the a_eq operations in that table, not the a_uniq operations.
For an unordered_multimap<Key, T> the key_type is Key,
the mapped_type is T,
and the value_type is pair<const Key, T>.
Subclause [unord.multimap] only describes operations on unordered_multimap
that are not described in one of the requirement tables, or for which
there is additional semantic information.
The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).
namespace std {
template<class Key,
class T,
class Hash = hash<Key>,
class Pred = equal_to<Key>,
class Allocator = allocator<pair<const Key, T>>>
class unordered_multimap {
public:
// types
using key_type = Key;
using mapped_type = T;
using value_type = pair<const Key, T>;
using hasher = Hash;
using key_equal = Pred;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using local_iterator = implementation-defined; // see [container.requirements]
using const_local_iterator = implementation-defined; // see [container.requirements]
using node_type = unspecified;
// [unord.multimap.cnstr], construct/copy/destroy
constexpr unordered_multimap();
constexpr explicit unordered_multimap(size_type n,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
template<class InputIterator>
constexpr unordered_multimap(InputIterator f, InputIterator l,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
template<container-compatible-range<value_type> R>
constexpr unordered_multimap(from_range_t, R&& rg,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
constexpr unordered_multimap(const unordered_multimap&);
constexpr unordered_multimap(unordered_multimap&&);
constexpr explicit unordered_multimap(const Allocator&);
constexpr unordered_multimap(const unordered_multimap&, const type_identity_t<Allocator>&);
constexpr unordered_multimap(unordered_multimap&&, const type_identity_t<Allocator>&);
constexpr unordered_multimap(initializer_list<value_type> il,
size_type n = see below,
const hasher& hf = hasher(),
const key_equal& eql = key_equal(),
const allocator_type& a = allocator_type());
constexpr unordered_multimap(size_type n, const allocator_type& a)
: unordered_multimap(n, hasher(), key_equal(), a) { }
constexpr unordered_multimap(size_type n, const hasher& hf, const allocator_type& a)
: unordered_multimap(n, hf, key_equal(), a) { }
template<class InputIterator>
constexpr unordered_multimap(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
: unordered_multimap(f, l, n, hasher(), key_equal(), a) { }
template<class InputIterator>
constexpr unordered_multimap(InputIterator f, InputIterator l, size_type n, const hasher& hf,
const allocator_type& a)</