Standard library header <iterator>

 

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Standard library headers

Language support <cfloat> <climits> <compare>(C++20) <contracts>(C++26) <coroutine>(C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint>(C++11) <cstdlib> <exception> <initializer_list>(C++11)    <limits> <new> <source_location>(C++20) <stdfloat>(C++23) <typeinfo> <version>(C++20) Concepts <concepts>(C++20) Diagnostics <cassert> <cerrno> <debugging>(C++26) <stacktrace>(C++23) <stdexcept> <system_error>(C++11) Memory management <memory> <memory_resource>(C++17) <scoped_allocator>(C++11) Metaprogramming <type_traits>(C++11) <ratio>(C++11)

General utilities <any>(C++17) <bitset> <bit>(C++20) <charconv>(C++17) <expected>(C++23) <format>(C++20) <functional> <optional>(C++17) <stdbit.h>(C++26) <tuple>(C++11) <typeindex>(C++11) <utility> <variant>(C++17) Containers <array>(C++11) <deque> <flat_map>(C++23) <flat_set>(C++23) <forward_list>(C++11) <hive>(C++26) <inplace_vector>(C++26)    <list> <map> <mdspan>(C++23) <queue> <set> <span>(C++20) <stack> <unordered_map>(C++11) <unordered_set>(C++11) <vector> Iterators <iterator> Ranges <generator>(C++23) <ranges>(C++20)

Algorithms <algorithm> <numeric> Strings <cctype> <cstring> <cuchar>(C++11) <cwchar> <cwctype> <string_view>(C++17) <string> Text processing <clocale> <codecvt>(C++11/17/26*) <locale> <regex>(C++11) <text_encoding>(C++26)    Numerics <cfenv>(C++11) <cmath> <complex> <linalg>(C++26) <numbers>(C++20) <random>(C++11) <simd>(C++26) <stdckdint.h>(C++26) <valarray> Time <chrono>(C++11) <ctime> C compatibility <ccomplex>(C++11/17/20*) <ciso646>(until C++20) <cstdalign>(C++11/17/20*) <cstdbool>(C++11/17/20*) <ctgmath>(C++11/17/20*)

Input/output <cinttypes>(C++11) <cstdio> <filesystem>(C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print>(C++23) <spanstream>(C++23) <sstream> <streambuf> <strstream>(C++98/26*) <syncstream>(C++20) Concurrency support <atomic>(C++11) <barrier>(C++20) <condition_variable>(C++11) <future>(C++11) <hazard_pointer>(C++26) <latch>(C++20) <mutex>(C++11) <rcu>(C++26) <semaphore>(C++20) <shared_mutex>(C++14) <stdatomic.h>(C++23) <stop_token>(C++20) <thread>(C++11) Execution support <execution>(C++17)

 

This header is part of the iterator library.

This header is a partial freestanding header. Everything inside this header is freestanding beside stream iterators.

(since C++23)

Concepts
Iterator concepts
indirectly_readable (C++20)	specifies that a type is indirectly readable by applying operator * (concept)
indirectly_writable (C++20)	specifies that a value can be written to an iterator's referenced object (concept)
weakly_incrementable (C++20)	specifies that a semiregular type can be incremented with pre- and post-increment operators (concept)
incrementable (C++20)	specifies that the increment operation on a weakly_incrementable type is equality-preserving and that the type is equality_comparable (concept)
input_or_output_iterator (C++20)	specifies that objects of a type can be incremented and dereferenced (concept)
sentinel_for (C++20)	specifies a type is a sentinel for an input_or_output_iterator type (concept)
sized_sentinel_for (C++20)	specifies that the - operator can be applied to an iterator and a sentinel to calculate their difference in constant time (concept)
input_iterator (C++20)	specifies that a type is an input iterator, that is, its referenced values can be read and it can be both pre- and post-incremented (concept)
output_iterator (C++20)	specifies that a type is an output iterator for a given value type, that is, values of that type can be written to it and it can be both pre- and post-incremented (concept)
forward_iterator (C++20)	specifies that an input_iterator is a forward iterator, supporting equality comparison and multi-pass (concept)
bidirectional_iterator (C++20)	specifies that a forward_iterator is a bidirectional iterator, supporting movement backwards (concept)
random_access_iterator (C++20)	specifies that a bidirectional_iterator is a random-access iterator, supporting advancement in constant time and subscripting (concept)
contiguous_iterator (C++20)	specifies that a random_access_iterator is a contiguous iterator, referring to elements that are contiguous in memory (concept)
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	specifies that a callable type can be invoked with the result of dereferencing an indirectly_readable type (concept)
indirect_unary_predicate (C++20)	specifies that a callable type, when invoked with the result of dereferencing an indirectly_readable type, satisfies predicate (concept)
indirect_binary_predicate (C++20)	specifies that a callable type, when invoked with the result of dereferencing two indirectly_readable types, satisfies predicate (concept)
indirect_equivalence_relation (C++20)	specifies that a callable type, when invoked with the result of dereferencing two indirectly_readable types, satisfies equivalence_relation (concept)
indirect_strict_weak_order (C++20)	specifies that a callable type, when invoked with the result of dereferencing two indirectly_readable types, satisfies strict_weak_order (concept)
Common algorithm requirements
indirectly_movable (C++20)	specifies that values may be moved from an indirectly_readable type to an indirectly_writable type (concept)
indirectly_movable_storable (C++20)	specifies that values may be moved from an indirectly_readable type to an indirectly_writable type and that the move may be performed via an intermediate object (concept)
indirectly_copyable (C++20)	specifies that values may be copied from an indirectly_readable type to an indirectly_writable type (concept)
indirectly_copyable_storable (C++20)	specifies that values may be copied from an indirectly_readable type to an indirectly_writable type and that the copy may be performed via an intermediate object (concept)
indirectly_swappable (C++20)	specifies that the values referenced by two indirectly_readable types can be swapped (concept)
indirectly_comparable (C++20)	specifies that the values referenced by two indirectly_readable types can be compared (concept)
permutable (C++20)	specifies the common requirements of algorithms that reorder elements in place (concept)
mergeable (C++20)	specifies the requirements of algorithms that merge sorted sequences into an output sequence by copying elements (concept)
sortable (C++20)	specifies the common requirements of algorithms that permute sequences into ordered sequences (concept)
Classes
Algorithm utilities
indirect_result_t (C++20)	computes the result of invoking a callable object on the result of dereferencing some set of indirectly_readable types (alias template)
projected (C++20)	helper template for specifying the constraints on algorithms that accept projections (alias template)
projected_value_t (C++26)	computes the value type of an indirectly_readable type by projection (alias template)
Associated types
incrementable_traits (C++20)	computes the difference type of a weakly_incrementable type (class template)
indirectly_readable_traits (C++20)	computes the value type of an indirectly_readable type (class template)
iter_value_titer_reference_titer_const_reference_titer_difference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++23)(C++20)(C++20)(C++20)	computes the associated types of an iterator (alias template)
Primitives
iterator_traits	provides uniform interface to the properties of an iterator (class template)
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	empty class types used to indicate iterator categories (class)
iterator (deprecated in C++17)	base class to ease the definition of required types for simple iterators (class template)
Adaptors
reverse_iterator	iterator adaptor for reverse-order traversal (class template)
move_iterator (C++11)	iterator adaptor which dereferences to an rvalue (class template)
move_sentinel (C++20)	sentinel adaptor for std::move_iterator (class template)
basic_const_iterator (C++23)	iterator adaptor that converts an iterator into a constant iterator (class template)
const_iterator (C++23)	computes a constant iterator type for a given type (alias template)
const_sentinel (C++23)	computes a sentinel type to be used with constant iterators (alias template)
common_iterator (C++20)	adapts an iterator type and its sentinel into a common iterator type (class template)
default_sentinel_t (C++20)	default sentinel for use with iterators that know the bound of their range (class)
counted_iterator (C++20)	iterator adaptor that tracks the distance to the end of the range (class template)
unreachable_sentinel_t (C++20)	sentinel that always compares unequal to any weakly_incrementable type (class)
back_insert_iterator	iterator adaptor for insertion at the end of a container (class template)
front_insert_iterator	iterator adaptor for insertion at the front of a container (class template)
insert_iterator	iterator adaptor for insertion into a container (class template)
Stream Iterators
istream_iterator	input iterator that reads from std::basic_istream (class template)
ostream_iterator	output iterator that writes to std::basic_ostream (class template)
istreambuf_iterator	input iterator that reads from std::basic_streambuf (class template)
ostreambuf_iterator	output iterator that writes to std::basic_streambuf (class template)
Customization point objects
Defined in namespace std::ranges
iter_move (C++20)	casts the result of dereferencing an object to its associated rvalue reference type (customization point object)
iter_swap (C++20)	swaps the values referenced by two dereferenceable objects (customization point object)
Constants
unreachable_sentinel (C++20)	an object of type unreachable_sentinel_t that always compares unequal to any weakly_incrementable type (constant)
default_sentinel (C++20)	an object of type default_sentinel_t used with iterators that know the bound of their range (constant)
Functions
Adaptors
make_reverse_iterator (C++14)	creates a std::reverse_iterator of type inferred from the argument (function template)
make_move_iterator (C++11)	creates a std::move_iterator of type inferred from the argument (function template)
make_const_iterator (C++23)	creates a std::const_iterator of type inferred from the argument (function template)
make_const_sentinel (C++23)	creates a std::const_sentinel of type inferred from the argument (function template)
front_inserter	creates a std::front_insert_iterator of type inferred from the argument (function template)
back_inserter	creates a std::back_insert_iterator of type inferred from the argument (function template)
inserter	creates a std::insert_iterator of type inferred from the argument (function template)
Non-member operators
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++11)(C++11)(removed in C++20)(C++11)(C++11)(C++11)(C++11)(C++20)	compares the underlying iterators (function template)
operator+ (C++11)	advances the iterator (function template)
operator- (C++11)	computes the distance between two iterator adaptors (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)	compares the underlying iterators (function template)
operator+	advances the iterator (function template)
operator-	computes the distance between two iterator adaptors (function template)
operator==operator<=> (C++20)	compares the distances to the end (function template)
operator+ (C++20)	advances the iterator (function template)
operator- (C++20)	computes the distance between two iterator adaptors (function template)
operator==operator!= (removed in C++20)	compares two istream_iterators (function template)
operator==operator!= (removed in C++20)	compares two istreambuf_iterators (function template)
Operations
advance	advances an iterator by given distance (function template)
distance	returns the distance between two iterators (function template)
next (C++11)	increment an iterator (function template)
prev (C++11)	decrement an iterator (function template)
ranges::advance (C++20)	advances an iterator by given distance or to a given bound (algorithm function object)
ranges::distance (C++20)	returns the distance between an iterator and a sentinel, or between the beginning and end of a range (algorithm function object)
ranges::next (C++20)	increment an iterator by a given distance or to a bound (algorithm function object)
ranges::prev (C++20)	decrement an iterator by a given distance or to a bound (algorithm function object)
Range access
begincbegin (C++11)(C++14)	returns an iterator to the beginning of a container or array (function template)
endcend (C++11)(C++14)	returns an iterator to the end of a container or array (function template)
rbegincrbegin (C++14)	returns a reverse iterator to the beginning of a container or array (function template)
rendcrend (C++14)	returns a reverse end iterator for a container or array (function template)
sizessize (C++17)(C++20)	returns the size of a container or array (function template)
empty (C++17)	checks whether the container is empty (function template)
data (C++17)	obtains the pointer to the underlying array (function template)

Synopsis

#include <compare>#include <concepts>   namespace std {template<class T>using/* with-reference */= T&;// exposition onlytemplate<class T> concept /* can-reference */// exposition only= requires {typename/* with-reference */<T>;};template<class T> concept /* dereferenceable */// exposition only= requires(T& t){{*t }->/* can-reference */;// not required to be equality-preserving};   // associated types// incrementable traitstemplate<class>struct incrementable_traits;template<class T>using iter_difference_t =/* see description */;   // indirectly readable traitstemplate<class>struct indirectly_readable_traits;template<class T>using iter_value_t =/* see description */;   // iterator traitstemplate<class I>struct iterator_traits;template<class T> requires is_object_v<T>struct iterator_traits<T*>;   template</* dereferenceable */ T>using iter_reference_t = decltype(*declval<T&>());   namespace ranges {// customization point objectsinlinenamespace/* unspecified */{// ranges::iter_moveinlineconstexpr/* unspecified */ iter_move =/* unspecified */;   // ranges::iter_swapinlineconstexpr/* unspecified */ iter_swap =/* unspecified */;}}   template</* dereferenceable */ T> requires requires(T& t){{ranges::iter_move(t)}->/* can-reference */;}using iter_rvalue_reference_t = decltype(ranges::iter_move(declval<T&>()));   // iterator concepts// concept indirectly_readabletemplate<class In> concept indirectly_readable =/* see description */;   template<indirectly_readable T>using iter_common_reference_t = common_reference_t<iter_reference_t<T>, iter_value_t<T>&>;   // concept indirectly_writabletemplate<class Out, class T> concept indirectly_writable =/* see description */;   // concept weakly_incrementabletemplate<class I> concept weakly_incrementable =/* see description */;   // concept incrementabletemplate<class I> concept incrementable =/* see description */;   // concept input_or_output_iteratortemplate<class I> concept input_or_output_iterator =/* see description */;   // concept sentinel_fortemplate<class S, class I> concept sentinel_for =/* see description */;   // concept sized_sentinel_fortemplate<class S, class I>inlineconstexprbool disable_sized_sentinel_for =false;   template<class S, class I> concept sized_sentinel_for =/* see description */;   // concept input_iteratortemplate<class I> concept input_iterator =/* see description */;   // concept output_iteratortemplate<class I, class T> concept output_iterator =/* see description */;   // concept forward_iteratortemplate<class I> concept forward_iterator =/* see description */;   // concept bidirectional_iteratortemplate<class I> concept bidirectional_iterator =/* see description */;   // concept random_access_iteratortemplate<class I> concept random_access_iterator =/* see description */;   // concept contiguous_iteratortemplate<class I> concept contiguous_iterator =/* see description */;   // indirect callable requirements// indirect callablestemplate<class F, class I> concept indirectly_unary_invocable =/* see description */;   template<class F, class I> concept indirectly_regular_unary_invocable =/* see description */;   template<class F, class I> concept indirect_unary_predicate =/* see description */;   template<class F, class I1, class I2> concept indirect_binary_predicate =/* see description */;   template<class F, class I1, class I2 = I1> concept indirect_equivalence_relation =/* see description */;   template<class F, class I1, class I2 = I1> concept indirect_strict_weak_order =/* see description */;   template<class F, class... Is> requires (indirectly_readable<Is>&& ...)&& invocable<F, iter_reference_t<Is>...>using indirect_result_t = invoke_result_t<F, iter_reference_t<Is>...>;   // projectedtemplate<indirectly_readable I, indirectly_regular_unary_invocable<I> Proj>usingprojected=/* see description */;   template<indirectly_­readable I, indirectly_­regular_­unary_­invocable<I> Proj>using projected_value_t = remove_cvref_t<invoke_result_t<Proj&, iter_value_t<I>&>>;   // common algorithm requirements// concept indirectly_movabletemplate<class In, class Out> concept indirectly_movable =/* see description */;   template<class In, class Out> concept indirectly_movable_storable =/* see description */;   // concept indirectly_copyabletemplate<class In, class Out> concept indirectly_copyable =/* see description */;   template<class In, class Out> concept indirectly_copyable_storable =/* see description */;   // concept indirectly_swappabletemplate<class I1, class I2 = I1> concept indirectly_swappable =/* see description */;   // concept indirectly_comparabletemplate<class I1, class I2, class R, class P1 = identity, class P2 = identity> concept indirectly_comparable =/* see description */;   // concept permutabletemplate<class I> concept permutable =/* see description */;   // concept mergeabletemplate<class I1, class I2, class Out, class R =ranges::less, class P1 = identity, class P2 = identity> concept mergeable =/* see description */;   // concept sortabletemplate<class I, class R =ranges::less, class P = identity> concept sortable =/* see description */;   // primitives// iterator tagsstruct input_iterator_tag {};struct output_iterator_tag {};struct forward_iterator_tag:public input_iterator_tag {};struct bidirectional_iterator_tag:public forward_iterator_tag {};struct random_access_iterator_tag:public bidirectional_iterator_tag {};struct contiguous_iterator_tag:public random_access_iterator_tag {};   // iterator operationstemplate<class InputIt, class Distance>constexprvoid advance(InputIt& i, Distance n);template<class InputIt>constexprtypename iterator_traits<InputIt>::difference_type distance(InputIt first, InputIt last);template<class InputIt>constexpr InputIt next(InputIt x, typename iterator_traits<InputIt>::difference_type n =1);template<class BidirIt>constexpr BidirIt prev(BidirIt x, typename iterator_traits<BidirIt>::difference_type n =1);   // range iterator operationsnamespace ranges {// ranges::advancetemplate<input_or_output_iterator I>constexprvoid advance(I& i, iter_difference_t<I> n);template<input_or_output_iterator I, sentinel_for<I> S>constexprvoid advance(I& i, S bound);template<input_or_output_iterator I, sentinel_for<I> S>constexpr iter_difference_t<I> advance(I& i, iter_difference_t<I> n, S bound);   // ranges::distancetemplate<class I, sentinel_for<I> S> requires (!sized_sentinel_for<S, I>)constexpr iter_difference_t<I> distance(I first, S last);template<class I, sized_sentinel_for<decay_t<I>> S>constexpr iter_difference_t<decay_t<I>> distance(I&& first, S last);template<range R>constexpr range_difference_t<R> distance(R&& r);   // ranges::nexttemplate<input_or_output_iterator I>constexpr I next(I x);template<input_or_output_iterator I>constexpr I next(I x, iter_difference_t<I> n);template<input_or_output_iterator I, sentinel_for<I> S>constexpr I next(I x, S bound);template<input_or_output_iterator I, sentinel_for<I> S>constexpr I next(I x, iter_difference_t<I> n, S bound);   // ranges::prevtemplate<bidirectional_iterator I>constexpr I prev(I x);template<bidirectional_iterator I>constexpr I prev(I x, iter_difference_t<I> n);template<bidirectional_iterator I>constexpr I prev(I x, iter_difference_t<I> n, I bound);}   // predefined iterators and sentinels// reverse iteratorstemplate<class It>class reverse_iterator;   template<class It1, class It2>constexprbool operator==(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y);template<class It1, class It2>constexprbool operator!=(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y);template<class It1, class It2>constexprbool operator<(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y);template<class It1, class It2>constexprbool operator>(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y);template<class It1, class It2>constexprbool operator<=(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y);template<class It1, class It2>constexprbool operator>=(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y);template<class It1, three_way_comparable_with<It1> It2>constexpr compare_three_way_result_t<It1, It2> operator<=>(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y);   template<class It1, class It2>constexprauto operator-(const reverse_iterator<It1>& x, const reverse_iterator<It2>& y)-> decltype(y.base()- x.base());template<class It>constexpr reverse_iterator<It> operator+(iter_difference_t<It> n, const reverse_iterator<It>& x);   template<class It>constexpr reverse_iterator<It> make_reverse_iterator(It i);   template<class It1, class It2> requires (!sized_sentinel_for<It1, It2>)inlineconstexprbool disable_sized_sentinel_for<reverse_iterator<It1>, reverse_iterator<It2>>=true;   // insert iteratorstemplate<class Container>class back_insert_iterator;template<class Container>constexpr back_insert_iterator<Container> back_inserter(Container& x);   template<class Container>class front_insert_iterator;template<class Container>constexpr front_insert_iterator<Container> front_inserter(Container& x);   template<class Container>class insert_iterator;template<class Container>constexpr insert_iterator<Container> inserter(Container& x, ranges::iterator_t<Container> i);   // move iterators and sentinelstemplate<class It>class move_iterator;   template<class It1, class It2>constexprbool operator==(const move_iterator<It1>& x, const move_iterator<It2>& y);template<class It1, class It2>constexprbool operator<(const move_iterator<It1>& x, const move_iterator<It2>& y);template<class It1, class It2>constexprbool operator>(const move_iterator<It1>& x, const move_iterator<It2>& y);template<class It1, class It2>constexprbool operator<=(const move_iterator<It1>& x, const move_iterator<It2>& y);template<class It1, class It2>constexprbool operator>=(const move_iterator<It1>& x, const move_iterator<It2>& y);template<class It1, three_way_comparable_with<It1> It2>constexpr compare_three_way_result_t<It1, It2> operator<=>(const move_iterator<It1>& x, const move_iterator<It2>& y);   template<class It1, class It2>constexprauto operator-(const move_iterator<It1>& x, const move_iterator<It2>& y)-> decltype(x.base()- y.base());template<class It>constexpr move_iterator<It> operator+(iter_difference_t<It> n, const move_iterator<It>& x);   template<class It>constexpr move_iterator<It> make_move_iterator(It i);   template<semiregular S>class move_sentinel;   // common iteratorstemplate<input_or_output_iterator I, sentinel_for<I> S> requires (!same_as<I, S>&& copyable<I>)class common_iterator;   template<class I, class S>struct incrementable_traits<common_iterator<I, S>>;   template<input_iterator I, class S>struct iterator_traits<common_iterator<I, S>>;   // default sentinelstruct default_sentinel_t;inlineconstexpr default_sentinel_t default_sentinel{};   // counted iteratorstemplate<input_or_output_iterator I>class counted_iterator;   template<input_iterator I> requires /* see description */struct iterator_traits<counted_iterator<I>>;   // unreachable sentinelstruct unreachable_sentinel_t;inlineconstexpr unreachable_sentinel_t unreachable_sentinel{};   // stream iteratorstemplate<class T, class CharT =char, class Traits = char_traits<CharT>, class Distance = ptrdiff_t>class istream_iterator;template<class T, class CharT, class Traits, class Distance>bool operator==(const istream_iterator<T, CharT, Traits, Distance>& x, const istream_iterator<T, CharT, Traits, Distance>& y);   template<class T, class CharT =char, class traits = char_traits<CharT>>class ostream_iterator;   template<class CharT, class Traits = char_traits<CharT>>class istreambuf_iterator;template<class CharT, class Traits>bool operator==(const istreambuf_iterator<CharT, Traits>& a, const istreambuf_iterator<CharT, Traits>& b);   template<class CharT, class Traits = char_traits<CharT>>class ostreambuf_iterator;   // range accesstemplate<class C>constexprauto begin(C& c)-> decltype(c.begin());template<class C>constexprauto begin(const C& c)-> decltype(c.begin());template<class C>constexprauto end(C& c)-> decltype(c.end());template<class C>constexprauto end(const C& c)-> decltype(c.end());template<class T, size_t N>constexpr T* begin(T (&a)[N])noexcept;template<class T, size_t N>constexpr T* end(T (&a)[N])noexcept;template<class C>constexprauto cbegin(const C& c)noexcept(noexcept(std::begin(c)))-> decltype(std::begin(c));template<class C>constexprauto cend(const C& c)noexcept(noexcept(std::end(c)))-> decltype(std::end(c));template<class C>constexprauto rbegin(C& c)-> decltype(c.rbegin());template<class C>constexprauto rbegin(const C& c)-> decltype(c.rbegin());template<class C>constexprauto rend(C& c)-> decltype(c.rend());template<class C>constexprauto rend(const C& c)-> decltype(c.rend());template<class T, size_t N>constexpr reverse_iterator<T*> rbegin(T (&a)[N]);template<class T, size_t N>constexpr reverse_iterator<T*> rend(T (&a)[N]);template<class E>constexpr reverse_iterator<const E*> rbegin(initializer_list<E> il);template<class E>constexpr reverse_iterator<const E*> rend(initializer_list<E> il);template<class C>constexprauto crbegin(const C& c)-> decltype(std::rbegin(c));template<class C>constexprauto crend(const C& c)-> decltype(std::rend(c));   template<class C>constexprauto size(const C& c)-> decltype(c.size());template<class T, size_t N>constexpr size_t size(const T (&a)[N])noexcept;template<class C>constexprauto ssize(const C& c)-> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;template<class T, ptrdiff_t N>constexpr ptrdiff_t ssize(const T (&a)[N])noexcept;template<class C>constexprauto empty(const C& c)-> decltype(c.empty());template<class T, size_t N>constexprbool empty(const T (&a)[N])noexcept;template<class E>constexprbool empty(initializer_list<E> il)noexcept;template<class C>constexprauto data(C& c)-> decltype(c.data());template<class C>constexprauto data(const C& c)-> decltype(c.data());template<class T, size_t N>constexpr T* data(T (&a)[N])noexcept;template<class E>constexprconst E* data(initializer_list<E> il)noexcept;}

Concept indirectly_readable

namespace std {template<class In> concept /*indirectlyReadableImpl*/=// exposition only requires(const In in){typename iter_value_t<In>;typename iter_reference_t<In>;typename iter_rvalue_reference_t<In>;{*in }-> same_as<iter_reference_t<In>>{ iter_move(in)}-> same_as<iter_rvalue_reference_t<In>>}&& common_reference_with<iter_reference_t<In>&&, iter_value_t<In>&>&& common_reference_with<iter_reference_t<In>&&, iter_rvalue_reference_t<In>&&>&& common_reference_with<iter_rvalue_reference_t<In>&&, const iter_value_t<In>&>;   template<class In> concept indirectly_readable =/*indirectlyReadableImpl*/<remove_cvref_t<In>>}

Concept indirectly_writable

namespace std {template<class Out, class T> concept indirectly_writable = requires(Out&& o, T&& t){*o =std::forward<T>(t);// not required to be equality-preserving*std::forward<Out>(o)=std::forward<T>(t);// not required to be equality-preservingconst_cast<const iter_reference_t<Out>&&>(*o)=std::forward<T>(t);// not required to be equality-preservingconst_cast<const iter_reference_t<Out>&&>(*std::forward<Out>(o))=std::forward<T>(t);// not required to be equality-preserving};}

Concept weakly_incrementable

namespace std {template<class T>inlineconstexprbool/*is_integer_like*/=/* see description */;// exposition only   template<class T>inlineconstexprbool/*is_signed_integer_like*/=// exposition only/* see description */;   template<class I> concept weakly_incrementable = default_initializable<I>&& movable<I>&& requires(I i){typename iter_difference_t<I>; requires /*is_signed_integer_like*/<iter_difference_t<I>>;{++i }-> same_as<I&>;// not required to be equality-preserving i++;// not required to be equality-preserving};}

Concept incrementable

namespace std {template<class I> concept incrementable = regular<I>&& weakly_incrementable<I>&& requires(I i){{ i++}-> same_as<I>;};}

Concept input_or_output_iterator

namespace std {template<class I> concept input_or_output_iterator = requires(I i){{*i }-> can-reference;}&& weakly_incrementable<I>;}

Concept sentinel_for

namespace std {template<class S, class I> concept sentinel_for = semiregular<S>&& input_or_output_iterator<I>&&/*WeaklyEqualityComparableWith*/<S, I>;}

Concept sized_sentinel_for

namespace std {template<class S, class I> concept sized_sentinel_for = sentinel_for<S, I>&&!disable_sized_sentinel<remove_cv_t<S>, remove_cv_t<I>>&& requires(const I& i, const S& s){{ s - i }-> same_as<iter_difference_t<I>>;{ i - s }-> same_as<iter_difference_t<I>>;};}

Concept input_iterator

namespace std {template<class I> concept input_iterator = input_or_output_iterator<I>&& indirectly_readable<I>&& requires {typename/* ITER_CONCEPT */(I);}&& derived_from</* ITER_CONCEPT */(I), input_iterator_tag>;}

Concept output_iterator

namespace std {template<class I, class T> concept output_iterator = input_or_output_iterator<I>&& indirectly_writable<I, T>&& requires(I i, T&& t){*i++=std::forward<T>(t);// not required to be equality-preserving};}

Concept forward_iterator

namespace std {template<class I> concept forward_iterator = input_iterator<I>&& derived_from</* ITER_CONCEPT */(I), forward_iterator_tag>&& incrementable<I>&& sentinel_for<I, I>;}

Concept bidirectional_iterator

namespace std {template<class I> concept bidirectional_iterator = forward_iterator<I>&& derived_from</* ITER_CONCEPT */(I), bidirectional_iterator_tag>&& requires(I i){{--i }-> same_as<I&>;{ i--}-> same_as<I>;};}

Concept random_access_iterator

namespace std {template<class I> concept random_access_iterator = bidirectional_iterator<I>&& derived_from</* ITER_CONCEPT */(I), random_access_iterator_tag>&& totally_ordered<I>&& sized_sentinel_for<I, I>&& requires(I i, const I j, const iter_difference_t<I> n){{ i += n }-> same_as<I&>;{ j + n }-> same_as<I>;{ n + j }-> same_as<I>;{ i -= n }-> same_as<I&>;{ j - n }-> same_as<I>;{ j[n]}-> same_as<iter_reference_t<I>>;};}

Concept contiguous_iterator

namespace std {template<class I> concept contiguous_iterator = random_access_iterator<I>&& derived_from</* ITER_CONCEPT */(I), contiguous_iterator_tag>&& is_lvalue_reference_v<iter_reference_t<I>>&& same_as<iter_value_t<I>, remove_cvref_t<iter_reference_t<I>>>&& requires(const I& i){{ to_address(i)}-> same_as<add_pointer_t<iter_reference_t<I>>>;};}

Concept indirectly_unary_invocable

namespace std {template<class F, class I> concept indirectly_unary_invocable = indirectly_readable<I>&& copy_constructible<F>&& invocable<F&, iter_value_t<I>&>&& invocable<F&, iter_reference_t<I>>&& common_reference_with< invoke_result_t<F&, iter_value_t<I>&>, invoke_result_t<F&, iter_reference_t<I>>>;}

Concept indirectly_regular_unary_invocable

namespace std {template<class F, class I> concept indirectly_regular_unary_invocable = indirectly_readable<I>&& copy_constructible<F>&& regular_invocable<F&, iter_value_t<I>&>&& regular_invocable<F&, iter_reference_t<I>>&& common_reference_with< invoke_result_t<F&, iter_value_t<I>&>, invoke_result_t<F&, iter_reference_t<I>>>;}

Concept indirect_unary_predicate

namespace std {template<class F, class I> concept indirect_unary_predicate = indirectly_readable<I>&& copy_constructible<F>&& predicate<F&, iter_value_t<I>&>&& predicate<F&, iter_reference_t<I>>;}

Concept indirect_binary_predicate

namespace std {template<class F, class I1, class I2 = I1> concept indirect_binary_predicate = indirectly_readable<I1>&& indirectly_readable<I2>&& copy_constructible<F>&& predicate<F&, iter_value_t<I1>&, iter_value_t<I2>&>&& predicate<F&, iter_value_t<I1>&, iter_reference_t<I2>>&& predicate<F&, iter_reference_t<I1>, iter_value_t<I2>&>&& predicate<F&, iter_reference_t<I1>, iter_reference_t<I2>>;}

Concept indirect_equivalence_relation

namespace std {template<class F, class I1, class I2 = I1> concept indirect_equivalence_relation = indirectly_readable<I1>&& indirectly_readable<I2>&& copy_constructible<F>&& equivalence_relation<F&, iter_value_t<I1>&, iter_value_t<I2>&>&& equivalence_relation<F&, iter_value_t<I1>&, iter_reference_t<I2>>&& equivalence_relation<F&, iter_reference_t<I1>, iter_value_t<I2>&>&& equivalence_relation<F&, iter_reference_t<I1>, iter_reference_t<I2>>;}

Concept indirect_strict_weak_order

namespace std {template<class F, class I1, class I2 = I1> concept indirect_strict_weak_order = indirectly_readable<I1>&& indirectly_readable<I2>&& copy_constructible<F>&& strict_weak_order<F&, iter_value_t<I1>&, iter_value_t<I2>&>&& strict_weak_order<F&, iter_value_t<I1>&, iter_reference_t<I2>>&& strict_weak_order<F&, iter_reference_t<I1>, iter_value_t<I2>&>&& strict_weak_order<F&, iter_reference_t<I1>, iter_reference_t<I2>>;}

Concept indirectly_movable

namespace std {template<class In, class Out> concept indirectly_movable = indirectly_readable<In>&& indirectly_writable<Out, iter_rvalue_reference_t<In>>;}

Concept indirectly_movable_storable

namespace std {template<class In, class Out> concept indirectly_movable_storable = indirectly_movable<In, Out>&& indirectly_writable<Out, iter_value_t<In>>&& movable<iter_value_t<In>>&& constructible_from<iter_value_t<In>, iter_rvalue_reference_t<In>>&& assignable_from<iter_value_t<In>&, iter_rvalue_reference_t<In>>;}

Concept indirectly_copyable

namespace std {template<class In, class Out> concept indirectly_copyable = indirectly_readable<In>&& indirectly_writable<Out, iter_reference_t<In>>;}

Concept indirectly_copyable_storable

namespace std {template<class In, class Out> concept indirectly_copyable_storable = indirectly_copyable<In, Out>&& indirectly_writable<Out, iter_value_t<In>&>&& indirectly_writable<Out, const iter_value_t<In>&>&& indirectly_writable<Out, iter_value_t<In>&&>&& indirectly_writable<Out, const iter_value_t<In>&&>&& copyable<iter_value_t<In>>&& constructible_from<iter_value_t<In>, iter_reference_t<In>>&& assignable_from<iter_value_t<In>&, iter_reference_t<In>>;}

Concept indirectly_swappable

namespace std {template<class I1, class I2 = I1> concept indirectly_swappable = indirectly_readable<I1>&& indirectly_readable<I2>&& requires(const I1 i1, const I2 i2){ranges::iter_swap(i1, i1);ranges::iter_swap(i2, i2);ranges::iter_swap(i1, i2);ranges::iter_swap(i2, i1);};}

Concept indirectly_comparable

namespace std {template<class I1, class I2, class R, class P1 = identity, class P2 = identity> concept indirectly_comparable = indirect_predicate<R, projected<I1, P1>, projected<I2, P2>>;}

Concept permutable

namespace std {template<class I> concept permutable = forward_iterator<I>&& indirectly_movable_storable<I, I>&& indirectly_swappable<I, I>;}

Concept mergeable

namespace std {template<class I1, class I2, class Out, class R =ranges::less, class P1 = identity, class P2 = identity> concept mergeable = input_iterator<I1>&& input_iterator<I2>&& weakly_incrementable<Out>&& indirectly_copyable<I1, Out>&& indirectly_copyable<I2, Out>&& indirect_strict_weak_order<R, projected<I1, P1>, projected<I2, P2>>;}

Concept sortable

namespace std {template<class I, class R =ranges::less, class P = identity> concept sortable = permutable<I>&& indirect_strict_weak_order<R, projected<I, P>>;}

Class template std::incrementable_traits

namespace std {template<class>struct incrementable_traits {};   template<class T> requires is_object_v<T>struct incrementable_traits<T*>{using difference_type = ptrdiff_t;};   template<class I>struct incrementable_traits<const I>: incrementable_traits<I>{};   template<class T> requires requires {typename T::difference_type;}struct incrementable_traits<T>{using difference_type =typename T::difference_type;};   template<class T> requires (!requires {typename T::difference_type;}&& requires(const T& a, const T& b){{ a - b }-> integral;})struct incrementable_traits<T>{using difference_type = make_signed_t<decltype(declval<T>()- declval<T>())>;};   template<class T>using iter_difference_t =/* see description */;}

Class template std::indirectly_readable_traits

namespace std {template<class>struct/*cond_value_type*/{};// exposition onlytemplate<class T> requires is_object_v<T>struct/*cond_value_type*/{using value_type = remove_cv_t<T>;};   template<class>struct indirectly_readable_traits {};   template<class T>struct indirectly_readable_traits<T*>:/*cond_value_type*/<T>{};   template<class I> requires is_array_v<I>struct indirectly_readable_traits<I>{using value_type = remove_cv_t<remove_extent_t<I>>;};   template<class I>struct indirectly_readable_traits<const I>: indirectly_readable_traits<I>{};   template<class T> requires requires {typename T::value_type;}struct indirectly_readable_traits<T>:/*cond_value_type*/<typename T::value_type>{};   template<class T> requires requires {typename T::element_type;}struct indirectly_readable_traits<T>:/*cond_value_type*/<typename T::element_type>{};}

Class template std::projected

namespace std {template<class I, class Proj>struct/*projected-impl*/{// exposition onlystruct/*type*/{// exposition onlyusing value_type = remove_cvref_t<indirect_result_t<Proj&, I>>;using difference_type = iter_difference_t<I>;// present only if I// models weakly_incrementable indirect_result_t<Proj&, I> operator*()const;// not defined};};   template<indirectly_readable I, indirectly_regular_unary_invocable<I> Proj>usingprojected=/*projected-impl*/<I, Proj>::/*type*/;}

Class template std::iterator_traits

namespace std {template<class I>struct iterator_traits {using iterator_category =/* see description */;using value_type =/* see description */;using difference_type =/* see description */;using pointer =/* see description */;using reference =/* see description */;};   template<class T> requires is_object_v<T>struct iterator_traits<T*>{using iterator_concept = contiguous_iterator_tag;using iterator_category = random_access_iterator_tag;using value_type = remove_cv_t<T>;using difference_type = ptrdiff_t;using pointer = T*;using reference = T&;};}

Iterator tags

namespace std {struct input_iterator_tag {};struct output_iterator_tag {};struct forward_iterator_tag:public input_iterator_tag {};struct bidirectional_iterator_tag:public forward_iterator_tag {};struct random_access_iterator_tag:public bidirectional_iterator_tag {};struct contiguous_iterator_tag:public random_access_iterator_tag {};}

Class template std::reverse_iterator

namespace std {template<class Iter>class reverse_iterator {public:using iterator_type = Iter;using iterator_concept =/* see description */;using iterator_category =/* see description */;using value_type = iter_value_t<Iter>;using difference_type = iter_difference_t<Iter>;using pointer =typename iterator_traits<Iter>::pointer;using reference = iter_reference_t<Iter>;   constexpr reverse_iterator();constexprexplicit reverse_iterator(Iter x);template<class U>constexpr reverse_iterator(const reverse_iterator<U>& u);template<class U>constexpr reverse_iterator& operator=(const reverse_iterator<U>& u);   constexpr Iter base()const;constexpr reference operator*()const;constexpr pointer operator->()const requires /* see description */;   constexpr reverse_iterator& operator++();constexpr reverse_iterator operator++(int);constexpr reverse_iterator& operator--();constexpr reverse_iterator operator--(int);   constexpr reverse_iterator operator+(difference_type n)const;constexpr reverse_iterator& operator+=(difference_type n);constexpr reverse_iterator operator-(difference_type n)const;constexpr reverse_iterator& operator-=(difference_type n);constexpr/* unspecified */ operator[](difference_type n)const;   friendconstexpr iter_rvalue_reference_t<Iter> iter_move(const reverse_iterator& i)noexcept(/* see description */);template<indirectly_swappable<Iter> Iter2>friendconstexprvoid iter_swap(const reverse_iterator& x, const reverse_iterator<Iter2>& y)noexcept(/* see description */);   protected: Iter current;};}

Class template std::back_insert_iterator

namespace std {template<class Container>class back_insert_iterator {protected: Container* container = nullptr;   public:using iterator_category = output_iterator_tag;using value_type =void;using difference_type = ptrdiff_t;using pointer =void;using reference =void;using container_type = Container;   constexpr back_insert_iterator()noexcept=default;constexprexplicit back_insert_iterator(Container& x);constexpr back_insert_iterator& operator=(consttypename Container::value_type& value);constexpr back_insert_iterator& operator=(typename Container::value_type&& value);   constexpr back_insert_iterator& operator*();constexpr back_insert_iterator& operator++();constexpr back_insert_iterator operator++(int);};}

Class template std::front_insert_iterator

namespace std {template<class Container>class front_insert_iterator {protected: Container* container = nullptr;   public:using iterator_category = output_iterator_tag;using value_type =void;using difference_type = ptrdiff_t;using pointer =void;using reference =void;using container_type = Container;   constexpr front_insert_iterator(Container& x)noexcept=default;constexprexplicit front_insert_iterator(Container& x);constexpr front_insert_iterator& operator=(consttypename Container::value_type& value);constexpr front_insert_iterator& operator=(typename Container::value_type&& value);   constexpr front_insert_iterator& operator*();constexpr front_insert_iterator& operator++();constexpr front_insert_iterator operator++(int);};}

Class template std::insert_iterator

namespace std {template<class Container>class insert_iterator {protected: Container* container = nullptr;ranges::iterator_t<Container> iter =ranges::iterator_t<Container>();   public:using iterator_category = output_iterator_tag;using value_type =void;using difference_type = ptrdiff_t;using pointer =void;using reference =void;using container_type = Container;   insert_iterator()=default;constexpr insert_iterator(Container& x, ranges::iterator_t<Container> i);constexpr insert_iterator& operator=(consttypename Container::value_type& value);constexpr insert_iterator& operator=(typename Container::value_type&& value);   constexpr insert_iterator& operator*();constexpr insert_iterator& operator++();constexpr insert_iterator& operator++(int);};}

Class template std::move_iterator

namespace std {template<class Iter>class move_iterator {public:using iterator_type = Iter;using iterator_concept =/* see description */;using iterator_category =/* see description */;using value_type = iter_value_t<Iter>;using difference_type = iter_difference_t<Iter>;using pointer = Iter;using reference = iter_rvalue_reference_t<Iter>;   constexpr move_iterator();constexprexplicit move_iterator(Iter i);template<class U>constexpr move_iterator(const move_iterator<U>& u);template<class U>constexpr move_iterator& operator=(const move_iterator<U>& u);   constexpr iterator_type base()const&;constexpr iterator_type base()&&;constexpr reference operator*()const;constexpr pointer operator->()const;   constexpr move_iterator& operator++();constexprauto operator++(int);constexpr move_iterator& operator--();constexpr move_iterator operator--(int);   constexpr move_iterator operator+(difference_type n)const;constexpr move_iterator& operator+=(difference_type n);constexpr move_iterator operator-(difference_type n)const;constexpr move_iterator& operator-=(difference_type n);constexpr reference operator[](difference_type n)const;   template<sentinel_for<Iter> S>friendconstexprbool operator==(const move_iterator& x, const move_sentinel<S>& y);template<sized_sentinel_for<Iter> S>friendconstexpr iter_difference_t<Iter> operator-(const move_sentinel<S>& x, const move_iterator& y);template<sized_sentinel_for<Iter> S>friendconstexpr iter_difference_t<Iter> operator-(const move_iterator& x, const move_sentinel<S>& y);friendconstexpr iter_rvalue_reference_t<Iter> iter_move(const move_iterator& i)noexcept(noexcept(ranges::iter_move(i.current)));template<indirectly_swappable<Iter> Iter2>friendconstexprvoid iter_swap(const move_iterator& x, const move_iterator<Iter2>& y)noexcept(noexcept(ranges::iter_swap(x.current, y.current)));   private: Iter current;// exposition only};}

Class template std::move_sentinel

namespace std {template<semiregular S>class move_sentinel {public:constexpr move_sentinel();constexprexplicit move_sentinel(S s);template<class S2> requires convertible_to<const S2&, S>constexpr move_sentinel(const move_sentinel<S2>& s);template<class S2> requires assignable_from<S&, const S2&>constexpr move_sentinel& operator=(const move_sentinel<S2>& s);   constexpr S base()const;private: S last;// exposition only};}

Class template std::common_iterator

namespace std {template<input_or_output_iterator I, sentinel_for<I> S> requires (!same_as<I, S>&& copyable<I>)class common_iterator {public:constexpr common_iterator()=default;constexpr common_iterator(I i);constexpr common_iterator(S s);template<class I2, class S2> requires convertible_to<const I2&, I>&& convertible_to<const S2&, S>constexpr common_iterator(const common_iterator<I2, S2>& x);   template<class I2, class S2> requires convertible_to<const I2&, I>&& convertible_to<const S2&, S>&& assignable_from<I&, const I2&>&& assignable_from<S&, const S2&> common_iterator& operator=(const common_iterator<I2, S2>& x);   decltype(auto) operator*(); decltype(auto) operator*()const requires dereferenceable<const I>; decltype(auto) operator->()const requires /* see description */;   common_iterator& operator++(); decltype(auto) operator++(int);   template<class I2, sentinel_for<I> S2> requires sentinel_for<S, I2>friendbool operator==(const common_iterator& x, const common_iterator<I2, S2>& y);template<class I2, sentinel_for<I> S2> requires sentinel_for<S, I2>&& equality_comparable_with<I, I2>friendbool operator==(const common_iterator& x, const common_iterator<I2, S2>& y);   template<sized_sentinel_for<I> I2, sized_sentinel_for<I> S2> requires sized_sentinel_for<S, I2>friend iter_difference_t<I2> operator-(const common_iterator& x, const common_iterator<I2, S2>& y);   friendconstexpr decltype(auto) iter_move(const common_iterator& i)noexcept(noexcept(ranges::iter_move(declval<const I&>()))) requires input_iterator<I>;template<indirectly_swappable<I> I2, class S2>friendvoid iter_swap(const common_iterator& x, const common_iterator<I2, S2>& y)noexcept(noexcept(ranges::iter_swap(declval<const I&>(), declval<const I2&>())));   private: variant<I, S> v_;// exposition only};   template<class I, class S>struct incrementable_traits<common_iterator<I, S>>{using difference_type = iter_difference_t<I>;};   template<input_iterator I, class S>struct iterator_traits<common_iterator<I, S>>{using iterator_concept =/* see description */;using iterator_category =/* see description */;using value_type = iter_value_t<I>;using difference_type = iter_difference_t<I>;using pointer =/* see description */;using reference = iter_reference_t<I>;};}

Class std::default_sentinel_t

namespace std {struct default_sentinel_t {};}

Class template std::counted_iterator

namespace std {template<input_or_output_iterator I>class counted_iterator {public:using iterator_type = I;   constexpr counted_iterator()=default;constexpr counted_iterator(I x, iter_difference_t<I> n);template<class I2> requires convertible_to<const I2&, I>constexpr counted_iterator(const counted_iterator<I2>& x);   template<class I2> requires assignable_from<I&, const I2&>constexpr counted_iterator& operator=(const counted_iterator<I2>& x);   constexpr I base()const& requires copy_constructible<I>;constexpr I base()&&;constexpr iter_difference_t<I> count()constnoexcept;constexpr decltype(auto) operator*();constexpr decltype(auto) operator*()const requires dereferenceable<const I>;constexprauto operator->()constnoexcept requires contiguous_iterator<I>;   constexpr counted_iterator& operator++(); decltype(auto) operator++(int);constexpr counted_iterator operator++(int) requires forward_iterator<I>;constexpr counted_iterator& operator--() requires bidirectional_iterator<I>;constexpr counted_iterator operator--(int) requires bidirectional_iterator<I>;   constexpr counted_iterator operator+(iter_difference_t<I> n)const requires random_access_iterator<I>;friendconstexpr counted_iterator operator+( iter_difference_t<I> n, const counted_iterator& x) requires random_access_iterator<I>;constexpr counted_iterator& operator+=(iter_difference_t<I> n) requires random_access_iterator<I>;   constexpr counted_iterator operator-(iter_difference_t<I> n)const requires random_access_iterator<I>;template<common_with<I> I2>friendconstexpr iter_difference_t<I2> operator-(const counted_iterator& x, const counted_iterator<I2>& y);friendconstexpr iter_difference_t<I> operator-(const counted_iterator& x, default_sentinel_t);friendconstexpr iter_difference_t<I> operator-( default_sentinel_t, const counted_iterator& y);constexpr counted_iterator& operator-=(iter_difference_t<I> n) requires random_access_iterator<I>;   constexpr decltype(auto) operator[](iter_difference_t<I> n)const requires random_access_iterator<I>;   template<common_with<I> I2>friendconstexprbool operator==(const counted_iterator& x, const counted_iterator<I2>& y);friendconstexprbool operator==(const counted_iterator& x, default_sentinel_t);   template<common_with<I> I2>friendconstexpr strong_ordering operator<=>(const counted_iterator& x, const counted_iterator<I2>& y);   friendconstexpr decltype(auto) iter_move(const counted_iterator& i)noexcept(noexcept(ranges::iter_move(i.current))) requires input_iterator<I>;template<indirectly_swappable<I> I2>friendconstexprvoid iter_swap(const counted_iterator& x, const counted_iterator<I2>& y)noexcept(noexcept(ranges::iter_swap(x.current, y.current)));   private: I current = I();// exposition only iter_difference_t<I> length =0;// exposition only};   template<input_iterator I>struct iterator_traits<counted_iterator<I>>: iterator_traits<I>{using pointer =void;};}

Class std::unreachable_sentinel_t

namespace std {struct unreachable_sentinel_t {template<weakly_incrementable I>friendconstexprbool operator==(unreachable_sentinel_t, const I&)noexcept{returnfalse;}};}

Class template std::istream_iterator

namespace std {template<class T, class CharT =char, class Traits = char_traits<CharT>, class Distance = ptrdiff_t>class istream_iterator {public:using iterator_category = input_iterator_tag;using value_type = T;using difference_type = Distance;using pointer =const T*;using reference =const T&;using char_type = CharT;using traits_type = Traits;using istream_type = basic_istream<CharT, Traits>;   constexpr istream_iterator();constexpr istream_iterator(default_sentinel_t); istream_iterator(istream_type& s); istream_iterator(const istream_iterator& x)=default; ~istream_iterator()=default; istream_iterator& operator=(const istream_iterator&)=default;   const T& operator*()const;const T* operator->()const; istream_iterator& operator++(); istream_iterator operator++(int);   friendbool operator==(const istream_iterator& i, default_sentinel_t);   private: basic_istream<CharT, Traits>* in_stream;// exposition only T value;// exposition only};}

Class template std::ostream_iterator

namespace std {template<class T, class CharT =char, classTraits = char_traits<CharT>>class ostream_iterator {public:using iterator_category = output_iterator_tag;using value_type =void;using difference_type = ptrdiff_t;using pointer =void;using reference =void;using char_type = CharT;using traits_type = Traits;using ostream_type = basic_ostream<CharT, Traits>;   constexpr ostreambuf_iterator()noexcept=default; ostream_iterator(ostream_type& s); ostream_iterator(ostream_type& s, const CharT* delimiter); ostream_iterator(const ostream_iterator& x); ~ostream_iterator(); ostream_iterator& operator=(const ostream_iterator&)=default; ostream_iterator& operator=(const T& value);   ostream_iterator& operator*(); ostream_iterator& operator++(); ostream_iterator& operator++(int);   private: basic_ostream<CharT, Traits>* out_stream = nullptr;// exposition onlyconst CharT* delim = nullptr;// exposition only};}

Class template std::istreambuf_iterator

namespace std {template<class CharT, class Traits = char_traits<CharT>>class istreambuf_iterator {public:using iterator_category = input_iterator_tag;using value_type = CharT;using difference_type =typename Traits::off_type;using pointer =/* unspecified */;using reference = CharT;using char_type = CharT;using traits_type = Traits;using int_type =typename Traits::int_type;using streambuf_type = basic_streambuf<CharT, Traits>;using istream_type = basic_istream<CharT, Traits>;   class proxy;// exposition only   constexpr istreambuf_iterator()noexcept;constexpr istreambuf_iterator(default_sentinel_t)noexcept; istreambuf_iterator(const istreambuf_iterator&)noexcept=default; ~istreambuf_iterator()=default; istreambuf_iterator(istream_type& s)noexcept; istreambuf_iterator(streambuf_type* s)noexcept; istreambuf_iterator(const proxy& p)noexcept; istreambuf_iterator& operator=(const istreambuf_iterator&)noexcept=default; CharT operator*()const; istreambuf_iterator& operator++(); proxy operator++(int);bool equal(const istreambuf_iterator& b)const;   friendbool operator==(const istreambuf_iterator& i, default_sentinel_t s);   private: streambuf_type* sbuf_;// exposition only};   template<class CharT, class Traits>class istreambuf_iterator<CharT, Traits>::proxy{// exposition only CharT keep_; basic_streambuf<CharT, Traits>* sbuf_; proxy(CharT c, basic_streambuf<CharT, Traits>* sbuf): keep_(c), sbuf_(sbuf){}public: CharT operator*(){return keep_;}};}

Class template std::ostreambuf_iterator

namespace std {template<class CharT, class Traits = char_traits<CharT>>class ostreambuf_iterator {public:using iterator_category = output_iterator_tag;using value_type =void;using difference_type = ptrdiff_t;using pointer =void;using reference =void;using char_type = CharT;using traits_type = Traits;using streambuf_type = basic_streambuf<CharT, Traits>;using ostream_type = basic_ostream<CharT, Traits>;   constexpr ostreambuf_iterator()noexcept=default; ostreambuf_iterator(ostream_type& s)noexcept; ostreambuf_iterator(streambuf_type* s)noexcept; ostreambuf_iterator& operator=(CharT c);   ostreambuf_iterator& operator*(); ostreambuf_iterator& operator++(); ostreambuf_iterator& operator++(int);bool failed()constnoexcept;   private: streambuf_type* sbuf_ = nullptr;// exposition only};}

Class template std::iterator

namespace std {template<class Category, class T, class Distance = ptrdiff_t, class Pointer = T*, class Reference = T&>struct iterator {typedef Category iterator_category;typedef T value_type;typedef Distance difference_type;typedef Pointer pointer;typedef Reference reference;};}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 349	C++98	the exposition-only member delim of std::ostream_iterator had type constchar*	corrected to const CharT*