标准库标头 <iterator>

此头文件是迭代器库的一部分。

概念
迭代器概念
indirectly_readable (C++20)	指定类型通过应用运算符 `*` 可读 (概念)
indirectly_writable (C++20)	指定可向迭代器所引用的对象写入值 (概念)
weakly_incrementable (C++20)	指定 `semiregular` 类型能以前后自增运算符自增 (概念)
incrementable (C++20)	指定 `weakly_incrementable` 类型上的自增操作保持相等性，而且该类型为 `equality_comparable` (概念)
input_or_output_iterator (C++20)	指定该类型对象可以自增且可以解引用 (概念)
sentinel_for (C++20)	指定类型为某个 `input_or_output_iterator` 类型的哨位类型 (概念)
sized_sentinel_for (C++20)	指定可对一个迭代器和一个哨位应用 `-` 运算符，以在常数时间计算其距离 (概念)
input_iterator (C++20)	指定类型为输入迭代器，即可读取其所引用的值，且可前/后自增 (概念)
output_iterator (C++20)	指定类型为给定的值类型的输出迭代器，即可向其写入该类型的值，且可前/后自增 (概念)
forward_iterator (C++20)	指定 `input_iterator` 为向前迭代器，支持相等比较与多趟操作 (概念)
bidirectional_iterator (C++20)	指定 `forward_iterator` 为双向迭代器，支持向后移动 (概念)
random_access_iterator (C++20)	指定 `bidirectional_iterator` 为随机访问迭代器，支持常数时间内的前进和下标访问 (概念)
contiguous_iterator (C++20)	指定 `random_access_iterator` 为连续迭代器，指代内存中连续相接的元素 (概念)
间接可调用概念
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	指定可调用类型能以解引用某个 `indirectly_readable` 类型的结果进行调用 (概念)
indirect_unary_predicate (C++20)	指定可调用类型，在以解引用一个 `indirectly_readable` 类型的结果进行调用时，满足 `predicate` (概念)
indirect_binary_predicate (C++20)	指定可调用类型，在以解引用两个 `indirectly_readable` 类型的结果进行调用时，满足 `predicate` (概念)
indirect_equivalence_relation (C++20)	指定可调用类型，在以解引用两个 `indirectly_readable` 类型的结果进行调用时，满足 `equivalence_relation` (概念)
indirect_strict_weak_order (C++20)	指定可调用类型，在以解引用两个 `indirectly_readable` 类型的结果进行调用时，满足 `strict_weak_order` (概念)
常用算法要求
indirectly_movable (C++20)	指定可从 `indirectly_readable` 类型移动值给 `indirectly_writable` 类型 (概念)
indirectly_movable_storable (C++20)	指定可从 `indirectly_readable` 类型移动值给 `indirectly_writable` 类型，且该移动可以通过中间对象进行 (概念)
indirectly_copyable (C++20)	指定可从 `indirectly_readable` 类型复制值给 `indirectly_writable` 类型 (概念)
indirectly_copyable_storable (C++20)	指定可从 `indirectly_readable` 类型复制值给 `indirectly_writable` 类型，且该复制可以通过中间对象进行 (概念)
indirectly_swappable (C++20)	指定能交换两个 `indirectly_readable` 类型所引用的值 (概念)
indirectly_comparable (C++20)	指定能比较两个 `indirectly_readable` 类型所引用的值 (概念)
permutable (C++20)	指定在原位重排元素的算法的共同要求 (概念)
mergeable (C++20)	指定通过复制元素将已排序序列归并到输出序列中的算法的要求 (概念)
sortable (C++20)	指定重排序列为有序序列的算法的共用要求 (概念)
类
算法工具
indirect_result_t (C++20)	计算在解引用某组 `indirectly_readable` 类型的结果上调用可调用对象的结果 (别名模板)
projected (C++20)	用于对接受投影的算法指定约束的辅助模板 (类模板)
关联类型
incrementable_traits (C++20)	计算 `weakly_incrementable` 类型的差类型 (类模板)
indirectly_readable_traits (C++20)	计算 `indirectly_readable` 类型的值类型 (类模板)
iter_value_titer_reference_titer_difference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++20)(C++20)	计算迭代器的关联类型 (别名模板)
原语
iterator_traits	为迭代器各项性质提供统一接口 (类模板)
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	用于指示迭代器类别的空类类型 (类)
iterator (C++17 中弃用)	用于简化简单的迭代器的必要类型定义的基类 (类模板)
适配器
reverse_iterator	逆序遍历的迭代器适配器 (类模板)
move_iterator (C++11)	解引用结果为右值引用的迭代器适配器 (类模板)
move_sentinel (C++20)	用于 std::move_iterator 的哨位适配器 (类模板)
common_iterator (C++20)	适配一个迭代器类型及其哨位为一个公共迭代器类型 (类模板)
default_sentinel_t (C++20)	用于知晓其边界的迭代器的默认哨位 (类)
counted_iterator (C++20)	对到范围结尾距离进行跟踪的迭代器适配器 (类模板)
unreachable_sentinel_t (C++20)	始终与任何 `weakly_incrementable` 类型比较都不相等的哨位 (类)
back_insert_iterator	用于在容器尾部插入的迭代器适配器 (类模板)
front_insert_iterator	用于在容器头部插入的迭代器适配器 (类模板)
insert_iterator	用于插入容器的迭代器适配器 (类模板)
流迭代器
istream_iterator	从 std::basic_istream 读取的输入迭代器 (类模板)
ostream_iterator	写入 std::basic_ostream 的输出迭代器 (类模板)
istreambuf_iterator	从 std::basic_streambuf 读取的输入迭代器 (类模板)
ostreambuf_iterator	写入 std::basic_streambuf 的输出迭代器 (类模板)
定制点对象
在命名空间 `std::ranges` 定义
iter_move (C++20)	将解引用迭代器的结果转型为其关联的右值引用类型 (定制点对象)
iter_swap (C++20)	交换两个可解引用对象所引用的值 (定制点对象)
函数
适配器
make_reverse_iterator (C++14)	创建拥有从实参推出的类型的 std::reverse_iterator (函数模板)
make_move_iterator (C++11)	创建拥有从实参推出的类型的 std::move_iterator (函数模板)
front_inserter	创建拥有从实参推出的类型的 std::front_insert_iterator (函数模板)
back_inserter	创建拥有从实参推出的类型的 std::back_insert_iterator (函数模板)
inserter	创建拥有从实参推出的类型的 std::insert_iterator (函数模板)
非成员函数
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++11)(C++11)(C++20 中移除)(C++11)(C++11)(C++11)(C++11)(C++20)	比较迭代器底层迭代器 (函数模板)
operator+ (C++11)	令迭代器前进 (函数模板)
operator- (C++11)	计算两个迭代器适配器间的距离 (函数模板)
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)	比较迭代器底层迭代器 (函数模板)
operator+	令迭代器前进 (函数模板)
operator-	计算两个迭代器适配器间的距离 (函数模板)
operator==operator!= (C++20 中移除)	比较两个 `istream_iterator` (函数模板)
operator==operator!= (C++20 中移除)	比较两个 `istreambuf_iterator` (函数模板)
操作
advance	令迭代器前进给定的距离 (函数模板)
distance	返回两个迭代器间的距离 (函数模板)
next (C++11)	令迭代器自增 (函数模板)
prev (C++11)	令迭代器自减 (函数模板)
ranges::advance (C++20)	令迭代器前进给定的距离或到给定的边界 (niebloid)
ranges::distance (C++20)	返回迭代器与哨位间的距离，或范围起始与结尾间的距离 (niebloid)
ranges::next (C++20)	自增迭代器给定的距离或到边界 (niebloid)
ranges::prev (C++20)	自减迭代器给定的距离或到边界 (niebloid)
范围访问
begincbegin (C++11)(C++14)	返回指向容器或数组起始的迭代器 (函数模板)
endcend (C++11)(C++14)	返回指向容器或数组结尾的迭代器 (函数模板)
rbegincrbegin (C++14)	返回指向一个容器或数组的逆向迭代器 (函数模板)
rendcrend (C++14)	返回容器或数组的逆向尾迭代器 (函数模板)
sizessize (C++17)(C++20)	返回容器或数组的大小 (函数模板)
empty (C++17)	检查容器是否为空 (函数模板)
data (C++17)	获得指向底层数组的指针 (函数模板)

概要

#include <concepts>
 
namespace std {
  template<class T> using __with_reference = T&;  // 仅用于阐释
  template<class T> concept __Referenceable       // 仅用于阐释
    = requires { typename __with_reference<T>; };
  template<class T> concept __Dereferenceable     // 仅用于阐释
    = requires(T& t) {
      { *t } -> __Referenceable;  // 不要求保持相等性
    };
 
  // 关联类型
  // 可自增特征
  template<class> struct incrementable_traits;
  template<class T>
    using iter_difference_t = /* 见描述 */;
 
  // 间接可读特征
  template<class> struct indirectly_readable_traits;
  template<class T>
    using iter_value_t = /* 见描述 */;
 
  // 迭代器特征
  template<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 {
    // 定制点
    inline namespace /* 未指明 */ {
      // ranges::iter_move
      inline constexpr /* 未指明 */ iter_move = /* 未指明 */;
 
      // ranges::iter_swap
      inline constexpr /* 未指明 */ iter_swap = /* 未指明 */;
    }
  }
 
  template<__Dereferenceable T>
    requires requires(T& t) {
      { ranges::iter_move(t) } -> __Referenceable;
    }
  using iter_rvalue_reference_t
    = decltype(ranges::iter_move(declval<T&>()));
 
  // 迭代器概念
  // 概念 indirectly_readable
  template<class In>
    concept indirectly_readable = /* 见描述 */;
 
  template<indirectly_readable T>
    using iter_common_reference_t =
      common_reference_t<iter_reference_t<T>, iter_value_t<T>&>;
 
  // 概念 indirectly_writable
  template<class Out, class T>
    concept indirectly_writable = /* 见描述 */;
 
  // 概念 weakly_incrementable
  template<class I>
    concept weakly_incrementable = /* 见描述 */;
 
  // 概念 incrementable
  template<class I>
    concept incrementable = /* 见描述 */;
 
  // 概念 input_or_output_iterator
  template<class I>
    concept input_or_output_iterator = /* 见描述 */;
 
  // 概念 sentinel_for
  template<class S, class I>
    concept sentinel_for = /* 见描述 */;
 
  // 概念 sized_sentinel_for
  template<class S, class I>
    inline constexpr bool disable_sized_sentinel = false;
 
  template<class S, class I>
    concept sized_sentinel_for = /* 见描述 */;
 
  // 概念 input_iterator
  template<class I>
    concept input_iterator = /* 见描述 */;
 
  // 概念 output_iterator
  template<class I, class T>
    concept output_iterator = /* 见描述 */;
 
  // 概念 forward_iterator
  template<class I>
    concept forward_iterator = /* 见描述 */;
 
  // 概念 bidirectional_iterator
  template<class I>
    concept bidirectional_iterator = /* 见描述 */;
 
  // 概念 random_access_iterator
  template<class I>
    concept random_access_iterator = /* 见描述 */;
 
  // 概念 contiguous_iterator
  template<class I>
    concept contiguous_iterator = /* 见描述 */;
 
  // 间接可调用要求
  // 间接可调用
  template<class F, class I>
    concept indirectly_unary_invocable = /* 见描述 */;
 
  template<class F, class I>
    concept indirectly_regular_unary_invocable = /* 见描述 */;
 
  template<class F, class I>
    concept indirect_unary_predicate = /* 见描述 */;
 
  template<class F, class I1, class I2>
    concept indirect_binary_predicate = /* 见描述 */;
 
  template<class F, class I1, class I2 = I1>
    concept indirect_equivalence_relation = /* 见描述 */;
 
  template<class F, class I1, class I2 = I1>
    concept indirect_strict_weak_order = /* 见描述 */;
 
  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>...>;
 
  // projected
  template<indirectly_readable I, indirectly_regular_unary_invocable<I> Proj>
    struct projected;
 
  template<weakly_incrementable I, class Proj>
    struct incrementable_traits<projected<I, Proj>>;
 
  // 常用算法要求
  // 概念 indirectly_movable
  template<class In, class Out>
    concept indirectly_movable = /* 见描述 */;
 
  template<class In, class Out>
    concept indirectly_movable_storable = /* 见描述 */;
 
  // 概念 indirectly_copyable
  template<class In, class Out>
    concept indirectly_copyable = /* 见描述 */;
 
  template<class In, class Out>
    concept indirectly_copyable_storable = /* 见描述 */;
 
  // 概念 indirectly_swappable
  template<class I1, class I2 = I1>
    concept indirectly_swappable = /* 见描述 */;
 
  // 概念 indirectly_comparable
  template<class I1, class I2, class R, class P1 = identity, class P2 = identity>
    concept indirectly_comparable = /* 见描述 */;
 
  // 概念 permutable
  template<class I>
    concept permutable = /* 见描述 */;
 
  // 概念 mergeable
  template<class I1, class I2, class Out,
      class R = ranges::less, class P1 = identity, class P2 = identity>
    concept mergeable = /* 见描述 */;
 
  // 概念 sortable
  template<class I, class R = ranges::less, class P = identity>
    concept sortable = /* 见描述 */;
 
  // 原语
  // 迭代器标签
  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 { };
 
  // 迭代器操作
  template<class InputIter, class Distance>
    constexpr void
      advance(InputIter& i, Distance n);
  template<class InputIter>
    constexpr typename iterator_traits<InputIter>::difference_type
      distance(InputIter first, InputIter last);
  template<class InputIter>
    constexpr InputIter
      next(InputIter x, typename iterator_traits<InputIter>::difference_type n = 1);
  template<class BidirectionalIter>
    constexpr BidirectionalIter
      prev(BidirectionalIter x,
           typename iterator_traits<BidirectionalIter>::difference_type n = 1);
 
  // 范围迭代器操作
  namespace ranges {
    // ranges::advance
    template<input_or_output_iterator I>
      constexpr void advance(I& i, iter_difference_t<I> n);
    template<input_or_output_iterator I, sentinel_for<I> S>
      constexpr void 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::distance
    template<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::next
    template<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::prev
    template<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);
  }
 
  // 预定义迭代器与哨位
  // 逆向迭代器
  template<class Iter> class reverse_iterator;
 
  template<class Iter1, class Iter2>
    constexpr bool operator==(
      const reverse_iterator<Iter1>& x,
      const reverse_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator!=(
      const reverse_iterator<Iter1>& x,
      const reverse_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator<(
      const reverse_iterator<Iter1>& x,
      const reverse_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator>(
      const reverse_iterator<Iter1>& x,
      const reverse_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator<=(
      const reverse_iterator<Iter1>& x,
      const reverse_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator>=(
      const reverse_iterator<Iter1>& x,
      const reverse_iterator<Iter2>& y);
  template<class Iter1, three_way_comparable_with<Iter1> Iter2>
    constexpr compare_three_way_result_t<Iter1, Iter2>
      operator<=>(const reverse_iterator<Iter1>& x, const reverse_iterator<Iter2>& y);
 
  template<class Iter1, class Iter2>
    constexpr auto operator-(
      const reverse_iterator<Iter1>& x,
      const reverse_iterator<Iter2>& y) -> decltype(y.base() - x.base());
  template<class Iter>
    constexpr reverse_iterator<Iter>
      operator+(
    typename reverse_iterator<Iter>::difference_type n,
    const reverse_iterator<Iter>& x);
 
  template<class Iter>
    constexpr reverse_iterator<Iter> make_reverse_iterator(Iter i);
 
  template<class Iter1, class Iter2>
      requires (!sized_sentinel_for<Iter1, Iter2>)
    inline constexpr bool disable_sized_sentinel<reverse_iterator<Iter1>,
                                                 reverse_iterator<Iter2>> = true;
 
  // 插入迭代器
  template<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);
 
  // 移动迭代器与哨位
  template<class Iter> class move_iterator;
 
  template<class Iter1, class Iter2>
    constexpr bool operator==(
      const move_iterator<Iter1>& x, const move_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator<(
      const move_iterator<Iter1>& x, const move_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator>(
      const move_iterator<Iter1>& x, const move_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator<=(
      const move_iterator<Iter1>& x, const move_iterator<Iter2>& y);
  template<class Iter1, class Iter2>
    constexpr bool operator>=(
      const move_iterator<Iter1>& x, const move_iterator<Iter2>& y);
  template<class Iter1, three_way_comparable_with<Iter1> Iter2>
    constexpr compare_three_way_result_t<Iter1, Iter2>
      operator<=>(const move_iterator<Iter1>& x, const move_iterator<Iter2>& y);
 
  template<class Iter1, class Iter2>
    constexpr auto operator-(
    const move_iterator<Iter1>& x,
    const move_iterator<Iter2>& y) -> decltype(x.base() - y.base());
  template<class Iter>
    constexpr move_iterator<Iter> operator+(
      typename move_iterator<Iter>::difference_type n, const move_iterator<Iter>& x);
 
  template<class Iter>
    constexpr move_iterator<Iter> make_move_iterator(Iter i);
 
  template<semiregular S> class move_sentinel;
 
  // 公共迭代器
  template<input_or_output_iterator I, sentinel_for<I> S>
    requires (!same_as<I, S>)
      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>>;
 
  // 默认哨位
  struct default_sentinel_t;
  inline constexpr default_sentinel_t default_sentinel{};
 
  // 计数迭代器
  template<input_or_output_iterator I> class counted_iterator;
 
  template<class I>
    struct incrementable_traits<counted_iterator<I>>;
 
  template<input_iterator I>
    struct iterator_traits<counted_iterator<I>>;
 
  // 不可达哨位
  struct unreachable_sentinel_t;
  inline constexpr unreachable_sentinel_t unreachable_sentinel{};
 
  // 流迭代器
  template<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;
 
  // 范围访问
  template<class C> constexpr auto begin(C& c) -> decltype(c.begin());
  template<class C> constexpr auto begin(const C& c) -> decltype(c.begin());
  template<class C> constexpr auto end(C& c) -> decltype(c.end());
  template<class C> constexpr auto 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> constexpr auto cbegin(const C& c) noexcept(noexcept(std::begin(c)))
    -> decltype(std::begin(c));
  template<class C> constexpr auto cend(const C& c) noexcept(noexcept(std::end(c)))
    -> decltype(std::end(c));
  template<class C> constexpr auto rbegin(C& c) -> decltype(c.rbegin());
  template<class C> constexpr auto rbegin(const C& c) -> decltype(c.rbegin());
  template<class C> constexpr auto rend(C& c) -> decltype(c.rend());
  template<class C> constexpr auto 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> constexpr auto crbegin(const C& c) -> decltype(std::rbegin(c));
  template<class C> constexpr auto crend(const C& c) -> decltype(std::rend(c));
 
  template<class C> constexpr auto 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> constexpr auto 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> [[nodiscard]] constexpr auto empty(const C& c) -> decltype(c.empty());
  template<class T, size_t N> [[nodiscard]] constexpr bool empty(const T (&a)[N]) noexcept;
  template<class E> [[nodiscard]] constexpr bool empty(initializer_list<E> il) noexcept;
  template<class C> constexpr auto data(C& c) -> decltype(c.data());
  template<class C> constexpr auto data(const C& c) -> decltype(c.data());
  template<class T, size_t N> constexpr T* data(T (&a)[N]) noexcept;
  template<class E> constexpr const E* data(initializer_list<E> il) noexcept;
}

概念 `indirectly_readable`

namespace std {
  template<class In>
    concept __IndirectlyReadableImpl = // 仅用于阐释
      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>>
}

概念 `indirectly_writable`

namespace std {
  template<class Out, class T>
    concept indirectly_writable =
      requires(Out&& o, T&& t) {
        *o = std::forward<T>(t); // 不要求保持相等性
        *std::forward<Out>(o) = std::forward<T>(t);
        // 不要求保持相等性
        const_cast<const iter_reference_t<Out>&&>(*o) =
        std::forward<T>(t); // 不要求保持相等性
        const_cast<const iter_reference_t<Out>&&>(*std::forward<Out>(o)) =
        std::forward<T>(t); // 不要求保持相等性
      };
}

概念 `weakly_incrementable`

namespace std {
  template<class T>
    inline constexpr bool __is_integer_like = /* 见描述 */; // 仅用于阐释
 
  template<class T>
    inline constexpr bool __is_signed_integer_like =  // 仅用于阐释
      /* 见描述 */;
 
  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&>;   // 不要求保持相等性
        i++;                      // 不要求保持相等性
      };
}

概念 `incrementable`

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

概念 `input_or_output_iterator`

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

概念 `sentinel_for`

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

概念 `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>>;
      };
}

概念 `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>;
}

概念 `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); // 不要求保持相等性
      };
}

概念 `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>;
}

概念 `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>;
      };
}

概念 `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>>;
      };
}

概念 `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>>>;
      };
}

概念 `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>> &&
      invocable<F&, iter_common_reference_t<I>> &&
      common_reference_with<
        invoke_result_t<F&, iter_value_t<I>&>,
        invoke_result_t<F&, iter_reference_t<I>>>;
}

概念 `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>> &&
      regular_invocable<F&, iter_common_reference_t<I>> &&
      common_reference_with<
        invoke_result_t<F&, iter_value_t<I>&>,
        invoke_result_t<F&, iter_reference_t<I>>>;
}

概念 `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>> &&
      predicate<F&, iter_common_reference_t<I>>;
}

概念 `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>> &&
      predicate<F&, iter_common_reference_t<I1>, iter_common_reference_t<I2>>;
}

概念 `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>> &&
      equivalence_relation<F&, iter_common_reference_t<I1>, iter_common_reference_t<I2>>;
}

概念 `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>> &&
      strict_weak_order<F&, iter_common_reference_t<I1>, iter_common_reference_t<I2>>;
}

概念 `indirectly_movable`

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

概念 `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>>;
}

概念 `indirectly_copyable`

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

概念 `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>>;
}

概念 `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);
      };
}

概念 `indirectly_comparable`

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

概念 `permutable`

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

概念 `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>>;
}

概念 `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>>;
}

类模板 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 = /* 见描述 */;
}

类模板 std::indirectly_readable_traits

namespace std {
  template<class> struct __cond_value_type { };   // 仅用于阐释
  template<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> { };
}

类模板 std::projected

namespace std {
  template<indirectly_readable I, indirectly_regular_unary_invocable<I> Proj>
  struct projected {
    using value_type = remove_cvref_t<indirect_result_t<Proj&, I>>;
    indirect_result_t<Proj&, I> operator*() const; // 不定义
  };
 
  template<weakly_incrementable I, class Proj>
  struct incrementable_traits<projected<I, Proj>> {
    using difference_type = iter_difference_t<I>;
  };
}

类模板 std::iterator_traits

namespace std {
  template<class I>
  struct iterator_traits {
    using iterator_category = /* 见描述 */;
    using value_type        = /* 见描述 */;
    using difference_type   = /* 见描述 */;
    using pointer           = /* 见描述 */;
    using reference         = /* 见描述 */;
  };
 
  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&;
  };
}

迭代器标签

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 { };
}

类模板 std::reverse_iterator

namespace std {
  template<class Iter>
  class reverse_iterator {
  public:
    using iterator_type     = Iter;
    using iterator_concept  = /* 见描述 */;
    using iterator_category = /* 见描述 */;
    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();
    constexpr explicit 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 /* 见描述 */;
 
    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 /* 未指明 */ operator[](difference_type n) const;
 
    friend constexpr iter_rvalue_reference_t<Iter>
      iter_move(const reverse_iterator& i) noexcept(/* 见描述 */);
    template<indirectly_swappable<Iter> Iter2>
      friend constexpr void
        iter_swap(const reverse_iterator& x,
                  const reverse_iterator<Iter2>& y) noexcept(/* 见描述 */);
 
  protected:
    Iter current;
  };
}

类模板 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;
    constexpr explicit back_insert_iterator(Container& x);
    constexpr back_insert_iterator& operator=(const typename 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);
  };
}

类模板 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;
    constexpr explicit front_insert_iterator(Container& x);
    constexpr front_insert_iterator&
      operator=(const typename 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);
  };
}

类模板 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=(const typename 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);
  };
}

类模板 std::move_iterator

namespace std {
  template<class Iter>
  class move_iterator {
  public:
    using iterator_type     = Iter;
    using iterator_concept  = input_iterator_tag;
    using iterator_category = /* 见描述 */;
    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();
    constexpr explicit 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++();
    constexpr auto 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>
      friend constexpr bool
        operator==(const move_iterator& x, const move_sentinel<S>& y);
    template<sized_sentinel_for<Iter> S>
      friend constexpr iter_difference_t<Iter>
        operator-(const move_sentinel<S>& x, const move_iterator& y);
    template<sized_sentinel_for<Iter> S>
      friend constexpr iter_difference_t<Iter>
        operator-(const move_iterator& x, const move_sentinel<S>& y);
    friend constexpr iter_rvalue_reference_t<Iter>
      iter_move(const move_iterator& i)
        noexcept(noexcept(ranges::iter_move(i.current)));
    template<indirectly_swappable<Iter> Iter2>
      friend constexpr void
        iter_swap(const move_iterator& x, const move_iterator<Iter2>& y)
          noexcept(noexcept(ranges::iter_swap(x.current, y.current)));
 
  private:
    Iter current;     // 仅用于阐释
  };
}

类模板 std::move_sentinel

namespace std {
  template<semiregular S>
  class move_sentinel {
  public:
    constexpr move_sentinel();
    constexpr explicit 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;     // 仅用于阐释
  };
}

类模板 std::common_iterator

namespace std {
  template<input_or_output_iterator I, sentinel_for<I> S>
    requires (!same_as<I, S>)
  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 /* 见描述 */;
 
    common_iterator& operator++();
    decltype(auto) operator++(int);
 
    template<class I2, sentinel_for<I> S2>
      requires sentinel_for<S, I2>
    friend bool 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>
    friend bool 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);
 
    friend iter_rvalue_reference_t<I> 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>
      friend void 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_;   // 仅用于阐释
  };
 
  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 = /* 见描述 */;
    using iterator_category = /* 见描述 */;
    using value_type = iter_value_t<I>;
    using difference_type = iter_difference_t<I>;
    using pointer = /* 见描述 */;
    using reference = iter_reference_t<I>;
  };
}

类 std::default_sentinel_t

namespace std {
  struct default_sentinel_t { };
}

类模板 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() const noexcept;
    constexpr decltype(auto) operator*();
    constexpr decltype(auto) operator*() const
      requires dereferenceable<const 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>;
    friend constexpr 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>
      friend constexpr iter_difference_t<I2> operator-(
        const counted_iterator& x, const counted_iterator<I2>& y);
    friend constexpr iter_difference_t<I> operator-(
      const counted_iterator& x, default_sentinel_t);
    friend constexpr 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>
      friend constexpr bool operator==(
        const counted_iterator& x, const counted_iterator<I2>& y);
    friend constexpr bool operator==(
      const counted_iterator& x, default_sentinel_t);
 
    template<common_with<I> I2>
      friend constexpr strong_ordering operator<=>(
        const counted_iterator& x, const counted_iterator<I2>& y);
 
    friend constexpr iter_rvalue_reference_t<I> iter_move(const counted_iterator& i)
      noexcept(noexcept(ranges::iter_move(i.current)))
        requires input_iterator<I>;
    template<indirectly_swappable<I> I2>
      friend constexpr void iter_swap(const counted_iterator& x,
                                      const counted_iterator<I2>& y)
        noexcept(noexcept(ranges::iter_swap(x.current, y.current)));
 
  private:
    I current = I();                    // 仅用于阐释
    iter_difference_t<I> length = 0;    // 仅用于阐释
  };
 
  template<class I>
  struct incrementable_traits<counted_iterator<I>> {
    using difference_type = iter_difference_t<I>;
  };
 
  template<input_iterator I>
  struct iterator_traits<counted_iterator<I>> : iterator_traits<I> {
    using pointer = void;
  };
}

类 std::unreachable_sentinel_t

namespace std {
  struct unreachable_sentinel_t {
    template<weakly_incrementable I>
      friend constexpr bool operator==(unreachable_sentinel_t, const I&) noexcept
      { return false; }
  };
}

类模板 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);
 
    friend bool operator==(const istream_iterator& i, default_sentinel_t);
 
  private:
    basic_istream<CharT, Traits>* in_stream; // 仅用于阐释
    T value;                                 // 仅用于阐释
  };
}

类模板 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;          // 仅用于阐释
    const CharT* delim = nullptr;                                // 仅用于阐释
  };
}

类模板 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           = /* 未指明 */;
    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;                          // 仅用于阐释
 
    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;
 
    friend bool operator==(const istreambuf_iterator& i, default_sentinel_t s);
 
  private:
    streambuf_type* sbuf_;                // 仅用于阐释
  };
 
  template<class CharT, class Traits>
  class istreambuf_iterator<CharT, Traits>::proxy { // 仅用于阐释
    CharT keep_;
    basic_streambuf<CharT, Traits>* sbuf_;
    proxy(CharT c, basic_streambuf<CharT, Traits>* sbuf)
      : keep_(c), sbuf_(sbuf) { }
  public:
    CharT operator*() { return keep_; }
  };
}

类模板 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() const noexcept;
 
  private:
    streambuf_type* sbuf_ = nullptr;    // 仅用于阐释
  };
}

类模板 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;
  };
}

缺陷报告

下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。

缺陷报告	应用于	出版时的行为	正确行为
LWG 349	C++98	std::ostream_iterator 的仅用于阐释的成员 `delim` 的类型是 const char*	改成 const CharT*

编译器支持
自立实现与有宿主实现
语言
标准库
标准库标头
具名要求
功能特性测试宏 (C++20)
语言支持库
概念库 (C++20)
元编程库 (C++11)
诊断库
通用工具库
字符串库
容器库
迭代器库
范围库 (C++20)
算法库
数值库
本地化库
输入/输出库
文件系统库 (C++17)
正则表达式库 (C++11)
并发支持库 (C++11)
技术规范
符号索引
外部库

标准库标头 <iterator>

概念

迭代器概念

间接可调用概念

常用算法要求

类

算法工具

关联类型

原语

适配器

流迭代器

定制点对象

函数

适配器

非成员函数

操作

范围访问

概要

概念 indirectly_readable

概念 indirectly_writable

概念 weakly_incrementable

概念 incrementable

概念 input_or_output_iterator

概念 sentinel_for

概念 sized_sentinel_for

概念 input_iterator

概念 output_iterator

概念 forward_iterator

概念 bidirectional_iterator

概念 random_access_iterator

概念 contiguous_iterator

概念 indirectly_unary_invocable

概念 indirectly_regular_unary_invocable

概念 indirect_unary_predicate

概念 indirect_binary_predicate

概念 indirect_equivalence_relation

概念 indirect_strict_weak_order

概念 indirectly_movable

概念 indirectly_movable_storable

概念 indirectly_copyable

概念 indirectly_copyable_storable

概念 indirectly_swappable

概念 indirectly_comparable

概念 permutable

概念 mergeable

概念 sortable

类模板 std::incrementable_traits

类模板 std::indirectly_readable_traits

类模板 std::projected

类模板 std::iterator_traits

迭代器标签

类模板 std::reverse_iterator

类模板 std::back_insert_iterator

类模板 std::front_insert_iterator

类模板 std::insert_iterator

类模板 std::move_iterator

类模板 std::move_sentinel

类模板 std::common_iterator

类 std::default_sentinel_t

类模板 std::counted_iterator

类 std::unreachable_sentinel_t

类模板 std::istream_iterator

类模板 std::ostream_iterator

类模板 std::istreambuf_iterator

类模板 std::ostreambuf_iterator

类模板 std::iterator

缺陷报告

导航

概念 `indirectly_readable`

概念 `indirectly_writable`

概念 `weakly_incrementable`

概念 `incrementable`

概念 `input_or_output_iterator`

概念 `sentinel_for`

概念 `sized_sentinel_for`

概念 `input_iterator`

概念 `output_iterator`

概念 `forward_iterator`

概念 `bidirectional_iterator`

概念 `random_access_iterator`

概念 `contiguous_iterator`

概念 `indirectly_unary_invocable`

概念 `indirectly_regular_unary_invocable`

概念 `indirect_unary_predicate`

概念 `indirect_binary_predicate`

概念 `indirect_equivalence_relation`

概念 `indirect_strict_weak_order`

概念 `indirectly_movable`

概念 `indirectly_movable_storable`

概念 `indirectly_copyable`

概念 `indirectly_copyable_storable`

概念 `indirectly_swappable`

概念 `indirectly_comparable`

概念 `permutable`

概念 `mergeable`

概念 `sortable`