标准库标头 <memory>

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C++
 
标准库标头
注：修订记号中的反斜杠 '/' 意味着此标头被弃用和/或被移除。
语言支持
概念
<concepts> (C++20)
诊断
<system_error> (C++11)
内存管理
<memory>
<memory_resource> (C++17)  
元编程
<type_traits> (C++11)
<ratio> (C++11)
通用工具
<utility>
<tuple> (C++11)
<optional> (C++17)
<variant> (C++17)
<any> (C++17)
<expected> (C++23)
<bitset>

<charconv> (C++17)
<format> (C++20)
<bit> (C++20)

字符串
<cuchar> (C++11)

容器
<flat_set> (C++23)
<span> (C++20)
<mdspan> (C++23)

迭代器
<iterator>
范围
<ranges> (C++20)
<generator> (C++23)
算法
数值
<cfenv> (C++11)
<complex>
<numbers> (C++20)

日期时间
<chrono> (C++11)
本地化
<codecvt> (C++11/17)
输入/输出
<filesystem> (C++17)
<cstdio>
<cinttypes> (C++11)
<strstream> (C++98/)
正则表达式
<regex>
并发支持
<stop_token> (C++20)
<thread> (C++11)
<atomic> (C++11)
<stdatomic.h> (C++23)
<mutex> (C++11)
<shared_mutex> (C++14)
<condition_variable> (C++11)  
<semaphore> (C++20)
<latch> (C++20)
<barrier> (C++20)
<future> (C++11)

C 兼容
<cstdbool> (C++11/17/20)  
<ccomplex> (C++11/17/20)
<ctgmath> (C++11/17/20)

<cstdalign> (C++11/17/20)

<ciso646> (C++20 前)

 

此头文件是动态内存管理库的一部分。

包含

(C++20)
 三路比较运算符支持

类

指针特征
(C++11)
 提供关于指针式类型的信息
(类模板)
垃圾收集器支持
(C++11)(C++23 中移除)
 列出指针安全模式
(枚举)
分配器
默认的分配器
(类模板)
(C++11)
 提供关于分配器类型的信息
(类模板)
(C++23)
 记录由 allocate_at_least 分配的存储的地址与实际大小
(类模板)
(C++11)
 标签类型，用于选择具分配器的构造函数重载
(类)
(C++11)
 检查指定的类型是否支持使用分配器的构造
(类模板)
未初始化存储
(C++17 中弃用)(C++20 中移除)
 允许标准算法存储结果于未初始化内存的迭代器
(类模板)
智能指针
(C++11)
 拥有独有对象所有权语义的智能指针
(类模板)
(C++11)
 拥有共享对象所有权语义的智能指针
(类模板)
(C++11)
 到 std::shared_ptr 所管理对象的弱引用
(类模板)
(C++17 中移除)
 拥有严格对象所有权语义的智能指针
(类模板)
辅助类
(C++20)
 原子共享指针
(类模板特化)
(C++20)
 原子弱指针
(类模板特化)
(C++11)
 提供基于所有者的，共享指针和弱指针的混合类型的排序
(类模板)
(C++11)
 允许对象创建指代自身的 shared_ptr
(类模板)
(C++11)
 访问指向已销毁对象的 weak_ptr 时抛出的异常
(类)
(C++11)
 unique_ptr 的默认删除器
(类模板)
(C++11)
 std::unique_ptr 的散列支持
(类模板特化)
(C++11)
 std::shared_ptr 的散列支持
(类模板特化)
智能指针适配器
(C++23)
 与外来指针设置器交互，并在析构时重设智能指针
(类模板)
(C++23)
 与外来指针设置器交互，从智能指针获得初始指针值，并在析构时重设它
(类模板)
前置声明
在标头 <functional> 定义
(C++11)
 散列函数对象
(类模板)
在标头 <atomic> 定义
(C++11)
 atomic 类模板及其针对布尔、整型和指针类型的特化
(类模板)

常量

(C++11)
 用于选择具分配器的构造函数的 std::allocator_arg_t 对象
(常量)

函数

杂项
(C++20)
 从指针式类型获得裸指针
(函数模板)
(C++11)
 获得对象的实际地址，即使其重载了 & 运算符
(函数模板)
(C++11)
 对齐缓冲区中的指针
(函数)
(C++20)
 告知编译器指针已对齐
(函数模板)
垃圾收集器支持
(C++11)(C++23 中移除)
 声明一个对象不能被回收
(函数)
(C++11)(C++23 中移除)
 声明一个对象可以被回收
(函数模板)
(C++11)(C++23 中移除)
 声明该内存区域不含可追踪指针
(函数)
(C++11)(C++23 中移除)
 取消 std::declare_no_pointers 的效果
(函数)
(C++11)(C++23 中移除)
 返回当前的指针安全模式
(函数)
未初始化存储
将范围内的对象复制到未初始化的内存区域
(函数模板)
(C++11)
 将指定数量的对象复制到未初始化的内存区域
(函数模板)
复制一个对象到以范围定义的未初始化内存区域
(函数模板)
复制一个对象到以起点和计数定义的未初始化内存区域
(函数模板)
(C++17)
 移动一个范围的对象到未初始化的内存区域
(函数模板)
(C++17)
 移动一定数量对象到未初始化内存区域
(函数模板)
(C++17)
 在范围所定义的未初始化的内存区域以默认初始化构造对象
(函数模板)
(C++17)
 在起始和计数所定义的未初始化内存区域用默认初始化构造对象
(函数模板)
(C++17)
 在范围所定义的未初始化内存中用值初始化构造对象
(函数模板)
(C++17)
 在起始和计数所定义的未初始化内存区域以值初始化构造对象
(函数模板)
(C++20)
 在给定地址创建对象
(函数模板)
(C++17)
 销毁在给定地址的对象
(函数模板)
(C++17)
 销毁一个范围中的对象
(函数模板)
(C++17)
 销毁范围中一定数量的对象
(函数模板)
(C++17 中弃用)(C++20 中移除)
 获得未初始化存储
(函数模板)
(C++17 中弃用)(C++20 中移除)
 释放未初始化存储
(函数模板)
智能指针非成员操作
(C++14)(C++20)
 创建管理一个新对象的独占指针
(函数模板)
(C++20 中移除)(C++20)
 与另一个 unique_ptr 或 nullptr 进行比较
(函数模板)
(C++20)
 创建管理一个新对象的共享指针
(函数模板)
(C++20)
 创建管理一个用分配器分配的新对象的共享指针
(函数模板)
(C++17)
 应用 static_cast、dynamic_cast、const_cast 或 reinterpret_cast 到被存储指针
(函数模板)
返回指定类型中的删除器，若其拥有
(函数模板)
(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20)
 与另一个 shared_ptr 或 nullptr 进行比较
(函数模板)
将存储的指针的值输出到输出流
(函数模板)
(C++11)
 特化 std::swap 算法
(函数模板)
(C++11)
 特化 std::swap 算法
(函数模板)
(C++11)
 特化 std::swap 算法
(函数模板)
智能指针适配器创建
(C++23)
 以关联的智能指针和重设参数创建 out_ptr_t
(函数模板)
(C++23)
 以关联的智能指针和重设参数创建 inout_ptr_t
(函数模板)
(C++20 中弃用)
 特化的原子操作
(函数模板)

仿函数实体

在命名空间 std::ranges 定义
未初始化存储
(C++20)
 复制元素范围到未初始化的内存区域
(niebloid)
(C++20)
 复制一定量元素到未初始化的内存区域
(niebloid)
(C++20)
 复制一个对象到范围所定义的未初始化的内存区域
(niebloid)
(C++20)
 复制一个对象到起始与计数所定义的未初始化的内存区域
(niebloid)
(C++20)
 移动对象范围到未初始化的内存区域
(niebloid)
(C++20)
 移动一定量对象到未初始化的内存区域
(niebloid)
(C++20)
 在范围所定义的未初始化的内存区域以默认初始化构造对象
(niebloid)
(C++20)
 在起始与计数所定义的未初始化的内存区域以默认初始化构造对象
(niebloid)
(C++20)
 在范围所定义的未初始化的内存区域以值初始化构造对象
(niebloid)
(C++20)
 在起始与计数所定义的未初始化的内存区域以值初始化构造对象
(niebloid)
(C++20)
 在给定地址创建对象
(niebloid)
(C++20)
 销毁位于给定地址的元素
(niebloid)
(C++20)
 销毁范围中的元素
(niebloid)
(C++20)
 销毁范围中一定量的元素
(niebloid)

概要

#include <compare>
 
namespace std {
  // 指针特征
  template<class Ptr> struct pointer_traits;
  template<class T> struct pointer_traits<T*>;
 
  // 指针转换
  template<class T>
    constexpr T* to_address(T* p) noexcept;
  template<class Ptr>
    constexpr auto to_address(const Ptr& p) noexcept;
 
  // 指针对齐
  void* align(size_t alignment, size_t size, void*& ptr, size_t& space);
  template<size_t N, class T>
    [[nodiscard]] constexpr T* assume_aligned(T* ptr);
 
  // 分配器参数标签
  struct allocator_arg_t { explicit allocator_arg_t() = default; };
  inline constexpr allocator_arg_t allocator_arg{};
 
  // uses_­allocator
  template<class T, class Alloc> struct uses_allocator;
 
  // uses_­allocator
  template<class T, class Alloc>
    inline constexpr bool uses_allocator_v = uses_allocator<T, Alloc>::value;
 
  // 使用分配器构造
  template<class T, class Alloc, class... Args>
    constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                    Args&&... args) noexcept;
  template<class T, class Alloc, class Tuple1, class Tuple2>
    constexpr auto uses_allocator_construction_args(const Alloc& alloc, piecewise_construct_t,
                                                    Tuple1&& x, Tuple2&& y) noexcept;
  template<class T, class Alloc>
    constexpr auto uses_allocator_construction_args(const Alloc& alloc) noexcept;
  template<class T, class Alloc, class U, class V>
    constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                    U&& u, V&& v) noexcept;
  template<class T, class Alloc, class U, class V>
    constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                    const pair<U, V>& pr) noexcept;
  template<class T, class Alloc, class U, class V>
    constexpr auto uses_allocator_construction_args(const Alloc& alloc,
                                                    pair<U, V>&& pr) noexcept;
  template<class T, class Alloc, class... Args>
    constexpr T make_obj_using_allocator(const Alloc& alloc, Args&&... args);
  template<class T, class Alloc, class... Args>
    constexpr T* uninitialized_construct_using_allocator(T* p, const Alloc& alloc,
                                                         Args&&... args);
 
  // 分配器特征
  template<class Alloc> struct allocator_traits;
 
  template<class Pointer, class SizeType = size_t>
  struct allocation_result {
    Pointer ptr;
    SizeType count;
  };
 
  // 默认分配器
  template<class T> class allocator;
  template<class T, class U>
    constexpr bool operator==(const allocator<T>&, const allocator<U>&) noexcept;
 
  // addressof
  template<class T>
    constexpr T* addressof(T& r) noexcept;
  template<class T>
    const T* addressof(const T&&) = delete;
 
  // 特化的算法
  // 特殊内存概念
  template<class I>
    concept no-throw-input-iterator = /* 见描述 */;    // 仅用于阐释
  template<class I>
    concept no-throw-forward-iterator = /* 见描述 */;  // 仅用于阐释
  template<class S, class I>
    concept no-throw-sentinel-for = /* 见描述 */;      // 仅用于阐释
  template<class R>
    concept no-throw-input-range = /* 见描述 */;       // 仅用于阐释
  template<class R>
    concept no-throw-forward-range = /* 见描述 */;     // 仅用于阐释
 
  template<class NoThrowForwardIt>
    void uninitialized_default_construct(NoThrowForwardIt first,
                                         NoThrowForwardIt last);
  template<class ExecutionPolicy, class NoThrowForwardIt>
    void uninitialized_default_construct(ExecutionPolicy&& exec,
                                         NoThrowForwardIt first,
                                         NoThrowForwardIt last);
  template<class NoThrowForwardIt, class Size>
    NoThrowForwardIt
      uninitialized_default_construct_n(NoThrowForwardIt first, Size n);
  template<class ExecutionPolicy, class NoThrowForwardIt, class Size>
    NoThrowForwardIt
      uninitialized_default_construct_n(ExecutionPolicy&& exec,
                                        NoThrowForwardIt first, Size n);
 
  namespace ranges {
    template<no-throw-forward-iterator I, no-throw-sentinel-for<I> S>
      requires default_­initializable<iter_value_t<I>>
        I uninitialized_default_construct(I first, S last);
    template<no-throw-forward-range R>
      requires default_­initializable<range_value_t<R>>
        borrowed_iterator_t<R> uninitialized_default_construct(R&& r);
 
    template<no-throw-forward-iterator I>
      requires default_­initializable<iter_value_t<I>>
        I uninitialized_default_construct_n(I first, iter_difference_t<I> n);
  }
 
  template<class NoThrowForwardIterator>
    void uninitialized_value_construct(NoThrowForwardIterator first,
                                       NoThrowForwardIterator last);
  template<class ExecutionPolicy, class NoThrowForwardIt>
    void uninitialized_value_construct(ExecutionPolicy&& exec,
                                       NoThrowForwardIt first,
                                       NoThrowForwardIt last);
  template<class NoThrowForwardIt, class Size>
    NoThrowForwardIt
      uninitialized_value_construct_n(NoThrowForwardIt first, Size n);
  template<class ExecutionPolicy, class NoThrowForwardIt, class Size>
    NoThrowForwardIt
      uninitialized_value_construct_n(ExecutionPolicy&& exec,
                                      NoThrowForwardIt first, Size n);
 
  namespace ranges {
    template<no-throw-forward-iterator I, no-throw-sentinel-for<I> S>
      requires default_­initializable<iter_value_t<I>>
        I uninitialized_value_construct(I first, S last);
    template<no-throw-forward-range R>
      requires default_­initializable<range_value_t<R>>
        borrowed_iterator_t<R> uninitialized_value_construct(R&& r);
 
    template<no-throw-forward-iterator I>
      requires default_­initializable<iter_value_t<I>>
        I uninitialized_value_construct_n(I first, iter_difference_t<I> n);
  }
 
  template<class InputIt, class NoThrowForwardIt>
    NoThrowForwardIt uninitialized_copy(InputIt first, InputIt last,
                                        NoThrowForwardIt result);
  template<class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt>
    NoThrowForwardIt uninitialized_copy(ExecutionPolicy&& exec,
                                        ForwardIt first, ForwardIt last,
                                        NoThrowForwardIt result);
  template<class InputIt, class Size, class NoThrowForwardIt>
    NoThrowForwardIt uninitialized_copy_n(InputIt first, Size n,
                                          NoThrowForwardIt result);
  template<class ExecutionPolicy, class ForwardIt, class Size,
           class NoThrowForwardIt>
    NoThrowForwardIt uninitialized_copy_n(ExecutionPolicy&& exec,
                                          ForwardIt first, Size n,
                                          NoThrowForwardIt result);
 
  namespace ranges {
    template<class I, class O>
      using uninitialized_copy_result = in_out_result<I, O>;
    template<input_­iterator I, sentinel_­for<I> S1,
             no-throw-forward-iterator O, no-throw-sentinel-for<O> S2>
      requires constructible_­from<iter_value_t<O>, iter_reference_t<I>>
        uninitialized_copy_result<I, O>
          uninitialized_copy(I ifirst, S1 ilast, O ofirst, S2 olast);
    template<input_­range IR, no-throw-forward-range OR>
      requires constructible_­from<range_value_t<OR>, range_reference_t<IR>>
        uninitialized_copy_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>
          uninitialized_copy(IR&& in_range, OR&& out_range);
 
    template<class I, class O>
      using uninitialized_copy_n_result = in_out_result<I, O>;
    template<input_­iterator I, no-throw-forward-iterator O, no-throw-sentinel-for<O> S>
      requires constructible_­from<iter_value_t<O>, iter_reference_t<I>>
        uninitialized_copy_n_result<I, O>
          uninitialized_copy_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast);
  }
 
  template<class InputIt, class NoThrowForwardIt>
    NoThrowForwardIt uninitialized_move(InputIt first, InputIt last,
                                        NoThrowForwardIt result);
  template<class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt>
    NoThrowForwardIt uninitialized_move(ExecutionPolicy&& exec,
                                        ForwardIt first, ForwardIt last,
                                        NoThrowForwardIt result);
  template<class InputIt, class Size, class NoThrowForwardIt>
    pair<InputIt, NoThrowForwardIt>
      uninitialized_move_n(InputIt first, Size n, NoThrowForwardIt result);
  template<class ExecutionPolicy, class ForwardIt, class Size,
           class NoThrowForwardIt>
    pair<ForwardIt, NoThrowForwardIt>
      uninitialized_move_n(ExecutionPolicy&& exec,
                           ForwardIt first, Size n, NoThrowForwardIt result);
 
  namespace ranges {
    template<class I, class O>
      using uninitialized_move_result = in_out_result<I, O>;
    template<input_­iterator I, sentinel_­for<I> S1,
             no-throw-forward-iterator O, no-throw-sentinel-for<O> S2>
      requires constructible_­from<iter_value_t<O>, iter_rvalue_reference_t<I>>
        uninitialized_move_result<I, O>
          uninitialized_move(I ifirst, S1 ilast, O ofirst, S2 olast);
    template<input_­range IR, no-throw-forward-range OR>
      requires constructible_­from<range_value_t<OR>, range_rvalue_reference_t<IR>>
        uninitialized_move_result<borrowed_iterator_t<IR>, borrowed_iterator_t<OR>>
          uninitialized_move(IR&& in_range, OR&& out_range);
 
    template<class I, class O>
      using uninitialized_move_n_result = in_out_result<I, O>;
    template<input_­iterator I,
             no-throw-forward-iterator O, no-throw-sentinel-for<O> S>
      requires constructible_­from<iter_value_t<O>, iter_rvalue_reference_t<I>>
        uninitialized_move_n_result<I, O>
          uninitialized_move_n(I ifirst, iter_difference_t<I> n, O ofirst, S olast);
  }
 
  template<class NoThrowForwardIt, class T>
    void uninitialized_fill(NoThrowForwardIt first, NoThrowForwardIt last,
                            const T& x);
  template<class ExecutionPolicy, class NoThrowForwardIt, class T>
    void uninitialized_fill(ExecutionPolicy&& exec,
                            NoThrowForwardIt first, NoThrowForwardIt last,
                            const T& x);
  template<class NoThrowForwardIt, class Size, class T>
    NoThrowForwardIt
      uninitialized_fill_n(NoThrowForwardIt first, Size n, const T& x);
  template<class ExecutionPolicy, class NoThrowForwardIt, class Size, class T>
    NoThrowForwardIt
      uninitialized_fill_n(ExecutionPolicy&& exec,
                           NoThrowForwardIt first, Size n, const T& x);
 
  namespace ranges {
    template<no-throw-forward-iterator I, no-throw-sentinel-for<I> S, class T>
      requires constructible_­from<iter_value_t<I>, const T&>
        I uninitialized_fill(I first, S last, const T& x);
    template<no-throw-forward-range R, class T>
      requires constructible_­from<range_value_t<R>, const T&>
        borrowed_iterator_t<R> uninitialized_fill(R&& r, const T& x);
 
    template<no-throw-forward-iterator I, class T>
      requires constructible_­from<iter_value_t<I>, const T&>
        I uninitialized_fill_n(I first, iter_difference_t<I> n, const T& x);
  }
 
  // construct_­at
  template<class T, class... Args>
    constexpr T* construct_at(T* location, Args&&... args);
 
  namespace ranges {
    template<class T, class... Args>
      constexpr T* construct_at(T* location, Args&&... args);
  }
 
  // destroy
  template<class T>
    constexpr void destroy_at(T* location);
  template<class NoThrowForwardIt>
    constexpr void destroy(NoThrowForwardIt first, NoThrowForwardIt last);
  template<class ExecutionPolicy, class NoThrowForwardIt>
    void destroy(ExecutionPolicy&& exec,
                 NoThrowForwardIt first, NoThrowForwardIt last);
  template<class NoThrowForwardIt, class Size>
    constexpr NoThrowForwardIt destroy_n(NoThrowForwardIt first, Size n);
  template<class ExecutionPolicy, class NoThrowForwardIt, class Size>
    NoThrowForwardIt destroy_n(ExecutionPolicy&& exec,
                               NoThrowForwardIt first, Size n);
 
  namespace ranges {
    template<destructible T>
      constexpr void destroy_at(T* location) noexcept;
 
    template<no-throw-input-iterator I, no-throw-sentinel-for<I> S>
      requires destructible<iter_value_t<I>>
        constexpr I destroy(I first, S last) noexcept;
    template<no-throw-input-range R>
      requires destructible<range_value_t<R>>
        constexpr borrowed_iterator_t<R> destroy(R&& r) noexcept;
 
    template<no-throw-input-iterator I>
      requires destructible<iter_value_t<I>>
        constexpr I destroy_n(I first, iter_difference_t<I> n) noexcept;
  }
 
  // 类模板 unique_­ptr
  template<class T> struct default_delete;
  template<class T> struct default_delete<T[]>;
  template<class T, class D = default_delete<T>> class unique_ptr;
  template<class T, class D> class unique_ptr<T[], D>;
 
  template<class T, class... Args>
    unique_ptr<T> make_unique(Args&&... args);                                  // T 非数组
  template<class T>
    unique_ptr<T> make_unique(size_t n);                                        // T 为 U[]
  template<class T, class... Args>
    /* 未指明 */ make_unique(Args&&...) = delete;                                // T 为 U[N]
 
  template<class T>
    unique_ptr<T> make_unique_for_overwrite();                                  // T 非数组
  template<class T>
    unique_ptr<T> make_unique_for_overwrite(size_t n);                          // T 为 U[]
  template<class T, class... Args>
    /* 未指明 */ make_unique_for_overwrite(Args&&...) = delete;                  // T 为 U[N]
 
  template<class T, class D>
    void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y) noexcept;
 
  template<class T1, class D1, class T2, class D2>
    bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
  template<class T1, class D1, class T2, class D2>
    bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
  template<class T1, class D1, class T2, class D2>
    bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
  template<class T1, class D1, class T2, class D2>
    bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
  template<class T1, class D1, class T2, class D2>
    bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
  template<class T1, class D1, class T2, class D2>
    requires three_­way_­comparable_­with<typename unique_ptr<T1, D1>::pointer,
                                       typename unique_ptr<T2, D2>::pointer>
    compare_three_way_result_t<typename unique_ptr<T1, D1>::pointer,
                               typename unique_ptr<T2, D2>::pointer>
      operator<=>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
 
  template<class T, class D>
    bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
  template<class T, class D>
    bool operator<(const unique_ptr<T, D>& x, nullptr_t);
  template<class T, class D>
    bool operator<(nullptr_t, const unique_ptr<T, D>& y);
  template<class T, class D>
    bool operator>(const unique_ptr<T, D>& x, nullptr_t);
  template<class T, class D>
    bool operator>(nullptr_t, const unique_ptr<T, D>& y);
  template<class T, class D>
    bool operator<=(const unique_ptr<T, D>& x, nullptr_t);
  template<class T, class D>
    bool operator<=(nullptr_t, const unique_ptr<T, D>& y);
  template<class T, class D>
    bool operator>=(const unique_ptr<T, D>& x, nullptr_t);
  template<class T, class D>
    bool operator>=(nullptr_t, const unique_ptr<T, D>& y);
  template<class T, class D>
    requires three_­way_­comparable<typename unique_ptr<T, D>::pointer>
    compare_three_way_result_t<typename unique_ptr<T, D>::pointer>
      operator<=>(const unique_ptr<T, D>& x, nullptr_t);
 
  template<class E, class T, class Y, class D>
    basic_ostream<E, T>& operator<<(basic_ostream<E, T>& os, const unique_ptr<Y, D>& p);
 
  // 类 bad_­weak_­ptr
  class bad_weak_ptr;
 
  // 类模板 shared_­ptr
  template<class T> class shared_ptr;
 
  // shared_­ptr 创建
  template<class T, class... Args>
    shared_ptr<T> make_shared(Args&&... args);                                  // T 非数组
  template<class T, class A, class... Args>
    shared_ptr<T> allocate_shared(const A& a, Args&&... args);                  // T 非数组
 
  template<class T>
    shared_ptr<T> make_shared(size_t N);                                        // T 为 U[]
  template<class T, class A>
    shared_ptr<T> allocate_shared(const A& a, size_t N);                        // T 为 U[]
 
  template<class T>
    shared_ptr<T> make_shared();                                                // T 为 U[N]
  template<class T, class A>
    shared_ptr<T> allocate_shared(const A& a);                                  // T 为 U[N]
 
  template<class T>
    shared_ptr<T> make_shared(size_t N, const remove_extent_t<T>& u);           // T 为 U[]
  template<class T, class A>
    shared_ptr<T> allocate_shared(const A& a, size_t N,
                                  const remove_extent_t<T>& u);                 // T 为 U[]
 
  template<class T>
    shared_ptr<T> make_shared(const remove_extent_t<T>& u);                     // T 为 U[N]
  template<class T, class A>
    shared_ptr<T> allocate_shared(const A& a, const remove_extent_t<T>& u);     // T 为 U[N]
 
  template<class T>
    shared_ptr<T> make_shared_for_overwrite();                                  // T 非 U[]
  template<class T, class A>
    shared_ptr<T> allocate_shared_for_overwrite(const A& a);                    // T 非 U[]
 
  template<class T>
    shared_ptr<T> make_shared_for_overwrite(size_t N);                          // T 为 U[]
  template<class T, class A>
    shared_ptr<T> allocate_shared_for_overwrite(const A& a, size_t N);          // T 为 U[]
 
  // shared_­ptr 比较
  template<class T, class U>
    bool operator==(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
  template<class T, class U>
    strong_ordering operator<=>(const shared_ptr<T>& a, const shared_ptr<U>& b) noexcept;
 
  template<class T>
    bool operator==(const shared_ptr<T>& x, nullptr_t) noexcept;
  template<class T>
    strong_ordering operator<=>(const shared_ptr<T>& x, nullptr_t) noexcept;
 
  // shared_­ptr 特化算法
  template<class T>
    void swap(shared_ptr<T>& a, shared_ptr<T>& b) noexcept;
 
  // shared_­ptr 转型
  template<class T, class U>
    shared_ptr<T> static_pointer_cast(const shared_ptr<U>& r) noexcept;
  template<class T, class U>
    shared_ptr<T> static_pointer_cast(shared_ptr<U>&& r) noexcept;
  template<class T, class U>
    shared_ptr<T> dynamic_pointer_cast(const shared_ptr<U>& r) noexcept;
  template<class T, class U>
    shared_ptr<T> dynamic_pointer_cast(shared_ptr<U>&& r) noexcept;
  template<class T, class U>
    shared_ptr<T> const_pointer_cast(const shared_ptr<U>& r) noexcept;
  template<class T, class U>
    shared_ptr<T> const_pointer_cast(shared_ptr<U>&& r) noexcept;
  template<class T, class U>
    shared_ptr<T> reinterpret_pointer_cast(const shared_ptr<U>& r) noexcept;
  template<class T, class U>
    shared_ptr<T> reinterpret_pointer_cast(shared_ptr<U>&& r) noexcept;
 
  // shared_­ptr get_­deleter
  template<class D, class T>
    D* get_deleter(const shared_ptr<T>& p) noexcept;
 
  // shared_­ptr I/O
  template<class E, class T, class Y>
    basic_ostream<E, T>& operator<<(basic_ostream<E, T>& os, const shared_ptr<Y>& p);
 
  // 类模板 weak_­ptr
  template<class T> class weak_ptr;
 
  // weak_­ptr 特化算法
  template<class T> void swap(weak_ptr<T>& a, weak_ptr<T>& b) noexcept;
 
  // 类模板 owner_­less
  template<class T = void> struct owner_less;
 
  // 类模板 enable_­shared_­from_­this
  template<class T> class enable_shared_from_this;
 
  // 散列支持
  template<class T> struct hash;
  template<class T, class D> struct hash<unique_ptr<T, D>>;
  template<class T> struct hash<shared_ptr<T>>;
 
  // 原子智能指针
  template<class T> struct atomic;
  template<class T> struct atomic<shared_ptr<T>>;
  template<class T> struct atomic<weak_ptr<T>>;
 
  // 类模板 out_­ptr_­t
  template<class Smart, class Pointer, class... Args>
    class out_ptr_t;
 
  // 函数模板 out_­ptr
  template<class Pointer = void, class Smart, class... Args>
    auto out_ptr(Smart& s, Args&&... args);
 
  // 类模板 inout_­ptr_­t
  template<class Smart, class Pointer, class... Args>
    class inout_ptr_t;
 
  // 函数模板 inout_­ptr
  template<class Pointer = void, class Smart, class... Args>
    auto inout_ptr(Smart& s, Args&&... args);
}
 
// 弃用
namespace std {
  template<class T>
    bool atomic_is_lock_free(const shared_ptr<T>* p);
 
  template<class T>
    shared_ptr<T> atomic_load(const shared_ptr<T>* p);
  template<class T>
    shared_ptr<T> atomic_load_explicit(const shared_ptr<T>* p, memory_order mo);
 
  template<class T>
    void atomic_store(shared_ptr<T>* p, shared_ptr<T> r);
  template<class T>
    void atomic_store_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);
 
  template<class T>
    shared_ptr<T> atomic_exchange(shared_ptr<T>* p, shared_ptr<T> r);
  template<class T>
    shared_ptr<T> atomic_exchange_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);
 
  template<class T>
    bool atomic_compare_exchange_weak(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
  template<class T>
    bool atomic_compare_exchange_strong(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
  template<class T>
    bool atomic_compare_exchange_weak_explicit(
      shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
      memory_order success, memory_order failure);
  template<class T>
    bool atomic_compare_exchange_strong_explicit(
      shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
      memory_order success, memory_order failure);
}

辅助概念

template<class I>
concept no-throw-input-iterator = // 仅用于阐释
  input_iterator<I> &&
  is_lvalue_reference_v<iter_reference_t<I>> &&
  same_as<remove_cvref_t<iter_reference_t<I>>, iter_value_t<I>>;
 
template<class S, class I>
concept no-throw-sentinel-for = sentinel_for<S, I>; // 仅用于阐释
 
template<class R>
concept no-throw-input-range = // 仅用于阐释
  ranges::range<R> &&
  no-throw-input-iterator<ranges::iterator_t<R>> &&
  no-throw-sentinel-for<ranges::sentinel_t<R>, ranges::iterator_t<R>>;
 
template<class I>
concept no-throw-forward-iterator = // 仅用于阐释
  no-throw-input-iterator<I> &&
  forward_iterator<I> &&
  no-throw-sentinel-for<I, I>;
 
template<class R>
concept no-throw-forward-range = // 仅用于阐释
  no-throw-input-range<R> &&
  no-throw-forward-iterator<ranges::iterator_t<R>>;

注意：这些名字仅用于阐释，它们不是接口的一部分。

类模板 std::pointer_traits

namespace std {
  template<class Ptr> struct pointer_traits {
    using pointer         = Ptr;
    using element_type    = /* 见描述 */;
    using difference_type = /* 见描述 */;
 
    template<class U> using rebind = /* 见描述 */;
 
    static pointer pointer_to(/* 见描述 */ r);
  };
 
  template<class T> struct pointer_traits<T*> {
    using pointer         = T*;
    using element_type    = T;
    using difference_type = ptrdiff_t;
 
    template<class U> using rebind = U*;
 
    static constexpr pointer pointer_to(/* 见描述 */ r) noexcept;
  };
}

类 std::allocator_arg_t

namespace std {
  struct allocator_arg_t { explicit allocator_arg_t() = default; };
  inline constexpr allocator_arg_t allocator_arg{};
}

类模板 std::allocator_traits

namespace std {
  template<class Alloc> struct allocator_traits {
    using allocator_type     = Alloc;
 
    using value_type         = typename Alloc::value_type;
 
    using pointer            = /* 见描述 */;
    using const_pointer      = /* 见描述 */;
    using void_pointer       = /* 见描述 */;
    using const_void_pointer = /* 见描述 */;
 
    using difference_type    = /* 见描述 */;
    using size_type          = /* 见描述 */;
 
    using propagate_on_container_copy_assignment = /* 见描述 */;
    using propagate_on_container_move_assignment = /* 见描述 */;
    using propagate_on_container_swap            = /* 见描述 */;
    using is_always_equal                        = /* 见描述 */;
 
    template<class T> using rebind_alloc = /* 见描述 */;
    template<class T> using rebind_traits = allocator_traits<rebind_alloc<T>>;
 
    [[nodiscard]] static pointer allocate(Alloc& a, size_type n);
    [[nodiscard]] static pointer allocate(Alloc& a, size_type n,
                                          const_void_pointer hint);
 
    [[nodiscard]] static constexpr allocation_result<pointer, size_type>
        allocate_at_least(Alloc& a, size_type n);
 
    static void deallocate(Alloc& a, pointer p, size_type n);
 
    template<class T, class... Args>
      static void construct(Alloc& a, T* p, Args&&... args);
 
    template<class T>
      static void destroy(Alloc& a, T* p);
 
    static size_type max_size(const Alloc& a) noexcept;
 
    static Alloc select_on_container_copy_construction(const Alloc& rhs);
  };
}

类模板 std::allocator

namespace std {
  template<class T> class allocator {
   public:
    using value_type                             = T;
    using size_type                              = size_t;
    using difference_type                        = ptrdiff_t;
    using propagate_on_container_move_assignment = true_type;
 
    constexpr allocator() noexcept;
    constexpr allocator(const allocator&) noexcept;
    template<class U> constexpr allocator(const allocator<U>&) noexcept;
    constexpr ~allocator();
    constexpr allocator& operator=(const allocator&) = default;
 
    [[nodiscard]] constexpr T* allocate(size_t n);
    [[nodiscard]] constexpr allocation_result<T*> allocate_at_least(size_t n);
    constexpr void deallocate(T* p, size_t n);
 
    // 弃用
    using is_always_equal = true_type;
  };
}

类模板 std::default_delete

namespace std {
  template<class T> struct default_delete {
    constexpr default_delete() noexcept = default;
    template<class U> default_delete(const default_delete<U>&) noexcept;
    void operator()(T*) const;
  };
 
  template<class T> struct default_delete<T[]> {
    constexpr default_delete() noexcept = default;
    template<class U> default_delete(const default_delete<U[]>&) noexcept;
    template<class U> void operator()(U* ptr) const;
  };
}

类模板 std::unique_ptr

namespace std {
  template<class T, class D = default_delete<T>> class unique_ptr {
  public:
    using pointer      = /* 见描述 */;
    using element_type = T;
    using deleter_type = D;
 
    // 构造函数
    constexpr unique_ptr() noexcept;
    explicit unique_ptr(pointer p) noexcept;
    unique_ptr(pointer p, /* 见描述 */ d1) noexcept;
    unique_ptr(pointer p, /* 见描述 */ d2) noexcept;
    unique_ptr(unique_ptr&& u) noexcept;
    constexpr unique_ptr(nullptr_t) noexcept;
    template<class U, class E>
      unique_ptr(unique_ptr<U, E>&& u) noexcept;
 
    // 析构函数
    ~unique_ptr();
 
    // 赋值
    unique_ptr& operator=(unique_ptr&& u) noexcept;
    template<class U, class E>
      unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
    unique_ptr& operator=(nullptr_t) noexcept;
 
    // 观察器
    add_lvalue_reference_t<T> operator*() const noexcept(/* 见描述 */);
    pointer operator->() const noexcept;
    pointer get() const noexcept;
    deleter_type& get_deleter() noexcept;
    const deleter_type& get_deleter() const noexcept;
    explicit operator bool() const noexcept;
 
    // 修改器
    pointer release() noexcept;
    void reset(pointer p = pointer()) noexcept;
    void swap(unique_ptr& u) noexcept;
 
    // 禁用从左值复制
    unique_ptr(const unique_ptr&) = delete;
    unique_ptr& operator=(const unique_ptr&) = delete;
  };
 
  template<class T, class D> class unique_ptr<T[], D> {
  public:
    using pointer      = /* 见描述 */;
    using element_type = T;
    using deleter_type = D;
 
    // 构造函数
    constexpr unique_ptr() noexcept;
    template<class U> explicit unique_ptr(U p) noexcept;
    template<class U> unique_ptr(U p, /* 见描述 */ d) noexcept;
    template<class U> unique_ptr(U p, /* 见描述 */ d) noexcept;
    unique_ptr(unique_ptr&& u) noexcept;
    template<class U, class E>
      unique_ptr(unique_ptr<U, E>&& u) noexcept;
    constexpr unique_ptr(nullptr_t) noexcept;
 
    // 析构函数
    ~unique_ptr();
 
    // 赋值
    unique_ptr& operator=(unique_ptr&& u) noexcept;
    template<class U, class E>
      unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
    unique_ptr& operator=(nullptr_t) noexcept;
 
    // 观察器
    T& operator[](size_t i) const;
    pointer get() const noexcept;
    deleter_type& get_deleter() noexcept;
    const deleter_type& get_deleter() const noexcept;
    explicit operator bool() const noexcept;
 
    // 修改器
    pointer release() noexcept;
    template<class U> void reset(U p) noexcept;
    void reset(nullptr_t = nullptr) noexcept;
    void swap(unique_ptr& u) noexcept;
 
    // 禁用从左值复制
    unique_ptr(const unique_ptr&) = delete;
    unique_ptr& operator=(const unique_ptr&) = delete;
  };
}

类 std::bad_weak_ptr

namespace std {
  class bad_weak_ptr : public exception {
  public:
    bad_weak_ptr() noexcept;
  };
}

类模板 std::shared_ptr

namespace std {
  template<class T> class shared_ptr {
  public:
    using element_type = remove_extent_t<T>;
    using weak_type    = weak_ptr<T>;
 
    // 构造函数
    constexpr shared_ptr() noexcept;
    constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
    template<class Y>
      explicit shared_ptr(Y* p);
    template<class Y, class D>
      shared_ptr(Y* p, D d);
    template<class Y, class D, class A>
      shared_ptr(Y* p, D d, A a);
    template<class D>
      shared_ptr(nullptr_t p, D d);
    template<class D, class A>
      shared_ptr(nullptr_t p, D d, A a);
    template<class Y>
      shared_ptr(const shared_ptr<Y>& r, element_type* p) noexcept;
    template<class Y>
      shared_ptr(shared_ptr<Y>&& r, element_type* p) noexcept;
    shared_ptr(const shared_ptr& r) noexcept;
    template<class Y>
      shared_ptr(const shared_ptr<Y>& r) noexcept;
    shared_ptr(shared_ptr&& r) noexcept;
    template<class Y>
      shared_ptr(shared_ptr<Y>&& r) noexcept;
    template<class Y>
      explicit shared_ptr(const weak_ptr<Y>& r);
    template<class Y, class D>
      shared_ptr(unique_ptr<Y, D>&& r);
 
    // 析构函数
    ~shared_ptr();
 
    // 赋值
    shared_ptr& operator=(const shared_ptr& r) noexcept;
    template<class Y>
      shared_ptr& operator=(const shared_ptr<Y>& r) noexcept;
    shared_ptr& operator=(shared_ptr&& r) noexcept;
    template<class Y>
      shared_ptr& operator=(shared_ptr<Y>&& r) noexcept;
    template<class Y, class D>
      shared_ptr& operator=(unique_ptr<Y, D>&& r);
 
    // 修改器
    void swap(shared_ptr& r) noexcept;
    void reset() noexcept;
    template<class Y>
      void reset(Y* p);
    template<class Y, class D>
      void reset(Y* p, D d);
    template<class Y, class D, class A>
      void reset(Y* p, D d, A a);
 
    // 观察器
    element_type* get() const noexcept;
    T& operator*() const noexcept;
    T* operator->() const noexcept;
    element_type& operator[](ptrdiff_t i) const;
    long use_count() const noexcept;
    explicit operator bool() const noexcept;
    template<class U>
      bool owner_before(const shared_ptr<U>& b) const noexcept;
    template<class U>
      bool owner_before(const weak_ptr<U>& b) const noexcept;
  };
 
  template<class T>
    shared_ptr(weak_ptr<T>) -> shared_ptr<T>;
  template<class T, class D>
    shared_ptr(unique_ptr<T, D>) -> shared_ptr<T>;
}

类模板 std::weak_ptr

namespace std {
  template<class T> class weak_ptr {
  public:
    using element_type = remove_extent_t<T>;
 
    // 构造函数
    constexpr weak_ptr() noexcept;
    template<class Y>
      weak_ptr(const shared_ptr<Y>& r) noexcept;
    weak_ptr(const weak_ptr& r) noexcept;
    template<class Y>
      weak_ptr(const weak_ptr<Y>& r) noexcept;
    weak_ptr(weak_ptr&& r) noexcept;
    template<class Y>
      weak_ptr(weak_ptr<Y>&& r) noexcept;
 
    // 析构函数
    ~weak_ptr();
 
    // 赋值
    weak_ptr& operator=(const weak_ptr& r) noexcept;
    template<class Y>
      weak_ptr& operator=(const weak_ptr<Y>& r) noexcept;
    template<class Y>
      weak_ptr& operator=(const shared_ptr<Y>& r) noexcept;
    weak_ptr& operator=(weak_ptr&& r) noexcept;
    template<class Y>
      weak_ptr& operator=(weak_ptr<Y>&& r) noexcept;
 
    // 修改器
    void swap(weak_ptr& r) noexcept;
    void reset() noexcept;
 
    // 观察器
    long use_count() const noexcept;
    bool expired() const noexcept;
    shared_ptr<T> lock() const noexcept;
    template<class U>
      bool owner_before(const shared_ptr<U>& b) const noexcept;
    template<class U>
      bool owner_before(const weak_ptr<U>& b) const noexcept;
  };
 
  template<class T>
    weak_ptr(shared_ptr<T>) -> weak_ptr<T>;
}

类模板 std::owner_less

namespace std {
  template<class T = void> struct owner_less;
 
  template<class T> struct owner_less<shared_ptr<T>> {
    bool operator()(const shared_ptr<T>&, const shared_ptr<T>&) const noexcept;
    bool operator()(const shared_ptr<T>&, const weak_ptr<T>&) const noexcept;
    bool operator()(const weak_ptr<T>&, const shared_ptr<T>&) const noexcept;
  };
 
  template<class T> struct owner_less<weak_ptr<T>> {
    bool operator()(const weak_ptr<T>&, const weak_ptr<T>&) const noexcept;
    bool operator()(const shared_ptr<T>&, const weak_ptr<T>&) const noexcept;
    bool operator()(const weak_ptr<T>&, const shared_ptr<T>&) const noexcept;
  };
 
  template<> struct owner_less<void> {
    template<class T, class U>
      bool operator()(const shared_ptr<T>&, const shared_ptr<U>&) const noexcept;
    template<class T, class U>
      bool operator()(const shared_ptr<T>&, const weak_ptr<U>&) const noexcept;
    template<class T, class U>
      bool operator()(const weak_ptr<T>&, const shared_ptr<U>&) const noexcept;
    template<class T, class U>
      bool operator()(const weak_ptr<T>&, const weak_ptr<U>&) const noexcept;
 
    using is_transparent = /* 未指明 */;
  };
}

类模板 std::enable_shared_from_this

namespace std {
  template<class T> class enable_shared_from_this {
  protected:
    constexpr enable_shared_from_this() noexcept;
    enable_shared_from_this(const enable_shared_from_this&) noexcept;
    enable_shared_from_this& operator=(const enable_shared_from_this&) noexcept;
    ~enable_shared_from_this();
 
  public:
    shared_ptr<T> shared_from_this();
    shared_ptr<T const> shared_from_this() const;
    weak_ptr<T> weak_from_this() noexcept;
    weak_ptr<T const> weak_from_this() const noexcept;
 
  private:
    mutable weak_ptr<T> weak_this;  // 仅用于阐释
  };
}

类模板 std::atomic 对 std::shared_ptr 的特化

namespace std {
  template<class T> struct atomic<shared_ptr<T>> {
    using value_type = shared_ptr<T>;
    static constexpr bool is_always_lock_free = /* 由实现定义 */;
 
    bool is_lock_free() const noexcept;
    void store(shared_ptr<T> desired, memory_order order = memory_order::seq_cst) noexcept;
    shared_ptr<T> load(memory_order order = memory_order::seq_cst) const noexcept;
    operator shared_ptr<T>() const noexcept;
 
    shared_ptr<T> exchange(shared_ptr<T> desired,
                           memory_order order = memory_order::seq_cst) noexcept;
 
    bool compare_exchange_weak(shared_ptr<T>& expected, shared_ptr<T> desired,
                               memory_order success, memory_order failure) noexcept;
    bool compare_exchange_strong(shared_ptr<T>& expected, shared_ptr<T> desired,
                                 memory_order success, memory_order failure) noexcept;
 
    bool compare_exchange_weak(shared_ptr<T>& expected, shared_ptr<T> desired,
                               memory_order order = memory_order::seq_cst) noexcept;
    bool compare_exchange_strong(shared_ptr<T>& expected, shared_ptr<T> desired,
                                 memory_order order = memory_order::seq_cst) noexcept;
 
    constexpr atomic() noexcept = default;
    atomic(shared_ptr<T> desired) noexcept;
    atomic(const atomic&) = delete;
    void operator=(const atomic&) = delete;
    void operator=(shared_ptr<T> desired) noexcept;
 
  private:
    shared_ptr<T> p;            // 仅用于阐释
  };
}

类模板 std::atomic 对 std::weak_ptr 的特化

namespace std {
  template<class T> struct atomic<weak_ptr<T>> {
    using value_type = weak_ptr<T>;
    static constexpr bool is_always_lock_free = /* 由实现定义 */;
 
    bool is_lock_free() const noexcept;
    void store(weak_ptr<T> desired, memory_order order = memory_order::seq_cst) noexcept;
    weak_ptr<T> load(memory_order order = memory_order::seq_cst) const noexcept;
    operator weak_ptr<T>() const noexcept;
 
    weak_ptr<T> exchange(weak_ptr<T> desired,
                         memory_order order = memory_order::seq_cst) noexcept;
 
    bool compare_exchange_weak(weak_ptr<T>& expected, weak_ptr<T> desired,
                               memory_order success, memory_order failure) noexcept;
    bool compare_exchange_strong(weak_ptr<T>& expected, weak_ptr<T> desired,
                                 memory_order success, memory_order failure) noexcept;
 
    bool compare_exchange_weak(weak_ptr<T>& expected, weak_ptr<T> desired,
                               memory_order order = memory_order::seq_cst) noexcept;
    bool compare_exchange_strong(weak_ptr<T>& expected, weak_ptr<T> desired,
                                 memory_order order = memory_order::seq_cst) noexcept;
 
    constexpr atomic() noexcept = default;
    atomic(weak_ptr<T> desired) noexcept;
    atomic(const atomic&) = delete;
    void operator=(const atomic&) = delete;
    void operator=(weak_ptr<T> desired) noexcept;
 
  private:
    weak_ptr<T> p;              // 仅用于阐释
  };
}

类模板 std::out_ptr_t

namespace std {
  template<class Smart, class Pointer, class... Args>
  class out_ptr_t {
  public:
    explicit out_ptr_t(Smart&, Args...);
    out_ptr_t(const out_ptr_t&) = delete;
 
    ~out_ptr_t();
 
    operator Pointer*() const noexcept;
    operator void**() const noexcept;
 
  private:
    Smart& s;                   // 仅用于阐释
    tuple<Args...> a;           // 仅用于阐释
    Pointer p;                  // 仅用于阐释
  };
}

类模板 std::in_out_ptr_t

namespace std {
  template<class Smart, class Pointer, class... Args>
  class inout_ptr_t {
  public:
    explicit inout_ptr_t(Smart&, Args...);
    inout_ptr_t(const inout_ptr_t&) = delete;
 
    ~inout_ptr_t();
 
    operator Pointer*() const noexcept;
    operator void**() const noexcept;
 
  private:
    Smart& s;                   // 仅用于阐释
    tuple<Args...> a;           // 仅用于阐释
    Pointer p;                  // 仅用于阐释
  };
}
来自“https://zh.cppreference.com/mwiki/index.php?title=cpp/header/memory&oldid=76877”