实验性库头文件 <experimental/optional>

 

C++

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标准库头文件

命名要求

特性测试宏 (C++20)

语言支持库

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技术规范

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外部库

 

标准库头文件

语言支持 <cfloat> <climits> <compare> (C++20) <contracts> (C++26) <coroutine> (C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint> (C++11) <cstdlib> <exception> <initializer_list> (C++11)    <limits> <new> <source_location> (C++20) <stdfloat> (C++23) <typeinfo> <version> (C++20) 概念 <concepts> (C++20) 诊断 <cassert> <cerrno> <debugging> (C++26) <stacktrace> (C++23) <stdexcept> <system_error> (C++11) 内存管理 <memory> <memory_resource> (C++17) <scoped_allocator> (C++11) 元编程 <type_traits> (C++11) <ratio> (C++11)

通用工具 <any> (C++17) <bitset> <bit> (C++20) <charconv> (C++17) <expected> (C++23) <format> (C++20) <functional> <optional> (C++17) <tuple> (C++11) <typeindex> (C++11) <utility> <variant> (C++17) 容器 <array> (C++11) <deque> <flat_map> (C++23) <flat_set> (C++23) <forward_list> (C++11) <hive> (C++26) <inplace_vector> (C++26)    <list> <map> <mdspan> (C++23) <queue> <set> <span> (C++20) <stack> <unordered_map> (C++11) <unordered_set> (C++11) <vector> 迭代器 <iterator> 范围 <generator> (C++23) <ranges> (C++20)

算法 <algorithm> <numeric> 字符串 <cctype> <cstring> <cuchar> (C++11) <cwchar> <cwctype> <string_view> (C++17) <string> 文本处理 <clocale> <codecvt> (C++11/17/26*) <locale> <regex> (C++11) <text_encoding> (C++26)    数值 <cfenv> (C++11) <cmath> <complex> <linalg> (C++26) <numbers> (C++20) <random> (C++11) <simd> (C++26) <valarray> 时间 <chrono> (C++11) <ctime> C 兼容性 <ccomplex> (C++11/17/20*) <ciso646> (until C++20) <cstdalign> (C++11/17/20*) <cstdbool> (C++11/17/20*) <ctgmath> (C++11/17/20*)

输入/输出 <cinttypes> (C++11) <cstdio> <filesystem> (C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print> (C++23) <spanstream> (C++23) <sstream> <streambuf> <strstream> (C++98/26*) <syncstream> (C++20) 并发支持 <atomic> (C++11) <barrier> (C++20) <condition_variable> (C++11) <future> (C++11) <hazard_pointer> (C++26) <latch> (C++20) <mutex> (C++11) <rcu> (C++26) <semaphore> (C++20) <shared_mutex> (C++14) <stdatomic.h> (C++23) <stop_token> (C++20) <thread> (C++11) 执行支持 <execution> (C++17)

 

实验性库头文件

执行 P2300
<experimental/execution>
文件系统 TS
<experimental/filesystem>
并行 TS (v1, v2)
experimental/algorithm experimental/execution_policy experimental/exception_list	experimental/numeric <experimental/simd> experimental/task_block
库基础 TS (v1, v2, v3)
experimental/algorithm <experimental/any> experimental/array experimental/chrono experimental/deque experimental/forward_list <experimental/functional> experimental/future experimental/iterator experimental/list experimental/map experimental/memory <experimental/memory_resource> experimental/numeric <experimental/optional> experimental/propagate_const	experimental/random experimental/ratio experimental/regex experimental/scope experimental/set experimental/source_location experimental/string <experimental/string_view> experimental/system_error experimental/tuple experimental/type_traits experimental/unordered_map experimental/unordered_set experimental/utility experimental/vector
并发 TS
experimental/atomic experimental/barrier	experimental/future experimental/latch
范围 TS
<experimental/ranges/algorithm> <experimental/ranges/concepts> <experimental/ranges/functional>         <experimental/ranges/iterator>	<experimental/ranges/random> <experimental/ranges/tuple> <experimental/ranges/type_traits> <experimental/ranges/utility>
协程 TS
experimental/coroutine
网络 TS
experimental/buffer experimental/executor experimental/internet experimental/io_context	<experimental/net> experimental/netfwd experimental/socket experimental/timer
反射 TS
<experimental/reflect>

 

此头文件是库基础 TS 的一部分 (v1, v2)。

类

名称	描述
optional (库基础 TS)	可能包含或不包含对象的包装器 (类模板)
bad_optional_access (库基础 TS)	指示对不包含值的 optional 进行检查访问的异常 (类)
in_place_t (库基础 TS)	用于 optional 类型就地构造的消歧标签类型 (类)
std::hash<std::experimental::optional>	专门化 std::hash 算法 (类模板特化)
nullopt_t (库基础 TS)	具有未初始化状态的 optional 类型的指示符 (类)

函数

比较
operator==operator!=operator<operator<=operator>operator>=	比较 optional 对象 (函数模板)
专用算法
std::swap(std::experimental::optional)	专门化 std::swap 算法 (函数)
make_optional	创建 optional 对象 (函数模板)
哈希支持

概要

namespace std {
  namespace experimental {
  inline namespace fundamentals_v1 {
 
    // 5.4, optional for object types
    template <class T> class optional;
 
    // 5.5, In-place construction
    struct in_place_t{};
    constexpr in_place_t in_place{};
 
    // 5.6, Disengaged state indicator
    struct nullopt_t{see below};
    constexpr nullopt_t nullopt(unspecified);
 
    // 5.7, Class bad_optional_access
    class bad_optional_access;
 
    // 5.8, Relational operators
    template <class T>
      constexpr bool operator==(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator!=(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator<(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator>(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator<=(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator>=(const optional<T>&, const optional<T>&);
 
    // 5.9, Comparison with nullopt
    template <class T> constexpr bool operator==(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator==(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator!=(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator!=(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator<(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator<(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator<=(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator<=(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator>(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator>(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator>=(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator>=(nullopt_t, const optional<T>&) noexcept;
 
    // 5.10, Comparison with T
    template <class T> constexpr bool operator==(const optional<T>&, const T&);
    template <class T> constexpr bool operator==(const T&, const optional<T>&);
    template <class T> constexpr bool operator!=(const optional<T>&, const T&);
    template <class T> constexpr bool operator!=(const T&, const optional<T>&);
    template <class T> constexpr bool operator<(const optional<T>&, const T&);
    template <class T> constexpr bool operator<(const T&, const optional<T>&);
    template <class T> constexpr bool operator<=(const optional<T>&, const T&);
    template <class T> constexpr bool operator<=(const T&, const optional<T>&);
    template <class T> constexpr bool operator>(const optional<T>&, const T&);
    template <class T> constexpr bool operator>(const T&, const optional<T>&);
    template <class T> constexpr bool operator>=(const optional<T>&, const T&);
    template <class T> constexpr bool operator>=(const T&, const optional<T>&);
 
    // 5.11, Specialized algorithms
    template <class T> void swap(optional<T>&, optional<T>&) noexcept(see below);
    template <class T> constexpr optional<see below> make_optional(T&&);
 
  } // namespace fundamentals_v1
  } // namespace experimental
 
  // 5.12, Hash support
  template <class T> struct hash;
  template <class T> struct hash<experimental::optional<T>>;
 
} // namespace std