Experimental library header <experimental/optional>

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Standard Library headers

Note: a slash '/' in a revision mark means that the header was deprecated and/or removed.

Language Support
<cstddef> <cstdlib> <version> (C++20) <limits> <climits>	<cfloat> <cstdint> (C++11) <new> <typeinfo>	<source_location> (C++20) <exception> <initializer_list> (C++11)   <compare> (C++20)	<coroutine> (C++20) <csignal> <csetjmp> <cstdarg>
Concepts
<concepts> (C++20)
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error> (C++11)
General utilities
<utility> <memory> <memory_resource> (C++17) <scoped_allocator> (C++11)   <expected> (C++23)	<bitset> <tuple> (C++11) <optional> (C++17) <any> (C++17)	<variant> (C++17) <type_traits> (C++11) <ratio> (C++11) <chrono> (C++11)	<typeindex> (C++11) <functional> <stacktrace> (C++23) <ctime>
Strings
<string> <string_view> (C++17) <cstring>	<charconv> (C++17) <format> (C++20)	<cctype> <cwctype>	<cwchar> <cuchar> (C++11)
Localization
<locale> <clocale>	<codecvt> (C++11/17)
Containers
<span> (C++20) <array> (C++11) <vector>	<deque> <forward_list> (C++11) <list>	<map> <set> <queue>	<unordered_map> (C++11) <unordered_set> (C++11) <stack>
Iterators
<iterator>
Ranges
<ranges> (C++20)
Algorithms
<algorithm>	<execution> (C++17)
Numerics
<complex> <random> (C++11)	<valarray> <numeric>	<bit> (C++20) <numbers> (C++20)	<cfenv> (C++11) <cmath>
Input/Output
<iosfwd> <ios> <iomanip> <streambuf>	<istream> <ostream> <iostream>	<syncstream> (C++20) <spanstream> (C++23) <sstream> <fstream>	<cstdio> <cinttypes> (C++11) <strstream> (C++98/)
Regular expressions
<regex> (C++11)
Filesystem support
<filesystem> (C++17)
Thread support
<thread> (C++11) <atomic> (C++11) <mutex> (C++11)	<shared_mutex> (C++14) <condition_variable> (C++11)   <future> (C++11)	<stop_token> (C++20) <semaphore> (C++20)	<latch> (C++20) <barrier> (C++20)
C compatibility
<cstdbool> (C++11/17/20) <ccomplex> (C++11/17/20)	<ctgmath> (C++11/17/20) <cstdalign> (C++11/17/20)	<ciso646> (until C++20) <stdatomic.h>

 

Experimental library headers

Filesystem TS
<experimental/filesystem>
Parallelism TS (v1, v2)
<experimental/algorithm> <experimental/execution_policy> <experimental/exception_list>	<experimental/numeric> <experimental/simd> <experimental/task_block>
Library Fundamentals 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>
Concurrency TS
<experimental/atomic> <experimental/barrier>	<experimental/future> <experimental/latch>
Ranges 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>
Coroutines TS
<experimental/coroutine>
Networking TS
<experimental/buffer> <experimental/executor> <experimental/internet> <experimental/io_context>	<experimental/net> <experimental/netfwd> <experimental/socket> <experimental/timer>
Reflection TS
<experimental/reflect>

 

This header is part of the Library Fundamentals TS (v1, v2).

Classes

Name	Description
optional (library fundamentals TS)	a wrapper that may or may not hold an object (class template)
bad_optional_access (library fundamentals TS)	exception indicating checked access to an optional that doesn't contain a value (class)
in_place_t (library fundamentals TS)	disambiguation tag type for in-place construction of optional types (class)
std::hash<std::experimental::optional>	specializes the std::hash algorithm (class template specialization)
nullopt_t (library fundamentals TS)	indicator of optional type with uninitialized state (class)

Functions

Comparison
operator==operator!=operator<operator<=operator>operator>=	compares optional objects (function template)
Specialized algorithms
std::swap(std::experimental::optional)	specializes the std::swap algorithm (function)
make_optional	creates an optional object (function template)
Hash support

Synopsis

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