std::nullopt - cppreference.com

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Utilities library

Language support

Type support (basic types, RTTI)

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initializer_list

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source_location

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Three-way comparison

three_way_comparablethree_way_comparable_with

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(C++20)

partial_ordering

(C++20)

common_comparison_category

(C++20)

compare_three_way_result

(C++20)

(C++20)

(C++20)

(C++20)

(C++20)

compare_strong_order_fallback

(C++20)

compare_weak_order_fallback

(C++20)

compare_partial_order_fallback

(C++20)

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(C++20)(C++20)(C++20)

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cmp_equalcmp_lesscmp_less_than

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cmp_not_equalcmp_greatercmp_greater_than

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pair
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variant (C++17)

tuple_size (C++11)
tuple_element (C++11)
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expected (C++23)

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std::optional

Member functions
optional::optional
optional::~optional
optional::operator=
Observers
optional::operator->optional::operator*
optional::operator booloptional::has_value
optional::value
optional::value_or
Iterators
optional::begin (C++26)
optional::end (C++26)
Monadic operations
optional::and_then (C++23)
optional::transform (C++23)
optional::or_else (C++23)
Modifiers
optional::emplace
optional::swap
optional::reset
Non-member functions
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)
make_optional
swap(std::optional)
Deduction guides
Helper classes
hash<std::optional>
nullopt_t
in_place_t
bad_optional_access
Helper objects
nullopt
in_place

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Defined in header `<optional>`
`inline constexpr nullopt_t nullopt{/unspecified/};`		(since C++17)

std::nullopt is a constant of type std::nullopt_t. Used to indicate that an std::optional does not contain a value.

See also