std::nullopt

Defined in header `<optional>`
constexpr nullopt_t nullopt{/unspecified/};		(since C++14)

std::nullopt is a constant of type std::nullopt_t that is used to indicate optional type with uninitialized state.

(C++14)

indicator of optional type with uninitialized state
(class)

Language
Standard library headers
Concepts
Utilities library
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Type support (basic types, RTTI, type traits)
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rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
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pair
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swap
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declval (C++11)