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std::nullopt

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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.

[edit] See also

(C++17)
indicator of an std::optional that does not contain a value
(class) [edit]
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