std::experimental::nullopt

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Defined in header <experimental/optional>
constexpr nullopt_t nullopt{/*unspecified*/};
(library fundamentals TS)

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

[edit] See also

(library fundamentals TS)
indicator of optional type with uninitialized state
(class)