std::nullopt

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

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

See also

(C++17)
 indicator of optional type with uninitialized state
(class)