# std::nullopt_t

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< cpp‎ | utility‎ | optional

Defined in header `<optional>` |  |
struct nullopt_t; |  | (since C++17)

`std::nullopt_t` is an empty class type used to indicate that an std::optional does not contain a value.

`std::nullopt_t` is a non-aggregate LiteralType that has no default constructor, no initializer-list constructor, but does have a `constexpr` constructor that takes an implementation-defined literal type.

### Notes

The constraints on `nullopt_t`'s constructors exist to support both op = {}; and op = nullopt; as the syntax for disengaging an optional object.

A possible implementation of this class is

    struct nullopt_t {
        constexpr explicit nullopt_t(int) {}
    };

### See also

nullopt (C++17) | an object of type `nullopt_t` (constant)

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