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{{cpp/title|nullopt_t}}
{{cpp/utility/optional/navbar}}
{{dcl begin}}
{{dcl header | optional}}
{{dcl | since=c++17 |1=
struct nullopt_t;
}}
{{dcl end}}

{{tt|std::nullopt_t}} is an empty class type used to indicate that an {{lc|std::optional}} does not contain a value.

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

===Notes===
The constraints on {{tt|nullopt_t}}'s constructors exist to support both {{c|1=op = {};}} and {{c|1=op = nullopt;}} as the syntax for disengaging an optional object. 

A possible implementation of this class is
{{source|
struct nullopt_t {
    constexpr explicit nullopt_t(int) {}
};
}}

===See also===
{{dsc begin}}
{{dsc inc | cpp/utility/dsc nullopt}}
{{dsc end}}

{{langlinks|es|ja|ru|zh}}

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