| Technical Specification | ||||
| Filesystem library(filesystem TS) | ||||
| Library fundamentals(library fundamentals TS) | ||||
| Library fundamentals 2(library fundamentals TS v2) | ||||
| Library fundamentals 3(library fundamentals TS v3) | ||||
| Extensions for parallelism(parallelism TS) | ||||
| Extensions for parallelism 2(parallelism TS v2) | ||||
| Extensions for concurrency(concurrency TS) | ||||
| Extensions for concurrency 2(concurrency TS v2) | ||||
| Concepts(concepts TS) | ||||
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| Mathematical special functions(special functions TR) | ||||
| Experimental Non-TS | ||||
| Pattern Matching | ||||
| Linear Algebra | ||||
| std::execution | ||||
| Contracts | ||||
| 2D Graphics |
| Member functions | ||||
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| Helper classes | ||||
nullopt_t | ||||
| Helper objects | ||||
Defined in header <experimental/optional> | ||
struct nullopt_t; | (library fundamentals TS) | |
std::experimental::nullopt_t is an empty class type used to indicateoptional type with uninitialized state. In particular,std::experimental::optional has a constructor withnullopt_t as a single argument, which creates an optional that does not contain a value.
std::experimental::nullopt_t must be aLiteralType and cannot have a default constructor.
It must have aconstexpr constructor that takes some implementation-defined literal type.
nullopt_t is notDefaultConstructible to support bothop={}; andop= nullopt; as the syntax for disengaging an optional object.
A possible implementation of this class is
struct nullopt_t{constexpr nullopt_t(int){}};
(C++17) | an object of typenullopt_t(constant)[edit] |
