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[syserr.errcat.overview]
19 Diagnostics library [diagnostics]
19.5 System error support [syserr]
19.5.3 Class error_category [syserr.errcat]
19.5.3.1 Overview [syserr.errcat.overview]
The class error_category serves as a base class for types used to identify the source and encoding of a particular category of error code.
Classes may be derived from error_category to support categories of errors in addition to those defined in this document.
Such classes shall behave as specified in subclause [syserr.errcat].
[Note 1:
error_category objects are passed by reference, and two such objects are equal if they have the same address.
If there is more than a single object of a custom error_category type, such equality comparisons can evaluate to false even for objects holding the same value.
â end note]
namespace std {class error_category {public:constexpr error_category() noexcept; virtual ~error_category(); error_category(const error_category&) = delete; error_category& operator=(const error_category&) = delete; virtual const char* name() const noexcept = 0; virtual error_condition default_error_condition(int ev) const noexcept; virtual bool equivalent(int code, const error_condition& condition) const noexcept; virtual bool equivalent(const error_code& code, int condition) const noexcept; virtual string message(int ev) const = 0; bool operator==(const error_category& rhs) const noexcept; strong_ordering operator<=>(const error_category& rhs) const noexcept; }; const error_category& generic_category() noexcept; const error_category& system_category() noexcept;}