virtual ~error_category();
Effects: Destroys an object of class
error_category. virtual const char* name() const noexcept = 0;
Returns: A string naming the error category
. virtual error_condition default_error_condition(int ev) const noexcept;
Returns:
error_condition(ev, *this). virtual bool equivalent(int code, const error_condition& condition) const noexcept;
Returns: default_error_condition(code) == condition. virtual bool equivalent(const error_code& code, int condition) const noexcept;
Returns: *this == code.category() && code.value() == condition. virtual string message(int ev) const = 0;
Returns: A string that describes the error condition denoted by
ev.