18 Diagnostics library [diagnostics]

18.5 System error support [syserr]

18.5.4 Class error_­condition [syserr.errcondition]

18.5.4.4 Observers [syserr.errcondition.observers]

int value() const noexcept;
Returns: val_­.
const error_category& category() const noexcept;
Returns: *cat_­.
string message() const;
Returns: category().message(value()).
explicit operator bool() const noexcept;
Returns: value() != 0.