22 Diagnostics library [diagnostics]

22.5 System error support [syserr]

22.5.3 Class error_­code [syserr.errcode] Class error_­code overview [syserr.errcode.overview]

The class error_­code describes an object used to hold error code values, such as those originating from the operating system or other low-level application program interfaces.
Class error_­code is an adjunct to error reporting by exception.
end note
namespace std {
  class error_code {
    // [syserr.errcode.constructors], constructors
    error_code() noexcept;
    error_code(int val, const error_category& cat) noexcept;
    template <class ErrorCodeEnum>
      error_code(ErrorCodeEnum e) noexcept;

    // [syserr.errcode.modifiers], modifiers
    void assign(int val, const error_category& cat) noexcept;
    template <class ErrorCodeEnum>
      error_code& operator=(ErrorCodeEnum e) noexcept;
    void clear() noexcept;

    // [syserr.errcode.observers], observers
    int value() const noexcept;
    const error_category& category() const noexcept;
    error_condition default_error_condition() const noexcept;
    string message() const;
    explicit operator bool() const noexcept;

    int val_;                   // exposition only
    const error_category* cat_; // exposition only

  // [syserr.errcode.nonmembers], non-member functions
  error_code make_error_code(errc e) noexcept;

  template <class charT, class traits>
    basic_ostream<charT, traits>&
      operator<<(basic_ostream<charT, traits>& os, const error_code& ec);