22 Diagnostics library [diagnostics]

22.5 System error support [syserr]

22.5.3 Class error_­code [syserr.errcode]

22.5.3.1 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.
[Note
:
Class error_­code is an adjunct to error reporting by exception.
end note
]
namespace std {
  class error_code {
  public:
    // [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;

  private:
    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);
}

22.5.3.2 Class error_­code constructors [syserr.errcode.constructors]

error_code() noexcept;
Effects: Constructs an object of type error_­code.
Postconditions: val_­ == 0 and cat_­ == &system_­category().
error_code(int val, const error_category& cat) noexcept;
Effects: Constructs an object of type error_­code.
Postconditions: val_­ == val and cat_­ == &cat.
template<class ErrorCodeEnum> error_code(ErrorCodeEnum e) noexcept;
Effects: Constructs an object of type error_­code.
Postconditions: *this == make_­error_­code(e).
Remarks: This constructor shall not participate in overload resolution unless
is_­error_­code_­enum_­v<ErrorCodeEnum> is true.

22.5.3.3 Class error_­code modifiers [syserr.errcode.modifiers]

void assign(int val, const error_category& cat) noexcept;
Postconditions: val_­ == val and cat_­ == &cat.
template<class ErrorCodeEnum> error_code& operator=(ErrorCodeEnum e) noexcept;
Postconditions: *this == make_­error_­code(e).
Returns: *this.
Remarks: This operator shall not participate in overload resolution unless
is_­error_­code_­enum_­v<ErrorCodeEnum> is true.
void clear() noexcept;
Postconditions: value() == 0 and category() == system_­category().

22.5.3.4 Class error_­code observers [syserr.errcode.observers]

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

22.5.3.5 Class error_­code non-member functions [syserr.errcode.nonmembers]

error_code make_error_code(errc e) noexcept;
Returns: error_­code(static_­cast<int>(e), generic_­category()).
template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const error_code& ec);
Effects: As if by: os << ec.category().name() << ':' << ec.value();