19 Diagnostics library [diagnostics]

19.5 System error support [syserr]

19.5.3 Class error_code [syserr.errcode]

19.5.3.1 Class error_code overview [syserr.errcode.overview]

1

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);
}

19.5.3.2 Class error_code constructors [syserr.errcode.constructors]

error_code() noexcept;

1

Effects: Constructs an object of type error_code.

2

Postconditions: val_ == 0 and cat_ == &system_category().

error_code(int val, const error_category& cat) noexcept;

3

Effects: Constructs an object of type error_code.

4

Postconditions: val_ == val and cat_ == &cat.

template <class ErrorCodeEnum> error_code(ErrorCodeEnum e) noexcept;

5

Effects: Constructs an object of type error_code.

6

Postconditions: *this == make_error_code(e).

7

Remarks: This constructor shall not participate in overload resolution unless is_error_code_enum_v<ErrorCodeEnum> is true.

19.5.3.3 Class error_code modifiers [syserr.errcode.modifiers]

void assign(int val, const error_category& cat) noexcept;

1

Postconditions: val_ == val and cat_ == &cat.

template <class ErrorCodeEnum> error_code& operator=(ErrorCodeEnum e) noexcept;

2

Postconditions: *this == make_error_code(e).

3

Returns: *this.

4

Remarks: This operator shall not participate in overload resolution unless is_error_code_enum_v<ErrorCodeEnum> is true.

void clear() noexcept;

5

Postconditions: value() == 0 and category() == system_category().

19.5.3.4 Class error_code observers [syserr.errcode.observers]

int value() const noexcept;

1

Returns: val_.

const error_category& category() const noexcept;

2

Returns: *cat_.

error_condition default_error_condition() const noexcept;

3

Returns: category().default_error_condition(value()).

string message() const;

4

Returns: category().message(value()).

explicit operator bool() const noexcept;

5

Returns: value() != 0.

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

error_code make_error_code(errc e) noexcept;

1

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);

2

Effects: As if by: os << ec.category().name() << ':' << ec.value();