18 Diagnostics library [diagnostics]

18.5 System error support [syserr]

18.5.3 Class error_­code [syserr.errcode]

18.5.3.1 Overview [syserr.errcode.overview]

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#
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);
}

18.5.3.2 Constructors [syserr.errcode.constructors]

🔗
error_code() noexcept;
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Effects: Constructs an object of type error_­code.
2
#
Ensures: 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
#
Ensures: val_­ == val and cat_­ == &cat.
🔗
template<class ErrorCodeEnum> error_code(ErrorCodeEnum e) noexcept;
5
#
Effects: Constructs an object of type error_­code.
6
#
Ensures: *this == make_­error_­code(e).
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#
Remarks: This constructor shall not participate in overload resolution unless
is_­error_­code_­enum_­v<ErrorCodeEnum> is true.

18.5.3.3 Modifiers [syserr.errcode.modifiers]

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void assign(int val, const error_category& cat) noexcept;
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#
Ensures: val_­ == val and cat_­ == &cat.
🔗
template<class ErrorCodeEnum> error_code& operator=(ErrorCodeEnum e) noexcept;
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#
Ensures: *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;
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#
Ensures: value() == 0 and category() == system_­category().

18.5.3.4 Observers [syserr.errcode.observers]

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int value() const noexcept;
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Returns: val_­.
🔗
const error_category& category() const noexcept;
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Returns: *cat_­.
🔗
error_condition default_error_condition() const noexcept;
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#
Returns: category().default_­error_­condition(value()).
🔗
string message() const;
4
#
Returns: category().message(value()).
🔗
explicit operator bool() const noexcept;
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Returns: value() != 0.

18.5.3.5 Non-member functions [syserr.errcode.nonmembers]

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error_code make_error_code(errc e) noexcept;
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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);
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#
Effects: As if by: os << ec.category().name() << ':' << ec.value();