19 Diagnostics library [diagnostics]

19.5 System error support [syserr]

19.5.4 Class error_­code [syserr.errcode]

19.5.4.1 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 1:
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); }

19.5.4.2 Constructors [syserr.errcode.constructors]

error_code() noexcept;
Effects: Initializes val_­ with 0 and cat_­ with &system_­category().
error_code(int val, const error_category& cat) noexcept;
Effects: Initializes val_­ with val and cat_­ with &cat.
template<class ErrorCodeEnum> error_code(ErrorCodeEnum e) noexcept;
Constraints: is_­error_­code_­enum_­v<ErrorCodeEnum> is true.
Effects: Equivalent to: error_code ec = make_error_code(e); assign(ec.value(), ec.category());

19.5.4.3 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;
Constraints: is_­error_­code_­enum_­v<ErrorCodeEnum> is true.
Effects: Equivalent to: error_code ec = make_error_code(e); assign(ec.value(), ec.category());
Returns: *this.
void clear() noexcept;
Postconditions: value() == 0 and category() == system_­category().

19.5.4.4 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.

19.5.4.5 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: Equivalent to: return os << ec.category().name() << ':' << ec.value();