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; bool operator<(const error_code& lhs, const error_code& rhs) noexcept; template <class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& os, const error_code& ec); } // namespace std