22 Diagnostics library [diagnostics]

22.5 System error support [syserr]

22.5.1 Header <system_­error> synopsis [system_error.syn]

namespace std {
  class error_category;
  const error_category& generic_category() noexcept;
  const error_category& system_category() noexcept;

  class error_code;
  class error_condition;
  class system_error;

  template<class T>
    struct is_error_code_enum : public false_type {};

  template<class T>
    struct is_error_condition_enum : public false_type {};

  enum class errc {
    address_family_not_supported,       // EAFNOSUPPORT
    address_in_use,                     // EADDRINUSE
    address_not_available,              // EADDRNOTAVAIL
    already_connected,                  // EISCONN
    argument_list_too_long,             // E2BIG
    argument_out_of_domain,             // EDOM
    bad_address,                        // EFAULT
    bad_file_descriptor,                // EBADF
    bad_message,                        // EBADMSG
    broken_pipe,                        // EPIPE
    connection_aborted,                 // ECONNABORTED
    connection_already_in_progress,     // EALREADY
    connection_refused,                 // ECONNREFUSED
    connection_reset,                   // ECONNRESET
    cross_device_link,                  // EXDEV
    destination_address_required,       // EDESTADDRREQ
    device_or_resource_busy,            // EBUSY
    directory_not_empty,                // ENOTEMPTY
    executable_format_error,            // ENOEXEC
    file_exists,                        // EEXIST
    file_too_large,                     // EFBIG
    filename_too_long,                  // ENAMETOOLONG
    function_not_supported,             // ENOSYS
    host_unreachable,                   // EHOSTUNREACH
    identifier_removed,                 // EIDRM
    illegal_byte_sequence,              // EILSEQ
    inappropriate_io_control_operation, // ENOTTY
    interrupted,                        // EINTR
    invalid_argument,                   // EINVAL
    invalid_seek,                       // ESPIPE
    io_error,                           // EIO
    is_a_directory,                     // EISDIR
    message_size,                       // EMSGSIZE
    network_down,                       // ENETDOWN
    network_reset,                      // ENETRESET
    network_unreachable,                // ENETUNREACH
    no_buffer_space,                    // ENOBUFS
    no_child_process,                   // ECHILD
    no_link,                            // ENOLINK
    no_lock_available,                  // ENOLCK
    no_message_available,               // ENODATA
    no_message,                         // ENOMSG
    no_protocol_option,                 // ENOPROTOOPT
    no_space_on_device,                 // ENOSPC
    no_stream_resources,                // ENOSR
    no_such_device_or_address,          // ENXIO
    no_such_device,                     // ENODEV
    no_such_file_or_directory,          // ENOENT
    no_such_process,                    // ESRCH
    not_a_directory,                    // ENOTDIR
    not_a_socket,                       // ENOTSOCK
    not_a_stream,                       // ENOSTR
    not_connected,                      // ENOTCONN
    not_enough_memory,                  // ENOMEM
    not_supported,                      // ENOTSUP
    operation_canceled,                 // ECANCELED
    operation_in_progress,              // EINPROGRESS
    operation_not_permitted,            // EPERM
    operation_not_supported,            // EOPNOTSUPP
    operation_would_block,              // EWOULDBLOCK
    owner_dead,                         // EOWNERDEAD
    permission_denied,                  // EACCES
    protocol_error,                     // EPROTO
    protocol_not_supported,             // EPROTONOSUPPORT
    read_only_file_system,              // EROFS
    resource_deadlock_would_occur,      // EDEADLK
    resource_unavailable_try_again,     // EAGAIN
    result_out_of_range,                // ERANGE
    state_not_recoverable,              // ENOTRECOVERABLE
    stream_timeout,                     // ETIME
    text_file_busy,                     // ETXTBSY
    timed_out,                          // ETIMEDOUT
    too_many_files_open_in_system,      // ENFILE
    too_many_files_open,                // EMFILE
    too_many_links,                     // EMLINK
    too_many_symbolic_link_levels,      // ELOOP
    value_too_large,                    // EOVERFLOW
    wrong_protocol_type,                // EPROTOTYPE
  };

  template<> struct is_error_condition_enum<errc> : true_type {};

  // [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);

  // [syserr.errcondition.nonmembers], non-member functions
  error_condition make_error_condition(errc e) noexcept;

  // [syserr.compare], comparison functions
  bool operator<(const error_code& lhs, const error_code& rhs) noexcept;
  bool operator<(const error_condition& lhs, const error_condition& rhs) noexcept;
  bool operator==(const error_code& lhs, const error_code& rhs) noexcept;
  bool operator==(const error_code& lhs, const error_condition& rhs) noexcept;
  bool operator==(const error_condition& lhs, const error_code& rhs) noexcept;
  bool operator==(const error_condition& lhs, const error_condition& rhs) noexcept;
  bool operator!=(const error_code& lhs, const error_code& rhs) noexcept;
  bool operator!=(const error_code& lhs, const error_condition& rhs) noexcept;
  bool operator!=(const error_condition& lhs, const error_code& rhs) noexcept;
  bool operator!=(const error_condition& lhs, const error_condition& rhs) noexcept;

  // [syserr.hash], hash support
  template<class T> struct hash;
  template<> struct hash<error_code>;
  template<> struct hash<error_condition>;

  // [syserr], system error support
  template<class T>
    inline constexpr bool is_error_code_enum_v = is_error_code_enum<T>::value;
  template<class T>
    inline constexpr bool is_error_condition_enum_v = is_error_condition_enum<T>::value;
}
The value of each enum errc constant shall be the same as the value of the <cerrno> macro shown in the above synopsis.
Whether or not the <system_­error> implementation exposes the <cerrno> macros is unspecified.
The is_­error_­code_­enum and is_­error_­condition_­enum may be specialized for user-defined types to indicate that such types are eligible for class error_­code and class error_­condition automatic conversions, respectively.