22 Diagnostics library [diagnostics]

22.1 General [diagnostics.general]

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This Clause describes components that C++ programs may use to detect and report error conditions.

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The following subclauses describe components for reporting several kinds of exceptional conditions, documenting program assertions, and a global variable for error number codes, as summarized in Table 33.

Table 33 — Diagnostics library summary
Subclause Header(s)
[std.exceptions] Exception classes <stdexcept>
[assertions] Assertions <cassert>
[errno] Error numbers <cerrno>
[syserr] System error support <system_­error>

22.2 Exception classes [std.exceptions]

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The C++ standard library provides classes to be used to report certain errors ([res.on.exception.handling]) in C++ programs. In the error model reflected in these classes, errors are divided into two broad categories: logic errors and runtime errors.

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The distinguishing characteristic of logic errors is that they are due to errors in the internal logic of the program. In theory, they are preventable.

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By contrast, runtime errors are due to events beyond the scope of the program. They cannot be easily predicted in advance. The header <stdexcept> defines several types of predefined exceptions for reporting errors in a C++ program. These exceptions are related by inheritance.

22.2.1 Header <stdexcept> synopsis [stdexcept.syn]

namespace std {
  class logic_error;
    class domain_error;
    class invalid_argument;
    class length_error;
    class out_of_range;
  class runtime_error;
    class range_error;
    class overflow_error;
    class underflow_error;
}

22.2.2 Class logic_­error [logic.error]

namespace std {
  class logic_error : public exception {
  public:
    explicit logic_error(const string& what_arg);
    explicit logic_error(const char* what_arg);
  };
}
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The class logic_­error defines the type of objects thrown as exceptions to report errors presumably detectable before the program executes, such as violations of logical preconditions or class invariants.

logic_error(const string& what_arg);

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Effects: Constructs an object of class logic_­error.

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Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

logic_error(const char* what_arg);

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Effects: Constructs an object of class logic_­error.

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Postconditions: strcmp(what(), what_­arg) == 0.

22.2.3 Class domain_­error [domain.error]

namespace std {
  class domain_error : public logic_error {
  public:
    explicit domain_error(const string& what_arg);
    explicit domain_error(const char* what_arg);
  };
}
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The class domain_­error defines the type of objects thrown as exceptions by the implementation to report domain errors.

domain_error(const string& what_arg);

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Effects: Constructs an object of class domain_­error.

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Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

domain_error(const char* what_arg);

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Effects: Constructs an object of class domain_­error.

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Postconditions: strcmp(what(), what_­arg) == 0.

22.2.4 Class invalid_­argument [invalid.argument]

namespace std {
  class invalid_argument : public logic_error {
  public:
    explicit invalid_argument(const string& what_arg);
    explicit invalid_argument(const char* what_arg);
  };
}
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The class invalid_­argument defines the type of objects thrown as exceptions to report an invalid argument.

invalid_argument(const string& what_arg);

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Effects: Constructs an object of class invalid_­argument.

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Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

invalid_argument(const char* what_arg);

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Effects: Constructs an object of class invalid_­argument.

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Postconditions: strcmp(what(), what_­arg) == 0.

22.2.5 Class length_­error [length.error]

namespace std {
  class length_error : public logic_error {
  public:
    explicit length_error(const string& what_arg);
    explicit length_error(const char* what_arg);
  };
}
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The class length_­error defines the type of objects thrown as exceptions to report an attempt to produce an object whose length exceeds its maximum allowable size.

length_error(const string& what_arg);

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Effects: Constructs an object of class length_­error.

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Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

length_error(const char* what_arg);

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Effects: Constructs an object of class length_­error.

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Postconditions: strcmp(what(), what_­arg) == 0.

22.2.6 Class out_­of_­range [out.of.range]

namespace std {
  class out_of_range : public logic_error {
  public:
    explicit out_of_range(const string& what_arg);
    explicit out_of_range(const char* what_arg);
  };
}
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The class out_­of_­range defines the type of objects thrown as exceptions to report an argument value not in its expected range.

out_of_range(const string& what_arg);

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Effects: Constructs an object of class out_­of_­range.

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Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

out_of_range(const char* what_arg);

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#

Effects: Constructs an object of class out_­of_­range.

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#

Postconditions: strcmp(what(), what_­arg) == 0.

22.2.7 Class runtime_­error [runtime.error]

namespace std {
  class runtime_error : public exception {
  public:
    explicit runtime_error(const string& what_arg);
    explicit runtime_error(const char* what_arg);
  };
}
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The class runtime_­error defines the type of objects thrown as exceptions to report errors presumably detectable only when the program executes.

runtime_error(const string& what_arg);

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Effects: Constructs an object of class runtime_­error.

3
#

Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

runtime_error(const char* what_arg);

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#

Effects: Constructs an object of class runtime_­error.

5
#

Postconditions: strcmp(what(), what_­arg) == 0.

22.2.8 Class range_­error [range.error]

namespace std {
  class range_error : public runtime_error {
  public:
    explicit range_error(const string& what_arg);
    explicit range_error(const char* what_arg);
  };
}
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The class range_­error defines the type of objects thrown as exceptions to report range errors in internal computations.

range_error(const string& what_arg);

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Effects: Constructs an object of class range_­error.

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Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

range_error(const char* what_arg);

4
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Effects: Constructs an object of class range_­error.

5
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Postconditions: strcmp(what(), what_­arg) == 0.

22.2.9 Class overflow_­error [overflow.error]

namespace std {
  class overflow_error : public runtime_error {
  public:
    explicit overflow_error(const string& what_arg);
    explicit overflow_error(const char* what_arg);
  };
}
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The class overflow_­error defines the type of objects thrown as exceptions to report an arithmetic overflow error.

overflow_error(const string& what_arg);

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Effects: Constructs an object of class overflow_­error.

3
#

Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

overflow_error(const char* what_arg);

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Effects: Constructs an object of class overflow_­error.

5
#

Postconditions: strcmp(what(), what_­arg) == 0.

22.2.10 Class underflow_­error [underflow.error]

namespace std {
  class underflow_error : public runtime_error {
  public:
    explicit underflow_error(const string& what_arg);
    explicit underflow_error(const char* what_arg);
  };
}
1
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The class underflow_­error defines the type of objects thrown as exceptions to report an arithmetic underflow error.

underflow_error(const string& what_arg);

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Effects: Constructs an object of class underflow_­error.

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#

Postconditions: strcmp(what(), what_­arg.c_­str()) == 0.

underflow_error(const char* what_arg);

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Effects: Constructs an object of class underflow_­error.

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Postconditions: strcmp(what(), what_­arg) == 0.

22.3 Assertions [assertions]

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The header <cassert> provides a macro for documenting C++ program assertions and a mechanism for disabling the assertion checks.

22.3.1 Header <cassert> synopsis [cassert.syn]

#define assert(E) see below
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The contents are the same as the C standard library header <assert.h>, except that a macro named static_­assert is not defined.

See also: ISO C 7.2.

22.3.2 The assert macro [assertions.assert]

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An expression assert(E) is a constant subexpression, if

22.4 Error numbers [errno]

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The contents of the header <cerrno> are the same as the POSIX header <errno.h>, except that errno shall be defined as a macro. [ Note: The intent is to remain in close alignment with the POSIX standard.  — end note ] A separate errno value shall be provided for each thread.

22.4.1 Header <cerrno> synopsis [cerrno.syn]

#define errno see below

#define E2BIG see below
#define EACCES see below
#define EADDRINUSE see below
#define EADDRNOTAVAIL see below
#define EAFNOSUPPORT see below
#define EAGAIN see below
#define EALREADY see below
#define EBADF see below
#define EBADMSG see below
#define EBUSY see below
#define ECANCELED see below
#define ECHILD see below
#define ECONNABORTED see below
#define ECONNREFUSED see below
#define ECONNRESET see below
#define EDEADLK see below
#define EDESTADDRREQ see below
#define EDOM see below
#define EEXIST see below
#define EFAULT see below
#define EFBIG see below
#define EHOSTUNREACH see below
#define EIDRM see below
#define EILSEQ see below
#define EINPROGRESS see below
#define EINTR see below
#define EINVAL see below
#define EIO see below
#define EISCONN see below
#define EISDIR see below
#define ELOOP see below
#define EMFILE see below
#define EMLINK see below
#define EMSGSIZE see below
#define ENAMETOOLONG see below
#define ENETDOWN see below
#define ENETRESET see below
#define ENETUNREACH see below
#define ENFILE see below
#define ENOBUFS see below
#define ENODATA see below
#define ENODEV see below
#define ENOENT see below
#define ENOEXEC see below
#define ENOLCK see below
#define ENOLINK see below
#define ENOMEM see below
#define ENOMSG see below
#define ENOPROTOOPT see below
#define ENOSPC see below
#define ENOSR see below
#define ENOSTR see below
#define ENOSYS see below
#define ENOTCONN see below
#define ENOTDIR see below
#define ENOTEMPTY see below
#define ENOTRECOVERABLE see below
#define ENOTSOCK see below
#define ENOTSUP see below
#define ENOTTY see below
#define ENXIO see below
#define EOPNOTSUPP see below
#define EOVERFLOW see below
#define EOWNERDEAD see below
#define EPERM see below
#define EPIPE see below
#define EPROTO see below
#define EPROTONOSUPPORT see below
#define EPROTOTYPE see below
#define ERANGE see below
#define EROFS see below
#define ESPIPE see below
#define ESRCH see below
#define ETIME see below
#define ETIMEDOUT see below
#define ETXTBSY see below
#define EWOULDBLOCK see below
#define EXDEV see below
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The meaning of the macros in this header is defined by the POSIX standard.

See also: ISO C 7.5.

22.5 System error support [syserr]

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This subclause describes components that the standard library and C++ programs may use to report error conditions originating from the operating system or other low-level application program interfaces.

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Components described in this subclause shall not change the value of errno. Implementations should leave the error states provided by other libraries unchanged.

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;
}
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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.

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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.

22.5.2 Class error_­category [syserr.errcat]

22.5.2.1 Class error_­category overview [syserr.errcat.overview]

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The class error_­category serves as a base class for types used to identify the source and encoding of a particular category of error code. Classes may be derived from error_­category to support categories of errors in addition to those defined in this International Standard. Such classes shall behave as specified in this subclause. [ Note: error_­category objects are passed by reference, and two such objects are equal if they have the same address. This means that applications using custom error_­category types should create a single object of each such type.  — end note ] 

namespace std {
  class error_category {
  public:
    constexpr error_category() noexcept;
    virtual ~error_category();
    error_category(const error_category&) = delete;
    error_category& operator=(const error_category&) = delete;
    virtual const char* name() const noexcept = 0;
    virtual error_condition default_error_condition(int ev) const noexcept;
    virtual bool equivalent(int code, const error_condition& condition) const noexcept;
    virtual bool equivalent(const error_code& code, int condition) const noexcept;
    virtual string message(int ev) const = 0;

    bool operator==(const error_category& rhs) const noexcept;
    bool operator!=(const error_category& rhs) const noexcept;
    bool operator<(const error_category& rhs) const noexcept;
  };

  const error_category& generic_category() noexcept;
  const error_category& system_category() noexcept;
}

22.5.2.2 Class error_­category virtual members [syserr.errcat.virtuals]

virtual ~error_category();

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Effects: Destroys an object of class error_­category.

virtual const char* name() const noexcept = 0;

2
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Returns: A string naming the error category.

virtual error_condition default_error_condition(int ev) const noexcept;

3
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Returns: error_­condition(ev, *this).

virtual bool equivalent(int code, const error_condition& condition) const noexcept;

4
#

Returns: default_­error_­condition(code) == condition.

virtual bool equivalent(const error_code& code, int condition) const noexcept;

5
#

Returns: *this == code.category() && code.value() == condition.

virtual string message(int ev) const = 0;

6
#

Returns: A string that describes the error condition denoted by ev.

22.5.2.3 Class error_­category non-virtual members [syserr.errcat.nonvirtuals]

constexpr error_category() noexcept;

1
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Effects: Constructs an object of class error_­category.

bool operator==(const error_category& rhs) const noexcept;

2
#

Returns: this == &rhs.

bool operator!=(const error_category& rhs) const noexcept;

3
#

Returns: !(*this == rhs).

bool operator<(const error_category& rhs) const noexcept;

4
#

Returns: less<const error_­category*>()(this, &rhs).

[ Note: less provides a total ordering for pointers.  — end note ]

22.5.2.4 Program defined classes derived from error_­category [syserr.errcat.derived]

virtual const char* name() const noexcept = 0;

1
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Returns: A string naming the error category.

virtual error_condition default_error_condition(int ev) const noexcept;

2
#

Returns: An object of type error_­condition that corresponds to ev.

virtual bool equivalent(int code, const error_condition& condition) const noexcept;

3
#

Returns: true if, for the category of error represented by *this, code is considered equivalent to condition; otherwise, false.

virtual bool equivalent(const error_code& code, int condition) const noexcept;

4
#

Returns: true if, for the category of error represented by *this, code is considered equivalent to condition; otherwise, false.

22.5.2.5 Error category objects [syserr.errcat.objects]

const error_category& generic_category() noexcept;

1
#

Returns: A reference to an object of a type derived from class error_­category. All calls to this function shall return references to the same object.

2
#

Remarks: The object's default_­error_­condition and equivalent virtual functions shall behave as specified for the class error_­category. The object's name virtual function shall return a pointer to the string "generic".

const error_category& system_category() noexcept;

3
#

Returns: A reference to an object of a type derived from class error_­category. All calls to this function shall return references to the same object.

4
#

Remarks: The object's equivalent virtual functions shall behave as specified for class error_­category. The object's name virtual function shall return a pointer to the string "system". The object's default_­error_­condition virtual function shall behave as follows:

If the argument ev corresponds to a POSIX errno value posv, the function shall return error_­condition(posv, generic_­category()). Otherwise, the function shall return error_­condition(ev, system_­category()). What constitutes correspondence for any given operating system is unspecified. [ Note: The number of potential system error codes is large and unbounded, and some may not correspond to any POSIX errno value. Thus implementations are given latitude in determining correspondence.  — end note ]

22.5.3 Class error_­code [syserr.errcode]

22.5.3.1 Class error_­code overview [syserr.errcode.overview]

1
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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);
}

22.5.3.2 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.

22.5.3.3 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().

22.5.3.4 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.

22.5.3.5 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();

22.5.4 Class error_­condition [syserr.errcondition]

22.5.4.1 Class error_­condition overview [syserr.errcondition.overview]

1
#

The class error_­condition describes an object used to hold values identifying error conditions. [ Note: error_­condition values are portable abstractions, while error_­code values are implementation specific.  — end note ] 

namespace std {
  class error_condition {
  public:
    // [syserr.errcondition.constructors], constructors
    error_condition() noexcept;
    error_condition(int val, const error_category& cat) noexcept;
    template <class ErrorConditionEnum>
      error_condition(ErrorConditionEnum e) noexcept;

    // [syserr.errcondition.modifiers], modifiers
    void assign(int val, const error_category& cat) noexcept;
    template <class ErrorConditionEnum>
      error_condition& operator=(ErrorConditionEnum e) noexcept;
    void clear() noexcept;

    // [syserr.errcondition.observers], observers
    int value() const noexcept;
    const error_category& category() const noexcept;
    string message() const;
    explicit operator bool() const noexcept;

  private:
    int val_;                   // exposition only
    const error_category* cat_; // exposition only
  };
}

22.5.4.2 Class error_­condition constructors [syserr.errcondition.constructors]

error_condition() noexcept;

1
#

Effects: Constructs an object of type error_­condition.

2
#

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

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

3
#

Effects: Constructs an object of type error_­condition.

4
#

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

template <class ErrorConditionEnum> error_condition(ErrorConditionEnum e) noexcept;

5
#

Effects: Constructs an object of type error_­condition.

6
#

Postconditions: *this == make_­error_­condition(e).

7
#

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

22.5.4.3 Class error_­condition modifiers [syserr.errcondition.modifiers]

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

1
#

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

template <class ErrorConditionEnum> error_condition& operator=(ErrorConditionEnum e) noexcept;

2
#

Postconditions: *this == make_­error_­condition(e).

3
#

Returns: *this.

4
#

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

void clear() noexcept;

5
#

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

22.5.4.4 Class error_­condition observers [syserr.errcondition.observers]

int value() const noexcept;

1
#

Returns: val_­.

const error_category& category() const noexcept;

2
#

Returns: *cat_­.

string message() const;

3
#

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

explicit operator bool() const noexcept;

4
#

Returns: value() != 0.

22.5.4.5 Class error_­condition non-member functions [syserr.errcondition.nonmembers]

error_condition make_error_condition(errc e) noexcept;

1
#

Returns: error_­condition(static_­cast<int>(e), generic_­category()).

22.5.5 Comparison functions [syserr.compare]

bool operator<(const error_code& lhs, const error_code& rhs) noexcept;

1
#

Returns: 

lhs.category() < rhs.category() ||
(lhs.category() == rhs.category() && lhs.value() < rhs.value());

bool operator<(const error_condition& lhs, const error_condition& rhs) noexcept;

2
#

Returns: lhs.category() < rhs.category() || lhs.category() == rhs.category() &&
lhs.value() < rhs.value().

bool operator==(const error_code& lhs, const error_code& rhs) noexcept;

3
#

Returns: lhs.category() == rhs.category() && lhs.value() == rhs.value().

bool operator==(const error_code& lhs, const error_condition& rhs) noexcept;

4
#

Returns: lhs.category().equivalent(lhs.value(), rhs) || rhs.category().equivalent(lhs, rhs.value()).

bool operator==(const error_condition& lhs, const error_code& rhs) noexcept;

5
#

Returns: rhs.category().equivalent(rhs.value(), lhs) || lhs.category().equivalent(rhs, lhs.value()).

bool operator==(const error_condition& lhs, const error_condition& rhs) noexcept;

6
#

Returns: lhs.category() == rhs.category() && lhs.value() == rhs.value().

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;

7
#

Returns: !(lhs == rhs).

22.5.6 System error hash support [syserr.hash]

template <> struct hash<error_code>; template <> struct hash<error_condition>;

1
#

The specializations are enabled ([unord.hash]).

22.5.7 Class system_­error [syserr.syserr]

22.5.7.1 Class system_­error overview [syserr.syserr.overview]

1
#

The class system_­error describes an exception object used to report error conditions that have an associated error code. Such error conditions typically originate from the operating system or other low-level application program interfaces.

2
#

[ Note: If an error represents an out-of-memory condition, implementations are encouraged to throw an exception object of type bad_­alloc rather than system_­error.  — end note ] 

namespace std {
  class system_error : public runtime_error {
  public:
    system_error(error_code ec, const string& what_arg);
    system_error(error_code ec, const char* what_arg);
    system_error(error_code ec);
    system_error(int ev, const error_category& ecat, const string& what_arg);
    system_error(int ev, const error_category& ecat, const char* what_arg);
    system_error(int ev, const error_category& ecat);
    const error_code& code() const noexcept;
    const char* what() const noexcept override;
  };
}

22.5.7.2 Class system_­error members [syserr.syserr.members]

system_error(error_code ec, const string& what_arg);

1
#

Effects: Constructs an object of class system_­error.

2
#

Postconditions: code() == ec.

string(what()).find(what_­arg) != string​::​npos.

system_error(error_code ec, const char* what_arg);

3
#

Effects: Constructs an object of class system_­error.

4
#

Postconditions: code() == ec.

string(what()).find(what_­arg) != string​::​npos.

system_error(error_code ec);

5
#

Effects: Constructs an object of class system_­error.

6
#

Postconditions: code() == ec.

system_error(int ev, const error_category& ecat, const string& what_arg);

7
#

Effects: Constructs an object of class system_­error.

8
#

Postconditions: code() == error_­code(ev, ecat).

string(what()).find(what_­arg) != string​::​npos.

system_error(int ev, const error_category& ecat, const char* what_arg);

9
#

Effects: Constructs an object of class system_­error.

10
#

Postconditions: code() == error_­code(ev, ecat).

string(what()).find(what_­arg) != string​::​npos.

system_error(int ev, const error_category& ecat);

11
#

Effects: Constructs an object of class system_­error.

12
#

Postconditions: code() == error_­code(ev, ecat).

const error_code& code() const noexcept;

13
#

Returns: ec or error_­code(ev, ecat), from the constructor, as appropriate.

const char* what() const noexcept override;

14
#

Returns: An ntbs incorporating the arguments supplied in the constructor.

[ Note: The returned ntbs might be the contents of what_­arg + ": " + code.message(). — end note ]