std::ios_base(3)

NAME
std::ios_base - The base of the I/O class hierarchy.

SYNOPSIS

  Classes
class failure
These are thrown to indicate problems with io.

  Public Types
enum event { erase_event, imbue_event, copyfmt_event }
The set of events that may be passed to an event callback.
typedef void(* event_callback) (event __e, ios_base &__b, int __i)
The type of an event callback function.
typedef _Ios_Fmtflags fmtflags
This is a bitmask type.
typedef int io_state
typedef _Ios_Iostate iostate
This is a bitmask type.
typedef int open_mode
typedef _Ios_Openmode openmode
This is a bitmask type.
typedef int seek_dir
typedef _Ios_Seekdir seekdir
This is an enumerated type.
typedef std::streamoff streamoff
typedef std::streampos streampos

  Public Member Functions
ios_base (const ios_base &)=delete
virtual ~ios_base ()
const locale & _M_getloc () const
Locale access.
fmtflags flags () const
Access to format flags.
fmtflags flags (fmtflags __fmtfl)
Setting new format flags all at once.
locale getloc () const
Locale access.
locale imbue (const locale &__loc) throw ()
Setting a new locale.
long & iword (int __ix)
Access to integer array.
ios_base & operator= (const ios_base &)=delete
streamsize precision () const
Flags access.
streamsize precision (streamsize __prec)
Changing flags.
void *& pword (int __ix)
Access to void pointer array.
void register_callback (event_callback __fn, int __index)
Add the callback __fn with parameter __index.
fmtflags setf (fmtflags __fmtfl)
Setting new format flags.
fmtflags setf (fmtflags __fmtfl, fmtflags __mask)
Setting new format flags.
void unsetf (fmtflags __mask)
Clearing format flags.
streamsize width () const
Flags access.
streamsize width (streamsize __wide)
Changing flags.

  Static Public Member Functions
static bool sync_with_stdio (bool __sync=true)
Interaction with the standard C I/O objects.
static int xalloc () throw ()
Access to unique indices.

  Static Public Attributes
static const fmtflags adjustfield
A mask of left|right|internal. Useful for the 2-arg form of setf.
static const openmode app
Seek to end before each write.
static const openmode ate
Open and seek to end immediately after opening.
static const iostate badbit
Indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file).
static const fmtflags basefield
A mask of dec|oct|hex. Useful for the 2-arg form of setf.
static const seekdir beg
Request a seek relative to the beginning of the stream.
static const openmode binary
Perform input and output in binary mode (as opposed to text mode). This is probably not what you think it is; see https://gcc.gnu.org/onlinedocs/libstdc++/manual/fstreams.html#std.io.filestreams.binary.
static const fmtflags boolalpha
Insert/extract bool in alphabetic rather than numeric format.
static const seekdir cur
Request a seek relative to the current position within the sequence.
static const fmtflags dec
Converts integer input or generates integer output in decimal base.
static const seekdir end
Request a seek relative to the current end of the sequence.
static const iostate eofbit
Indicates that an input operation reached the end of an input sequence.
static const iostate failbit
Indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.
static const fmtflags fixed
Generate floating-point output in fixed-point notation.
static const fmtflags floatfield
A mask of scientific|fixed. Useful for the 2-arg form of setf.
static const iostate goodbit
Indicates all is well.
static const fmtflags hex
Converts integer input or generates integer output in hexadecimal base.
static const openmode in
Open for input. Default for ifstream and fstream.
static const fmtflags internal
Adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated.
static const fmtflags left
Adds fill characters on the right (final positions) of certain generated output. (I.e., the thing you print is flush left.)
static const fmtflags oct
Converts integer input or generates integer output in octal base.
static const openmode out
Open for output. Default for ofstream and fstream.
static const fmtflags right
Adds fill characters on the left (initial positions) of certain generated output. (I.e., the thing you print is flush right.)
static const fmtflags scientific
Generates floating-point output in scientific notation.
static const fmtflags showbase
Generates a prefix indicating the numeric base of generated integer output.
static const fmtflags showpoint
Generates a decimal-point character unconditionally in generated floating-point output.
static const fmtflags showpos
Generates a + sign in non-negative generated numeric output.
static const fmtflags skipws
Skips leading white space before certain input operations.
static const openmode trunc
Truncate an existing stream when opening. Default for ofstream.
static const fmtflags unitbuf
Flushes output after each output operation.
static const fmtflags uppercase
Replaces certain lowercase letters with their uppercase equivalents in generated output.

  Protected Types
enum { _S_local_word_size }

  Protected Member Functions
void _M_call_callbacks (event __ev) throw ()
void _M_dispose_callbacks (void) throw ()
_Words & _M_grow_words (int __index, bool __iword)
void _M_init () throw ()
void _M_move (ios_base &) noexcept
void _M_swap (ios_base &__rhs) noexcept

  Protected Attributes
_Callback_list * _M_callbacks
iostate _M_exception
fmtflags _M_flags
locale _M_ios_locale
_Words _M_local_word [_S_local_word_size]
streamsize _M_precision
iostate _M_streambuf_state
streamsize _M_width
_Words * _M_word
int _M_word_size
_Words _M_word_zero

Detailed Description

The base of the I/O class hierarchy. This class defines everything that can be defined about I/O that does not depend on the type of characters being input or output. Most people will only see ios_base when they need to specify the full name of the various I/O flags (e.g., the openmodes).

Definition at line 228 of file ios_base.h.

Member Typedef Documentation

  typedef void(* std::ios_base::event_callback) (event __e, ios_base &__b, int __i)

The type of an event callback function.

Parameters
    __e One of the members of the event enum.
    __b Reference to the ios_base object.
    __i The integer provided when the callback was registered.

Event callbacks are user defined functions that get called during several ios_base and basic_ios functions, specifically imbue(), copyfmt(), and ~ios().

Definition at line 506 of file ios_base.h.

  typedef _Ios_Fmtflags std::ios_base::fmtflags

This is a bitmask type. _Ios_Fmtflags is implementation-defined, but it is valid to perform bitwise operations on these values and expect the Right Thing to happen. Defined objects of type fmtflags are:

•   boolalpha

•   dec

•   fixed

•   hex

•   internal

•   left

•   oct

•   right

•   scientific

•   showbase

•   showpoint

•   showpos

•   skipws

•   unitbuf

•   uppercase

•   adjustfield

•   basefield

•   floatfield

Definition at line 323 of file ios_base.h.

  typedef _Ios_Iostate std::ios_base::iostate

This is a bitmask type. _Ios_Iostate is implementation-defined, but it is valid to perform bitwise operations on these values and expect the Right Thing to happen. Defined objects of type iostate are:

•   badbit

•   eofbit

•   failbit

•   goodbit

Definition at line 398 of file ios_base.h.

  typedef _Ios_Openmode std::ios_base::openmode

This is a bitmask type. _Ios_Openmode is implementation-defined, but it is valid to perform bitwise operations on these values and expect the Right Thing to happen. Defined objects of type openmode are:

•   app

•   ate

•   binary

•   in

•   out

•   trunc

Definition at line 429 of file ios_base.h.

  typedef _Ios_Seekdir std::ios_base::seekdir

This is an enumerated type. _Ios_Seekdir is implementation-defined. Defined values of type seekdir are:

•   beg

•   cur, equivalent to SEEK_CUR in the C standard library.

•   end, equivalent to SEEK_END in the C standard library.

Definition at line 461 of file ios_base.h.

Member Enumeration Documentation

  enum std::ios_base::event

The set of events that may be passed to an event callback. erase_event is used during ~ios() and copyfmt(). imbue_event is used during imbue(). copyfmt_event is used during copyfmt().

Definition at line 489 of file ios_base.h.

Constructor & Destructor Documentation

  virtual std::ios_base::~ios_base () [virtual]
Invokes each callback with erase_event. Destroys local storage.

Note that the ios_base object for the standard streams never gets destroyed. As a result, any callbacks registered with the standard streams will not get invoked with erase_event (unless copyfmt is used).

Member Function Documentation

  const locale& std::ios_base::_M_getloc () const [inline]

Locale access.

Returns
    A reference to the current locale.

Like getloc above, but returns a reference instead of generating a copy.

Definition at line 781 of file ios_base.h.

Referenced by std::time_get< _CharT, _InIter >::do_get(), std::money_get< _CharT, _InIter >::do_get(), std::num_get< _CharT, _InIter >::do_get(), std::time_get< _CharT, _InIter >::do_get_date(), std::time_get< _CharT, _InIter >::do_get_monthname(), std::time_get< _CharT, _InIter >::do_get_time(), std::time_get< _CharT, _InIter >::do_get_weekday(), std::time_put< _CharT, _OutIter >::do_put(), std::num_put< _CharT, _OutIter >::do_put(), std::time_get< _CharT, _InIter >::get(), and std::time_put< _CharT, _OutIter >::put().

  fmtflags std::ios_base::flags () const [inline]

Access to format flags.

Returns
    The format control flags for both input and output.

Definition at line 626 of file ios_base.h.

Referenced by std::num_get< _CharT, _InIter >::do_get(), and std::num_put< _CharT, _OutIter >::do_put().

  fmtflags std::ios_base::flags (fmtflags __fmtfl) [inline]

Setting new format flags all at once.

Parameters
    __fmtfl The new flags to set.

Returns
    The previous format control flags.

This function overwrites all the format flags with __fmtfl.

Definition at line 637 of file ios_base.h.

  locale std::ios_base::getloc () const [inline]

Locale access.

Returns
    A copy of the current locale.

If imbue(loc) has previously been called, then this function returns loc. Otherwise, it returns a copy of std::locale(), the global C++ locale.

Definition at line 770 of file ios_base.h.

Referenced by std::money_put< _CharT, _OutIter >::do_put().

  locale std::ios_base::imbue (const locale & __loc)

Setting a new locale.

Parameters
    __loc The new locale.

Returns
    The previous locale.

Sets the new locale for this stream, and then invokes each callback with imbue_event.

Referenced by std::basic_ios< _CharT, _Traits >::imbue().

  long& std::ios_base::iword (int __ix) [inline]

Access to integer array.

Parameters
    __ix Index into the array.

Returns
    A reference to an integer associated with the index.

The iword function provides access to an array of integers that can be used for any purpose. The array grows as required to hold the supplied index. All integers in the array are initialized to 0.

The implementation reserves several indices. You should use xalloc to obtain an index that is safe to use. Also note that since the array can grow dynamically, it is not safe to hold onto the reference.

Definition at line 816 of file ios_base.h.

  streamsize std::ios_base::precision () const [inline]

Flags access.

Returns
    The precision to generate on certain output operations.

Be careful if you try to give a definition of precision here; see DR 189.

Definition at line 696 of file ios_base.h.

  streamsize std::ios_base::precision (streamsize __prec) [inline]

Changing flags.

Parameters
    __prec The new precision value.

Returns
    The previous value of precision().

Definition at line 705 of file ios_base.h.

  void*& std::ios_base::pword (int __ix) [inline]

Access to void pointer array.

Parameters
    __ix Index into the array.

Returns
    A reference to a void* associated with the index.

The pword function provides access to an array of pointers that can be used for any purpose. The array grows as required to hold the supplied index. All pointers in the array are initialized to 0.

The implementation reserves several indices. You should use xalloc to obtain an index that is safe to use. Also note that since the array can grow dynamically, it is not safe to hold onto the reference.

Definition at line 837 of file ios_base.h.

  void std::ios_base::register_callback (event_callback __fn, int __index)

Add the callback __fn with parameter __index.

Parameters
    __fn The function to add.
    __index The integer to pass to the function when invoked.

Registers a function as an event callback with an integer parameter to be passed to the function when invoked. Multiple copies of the function are allowed. If there are multiple callbacks, they are invoked in the order they were registered.

  fmtflags std::ios_base::setf (fmtflags __fmtfl) [inline]

Setting new format flags.

Parameters
    __fmtfl Additional flags to set.

Returns
    The previous format control flags.

This function sets additional flags in format control. Flags that were previously set remain set.

Definition at line 653 of file ios_base.h.

  fmtflags std::ios_base::setf (fmtflags __fmtfl, fmtflags __mask) [inline]

Setting new format flags.

Parameters
    __fmtfl Additional flags to set.
    __mask The flags mask for fmtfl.

Returns
    The previous format control flags.

This function clears mask in the format flags, then sets fmtfl & mask. An example mask is ios_base::adjustfield.

Definition at line 670 of file ios_base.h.

  static bool std::ios_base::sync_with_stdio (bool __sync = true) [static]

Interaction with the standard C I/O objects.

Parameters
    __sync Whether to synchronize or not.

Returns
    True if the standard streams were previously synchronized.

The synchronization referred to is only that between the standard C facilities (e.g., stdout) and the standard C++ objects (e.g., cout). User-declared streams are unaffected. See https://gcc.gnu.org/onlinedocs/libstdc++/manual/fstreams.html#std.io.filestreams.binary

  void std::ios_base::unsetf (fmtflags __mask) [inline]

Clearing format flags.

Parameters
    __mask The flags to unset.

This function clears __mask in the format flags.

Definition at line 685 of file ios_base.h.

  streamsize std::ios_base::width () const [inline]

Flags access.

Returns
    The minimum field width to generate on output operations.

Minimum field width refers to the number of characters.

Definition at line 719 of file ios_base.h.

Referenced by std::num_put< _CharT, _OutIter >::do_put().

  streamsize std::ios_base::width (streamsize __wide) [inline]

Changing flags.

Parameters
    __wide The new width value.

Returns
    The previous value of width().

Definition at line 728 of file ios_base.h.

  static int std::ios_base::xalloc () [static]

Access to unique indices.

Returns
    An integer different from all previous calls.

This function returns a unique integer every time it is called. It can be used for any purpose, but is primarily intended to be a unique index for the iword and pword functions. The expectation is that an application calls xalloc in order to obtain an index in the iword and pword arrays that can be used without fear of conflict.

The implementation maintains a static variable that is incremented and returned on each invocation. xalloc is guaranteed to return an index that is safe to use in the iword and pword arrays.

Member Data Documentation

  const fmtflags std::ios_base::adjustfield [static]

A mask of left|right|internal. Useful for the 2-arg form of setf.

Definition at line 378 of file ios_base.h.

Referenced by std::num_put< _CharT, _OutIter >::do_put(), std::internal(), std::left(), and std::right().

  const openmode std::ios_base::app [static]

Seek to end before each write.

Definition at line 432 of file ios_base.h.

Referenced by std::basic_filebuf< char_type, traits_type >::_M_set_buffer(), std::basic_filebuf< _CharT, _Traits >::overflow(), and std::basic_filebuf< _CharT, _Traits >::xsputn().

  const openmode std::ios_base::ate [static]

Open and seek to end immediately after opening.

Definition at line 435 of file ios_base.h.

Referenced by std::basic_filebuf< _CharT, _Traits >::open().

  const iostate std::ios_base::badbit [static]

Indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file).

Definition at line 402 of file ios_base.h.

Referenced by std::basic_ostream< char >::_M_write(), std::basic_istream< char >::get(), std::basic_istream< char >::read(), and std::basic_ostream< _CharT, _Traits >::sentry::~sentry().

  const fmtflags std::ios_base::basefield [static]

A mask of dec|oct|hex. Useful for the 2-arg form of setf.

Definition at line 381 of file ios_base.h.

Referenced by std::dec(), std::hex(), and std::oct().

  const seekdir std::ios_base::beg [static]

Request a seek relative to the beginning of the stream.

Definition at line 464 of file ios_base.h.

Referenced by __gnu_cxx::stdio_sync_filebuf< _CharT, _Traits >::seekpos(), and std::basic_filebuf< _CharT, _Traits >::seekpos().

  const openmode std::ios_base::binary [static]

Perform input and output in binary mode (as opposed to text mode). This is probably not what you think it is; see https://gcc.gnu.org/onlinedocs/libstdc++/manual/fstreams.html#std.io.filestreams.binary.

Definition at line 440 of file ios_base.h.

  const fmtflags std::ios_base::boolalpha [static]

Insert/extract bool in alphabetic rather than numeric format.

Definition at line 326 of file ios_base.h.

Referenced by std::boolalpha(), std::num_get< _CharT, _InIter >::do_get(), std::num_put< _CharT, _OutIter >::do_put(), and std::noboolalpha().

  const seekdir std::ios_base::cur [static]

Request a seek relative to the current position within the sequence.

Definition at line 467 of file ios_base.h.

Referenced by std::basic_filebuf< _CharT, _Traits >::imbue(), std::basic_filebuf< _CharT, _Traits >::overflow(), std::basic_filebuf< _CharT, _Traits >::pbackfail(), and std::basic_filebuf< _CharT, _Traits >::seekoff().

  const fmtflags std::ios_base::dec [static]

Converts integer input or generates integer output in decimal base.

Definition at line 329 of file ios_base.h.

Referenced by std::dec().

  const seekdir std::ios_base::end [static]

Request a seek relative to the current end of the sequence.

Definition at line 470 of file ios_base.h.

Referenced by std::basic_filebuf< _CharT, _Traits >::open().

  const iostate std::ios_base::eofbit [static]

Indicates that an input operation reached the end of an input sequence.

Definition at line 405 of file ios_base.h.

Referenced by std::time_get< _CharT, _InIter >::do_get(), std::num_get< _CharT, _InIter >::do_get(), std::time_get< _CharT, _InIter >::do_get_date(), std::time_get< _CharT, _InIter >::do_get_monthname(), std::time_get< _CharT, _InIter >::do_get_time(), std::time_get< _CharT, _InIter >::do_get_weekday(), std::time_get< _CharT, _InIter >::do_get_year(), std::time_get< _CharT, _InIter >::get(), std::basic_istream< char >::getline(), std::basic_istream< _CharT, _Traits >::putback(), std::basic_istream< _CharT, _Traits >::seekg(), std::basic_istream< _CharT, _Traits >::unget(), and std::ws().

  const iostate std::ios_base::failbit [static]

Indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.

Definition at line 410 of file ios_base.h.

Referenced by std::basic_ifstream< _CharT, _Traits >::close(), std::basic_ofstream< _CharT, _Traits >::close(), std::basic_fstream< _CharT, _Traits >::close(), std::num_get< _CharT, _InIter >::do_get(), std::time_get< _CharT, _InIter >::do_get_monthname(), std::time_get< _CharT, _InIter >::do_get_weekday(), std::time_get< _CharT, _InIter >::do_get_year(), std::time_get< _CharT, _InIter >::get(), std::basic_istream< char >::getline(), std::basic_ifstream< _CharT, _Traits >::open(), std::basic_ofstream< _CharT, _Traits >::open(), std::basic_fstream< _CharT, _Traits >::open(), std::basic_istream< char >::operator>>(), std::operator>>(), and std::basic_ostream< _CharT, _Traits >::sentry::sentry().

  const fmtflags std::ios_base::fixed [static]

Generate floating-point output in fixed-point notation.

Definition at line 332 of file ios_base.h.

Referenced by std::fixed(), and std::hexfloat().

  const fmtflags std::ios_base::floatfield [static]

A mask of scientific|fixed. Useful for the 2-arg form of setf.

Definition at line 384 of file ios_base.h.

Referenced by std::defaultfloat(), std::fixed(), std::hexfloat(), and std::scientific().

  const iostate std::ios_base::goodbit [static]

Indicates all is well.

Definition at line 413 of file ios_base.h.

Referenced by std::time_get< _CharT, _InIter >::do_get(), std::num_get< _CharT, _InIter >::do_get(), std::time_get< _CharT, _InIter >::do_get_monthname(), std::time_get< _CharT, _InIter >::do_get_weekday(), std::time_get< _CharT, _InIter >::do_get_year(), std::basic_ostream< _CharT, _Traits >::flush(), std::basic_istream< _CharT, _Traits >::get(), std::basic_istream< char >::get(), std::time_get< _CharT, _InIter >::get(), std::basic_istream< _CharT, _Traits >::getline(), std::basic_istream< _CharT, _Traits >::ignore(), std::basic_ostream< _CharT, _Traits >::operator<<(), std::basic_istream< _CharT, _Traits >::operator>>(), std::basic_istream< char >::operator>>(), std::operator>>(), std::basic_istream< _CharT, _Traits >::peek(), std::basic_istream< char >::peek(), std::basic_ostream< _CharT, _Traits >::put(), std::basic_istream< _CharT, _Traits >::putback(), std::basic_istream< _CharT, _Traits >::read(), std::basic_istream< char >::readsome(), std::basic_istream< _CharT, _Traits >::readsome(), std::basic_istream< _CharT, _Traits >::seekg(), std::basic_ostream< _CharT, _Traits >::seekp(), std::basic_istream< _CharT, _Traits >::sentry::sentry(), std::basic_istream< _CharT, _Traits >::sync(), and std::basic_istream< _CharT, _Traits >::unget().

  const fmtflags std::ios_base::hex [static]

Converts integer input or generates integer output in hexadecimal base.

Definition at line 335 of file ios_base.h.

Referenced by std::hex().

  const openmode std::ios_base::in [static]

Open for input. Default for ifstream and fstream.

Definition at line 443 of file ios_base.h.

Referenced by std::basic_filebuf< char_type, traits_type >::_M_set_buffer(), std::basic_ifstream< _CharT, _Traits >::open(), std::basic_filebuf< _CharT, _Traits >::pbackfail(), std::basic_filebuf< _CharT, _Traits >::showmanyc(), std::basic_filebuf< _CharT, _Traits >::underflow(), and std::basic_filebuf< _CharT, _Traits >::xsgetn().

  const fmtflags std::ios_base::internal [static]

Adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated.

Definition at line 340 of file ios_base.h.

Referenced by std::internal().

  const fmtflags std::ios_base::left [static]

Adds fill characters on the right (final positions) of certain generated output. (I.e., the thing you print is flush left.)

Definition at line 344 of file ios_base.h.

Referenced by std::num_put< _CharT, _OutIter >::do_put(), and std::left().

  const fmtflags std::ios_base::oct [static]

Converts integer input or generates integer output in octal base.

Definition at line 347 of file ios_base.h.

Referenced by std::oct().

  const openmode std::ios_base::out [static]

Open for output. Default for ofstream and fstream.

Definition at line 446 of file ios_base.h.

Referenced by std::basic_filebuf< char_type, traits_type >::_M_set_buffer(), std::basic_ofstream< _CharT, _Traits >::open(), std::basic_filebuf< _CharT, _Traits >::overflow(), and std::basic_filebuf< _CharT, _Traits >::xsputn().

  const fmtflags std::ios_base::right [static]

Adds fill characters on the left (initial positions) of certain generated output. (I.e., the thing you print is flush right.)

Definition at line 351 of file ios_base.h.

Referenced by std::right().

  const fmtflags std::ios_base::scientific [static]

Generates floating-point output in scientific notation.

Definition at line 354 of file ios_base.h.

Referenced by std::hexfloat(), and std::scientific().

  const fmtflags std::ios_base::showbase [static]

Generates a prefix indicating the numeric base of generated integer output.

Definition at line 358 of file ios_base.h.

Referenced by std::noshowbase(), and std::showbase().

  const fmtflags std::ios_base::showpoint [static]

Generates a decimal-point character unconditionally in generated floating-point output.

Definition at line 362 of file ios_base.h.

Referenced by std::noshowpoint(), and std::showpoint().

  const fmtflags std::ios_base::showpos [static]

Generates a + sign in non-negative generated numeric output.

Definition at line 365 of file ios_base.h.

Referenced by std::noshowpos(), and std::showpos().

  const fmtflags std::ios_base::skipws [static]

Skips leading white space before certain input operations.

Definition at line 368 of file ios_base.h.

Referenced by std::noskipws(), std::__detail::operator>>(), and std::skipws().

  const openmode std::ios_base::trunc [static]

Truncate an existing stream when opening. Default for ofstream.

Definition at line 449 of file ios_base.h.

  const fmtflags std::ios_base::unitbuf [static]

Flushes output after each output operation.

Definition at line 371 of file ios_base.h.

Referenced by std::nounitbuf(), std::unitbuf(), and std::basic_ostream< _CharT, _Traits >::sentry::~sentry().

  const fmtflags std::ios_base::uppercase [static]

Replaces certain lowercase letters with their uppercase equivalents in generated output.

Definition at line 375 of file ios_base.h.

Referenced by std::nouppercase(), and std::uppercase().

Author

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