std::ios_base

 

C++

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Input/output library

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basic_streambuf

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basic_spanbuf (C++23)

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Abstractions

ios_base

basic_ios

basic_istream

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basic_istringstream

basic_ostringstream

basic_stringstream

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basic_spanstream (C++23)

istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::ios_base

Member functions

ios_base::ios_base

ios_base::~ios_base

ios_base::operator=

Formatting

ios_base::flags

ios_base::setf

ios_base::unsetf

ios_base::precision

ios_base::width

Locales

ios_base::imbue

ios_base::getloc

Internal extensible array

ios_base::xalloc

ios_base::iword

ios_base::pword

Miscellaneous

ios_base::register_callback

ios_base::sync_with_stdio

Member classes

ios_base::failure

ios_base::Init

Member types

ios_base::openmode

ios_base::fmtflags

ios_base::iostate

ios_base::seekdir

ios_base::event

ios_base::event_callback

 

Defined in header <ios>
class ios_base;

The class ios_base is a multipurpose class that serves as the base class for all I/O stream classes. It maintains several kinds of data:

1) state information: stream status flags.

2) control information: flags that control formatting of both input and output sequences and the imbued locale.

3) private storage: indexed extensible data structure that allows both long and void* members, which may be implemented as two arbitrary-length arrays or a single array of two-element structs or another container.

4) callbacks: arbitrary number of user-defined functions to be called from imbue(), std::basic_ios::copyfmt(), and ~ios_base().

Typical implementation holds member constants corresponding to all values of fmtflags, iostate, openmode, and seekdir shown below, member variables to maintain current precision, width, and formatting flags, the exception mask, the buffer error state, a resizeable container holding the callbacks, the currently imbued locale, the private storage, and a static integer variable for xalloc().

Member functions

(constructor)	constructs the object (protected member function)
(destructor) [virtual]	destructs the object (virtual public member function)
operator=	assigns to the stream (public member function)
Formatting
flags	manages format flags (public member function)
setf	sets specific format flag (public member function)
unsetf	clears specific format flag (public member function)
precision	manages decimal precision of floating point operations (public member function)
width	manages field width (public member function)
Locales
imbue	sets locale (public member function)
getloc	returns current locale (public member function)
Internal extensible array
xalloc [static]	returns a program-wide unique integer that is safe to use as index to pword() and iword() (public static member function)
iword	resizes the private storage if necessary and access to the long element at the given index (public member function)
pword	resizes the private storage if necessary and access to the void* element at the given index (public member function)
Miscellaneous
register_callback	registers event callback function (public member function)
sync_with_stdio [static]	sets whether C++ and C I/O libraries are interoperable (public static member function)
Member classes
failure	stream exception (public member class)
Init	initializes standard stream objects (public member class)

Member types and constants
Type	Explanation
openmode	stream open mode type The following constants are also defined: Constant Explanation app seek to the end of stream before each write binary open in binary mode in open for reading out open for writing trunc discard the contents of the stream when opening ate seek to the end of stream immediately after open noreplace (C++23) open in exclusive mode (typedef)
fmtflags	formatting flags type The following constants are also defined: Constant Explanation dec use decimal base for integer I/O: see std::dec oct use octal base for integer I/O: see std::oct hex use hexadecimal base for integer I/O: see std::hex basefield dec | oct | hex. Useful for masking operations left left adjustment (adds fill characters to the right): see std::left right right adjustment (adds fill characters to the left): see std::right internal internal adjustment (adds fill characters to the internal designated point): see std::internal adjustfield left | right | internal. Useful for masking operations scientific generate floating point types using scientific notation, or hex notation if combined with fixed: see std::scientific fixed generate floating point types using fixed notation, or hex notation if combined with scientific: see std::fixed floatfield scientific | fixed. Useful for masking operations boolalpha insert and extract bool type in alphanumeric format: see std::boolalpha showbase generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O: see std::showbase showpoint generate a decimal-point character unconditionally for floating-point number output: see std::showpoint showpos generate a + character for non-negative numeric output: see std::showpos skipws skip leading whitespace before certain input operations: see std::skipws unitbuf flush the output after each output operation: see std::unitbuf uppercase replace certain lowercase letters with their uppercase equivalents in certain output operations: see std::uppercase (typedef)
iostate	state of the stream type The following constants are also defined: Constant Explanation goodbit no error badbit irrecoverable stream error failbit input/output operation failed (formatting or extraction error) eofbit associated input sequence has reached end-of-file (typedef)
seekdir	seeking direction type The following constants are also defined: Constant Explanation beg the beginning of a stream end the ending of a stream cur the current position of stream position indicator (typedef)
event	specifies event type (enum)
event_callback	callback function type (typedef)

Deprecated member types Type Explanation io_state (deprecated) integer type that may be used like iostate open_mode (deprecated) integer type that may be used like openmode seek_dir (deprecated) integer type that may be used like seekdir streamoff (deprecated) unspecified type that may be used like off_type, not necessarily std::streamoff streampos (deprecated) unspecified type that may be used like pos_type, not necessarily std::streampos

(until C++17)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 1357 (N3110)	C++98	std::ios_base defined operator~, operator& and operator| for types openmode, fmtflags and iostate, violating the requirements of BitmaskType	removed these definitions

See also

basic_ios

manages an arbitrary stream buffer (class template)