NAME¶

std::basic_ios - std::basic_ios

Synopsis¶

Defined in header <ios>
template<

class CharT,
class Traits = std::char_traits<CharT>
> class basic_ios

: public std::ios_base

The class std::basic_ios provides facilities for interfacing with objects that have
std::basic_streambuf interface. Several std::basic_ios objects can refer to one
actual std::basic_streambuf object.

std-basic ios-inheritance.svg

Inheritance diagram

Several typedefs for common character types are provided:

Defined in header <ios>
Type Definition
std::ios std::basic_ios<char>
std::wios std::basic_ios<wchar_t>

Member types¶

Member type Definition
char_type CharT
traits_type Traits; the program is ill-formed if Traits::char_type is not
CharT.
int_type Traits::int_type
pos_type Traits::pos_type
off_type Traits::off_type

Public member functions¶

constructor constructs the object
(public member function)
destructor destructs the object
[virtual] (virtual public member function)
operator= the copy assignment operator is deleted
(public member function)

State functions¶

good checks if no error has occurred i.e. I/O operations are available
(public member function)
eof checks if end-of-file has been reached
(public member function)
fail checks if an error has occurred
(public member function)
bad checks if a non-recoverable error has occurred
(public member function)
operator! checks if an error has occurred (synonym of fail())
(public member function)
operator bool checks if no error has occurred (synonym of !fail())
(public member function)
rdstate returns state flags
(public member function)
setstate sets state flags
(public member function)
clear modifies state flags
(public member function)

Formatting¶

copyfmt copies formatting information
(public member function)
fill manages the fill character
(public member function)

Miscellaneous¶

exceptions manages exception mask
(public member function)
imbue sets the locale
(public member function)
rdbuf manages associated stream buffer
(public member function)
tie manages tied stream
(public member function)
narrow narrows characters
(public member function)
widen widens characters
(public member function)

Protected member functions¶

init initializes a default-constructed std::basic_ios
(protected member function)
move moves from another std::basic_ios except for rdbuf
(C++11) (protected member function)
swap swaps with another std::basic_ios except for rdbuf
(C++11) (protected member function)
set_rdbuf replaces the rdbuf without clearing its error state
(protected member function)

Inherited from std::ios_base

Member functions¶

Formatting¶

flags manages format flags
(public member function of std::ios_base)
setf sets specific format flag
(public member function of std::ios_base)
unsetf clears specific format flag
(public member function of std::ios_base)
precision manages decimal precision of floating point operations
(public member function of std::ios_base)
width manages field width
(public member function of std::ios_base)

Locales¶

imbue sets locale
(public member function of std::ios_base)
getloc returns current locale
(public member function of std::ios_base)

Internal extensible array¶

xalloc returns a program-wide unique integer that is safe to use as index
[static] to pword() and iword()
(public static member function of std::ios_base)
resizes the private storage if necessary and access to the long
iword element at the given index
(public member function of std::ios_base)
resizes the private storage if necessary and access to the void*
pword element at the given index
(public member function of std::ios_base)

Miscellaneous¶

register_callback registers event callback function
(public member function of std::ios_base)
sync_with_stdio sets whether C++ and C I/O libraries are interoperable
[static] (public static member function of std::ios_base)

Member classes¶

failure stream exception
(public member class of std::ios_base)
Init initializes standard stream objects
(public member class of std::ios_base)

Member types and constants¶

Type Explanation
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
openmode 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)
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
generate floating point types using scientific notation,
scientific or hex notation if combined with fixed: see
std::scientific
fmtflags generate floating point types using fixed notation, or
fixed 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
generate a prefix indicating the numeric base for integer
showbase 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
replace certain lowercase letters with their uppercase
uppercase equivalents in certain output operations: see
std::uppercase

(typedef)
state of the stream type

The following constants are also defined:

Constant Explanation
iostate 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)
seeking direction type

The following constants are also defined:

seekdir 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)

Notes¶

Straightforward implementation of std::basic_ios stores only the following members
(which all depend on the template parameters and thus cannot be part of
std::ios_base):

* the fill character (see fill())
* the tied stream pointer (see tie())
* the associated stream buffer pointer (see rdbuf()).

Actual implementations vary:

Microsoft Visual Studio stores just those three members.

LLVM libc++ stores 1 less member: it maintains the rdbuf pointer as a void* member
of ios_base.

GNU libstdc++ stores 4 additional members: three cached facets and a flag to
indicate that fill was initialized.