std::basic_ios

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.

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) [virtual]	destructs the object (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 (C++11)	moves from another `std::basic_ios` except for `rdbuf` (protected member function)
swap (C++11)	swaps with another `std::basic_ios` except for `rdbuf` (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 [static]	returns a program-wide unique integer that is safe to use as index to `pword()` and `iword()` (public static member function of `std::ios_base`)
iword	resizes the private storage if necessary and access to the long element at the given index (public member function of `std::ios_base`)
pword	resizes the private storage if necessary and access to the void* 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 [static]	sets whether C++ and C I/O libraries are interoperable (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

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)

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.

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std::basic_ios

Member types

Public member functions

State functions

Formatting

Miscellaneous

Protected member functions

Inherited from std::ios_base

Member functions

Formatting

Locales

Internal extensible array

Miscellaneous

Member classes

Member types and constants

Notes