From cppreference.com
Defined in header
classios_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.
Typical implementation holds member constants corresponding to all values of
,
,
, and
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
.
Member functions
constructs the object
(protected member function)
[virtual]
destructs the object
(virtual public member function)
assigns to the stream
(public member function)
Formatting
manages format flags
(public member function)
sets specific format flag
(public member function)
clears specific format flag
(public member function)
manages decimal precision of floating point operations
(public member function)
manages field width
(public member function)
Locales
sets locale
(public member function)
returns current locale
(public member function)
Internal extensible array
[static]
returns a program-wide unique integer that is safe to use as index to
and
(public static member function)
resizes the private storage if necessary and access to the long element at the given index
(public member function)
resizes the private storage if necessary and access to the void* element at the given index
(public member function)
Miscellaneous
registers event callback function
(public member function)
[static]
sets whether C++ and C I/O libraries are interoperable
(public static member function)
Member classes
stream exception
(public member class)
initializes standard stream objects
(public member class)
Member types and constants
Type Explanation stream open mode type The following constants are also defined:
Constant Explanation
seek to the end of stream before each write
open in
open for reading
open for writing
discard the contents of the stream when opening
seek to the end of stream immediately after open
(C++23)open in exclusive mode
(typedef)
formatting flags type The following constants are also defined:
Constant Explanation
use decimal base for integer I/O: see
use octal base for integer I/O: see
use hexadecimal base for integer I/O: see
dec|oct|hex. Useful for masking operations
left adjustment (adds fill characters to the right): see
right adjustment (adds fill characters to the left): see
internal adjustment (adds fill characters to the internal designated point): see
left|right|internal. Useful for masking operations
generate floating point types using scientific notation, or hex notation if combined with fixed: see
generate floating point types using fixed notation, or hex notation if combined with scientific: see
scientific|fixed. Useful for masking operations
insert and extract bool type in alphanumeric format: see
generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O: see
generate a decimal-point character unconditionally for floating-point number output: see
generate a + character for non-negative numeric output: see
skip leading whitespace before certain input operations: see
flush the output after each output operation: see
replace certain lowercase letters with their uppercase equivalents in certain output operations: see
(typedef)
state of the stream type The following constants are also defined:
(typedef)
seeking direction type The following constants are also defined:
(typedef)
specifies event type
(enum)
callback function type
(typedef)
Deprecated member types Type Explanation io_state(deprecated)integer type that may be used like iostateopen_mode(deprecated)integer type that may be used like openmodeseek_dir(deprecated)integer type that may be used like seekdirstreamoff(deprecated)unspecified type that may be used like off_type, not necessarily
streampos(deprecated)unspecified type that may be used like pos_type, not necessarily
(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
(
) C++98 std::ios_base defined operator~, operator&
and operator| for types openmode, fmtflags and
iostate, violating the requirements of
removed these definitions
A
needs to support bitwise opertaions on its own. The bitwise operation support should not be provided externally.
See also