# std::basic_iostream

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< cpp‎ | io

Defined in header `<istream>` |  |
template< class CharT, class Traits = std::char_traits <CharT> > class basic_iostream : public basic_istream<CharT, Traits>, public basic_ostream<CharT, Traits> |  |

The class template `basic_iostream` provides support for high level input/output operations on streams. The supported operations include sequential reading or writing and formatting. This functionality is implemented over the interface provided by the std::basic_streambuf class. It is accessed through std::basic_ios class.

Inheritance diagram

Several typedefs for common character types are provided:

Defined in header `<istream>`
Type | Definition
`std::iostream` | std::basic_iostream<char>
`std::wiostream` | std::basic_iostream<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`

### Member functions

(constructor) | constructs the object (public member function)
(destructor) [virtual] | destructs the object (virtual public member function)

### Protected member functions

operator= (C++11) | move-assigns another `basic_iostream` (protected member function)
swap (C++11) | exchanges the state with another `basic_iostream` (public member function)

## Inherited from std::basic_istream

### Member functions

##### Formatted input

operator>> | extracts formatted data (public member function of `std::basic_istream<CharT,Traits>`)

##### Unformatted input

get | extracts characters (public member function of `std::basic_istream<CharT,Traits>`)
peek | reads the next character without extracting it (public member function of `std::basic_istream<CharT,Traits>`)
unget | unextracts a character (public member function of `std::basic_istream<CharT,Traits>`)
putback | puts a character into input stream (public member function of `std::basic_istream<CharT,Traits>`)
getline | extracts characters until the given character is found (public member function of `std::basic_istream<CharT,Traits>`)
ignore | extracts and discards characters until the given character is found (public member function of `std::basic_istream<CharT,Traits>`)
read | extracts blocks of characters (public member function of `std::basic_istream<CharT,Traits>`)
readsome | extracts already available blocks of characters (public member function of `std::basic_istream<CharT,Traits>`)
gcount | returns number of characters extracted by last unformatted input operation (public member function of `std::basic_istream<CharT,Traits>`)

##### Positioning

tellg | returns the input position indicator (public member function of `std::basic_istream<CharT,Traits>`)
seekg | sets the input position indicator (public member function of `std::basic_istream<CharT,Traits>`)

##### Miscellaneous

sync | synchronizes with the underlying storage device (public member function of `std::basic_istream<CharT,Traits>`)

### Member classes

sentry | implements basic logic for preparation of the stream for input operations (public member class of `std::basic_istream<CharT,Traits>`)

## Inherited from std::basic_ostream

### Member functions

##### Formatted output

operator<< | inserts formatted data (public member function of `std::basic_ostream<CharT,Traits>`)

##### Unformatted output

put | inserts a character (public member function of `std::basic_ostream<CharT,Traits>`)
write | inserts blocks of characters (public member function of `std::basic_ostream<CharT,Traits>`)

##### Positioning

tellp | returns the output position indicator (public member function of `std::basic_ostream<CharT,Traits>`)
seekp | sets the output position indicator (public member function of `std::basic_ostream<CharT,Traits>`)

##### Miscellaneous

flush | synchronizes with the underlying storage device (public member function of `std::basic_ostream<CharT,Traits>`)

### Member classes

sentry | implements basic logic for preparation of the stream for output operations (public member class of `std::basic_ostream<CharT,Traits>`)

## Inherited from std::basic_ios

### Member types

Member type | Definition
`char_type` | `CharT`
`traits_type` | `Traits`
`int_type` | `Traits::int_type`
`pos_type` | `Traits::pos_type`
`off_type` | `Traits::off_type`

### Member functions

##### State functions

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

##### Formatting

copyfmt | copies formatting information (public member function of `std::basic_ios<CharT,Traits>`)
fill | manages the fill character (public member function of `std::basic_ios<CharT,Traits>`)

##### Miscellaneous

exceptions | manages exception mask (public member function of `std::basic_ios<CharT,Traits>`)
imbue | sets the locale (public member function of `std::basic_ios<CharT,Traits>`)
rdbuf | manages associated stream buffer (public member function of `std::basic_ios<CharT,Traits>`)
tie | manages tied stream (public member function of `std::basic_ios<CharT,Traits>`)
narrow | narrows characters (public member function of `std::basic_ios<CharT,Traits>`)
widen | widens characters (public member function of `std::basic_ios<CharT,Traits>`)

## 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)

### 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 271 | C++98 | the member types `char_type`, `traits_type`, `int_type`, `pos_type` and `off_type` were not defined (std::basic_istream and std::basic_ostream both define these types, resulted in ambiguity) | define these types

### See also

- Input/output manipulators

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