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std::basic_istream

Defined in header <istream> 
template< 
    class CharT, 
    class Traits = std::char_traits<CharT>
> class basic_istream : virtual public std::basic_ios<CharT, Traits>

The class template basic_istream provides support for high level input operations on character streams. The supported operations include formatted input (e.g. integer values or whitespace-separated characters and characters strings) and unformatted input (e.g. raw characters and character arrays). This functionality is implemented in terms of the interface provided by the underlying basic_streambuf class, accessed through the basic_ios base class. The only non-inherited data member of basic_istream, in most implementations, is the value returned by basic_istream::gcount().

cpp/io/ios base cpp/io/basic iosstd-basic istream-inheritance.svg

Inheritance diagram

Several typedefs for common character types are provided:

Defined in header <istream>
Type Definition
std::istream std::basic_istream<char>
std::wistream std::basic_istream<wchar_t>

Global objects

Two global basic_istream objects are provided by the standard library.

Defined in header <iostream>
reads from the standard C input stream stdin
(global object)

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

constructs the object
(public member function)
[virtual]
destructs the object
(virtual public member function)
(C++11)
move-assigns from another basic_istream
(protected member function)
Formatted input
extracts formatted data
(public member function)
Unformatted input
extracts characters
(public member function)
reads the next character without extracting it
(public member function)
unextracts a character
(public member function)
puts a character into input stream
(public member function)
extracts characters until the given character is found
(public member function)
extracts and discards characters until the given character is found
(public member function)
extracts blocks of characters
(public member function)
extracts already available blocks of characters
(public member function)
returns number of characters extracted by last unformatted input operation
(public member function)
Positioning
returns the input position indicator
(public member function)
sets the input position indicator
(public member function)
Miscellaneous
synchronizes with the underlying storage device
(public member function)
(C++11)
swaps stream objects, except for the associated buffer
(protected member function)

Member classes

implements basic logic for preparation of the stream for input operations
(public member class)

Non-member functions

extracts characters and character arrays
(function template)

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
checks if no error has occurred i.e. I/O operations are available
(public member function of std::basic_ios<CharT,Traits>)
checks if end-of-file has been reached
(public member function of std::basic_ios<CharT,Traits>)
checks if an error has occurred
(public member function of std::basic_ios<CharT,Traits>)
checks if a non-recoverable error has occurred
(public member function of std::basic_ios<CharT,Traits>)
checks if an error has occurred (synonym of fail())
(public member function of std::basic_ios<CharT,Traits>)
checks if no error has occurred (synonym of !fail())
(public member function of std::basic_ios<CharT,Traits>)
returns state flags
(public member function of std::basic_ios<CharT,Traits>)
sets state flags
(public member function of std::basic_ios<CharT,Traits>)
modifies state flags
(public member function of std::basic_ios<CharT,Traits>)
Formatting
copies formatting information
(public member function of std::basic_ios<CharT,Traits>)
manages the fill character
(public member function of std::basic_ios<CharT,Traits>)
Miscellaneous
manages exception mask
(public member function of std::basic_ios<CharT,Traits>)
sets the locale
(public member function of std::basic_ios<CharT,Traits>)
manages associated stream buffer
(public member function of std::basic_ios<CharT,Traits>)
manages tied stream
(public member function of std::basic_ios<CharT,Traits>)
narrows characters
(public member function of std::basic_ios<CharT,Traits>)
widens characters
(public member function of std::basic_ios<CharT,Traits>)

Inherited from std::ios_base

Member functions

Formatting
manages format flags
(public member function of std::ios_base)
sets specific format flag
(public member function of std::ios_base)
clears specific format flag
(public member function of std::ios_base)
manages decimal precision of floating point operations
(public member function of std::ios_base)
manages field width
(public member function of std::ios_base)
Locales
sets locale
(public member function of std::ios_base)
returns current locale
(public member function of std::ios_base)
Internal extensible array
[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)
resizes the private storage if necessary and access to the long element at the given index
(public member function of std::ios_base)
resizes the private storage if necessary and access to the void* element at the given index
(public member function of std::ios_base)
Miscellaneous
registers event callback function
(public member function of std::ios_base)
[static]
sets whether C++ and C I/O libraries are interoperable
(public static member function of std::ios_base)
Member classes
stream exception
(public member class of std::ios_base)
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
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
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)
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)
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)
specifies event type
(enum)
callback function type
(typedef)

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