Difference between revisions of "cpp/io/basic istream"

Latest revision as of 01:00, 7 December 2023

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().

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>

[edit] Global objects

Two global basic_istream objects are provided by the standard library.

Defined in header `<iostream>`
cinwcin	reads from the standard C input stream stdin (global object)[edit]

[edit] Member types

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

[edit] Member functions

(constructor)	constructs the object (public member function) [edit]
(destructor) [virtual]	destructs the object (virtual public member function) [edit]
operator= (C++11)	move-assigns from another `basic_istream` (protected member function) [edit]
Formatted input
operator>>	extracts formatted data (public member function) [edit]
Unformatted input
get	extracts characters (public member function) [edit]
peek	reads the next character without extracting it (public member function) [edit]
unget	unextracts a character (public member function) [edit]
putback	puts a character into input stream (public member function) [edit]
getline	extracts characters until the given character is found (public member function) [edit]
ignore	extracts and discards characters until the given character is found (public member function) [edit]
read	extracts blocks of characters (public member function) [edit]
readsome	extracts already available blocks of characters (public member function) [edit]
gcount	returns number of characters extracted by last unformatted input operation (public member function) [edit]
Positioning
tellg	returns the input position indicator (public member function) [edit]
seekg	sets the input position indicator (public member function) [edit]
Miscellaneous
sync	synchronizes with the underlying storage device (public member function) [edit]
swap (C++11)	swaps stream objects, except for the associated buffer (protected member function) [edit]

[edit] Member classes

sentry

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

[edit] Non-member functions

operator>>(std::basic_istream)

extracts characters and character arrays
(function template) [edit]

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>`) [edit]
eof	checks if end-of-file has been reached (public member function of `std::basic_ios<CharT,Traits>`) [edit]
fail	checks if an error has occurred (public member function of `std::basic_ios<CharT,Traits>`) [edit]
bad	checks if a non-recoverable error has occurred (public member function of `std::basic_ios<CharT,Traits>`) [edit]
operator!	checks if an error has occurred (synonym of fail()) (public member function of `std::basic_ios<CharT,Traits>`) [edit]
operator bool	checks if no error has occurred (synonym of `!`fail()) (public member function of `std::basic_ios<CharT,Traits>`) [edit]
rdstate	returns state flags (public member function of `std::basic_ios<CharT,Traits>`) [edit]
setstate	sets state flags (public member function of `std::basic_ios<CharT,Traits>`) [edit]
clear	modifies state flags (public member function of `std::basic_ios<CharT,Traits>`) [edit]
Formatting
copyfmt	copies formatting information (public member function of `std::basic_ios<CharT,Traits>`) [edit]
fill	manages the fill character (public member function of `std::basic_ios<CharT,Traits>`) [edit]
Miscellaneous
exceptions	manages exception mask (public member function of `std::basic_ios<CharT,Traits>`) [edit]
imbue	sets the locale (public member function of `std::basic_ios<CharT,Traits>`) [edit]
rdbuf	manages associated stream buffer (public member function of `std::basic_ios<CharT,Traits>`) [edit]
tie	manages tied stream (public member function of `std::basic_ios<CharT,Traits>`) [edit]
narrow	narrows characters (public member function of `std::basic_ios<CharT,Traits>`) [edit]
widen	widens characters (public member function of `std::basic_ios<CharT,Traits>`) [edit]

Inherited from std::ios_base

Member functions

Formatting
flags	manages format flags (public member function of `std::ios_base`) [edit]
setf	sets specific format flag (public member function of `std::ios_base`) [edit]
unsetf	clears specific format flag (public member function of `std::ios_base`) [edit]
precision	manages decimal precision of floating point operations (public member function of `std::ios_base`) [edit]
width	manages field width (public member function of `std::ios_base`) [edit]
Locales
imbue	sets locale (public member function of `std::ios_base`) [edit]
getloc	returns current locale (public member function of `std::ios_base`) [edit]
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`) [edit]
iword	resizes the private storage if necessary and access to the long element at the given index (public member function of `std::ios_base`) [edit]
pword	resizes the private storage if necessary and access to the void* element at the given index (public member function of `std::ios_base`) [edit]
Miscellaneous
register_callback	registers event callback function (public member function of `std::ios_base`) [edit]
sync_with_stdio [static]	sets whether C++ and C I/O libraries are interoperable (public static member function of `std::ios_base`) [edit]
Member classes
failure	stream exception (public member class of `std::ios_base`) [edit]
Init	initializes standard stream objects (public member class of `std::ios_base`) [edit]

Member types and constants

Type Explanation

openmode

stream open mode type

The following constants are also defined:

Constant	Explanation[edit]
`app`	seek to the end of stream before each write[edit]
`binary`	open in binary mode[edit]
`in`	open for reading[edit]
`out`	open for writing[edit]
`trunc`	discard the contents of the stream when opening[edit]
`ate`	seek to the end of stream immediately after open[edit]
`noreplace` (C++23)	open in exclusive mode[edit]

(typedef) [edit]

fmtflags

formatting flags type

The following constants are also defined:

Constant	Explanation[edit]
`dec`	use decimal base for integer I/O: see std::dec[edit]
`oct`	use octal base for integer I/O: see std::oct[edit]
`hex`	use hexadecimal base for integer I/O: see std::hex[edit]
`basefield`	dec \| oct \| hex. Useful for masking operations[edit]
`left`	left adjustment (adds fill characters to the right): see std::left[edit]
`right`	right adjustment (adds fill characters to the left): see std::right[edit]
`internal`	internal adjustment (adds fill characters to the internal designated point): see std::internal[edit]
`adjustfield`	left \| right \| internal. Useful for masking operations[edit]
`scientific`	generate floating point types using scientific notation, or hex notation if combined with fixed: see std::scientific[edit]
`fixed`	generate floating point types using fixed notation, or hex notation if combined with scientific: see std::fixed[edit]
`floatfield`	scientific \| fixed. Useful for masking operations[edit]
`boolalpha`	insert and extract bool type in alphanumeric format: see std::boolalpha[edit]
`showbase`	generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O: see std::showbase[edit]
`showpoint`	generate a decimal-point character unconditionally for floating-point number output: see std::showpoint[edit]
`showpos`	generate a + character for non-negative numeric output: see std::showpos[edit]
`skipws`	skip leading whitespace before certain input operations: see std::skipws[edit]
`unitbuf`	flush the output after each output operation: see std::unitbuf[edit]
`uppercase`	replace certain lowercase letters with their uppercase equivalents in certain output operations: see std::uppercase[edit]

(typedef) [edit]

iostate

state of the stream type

The following constants are also defined:

Constant	Explanation[edit]
`goodbit`	no error[edit]
`badbit`	irrecoverable stream error[edit]
`failbit`	input/output operation failed (formatting or extraction error)[edit]
`eofbit`	associated input sequence has reached end-of-file[edit]

(typedef) [edit]

seekdir

seeking direction type

The following constants are also defined:

Constant	Explanation[edit]
`beg`	the beginning of a stream[edit]
`end`	the ending of a stream[edit]
`cur`	the current position of stream position indicator[edit]

(typedef) [edit]

event

specifies event type
(enum) [edit]

event_callback

callback function type
(typedef) [edit]

@@ Line 1: / Line 1: @@
 {{cpp/title|basic_istream}}
 {{cpp/io/basic_istream/navbar}}
-{{ddcl | header=istream |
+{{ddcl|header=istream|1=
 template<
      class CharT,
-     class Traits {{=}} std::char_traits<CharT>
+     class Traits = std::char_traits<CharT>
 > class basic_istream : virtual public std::basic_ios<CharT, Traits>
 }}
-The class template {{tt|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 {{tt|basic_streambuf}} class, accessed through the {{tt|basic_ios}} base class. The only non-inherited data member of {{tt|basic_istream}}, in most implementations, is the value returned by {{ltt|cpp/io/basic_istream/gcount|basic_istream::gcount()}}.
+The class template {{tt|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 {{tt|basic_streambuf}} class, accessed through the {{tt|basic_ios}} base class. The only non-inherited data member of {{tt|basic_istream}}, in most implementations, is the value returned by {{l2tf|cpp/io/basic_istream/gcount}}.
-{{inheritance diagram|image=std-basic_istream-inheritance.svg|map=
+{{inheritance diagram/std-basic_istream}}
-rect 5 6 107 39 [[cpp/io/ios_base]]
-rect 142 4 263 42 [[cpp/io/basic_ios]]
-}}
-Two specializations for common character types are defined:
-{{dcl list begin}}
+{{cpp/basic char typedefs|istream}}
-{{dcl list header | istream}}
-{{dcl list hitem | Type | Definition}}
-{{dcl list item | {{tt|istream}} | {{c|basic_istream<char>}}}}
-{{dcl list item | {{tt|wistream}} | {{c|basic_istream<wchar_t>}}}}
-{{dcl list end}}
 ===Global objects===
 Two global basic_istream objects are provided by the standard library.
-{{dcl list begin}}
+{{dsc begin}}
-{{dcl list header | iostream}}
+{{dsc header|iostream}}
-{{dcl list template | cpp/io/dcl list cin}}
+{{dsc inc|cpp/io/dsc cin}}
-{{dcl list end}}
+{{dsc end}}
-===Member types===
+{{cpp/io/member types}}
-{{dcl list begin}}
-{{dcl list hitem | Member type | Definition}}
-{{dcl list template | cpp/io/dcl list char_type}}
-{{dcl list template | cpp/io/dcl list traits_type}}
-{{dcl list template | cpp/io/dcl list int_type}}
-{{dcl list template | cpp/io/dcl list pos_type}}
-{{dcl list template | cpp/io/dcl list off_type}}
-{{dcl list end}}
 ===Member functions===
-{{dcl list begin}}
+{{dsc begin}}
-{{dcl list template | cpp/io/basic_istream/dcl list constructor}}
+{{dsc inc|cpp/io/basic_istream/dsc constructor}}
-{{dcl list template | cpp/io/basic_istream/dcl list destructor}}
+{{dsc inc|cpp/io/basic_istream/dsc destructor}}
-{{dcl list template | cpp/io/basic_istream/dcl list operator{{=}}}}
+{{dsc inc|cpp/io/basic_istream/dsc operator{{=}}}}
-{{dcl list h2 | Formatted input}}
+{{dsc h2|Formatted input}}
-{{dcl list template | cpp/io/basic_istream/dcl list operator_gtgt}}
+{{dsc inc|cpp/io/basic_istream/dsc operator_gtgt}}
-{{dcl list h2 | Unformatted input}}
+{{dsc h2|Unformatted input}}
-{{dcl list template | cpp/io/basic_istream/dcl list get}}
+{{dsc inc|cpp/io/basic_istream/dsc get}}
-{{dcl list template | cpp/io/basic_istream/dcl list peek}}
+{{dsc inc|cpp/io/basic_istream/dsc peek}}
-{{dcl list template | cpp/io/basic_istream/dcl list unget}}
+{{dsc inc|cpp/io/basic_istream/dsc unget}}
-{{dcl list template | cpp/io/basic_istream/dcl list putback}}
+{{dsc inc|cpp/io/basic_istream/dsc putback}}
-{{dcl list template | cpp/io/basic_istream/dcl list getline}}
+{{dsc inc|cpp/io/basic_istream/dsc getline}}
-{{dcl list template | cpp/io/basic_istream/dcl list ignore}}
+{{dsc inc|cpp/io/basic_istream/dsc ignore}}
-{{dcl list template | cpp/io/basic_istream/dcl list read}}
+{{dsc inc|cpp/io/basic_istream/dsc read}}
-{{dcl list template | cpp/io/basic_istream/dcl list readsome}}
+{{dsc inc|cpp/io/basic_istream/dsc readsome}}
-{{dcl list template | cpp/io/basic_istream/dcl list gcount}}
+{{dsc inc|cpp/io/basic_istream/dsc gcount}}
-{{dcl list h2 | Positioning}}
+{{dsc h2|Positioning}}
-{{dcl list template | cpp/io/basic_istream/dcl list tellg}}
+{{dsc inc|cpp/io/basic_istream/dsc tellg}}
-{{dcl list template | cpp/io/basic_istream/dcl list seekg}}
+{{dsc inc|cpp/io/basic_istream/dsc seekg}}
-{{dcl list h2 | Miscellaneous}}
+{{dsc h2|Miscellaneous}}
-{{dcl list template | cpp/io/basic_istream/dcl list sync}}
+{{dsc inc|cpp/io/basic_istream/dsc sync}}
-{{dcl list template | cpp/io/basic_istream/dcl list swap}}
+{{dsc inc|cpp/io/basic_istream/dsc swap}}
-{{dcl list end}}
+{{dsc end}}
 ===Member classes===
-{{dcl list begin}}
+{{dsc begin}}
-{{dcl list template | cpp/io/basic_istream/dcl list sentry}}
+{{dsc inc|cpp/io/basic_istream/dsc sentry}}
-{{dcl list end}}
+{{dsc end}}
 ===Non-member functions===
-{{dcl list begin}}
+{{dsc begin}}
-{{dcl list template | cpp/io/basic_istream/dcl list operator_gtgt2}}
+{{dsc inc|cpp/io/basic_istream/dsc operator_gtgt2}}
-{{dcl list end}}
+{{dsc end}}
 {{cpp/io/basic_ios/inherit}}
 {{cpp/io/ios_base/inherit}}
+{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Compiler support
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Language
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Feature test macros (C++20)
Language support library
Concepts library (C++20)
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Diagnostics library
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Containers library
Iterators library
Ranges library (C++20)
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Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

I/O manipulators
Print functions (C++23)
C-style I/O
Buffers
basic_streambuf
basic_filebuf
basic_stringbuf
basic_spanbuf (C++23)
strstreambuf (C++98/26*)
basic_syncbuf (C++20)
Streams
Abstractions
ios_base
basic_ios
basic_istream
basic_ostream
basic_iostream
File I/O
basic_ifstream
basic_ofstream
basic_fstream
String I/O
basic_istringstream
basic_ostringstream
basic_stringstream
Array I/O
basic_ispanstream (C++23)
basic_ospanstream (C++23)
basic_spanstream (C++23)
istrstream (C++98/26*)
ostrstream (C++98/26*)
strstream (C++98/26*)
Synchronized Output
basic_osyncstream (C++20)
Types
streamoff
streamsize
fpos
Error category interface
iostream_category (C++11)
io_errc (C++11)

Global objects
cinwcin
Member functions
basic_istream::basic_istream
basic_istream::~basic_istream
basic_istream::operator= (C++11)
Formatted input
basic_istream::operator>>
Unformatted input
basic_istream::get
basic_istream::peek
basic_istream::unget
basic_istream::putback
basic_istream::getline
basic_istream::ignore
basic_istream::read
basic_istream::readsome
basic_istream::gcount
Positioning
basic_istream::tellg
basic_istream::seekg
Miscellaneous
basic_istream::sync
basic_istream::swap (C++11)
Member classes
basic_istream::sentry
Non-member functions
operator>>(std::basic_istream)

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Difference between revisions of "cpp/io/basic istream"

Latest revision as of 01:00, 7 December 2023

Contents

[edit] Global objects

[edit] Member types

[edit] Member functions

Formatted input

Unformatted input

Positioning

Miscellaneous

[edit] Member classes

[edit] Non-member functions

Inherited from std::basic_ios

Member types

Member functions

State functions

Formatting

Miscellaneous

Inherited from std::ios_base

Member functions

Formatting

Locales

Internal extensible array

Miscellaneous

Member classes

Member types and constants

Navigation

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