std::basic_ifstream

From cppreference.com

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

[edit]

Input/output library

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)

[edit]

std::basic_ifstream

Member functions
basic_ifstream::basic_ifstream
basic_ifstream::operator= (C++11)
basic_ifstream::swap (C++11)
basic_ifstream::rdbuf
basic_ifstream::native_handle (C++26)
File operations
basic_ifstream::is_open
basic_ifstream::open
basic_ifstream::close
Non-member functions
swap(std::basic_ifstream) (C++11)

[edit]

Defined in header`<fstream>`
template< class CharT, class Traits=std::char_traits<CharT> >class basic_ifstream:publicstd::basic_istream<CharT, Traits>

The class templatebasic_ifstream implements high-level input operations on file-based streams. It interfaces a file-based streambuffer (std::basic_filebuf) with the high-level interface of (std::basic_istream).

A typical implementation ofstd::basic_ifstream holds only one non-derived data member: an instance ofstd::basic_filebuf<CharT, Traits>.

Inheritance diagram

Several typedefs for common character types are provided:

Defined in header`<fstream>`
Type	Definition
`std::ifstream`	std::basic_ifstream<char>
`std::wifstream`	std::basic_ifstream<wchar_t>

[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]
`native_handle_type`(C++26)	implementation-defined type that isTriviallyCopyable and`semiregular`[edit]

[edit]Member functions

(constructor)	constructs the file stream (public member function)[edit]
(destructor) [virtual](implicitly declared)	destructs the`basic_ifstream` and the associated buffer, closes the file (virtual public member function)[edit]
operator= (C++11)	moves the file stream (public member function)[edit]
swap (C++11)	swaps two file streams (public member function)[edit]
rdbuf	returns the underlying raw file device object (public member function)[edit]
native_handle (C++26)	returns the underlying implementation-defined handle (public member function)[edit]
File operations
is_open	checks if the stream has an associated file (public member function)[edit]
open	opens a file and associates it with the stream (public member function)[edit]
close	closes the associated file (public member function)[edit]

[edit]Non-member functions

std::swap(std::basic_ifstream)

(C++11)

specializes thestd::swap algorithm
(function template)[edit]

Inherited fromstd::basic_istream

Member functions

Formatted input
operator>>	extracts formatted data (public member function of`std::basic_istream<CharT,Traits>`)[edit]
Unformatted input
get	extracts characters (public member function of`std::basic_istream<CharT,Traits>`)[edit]
peek	reads the next character without extracting it (public member function of`std::basic_istream<CharT,Traits>`)[edit]
unget	unextracts a character (public member function of`std::basic_istream<CharT,Traits>`)[edit]
putback	puts a character into input stream (public member function of`std::basic_istream<CharT,Traits>`)[edit]
getline	extracts characters until the given character is found (public member function of`std::basic_istream<CharT,Traits>`)[edit]
ignore	extracts and discards characters until the given character is found (public member function of`std::basic_istream<CharT,Traits>`)[edit]
read	extracts blocks of characters (public member function of`std::basic_istream<CharT,Traits>`)[edit]
readsome	extracts already available blocks of characters (public member function of`std::basic_istream<CharT,Traits>`)[edit]
gcount	returns number of characters extracted by last unformatted input operation (public member function of`std::basic_istream<CharT,Traits>`)[edit]
Positioning
tellg	returns the input position indicator (public member function of`std::basic_istream<CharT,Traits>`)[edit]
seekg	sets the input position indicator (public member function of`std::basic_istream<CharT,Traits>`)[edit]
Miscellaneous
sync	synchronizes with the underlying storage device (public member function of`std::basic_istream<CharT,Traits>`)[edit]

Member classes

sentry

implements basic logic for preparation of the stream for input operations
(public member class ofstd::basic_istream<CharT,Traits>)[edit]

Inherited fromstd::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 offail()) (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 fromstd::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 thelong element at the given index (public member function of`std::ios_base`)[edit]
pword	resizes the private storage if necessary and access to thevoid* 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 inbinary 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: seestd::dec[edit]
`oct`	use octal base for integer I/O: seestd::oct[edit]
`hex`	use hexadecimal base for integer I/O: seestd::hex[edit]
`basefield`	dec\| oct\| hex. Useful for masking operations[edit]
`left`	left adjustment (adds fill characters to the right): seestd::left[edit]
`right`	right adjustment (adds fill characters to the left): seestd::right[edit]
`internal`	internal adjustment (adds fill characters to the internal designated point): seestd::internal[edit]
`adjustfield`	left\| right\| internal. Useful for masking operations[edit]
`scientific`	generate floating point types using scientific notation, or hex notation if combined withfixed: seestd::scientific[edit]
`fixed`	generate floating point types using fixed notation, or hex notation if combined withscientific: seestd::fixed[edit]
`floatfield`	scientific\| fixed. Useful for masking operations[edit]
`boolalpha`	insert and extractbool type in alphanumeric format: seestd::boolalpha[edit]
`showbase`	generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O: seestd::showbase[edit]
`showpoint`	generate a decimal-point character unconditionally for floating-point number output: seestd::showpoint[edit]
`showpos`	generate a+ character for non-negative numeric output: seestd::showpos[edit]
`skipws`	skip leading whitespace before certain input operations: seestd::skipws[edit]
`unitbuf`	flush the output after each output operation: seestd::unitbuf[edit]
`uppercase`	replace certain lowercase letters with their uppercase equivalents in certain output operations: seestd::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]

[edit]Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_fstream_native_handle`	`202306L`	(C++26)	native handles support

[edit]Example

Run this code

#include <fstream>#include <iostream>#include <string> int main(){std::string filename="Test.b"; // prepare a file to readdouble d=3.14;std::ofstream(filename, std::ios::binary)        .write(reinterpret_cast<char*>(&d), sizeof d)<<123<<"abc"; // open file for reading    std::ifstream istrm(filename, std::ios::binary);if(!istrm.is_open())std::cout<<"failed to open "<< filename<<'\n';else{double d;        istrm.read(reinterpret_cast<char*>(&d), sizeof d);// binary inputint n;std::string s;if(istrm>> n>> s)// text inputstd::cout<<"read back from file: "<< d<<' '<< n<<' '<< s<<'\n';}}

Output:

read back from file: 3.14 123 abc

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/io/basic_ifstream&oldid=158179"

Movatterモバイル変換

cppreference.com

Namespaces

Variants

Views

Actions

std::basic_ifstream

Contents

[edit]Member types

[edit]Member functions

File operations

[edit]Non-member functions

Inherited fromstd::basic_istream

Member functions

Formatted input

Unformatted input

Positioning

Miscellaneous

Member classes

Inherited fromstd::basic_ios

Member types

Member functions

State functions

Formatting

Miscellaneous

Inherited fromstd::ios_base

Member functions

Formatting

Locales

Internal extensible array

Miscellaneous

Member classes

Member types and constants

[edit]Notes

[edit]Example

Navigation

Toolbox