std:: basic_ifstream
From cppreference.com
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Defined in header
<fstream>
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template
<
class
CharT,
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The class template
basic_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 of
std::basic_ifstream
holds only one non-derived data member: an instance of
std::
basic_filebuf
<
CharT, Traits
>
.
Inheritance diagram
Several typedefs for common character types are provided:
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Defined in header
<fstream>
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| Type | Definition |
std::ifstream
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std :: basic_ifstream < char > |
std::wifstream
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std :: basic_ifstream < wchar_t > |
Member types
| Member type | Definition |
char_type
|
CharT
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traits_type
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Traits
; the program is ill-formed if
Traits::char_type
is not
CharT
.
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int_type
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Traits::int_type
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pos_type
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Traits::pos_type
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off_type
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Traits::off_type
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native_handle_type
(C++26)
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implementation-defined
type that is
TriviallyCopyable
and
semiregular
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Member functions
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constructs the file stream
(public member function) |
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(destructor)
[virtual]
(implicitly declared)
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destructs the
basic_ifstream
and the associated buffer, closes the file
(virtual public member function) |
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(C++11)
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moves the file stream
(public member function) |
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(C++11)
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swaps two file streams
(public member function) |
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returns the underlying raw file device object
(public member function) |
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(C++26)
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returns the underlying implementation-defined handle
(public member function) |
File operations |
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checks if the stream has an associated file
(public member function) |
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opens a file and associates it with the stream
(public member function) |
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closes the associated file
(public member function) |
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Non-member functions
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(C++11)
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specializes the
std::swap
algorithm
(function template) |
Inherited from std:: basic_istream
Member functions
Formatted input |
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extracts formatted data
(public member function of
std::basic_istream<CharT,Traits>
)
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Unformatted input |
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extracts characters
(public member function of
std::basic_istream<CharT,Traits>
)
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reads the next character without extracting it
(public member function of
std::basic_istream<CharT,Traits>
)
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unextracts a character
(public member function of
std::basic_istream<CharT,Traits>
)
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puts a character into input stream
(public member function of
std::basic_istream<CharT,Traits>
)
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extracts characters until the given character is found
(public member function of
std::basic_istream<CharT,Traits>
)
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extracts and discards characters until the given character is found
(public member function of
std::basic_istream<CharT,Traits>
)
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extracts blocks of characters
(public member function of
std::basic_istream<CharT,Traits>
)
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extracts already available blocks of characters
(public member function of
std::basic_istream<CharT,Traits>
)
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returns number of characters extracted by last unformatted input operation
(public member function of
std::basic_istream<CharT,Traits>
)
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Positioning |
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returns the input position indicator
(public member function of
std::basic_istream<CharT,Traits>
)
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sets the input position indicator
(public member function of
std::basic_istream<CharT,Traits>
)
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Miscellaneous |
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synchronizes with the underlying storage device
(public member function of
std::basic_istream<CharT,Traits>
)
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Member classes
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implements basic logic for preparation of the stream for input operations
(public member class of
std::basic_istream<CharT,Traits>
)
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Inherited from std:: basic_ios
Member types
| Member type | Definition |
char_type
|
CharT
|
traits_type
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Traits
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int_type
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Traits::int_type
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pos_type
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Traits::pos_type
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off_type
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Traits::off_type
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Member functions
State functions |
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checks if no error has occurred i.e. I/O operations are available
(public member function of
std::basic_ios<CharT,Traits>
)
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checks if end-of-file has been reached
(public member function of
std::basic_ios<CharT,Traits>
)
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checks if an error has occurred
(public member function of
std::basic_ios<CharT,Traits>
)
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checks if a non-recoverable error has occurred
(public member function of
std::basic_ios<CharT,Traits>
)
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checks if an error has occurred (synonym of
fail()
)
(public member function of
std::basic_ios<CharT,Traits>
)
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checks if no error has occurred (synonym of
!
fail()
)
(public member function of
std::basic_ios<CharT,Traits>
)
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returns state flags
(public member function of
std::basic_ios<CharT,Traits>
)
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sets state flags
(public member function of
std::basic_ios<CharT,Traits>
)
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modifies state flags
(public member function of
std::basic_ios<CharT,Traits>
)
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Formatting |
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copies formatting information
(public member function of
std::basic_ios<CharT,Traits>
)
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manages the fill character
(public member function of
std::basic_ios<CharT,Traits>
)
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Miscellaneous |
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manages exception mask
(public member function of
std::basic_ios<CharT,Traits>
)
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sets the locale
(public member function of
std::basic_ios<CharT,Traits>
)
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manages associated stream buffer
(public member function of
std::basic_ios<CharT,Traits>
)
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manages tied stream
(public member function of
std::basic_ios<CharT,Traits>
)
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narrows characters
(public member function of
std::basic_ios<CharT,Traits>
)
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widens characters
(public member function of
std::basic_ios<CharT,Traits>
)
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Inherited from std:: ios_base
Member functions
Formatting |
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manages format flags
(public member function of
std::ios_base
)
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sets specific format flag
(public member function of
std::ios_base
)
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clears specific format flag
(public member function of
std::ios_base
)
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manages decimal precision of floating point operations
(public member function of
std::ios_base
)
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manages field width
(public member function of
std::ios_base
)
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Locales |
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sets locale
(public member function of
std::ios_base
)
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returns current locale
(public member function of
std::ios_base
)
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Internal extensible array |
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[static]
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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
)
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resizes the private storage if necessary and access to the
long
element at the given index
(public member function of
std::ios_base
)
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resizes the private storage if necessary and access to the
void
*
element at the given index
(public member function of
std::ios_base
)
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Miscellaneous |
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registers event callback function
(public member function of
std::ios_base
)
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[static]
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sets whether C++ and C I/O libraries are interoperable
(public static member function of
std::ios_base
)
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Member classes |
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stream exception
(public member class of
std::ios_base
)
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initializes standard stream objects
(public member class of
std::ios_base
)
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Member types and constants |
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| Type | Explanation | ||||||||||||||||||||||||||||||||||||||
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stream open mode type
The following constants are also defined:
(typedef) |
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formatting flags type
The following constants are also defined:
(typedef) |
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state of the stream type
The following constants are also defined:
(typedef) |
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seeking direction type
The following constants are also defined:
(typedef) |
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specifies event type
(enum) |
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callback function type
(typedef) |
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Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_fstream_native_handle
|
202306L | (C++26) | native handles support |
Example
Run this code
#include <fstream> #include <iostream> #include <string> int main() { std::string filename = "Test.b"; // prepare a file to read double 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 input int n; std::string s; if (istrm >> n >> s) // text input std::cout << "read back from file: " << d << ' ' << n << ' ' << s << '\n'; } }
Output:
read back from file: 3.14 123 abc