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std::basic_ifstream

From cppreference.com
< cpp‎ | io
Defined in header <fstream>
template<

    class CharT,
    class Traits = std::char_traits<CharT>

> class basic_ifstream : public std::basic_istream<CharT, Traits>

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>.

cpp/io/ios basecpp/io/basic ioscpp/io/basic istreamstd-basic ifstream-inheritance.svg
About this image

Inheritance diagram

Two specializations for common character types are also defined:

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

Contents

[edit] Member types

Member type Definition
char_type CharT[edit]
traits_type Traits[edit]
int_type Traits::int_type[edit]
pos_type Traits::pos_type[edit]
off_type Traits::off_type[edit]

[edit] Member functions

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]
(C++11)
moves the file stream
(public member function) [edit]
(C++11)
swaps two file streams
(public member function) [edit]
returns the underlying raw file device object
(public member function) [edit]
File operations
checks if the stream has an associated file
(public member function) [edit]
opens a file and associates it with the stream
(public member function) [edit]
closes the associated file
(public member function) [edit]

[edit] Non-member functions

specializes the std::swap algorithm
(function template) [edit]


Inherited from std::basic_istream

Member functions

Formatted input
extracts formatted data
(public member function of std::basic_istream) [edit]
Unformatted input
extracts characters
(public member function of std::basic_istream) [edit]
reads the next character without extracting it
(public member function of std::basic_istream) [edit]
unextracts a character
(public member function of std::basic_istream) [edit]
puts character into input stream
(public member function of std::basic_istream) [edit]
extracts characters until the given character is found
(public member function of std::basic_istream) [edit]
extracts and discards characters until the given character is found
(public member function of std::basic_istream) [edit]
extracts blocks of characters
(public member function of std::basic_istream) [edit]
extracts already available blocks of characters
(public member function of std::basic_istream) [edit]
returns number of characters extracted by last unformatted input operation
(public member function of std::basic_istream) [edit]
Positioning
returns the input position indicator
(public member function of std::basic_istream) [edit]
sets the input position indicator
(public member function of std::basic_istream) [edit]
Miscellaneous
synchronizes with the underlying storage device
(public member function of std::basic_istream) [edit]

Member classes

implements basic logic for preparation of the stream for input operations
(public member class of std::basic_istream) [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
checks if no error has occurred i.e. I/O operations are available
(public member function of std::basic_ios) [edit]
checks if end-of-file has been reached
(public member function of std::basic_ios) [edit]
checks if an error has occurred
(public member function of std::basic_ios) [edit]
checks if a non-recoverable error has occurred
(public member function of std::basic_ios) [edit]
checks if an error has occurred (synonym of fail())
(public member function of std::basic_ios) [edit]
(until C++11)(since C++11)
checks if no error has occurred (synonym of !fail())
(public member function of std::basic_ios) [edit]
returns state flags
(public member function of std::basic_ios) [edit]
sets state flags
(public member function of std::basic_ios) [edit]
modifies state flags
(public member function of std::basic_ios) [edit]
Formatting
copies formatting information
(public member function of std::basic_ios) [edit]
manages the fill character
(public member function of std::basic_ios) [edit]
Miscellaneous
manages exception mask
(public member function of std::basic_ios) [edit]
sets the locale
(public member function of std::basic_ios) [edit]
manages associated stream buffer
(public member function of std::basic_ios) [edit]
manages tied stream
(public member function of std::basic_ios) [edit]
narrows characters
(public member function of std::basic_ios) [edit]
widens characters
(public member function of std::basic_ios) [edit]

Inherited from std::ios_base

Member functions

Formatting
manages format flags
(public member function of std::ios_base) [edit]
sets specific format flag
(public member function of std::ios_base) [edit]
clears specific format flag
(public member function of std::ios_base) [edit]
manages decimal precision of floating point operations
(public member function of std::ios_base) [edit]
manages field width
(public member function of std::ios_base) [edit]
Locales
sets locale
(public member function of std::ios_base) [edit]
returns current locale
(public member function of std::ios_base) [edit]
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) [edit]
resizes the private storage if necessary and access to the long element at the given index
(public member function of std::ios_base) [edit]
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
registers event callback function
(public member function of std::ios_base) [edit]
sets whether C++ and C IO libraries are interoperable
(public static member function of std::ios_base) [edit]
Member classes
stream exception
(public member class of std::ios_base) [edit]
initializes standard stream objects
(public member class of std::ios_base) [edit]

Member types and constants

Type Explanation
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]

(typedef) [edit]
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]
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]
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]
specifies event type
(enum) [edit]
callback function type
(typedef) [edit]

[edit] Example

#include <iostream>
#include <fstream>
#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