std::ifstream (3) - Linux Manuals

std::ifstream: std::basic_ifstream

NAME

std::basic_ifstream - std::basic_ifstream

Synopsis

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>.
 std-basic ifstream-inheritance.svg
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>

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 file stream
constructor (public member function)

destructor destructs the basic_ifstream and the associated buffer, closes the file
                                (virtual public member function)
[virtual] (implicitly declared)

operator= moves the file stream
                                (public member function)
(C++11)

swap swaps two file streams
                                (public member function)
(C++11)
                                returns the underlying raw file device object
rdbuf (public member function)

File operations

                                checks if the stream has an associated file
is_open (public member function)
                                opens a file and associates it with the stream
open (public member function)
                                closes the associated file
close (public member function)

Non-member functions

std::swap(std::basic_ifstream) specializes the std::swap algorithm
                               (function template)
(C++11)

Inherited from std::basic_istream

Member functions

Formatted input

           extracts formatted data
operator>> (public member function of std::basic_istream<CharT,Traits>)

Unformatted input

           extracts characters
get (public member function of std::basic_istream<CharT,Traits>)
           reads the next character without extracting it
peek (public member function of std::basic_istream<CharT,Traits>)
           unextracts a character
unget (public member function of std::basic_istream<CharT,Traits>)
           puts character into input stream
putback (public member function of std::basic_istream<CharT,Traits>)
           extracts characters until the given character is found
getline (public member function of std::basic_istream<CharT,Traits>)
           extracts and discards characters until the given character is found
ignore (public member function of std::basic_istream<CharT,Traits>)
           extracts blocks of characters
read (public member function of std::basic_istream<CharT,Traits>)
           extracts already available blocks of characters
readsome (public member function of std::basic_istream<CharT,Traits>)
           returns number of characters extracted by last unformatted input operation
gcount (public member function of std::basic_istream<CharT,Traits>)

Positioning

           returns the input position indicator
tellg (public member function of std::basic_istream<CharT,Traits>)
           sets the input position indicator
seekg (public member function of std::basic_istream<CharT,Traits>)

Miscellaneous

           synchronizes with the underlying storage device
sync (public member function of std::basic_istream<CharT,Traits>)

Member classes

       implements basic logic for preparation of the stream for input operations
sentry (public member class of std::basic_istream<CharT,Traits>)

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
good (public member function of std::basic_ios<CharT,Traits>)
               checks if end-of-file has been reached
eof (public member function of std::basic_ios<CharT,Traits>)
               checks if an error has occurred
fail (public member function of std::basic_ios<CharT,Traits>)
               checks if a non-recoverable error has occurred
bad (public member function of std::basic_ios<CharT,Traits>)
               checks if an error has occurred (synonym of fail())
operator! (public member function of std::basic_ios<CharT,Traits>)

operator_void*
operator_bool checks if no error has occurred (synonym of !fail())
               (public member function of std::basic_ios<CharT,Traits>)
(until C++11)
(since C++11)
               returns state flags
rdstate (public member function of std::basic_ios<CharT,Traits>)
               sets state flags
setstate (public member function of std::basic_ios<CharT,Traits>)
               modifies state flags
clear (public member function of std::basic_ios<CharT,Traits>)

Formatting

               copies formatting information
copyfmt (public member function of std::basic_ios<CharT,Traits>)
               manages the fill character
fill (public member function of std::basic_ios<CharT,Traits>)

Miscellaneous

               manages exception mask
exceptions (public member function of std::basic_ios<CharT,Traits>)
               sets the locale
imbue (public member function of std::basic_ios<CharT,Traits>)
               manages associated stream buffer
rdbuf (public member function of std::basic_ios<CharT,Traits>)
               manages tied stream
tie (public member function of std::basic_ios<CharT,Traits>)
               narrows characters
narrow (public member function of std::basic_ios<CharT,Traits>)
               widens characters
widen (public member function of std::basic_ios<CharT,Traits>)

Inherited from std::ios_base

Member functions

Formatting

                  manages format flags
flags (public member function of std::ios_base)
                  sets specific format flag
setf (public member function of std::ios_base)
                  clears specific format flag
unsetf (public member function of std::ios_base)
                  manages decimal precision of floating point operations
precision (public member function of std::ios_base)
                  manages field width
width (public member function of std::ios_base)

Locales

                  sets locale
imbue (public member function of std::ios_base)
                  returns current locale
getloc (public member function of std::ios_base)

Internal extensible array

xalloc 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)
[static]
                  resizes the private storage if necessary and access to the long element at the given index
iword (public member function of std::ios_base)
                  resizes the private storage if necessary and access to the void* element at the given index
pword (public member function of std::ios_base)

Miscellaneous

                  registers event callback function
register_callback (public member function of std::ios_base)

sync_with_stdio sets whether C++ and C IO libraries are interoperable
                  (public static member function of std::ios_base)
[static]

Member classes

                  stream exception
failure (public member class of std::ios_base)
                  initializes standard stream objects
Init (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
openmode 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

               (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
fmtflags 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
iostate 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
seekdir end the ending of a stream
               cur the current position of stream position indicator

               (typedef)
               specifies event type
event (enum)
               callback function type
event_callback (typedef)

Example

// Run this code

  #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