NAME¶

std::basic_filebuf - std::basic_filebuf

Synopsis¶

Defined in header <fstream>
template<

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

> class basic_filebuf : public std::basic_streambuf<CharT, Traits>

std::basic_filebuf is a std::basic_streambuf whose associated character sequence is
a file. Both the input sequence and the output sequence are associated with the same
file, and a joint file position is maintained for both operations. The restrictions
on reading and writing a sequence with std::basic_filebuf are the same as
std::FILEs.

The functions underflow() and overflow() / sync() perform the actual I/O between the
file and the get and put areas of the buffer. When CharT is not char, most
implementations store multibyte characters in the file and a std::codecvt facet is
used to perform wide/multibyte character conversion.

Several typedefs for common character types are provided:

Defined in header <streambuf>
Type Definition
std::filebuf std::basic_filebuf<char>
std::wfilebuf std::basic_filebuf<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 which is required to be
std::fpos<Traits::state_type>
off_type Traits::off_type
native_handle_type(C++26) implementation-defined type that is TriviallyCopyable and
semiregular

Member functions¶

Public member functions¶

constructor constructs a basic_filebuf object
(public member function)
operator= assigns a basic_filebuf object
(C++11) (public member function)
swap swaps two basic_filebuf objects
(C++11) (public member function)
native_handle returns the underlying implementation-defined handle
(C++26) (public member function)
destructor destructs a basic_filebuf object and closes the file if it is open
[virtual] (virtual public member function)
is_open checks if the associated file is open
(public member function)
open opens a file and configures it as the associated character sequence
(public member function)
close flushes the put area buffer and closes the associated file
(public member function)

Protected member functions¶

showmanyc optionally provides the number of characters available for input from
[virtual] the file
(virtual protected member function)
underflow reads from the associated file
[virtual] (virtual protected member function)
uflow reads from the associated file and advances the next pointer in the
[virtual] get area
(virtual protected member function)
pbackfail backs out the input sequence to unget a character, not affecting the
[virtual] associated file
(virtual protected member function)
overflow writes characters to the associated file from the put area
[virtual] (virtual protected member function)
setbuf provides user-supplied buffer or turns this filebuf unbuffered
[virtual] (virtual protected member function)
seekoff repositions the file position, using relative addressing
[virtual] (virtual protected member function)
seekpos repositions the file position, using absolute addressing
[virtual] (virtual protected member function)
sync writes characters to the associated file from the put area
[virtual] (virtual protected member function)
imbue changes the associated locale
[virtual] (virtual protected member function)

Non-member functions¶

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

Inherited from std::basic_streambuf

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¶

destructor destructs the basic_streambuf object
[virtual] (virtual public member function of
std::basic_streambuf<CharT,Traits>)

Locales¶

invokes imbue()
pubimbue (public member function of std::basic_streambuf<CharT,Traits>)

obtains a copy of the associated locale
getloc (public member function of std::basic_streambuf<CharT,Traits>)

Positioning¶

invokes setbuf()
pubsetbuf (public member function of std::basic_streambuf<CharT,Traits>)

invokes seekoff()
pubseekoff (public member function of std::basic_streambuf<CharT,Traits>)

invokes seekpos()
pubseekpos (public member function of std::basic_streambuf<CharT,Traits>)

invokes sync()
pubsync (public member function of std::basic_streambuf<CharT,Traits>)

Get area¶

obtains the number of characters immediately available in the get
in_avail area
(public member function of std::basic_streambuf<CharT,Traits>)

advances the input sequence, then reads one character without
snextc advancing again
(public member function of std::basic_streambuf<CharT,Traits>)

sbumpc reads one character from the input sequence and advances the
stossc sequence
(removed in C++17) (public member function of std::basic_streambuf<CharT,Traits>)

reads one character from the input sequence without advancing the
sgetc sequence
(public member function of std::basic_streambuf<CharT,Traits>)

invokes xsgetn()
sgetn (public member function of std::basic_streambuf<CharT,Traits>)

Put area¶

writes one character to the put area and advances the next
sputc pointer
(public member function of std::basic_streambuf<CharT,Traits>)

invokes xsputn()
sputn (public member function of std::basic_streambuf<CharT,Traits>)

Putback¶

puts one character back in the input sequence
sputbackc (public member function of std::basic_streambuf<CharT,Traits>)

moves the next pointer in the input sequence back by one
sungetc (public member function of std::basic_streambuf<CharT,Traits>)

Protected member functions¶

constructor constructs a basic_streambuf object
(protected member function)
operator= replaces a basic_streambuf object
(C++11) (protected member function)
swap swaps two basic_streambuf objects
(C++11) (protected member function)

Locales¶

imbue changes the associated locale
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)

Positioning¶

setbuf replaces the buffer with user-defined array, if permitted
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
repositions the next pointer in the input sequence, output sequence,
seekoff or both, using relative addressing
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
repositions the next pointer in the input sequence, output sequence,
seekpos or both using absolute addressing
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
sync synchronizes the buffers with the associated character sequence
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)

Get area¶

obtains the number of characters available for input in the associated
showmanyc input sequence, if known
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
underflow reads characters from the associated input sequence to the get area
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
reads characters from the associated input sequence to the get area
uflow and advances the next pointer
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
xsgetn reads multiple characters from the input sequence
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
eback returns a pointer to the beginning, current character and the end of
gptr the get area
egptr (protected member function)
gbump advances the next pointer in the input sequence
(protected member function)
repositions the beginning, next, and end pointers of the input
setg sequence
(protected member function)

Put area¶

xsputn writes multiple characters to the output sequence
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
overflow writes characters to the associated output sequence from the put area
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)
pbase returns a pointer to the beginning, current character and the end of
pptr the put area
epptr (protected member function)
pbump advances the next pointer of the output sequence
(protected member function)
repositions the beginning, next, and end pointers of the output
setp sequence
(protected member function)

Putback¶

puts a character back into the input sequence, possibly modifying the
pbackfail input sequence
[virtual] (virtual protected member function of
std::basic_streambuf<CharT,Traits>)

Notes¶

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

See also¶

object type, capable of holding all information needed to control a C I/O
FILE stream
(typedef)