# std::basic_filebuf

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< cpp‎ | io

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 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.

Two specializations for common character types are also defined:

Defined in header `<streambuf>`
Type | Definition
`filebuf` | basic_filebuf<char>
`wfilebuf` | 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

### Member functions

### Public member functions

(constructor) | constructs a basic_filebuf object (public member function)
operator= (C++11) | assigns a basic_filebuf object (public member function)
swap (C++11) | swaps two basic_filebuf objects (public member function)
(destructor) [virtual] | destructs a basic_filebuf object and closes the file if it is open (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 [virtual] | optionally provides the number of characters available for input from the file (virtual protected member function)
underflow [virtual] | reads from the associated file (virtual protected member function)
uflow [virtual] | reads from the associated file and advances the next pointer in the get area (virtual protected member function)
pbackfail [virtual] | backs out the input sequence to unget a character, not affecting the associated file (virtual protected member function)
overflow [virtual] | writes characters to the associated file from the put area (virtual protected member function)
setbuf [virtual] | provides user-supplied buffer or turns this filebuf unbuffered (virtual protected member function)
seekoff [virtual] | repositions the file position, using relative addressing (virtual protected member function)
seekpos [virtual] | repositions the file position, using absolute addressing (virtual protected member function)
sync [virtual] | writes characters to the associated file from the put area (virtual protected member function)
imbue [virtual] | changes the associated locale (virtual protected member function)

### Non-member functions

std::swap(std::basic_filebuf) (C++11) | specializes the std::swap algorithm (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) [virtual] | destructs the basic_streambuf object (virtual public member function of `std::basic_streambuf<CharT,Traits>`)

##### Locales

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

##### Positioning

pubsetbuf | invokes setbuf() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekoff | invokes seekoff() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekpos | invokes seekpos() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubsync | invokes sync() (public member function of `std::basic_streambuf<CharT,Traits>`)

##### Get area

in_avail | obtains the number of characters immediately available in the get area (public member function of `std::basic_streambuf<CharT,Traits>`)
snextc | advances the input sequence, then reads one character without advancing again (public member function of `std::basic_streambuf<CharT,Traits>`)
sbumpc | reads one character from the input sequence and advances the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
stossc (deprecated in C++98)(removed in C++17) | advances the input sequence as if by calling sbumpc() and discarding the result (public member function)
sgetc | reads one character from the input sequence without advancing the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sgetn | invokes xsgetn() (public member function of `std::basic_streambuf<CharT,Traits>`)

##### Put area

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

##### Putback

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

### Protected member functions

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

##### Locales

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

##### Positioning

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

##### Get area

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

##### Put area

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

##### Putback

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

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