std::basic_filebuf

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basic_filebuf
(C++23)
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std::basic_filebuf
 
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.

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

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

Protected member functions

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

Non-member functions

(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

[virtual]
 destructs the basic_streambuf object
(virtual public member function of std::basic_streambuf<CharT,Traits>)
Locales
invokes imbue()
(public member function of std::basic_streambuf<CharT,Traits>)
obtains a copy of the associated locale
(public member function of std::basic_streambuf<CharT,Traits>)
Positioning
invokes setbuf()
(public member function of std::basic_streambuf<CharT,Traits>)
invokes seekoff()
(public member function of std::basic_streambuf<CharT,Traits>)
invokes seekpos()
(public member function of std::basic_streambuf<CharT,Traits>)
invokes sync()
(public member function of std::basic_streambuf<CharT,Traits>)
Get area
obtains the number of characters immediately available in the get area
(public member function of std::basic_streambuf<CharT,Traits>)
advances the input sequence, then reads one character without advancing again
(public member function of std::basic_streambuf<CharT,Traits>)
(removed in C++17)
 reads one character from the input sequence and advances the sequence
(public member function of std::basic_streambuf<CharT,Traits>)
reads one character from the input sequence without advancing the sequence
(public member function of std::basic_streambuf<CharT,Traits>)
invokes xsgetn()
(public member function of std::basic_streambuf<CharT,Traits>)
Put area
writes one character to the put area and advances the next pointer
(public member function of std::basic_streambuf<CharT,Traits>)
invokes xsputn()
(public member function of std::basic_streambuf<CharT,Traits>)
Putback
puts one character back in the input sequence
(public member function of std::basic_streambuf<CharT,Traits>)
moves the next pointer in the input sequence back by one
(public member function of std::basic_streambuf<CharT,Traits>)

Protected member functions

 constructs a basic_streambuf object
(protected member function)
(C++11)
 replaces a basic_streambuf object
(protected member function)
(C++11)
 swaps two basic_streambuf objects
(protected member function)
Locales
[virtual]
 changes the associated locale
(virtual protected member function of std::basic_streambuf<CharT,Traits>)
Positioning
[virtual]
 replaces the buffer with user-defined array, if permitted
(virtual protected member function of std::basic_streambuf<CharT,Traits>)
[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>)
[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>)
[virtual]
 synchronizes the buffers with the associated character sequence
(virtual protected member function of std::basic_streambuf<CharT,Traits>)
Get area
[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>)
[virtual]
 reads characters from the associated input sequence to the get area
(virtual protected member function of std::basic_streambuf<CharT,Traits>)
[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>)
[virtual]
 reads multiple characters from the input sequence
(virtual protected member function of std::basic_streambuf<CharT,Traits>)
returns a pointer to the beginning, current character and the end of the get area
(protected member function)
advances the next pointer in the input sequence
(protected member function)
repositions the beginning, next, and end pointers of the input sequence
(protected member function)
Put area
[virtual]
 writes multiple characters to the output sequence
(virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]
 writes characters to the associated output sequence from the put area
(virtual protected member function of std::basic_streambuf<CharT,Traits>)
returns a pointer to the beginning, current character and the end of the put area
(protected member function)
advances the next pointer of the output sequence
(protected member function)
repositions the beginning, next, and end pointers of the output sequence
(protected member function)
Putback
[virtual]
 puts a character back into the input sequence, possibly modifying the input sequence
(virtual protected member function of std::basic_streambuf<CharT,Traits>)

Notes

Feature-test macro Value Std Comment
__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 stream
(typedef)
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