std::basic_fil...harT, _Traits >(3cxx) std::basic_fil...harT, _Traits >(3cxx)
NAME
std::basic_filebuf< _CharT, _Traits > - The actual work of input and
output (for files).
SYNOPSIS
#include <fstream>
Inherits std::basic_streambuf< _CharT, _Traits >.
Inherited by __gnu_cxx::stdio_filebuf< _CharT, _Traits >.
Public Types
typedef codecvt< char_type, char, __state_type > __codecvt_type
typedef __basic_file< char > __file_type
typedef basic_filebuf< char_type, traits_type > __filebuf_type
typedef traits_type::state_type __state_type
typedef basic_streambuf< char_type, traits_type > __streambuf_type
typedef _CharT char_type
typedef traits_type::int_type int_type
typedef traits_type::off_type off_type
typedef traits_type::pos_type pos_type
typedef _Traits traits_type
Public Member Functions
basic_filebuf ()
Does not open any files.
basic_filebuf (basic_filebuf &&)
basic_filebuf (const basic_filebuf &)=delete
virtual ~basic_filebuf ()
The destructor closes the file first.
__filebuf_type * close ()
Closes the currently associated file.
locale getloc () const
Locale access.
streamsize in_avail ()
Looking ahead into the stream.
bool is_open () const throw ()
Returns true if the external file is open.
template<typename _Path > _If_fs_path< _Path, __filebuf_type * > open
(const _Path &__s, ios_base::openmode __mode)
Opens an external file.
__filebuf_type * open (const char *__s, ios_base::openmode __mode)
Opens an external file.
__filebuf_type * open (const std::string &__s, ios_base::openmode
__mode)
Opens an external file.
basic_filebuf & operator= (basic_filebuf &&)
basic_filebuf & operator= (const basic_filebuf &)=delete
locale pubimbue (const locale &__loc)
Entry point for imbue().
int_type sbumpc ()
Getting the next character.
int_type sgetc ()
Getting the next character.
streamsize sgetn (char_type *__s, streamsize __n)
Entry point for xsgetn.
int_type snextc ()
Getting the next character.
int_type sputbackc (char_type __c)
Pushing characters back into the input stream.
int_type sputc (char_type __c)
Entry point for all single-character output functions.
streamsize sputn (const char_type *__s, streamsize __n)
Entry point for all single-character output functions.
int_type sungetc ()
Moving backwards in the input stream.
void swap (basic_filebuf &)
basic_streambuf * pubsetbuf (char_type *__s, streamsize __n)
Entry points for derived buffer functions.
pos_type pubseekoff (off_type __off, ios_base::seekdir __way,
ios_base::openmode __mode=ios_base::in|ios_base::out)
Alters the stream position.
pos_type pubseekpos (pos_type __sp, ios_base::openmode
__mode=ios_base::in|ios_base::out)
Alters the stream position.
int pubsync ()
Calls virtual sync function.
Protected Member Functions
void __safe_gbump (streamsize __n)
void __safe_pbump (streamsize __n)
void _M_allocate_internal_buffer ()
bool _M_convert_to_external (char_type *, streamsize)
void _M_create_pback ()
void _M_destroy_internal_buffer () throw ()
void _M_destroy_pback () throw ()
int _M_get_ext_pos (__state_type &__state)
pos_type _M_seek (off_type __off, ios_base::seekdir __way, __state_type
__state)
void _M_set_buffer (streamsize __off)
bool _M_terminate_output ()
void gbump (int __n)
Moving the read position.
virtual void imbue (const locale &__loc)
Changes translations.
virtual int_type overflow (int_type __c=_Traits::eof())
Consumes data from the buffer; writes to the controlled sequence.
virtual int_type pbackfail (int_type __c=_Traits::eof())
Tries to back up the input sequence.
void pbump (int __n)
Moving the write position.
virtual pos_type seekoff (off_type __off, ios_base::seekdir __way,
ios_base::openmode __mode=ios_base::in|ios_base::out)
Alters the stream positions.
virtual pos_type seekpos (pos_type __pos, ios_base::openmode
__mode=ios_base::in|ios_base::out)
Alters the stream positions.
virtual __streambuf_type * setbuf (char_type *__s, streamsize __n)
Manipulates the buffer.
void setg (char_type *__gbeg, char_type *__gnext, char_type *__gend)
Setting the three read area pointers.
void setp (char_type *__pbeg, char_type *__pend)
Setting the three write area pointers.
virtual streamsize showmanyc ()
Investigating the data available.
void swap (basic_streambuf &__sb)
virtual int sync ()
Synchronizes the buffer arrays with the controlled sequences.
virtual int_type uflow ()
Fetches more data from the controlled sequence.
virtual int_type underflow ()
Fetches more data from the controlled sequence.
virtual streamsize xsgetn (char_type *__s, streamsize __n)
Multiple character extraction.
virtual streamsize xsputn (const char_type *__s, streamsize __n)
Multiple character insertion.
char_type * eback () const
Access to the get area.
char_type * gptr () const
Access to the get area.
char_type * egptr () const
Access to the get area.
char_type * pbase () const
Access to the put area.
char_type * pptr () const
Access to the put area.
char_type * epptr () const
Access to the put area.
Protected Attributes
char_type * _M_buf
Pointer to the beginning of internal buffer.
bool _M_buf_allocated
locale _M_buf_locale
Current locale setting.
size_t _M_buf_size
const __codecvt_type * _M_codecvt
char * _M_ext_buf
streamsize _M_ext_buf_size
char * _M_ext_end
const char * _M_ext_next
__file_type _M_file
char_type * _M_in_beg
Start of get area.
char_type * _M_in_cur
Current read area.
char_type * _M_in_end
End of get area.
__c_lock _M_lock
ios_base::openmode _M_mode
Place to stash in || out || in | out settings for current filebuf.
char_type * _M_out_beg
Start of put area.
char_type * _M_out_cur
Current put area.
char_type * _M_out_end
End of put area.
bool _M_reading
__state_type _M_state_beg
__state_type _M_state_cur
__state_type _M_state_last
bool _M_writing
char_type _M_pback
char_type * _M_pback_cur_save
char_type * _M_pback_end_save
bool _M_pback_init
Friends
class ios_base
Detailed Description
template<typename _CharT, typename _Traits>
class std::basic_filebuf< _CharT, _Traits >"The actual work of input and
output (for files).
Template Parameters
_CharT Type of character stream.
_Traits Traits for character type, defaults to char_traits<_CharT>.
This class associates both its input and output sequence with an
external disk file, and maintains a joint file position for both
sequences. Many of its semantics are described in terms of similar
behavior in the Standard C Library's FILE streams.
Requirements on traits_type, specific to this class:
• traits_type::pos_type must be fpos<traits_type::state_type>
• traits_type::off_type must be streamoff
• traits_type::state_type must be Assignable and DefaultConstructible,
• traits_type::state_type() must be the initial state for codecvt.
Constructor & Destructor Documentation
template<typename _CharT , typename _Traits > std::basic_filebuf< _CharT,
_Traits >::basic_filebuf ()
Does not open any files. The default constructor initializes the parent
class using its own default ctor.
References std::basic_streambuf< _CharT, _Traits >::_M_buf_locale.
template<typename _CharT , typename _Traits > virtual std::basic_filebuf<
_CharT, _Traits >::~basic_filebuf () [inline], [virtual]
The destructor closes the file first.
Member Function Documentation
template<typename _CharT , typename _Traits > void std::basic_filebuf<
_CharT, _Traits >::_M_create_pback () [inline], [protected]
Initializes pback buffers, and moves normal buffers to safety.
Assumptions: _M_in_cur has already been moved back
template<typename _CharT , typename _Traits > void std::basic_filebuf<
_CharT, _Traits >::_M_destroy_pback () [inline], [protected]
Deactivates pback buffer contents, and restores normal buffer.
Assumptions: The pback buffer has only moved forward.
template<typename _CharT , typename _Traits > void std::basic_filebuf<
_CharT, _Traits >::_M_set_buffer (streamsize __off) [inline],
[protected]
This function sets the pointers of the internal buffer, both get and put
areas. Typically:
__off == egptr() - eback() upon underflow/uflow (read mode); __off == 0
upon overflow (write mode); __off == -1 upon open, setbuf, seekoff/pos
(uncommitted mode).
NB: epptr() - pbase() == _M_buf_size - 1, since _M_buf_size reflects the
actual allocated memory and the last cell is reserved for the overflow
char of a full put area.
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::__filebuf_type * std::basic_filebuf< _CharT, _Traits >::close ()
Closes the currently associated file.
Returns
this on success, NULL on failure
If no file is currently open, this function immediately fails.
If a put buffer area exists, overflow(eof) is called to flush all the
characters. The file is then closed.
If any operations fail, this function also fails.
template<typename _CharT , typename _Traits > char_type *
std::basic_streambuf< _CharT, _Traits >::eback () const [inline],
[protected], [inherited]
Access to the get area. These functions are only available to other
protected functions, including derived classes.
• eback() returns the beginning pointer for the input sequence
• gptr() returns the next pointer for the input sequence
• egptr() returns the end pointer for the input sequence
template<typename _CharT , typename _Traits > char_type *
std::basic_streambuf< _CharT, _Traits >::egptr () const [inline],
[protected], [inherited]
Access to the get area. These functions are only available to other
protected functions, including derived classes.
• eback() returns the beginning pointer for the input sequence
• gptr() returns the next pointer for the input sequence
• egptr() returns the end pointer for the input sequence
Referenced by std::wbuffer_convert< _Codecvt, _Elem, _Tr >::underflow().
template<typename _CharT , typename _Traits > char_type *
std::basic_streambuf< _CharT, _Traits >::epptr () const [inline],
[protected], [inherited]
Access to the put area. These functions are only available to other
protected functions, including derived classes.
• pbase() returns the beginning pointer for the output sequence
• pptr() returns the next pointer for the output sequence
• epptr() returns the end pointer for the output sequence
template<typename _CharT , typename _Traits > void std::basic_streambuf<
_CharT, _Traits >::gbump (int __n) [inline], [protected], [inherited]
Moving the read position.
Parameters
__n The delta by which to move.
This just advances the read position without returning any data.
template<typename _CharT , typename _Traits > locale std::basic_streambuf<
_CharT, _Traits >::getloc () const [inline], [inherited]
Locale access.
Returns
The current locale in effect.
If pubimbue(loc) has been called, then the most recent loc is returned.
Otherwise the global locale in effect at the time of construction is
returned.
template<typename _CharT , typename _Traits > char_type *
std::basic_streambuf< _CharT, _Traits >::gptr () const [inline],
[protected], [inherited]
Access to the get area. These functions are only available to other
protected functions, including derived classes.
• eback() returns the beginning pointer for the input sequence
• gptr() returns the next pointer for the input sequence
• egptr() returns the end pointer for the input sequence
Referenced by std::wbuffer_convert< _Codecvt, _Elem, _Tr >::underflow().
template<typename _CharT , typename _Traits > void std::basic_filebuf<
_CharT, _Traits >::imbue (const locale & __loc) [protected], [virtual]
Changes translations.
Parameters
__loc A new locale.
Translations done during I/O which depend on the current locale are
changed by this call. The standard adds, Between invocations of this
function a class derived from streambuf can safely cache results of
calls to locale functions and to members of facets so obtained.
Note
Base class version does nothing.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::cur.
template<typename _CharT , typename _Traits > streamsize
std::basic_streambuf< _CharT, _Traits >::in_avail () [inline],
[inherited]
Looking ahead into the stream.
Returns
The number of characters available.
If a read position is available, returns the number of characters
available for reading before the buffer must be refilled. Otherwise
returns the derived showmanyc().
template<typename _CharT , typename _Traits > bool std::basic_filebuf<
_CharT, _Traits >::is_open () const [inline]
Returns true if the external file is open.
template<typename _CharT , typename _Traits > template<typename _Path >
_If_fs_path< _Path, __filebuf_type * > std::basic_filebuf< _CharT,
_Traits >::open (const _Path & __s, ios_base::openmode __mode) [inline]
Opens an external file.
Parameters
__s The name of the file, as a filesystem::path.
__mode The open mode flags.
Returns
this on success, NULL on failure
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::__filebuf_type * std::basic_filebuf< _CharT, _Traits >::open (const
char * __s, ios_base::openmode __mode)
Opens an external file.
Parameters
__s The name of the file.
__mode The open mode flags.
Returns
this on success, NULL on failure
If a file is already open, this function immediately fails. Otherwise it
tries to open the file named __s using the flags given in __mode.
Table 92, adapted here, gives the relation between openmode combinations
and the equivalent fopen() flags. (NB: lines app, in|out|app, in|app,
binary|app, binary|in|out|app, and binary|in|app per DR 596)
+---------------------------------------------------------+
| ios_base Flag combination stdio equivalent |
|binary in out trunc app |
+---------------------------------------------------------+
| + w |
| + + a |
| + a |
| + + w |
| + r |
| + + r+ |
| + + + w+ |
| + + + a+ |
| + + a+ |
+---------------------------------------------------------+
| + + wb |
| + + + ab |
| + + ab |
| + + + wb |
| + + rb |
| + + + r+b |
| + + + + w+b |
| + + + + a+b |
| + + + a+b |
+---------------------------------------------------------+
References std::ios_base::ate, and std::ios_base::end.
template<typename _CharT , typename _Traits > __filebuf_type *
std::basic_filebuf< _CharT, _Traits >::open (const std::string & __s,
ios_base::openmode __mode) [inline]
Opens an external file.
Parameters
__s The name of the file.
__mode The open mode flags.
Returns
this on success, NULL on failure
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::int_type std::basic_filebuf< _CharT, _Traits >::overflow (int_type
__c = _Traits::eof()) [protected], [virtual]
Consumes data from the buffer; writes to the controlled sequence.
Parameters
__c An additional character to consume.
Returns
eof() to indicate failure, something else (usually __c, or
not_eof())
Informally, this function is called when the output buffer is full (or
does not exist, as buffering need not actually be done). If a buffer
exists, it is consumed, with some effect on the controlled sequence.
(Typically, the buffer is written out to the sequence verbatim.) In
either case, the character c is also written out, if __c is not eof().
For a formal definition of this function, see a good text such as Langer
& Kreft, or [27.5.2.4.5]/3-7.
A functioning output streambuf can be created by overriding only this
function (no buffer area will be used).
Note
Base class version does nothing, returns eof().
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::app, std::ios_base::cur, and
std::ios_base::out.
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::int_type std::basic_filebuf< _CharT, _Traits >::pbackfail (int_type
__c = _Traits::eof()) [protected], [virtual]
Tries to back up the input sequence.
Parameters
__c The character to be inserted back into the sequence.
Returns
eof() on failure, some other value on success
Postcondition
The constraints of gptr(), eback(), and pptr() are the same as for
underflow().
Note
Base class version does nothing, returns eof().
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::cur, and std::ios_base::in.
template<typename _CharT , typename _Traits > char_type *
std::basic_streambuf< _CharT, _Traits >::pbase () const [inline],
[protected], [inherited]
Access to the put area. These functions are only available to other
protected functions, including derived classes.
• pbase() returns the beginning pointer for the output sequence
• pptr() returns the next pointer for the output sequence
• epptr() returns the end pointer for the output sequence
template<typename _CharT , typename _Traits > void std::basic_streambuf<
_CharT, _Traits >::pbump (int __n) [inline], [protected], [inherited]
Moving the write position.
Parameters
__n The delta by which to move.
This just advances the write position without returning any data.
template<typename _CharT , typename _Traits > char_type *
std::basic_streambuf< _CharT, _Traits >::pptr () const [inline],
[protected], [inherited]
Access to the put area. These functions are only available to other
protected functions, including derived classes.
• pbase() returns the beginning pointer for the output sequence
• pptr() returns the next pointer for the output sequence
• epptr() returns the end pointer for the output sequence
template<typename _CharT , typename _Traits > locale std::basic_streambuf<
_CharT, _Traits >::pubimbue (const locale & __loc) [inline],
[inherited]
Entry point for imbue().
Parameters
__loc The new locale.
Returns
The previous locale.
Calls the derived imbue(__loc).
template<typename _CharT , typename _Traits > pos_type std::basic_streambuf<
_CharT, _Traits >::pubseekoff (off_type __off, ios_base::seekdir __way,
ios_base::openmode __mode = ios_base::in | ios_base::out) [inline],
[inherited]
Alters the stream position.
Parameters
__off Offset.
__way Value for ios_base::seekdir.
__mode Value for ios_base::openmode.
Calls virtual seekoff function.
template<typename _CharT , typename _Traits > pos_type std::basic_streambuf<
_CharT, _Traits >::pubseekpos (pos_type __sp, ios_base::openmode __mode
= ios_base::in | ios_base::out) [inline], [inherited]
Alters the stream position.
Parameters
__sp Position
__mode Value for ios_base::openmode.
Calls virtual seekpos function.
template<typename _CharT , typename _Traits > basic_streambuf *
std::basic_streambuf< _CharT, _Traits >::pubsetbuf (char_type * __s,
streamsize __n) [inline], [inherited]
Entry points for derived buffer functions. The public versions of pubfoo
dispatch to the protected derived foo member functions, passing the
arguments (if any) and returning the result unchanged.
template<typename _CharT , typename _Traits > int std::basic_streambuf<
_CharT, _Traits >::pubsync () [inline], [inherited]
Calls virtual sync function.
template<typename _CharT , typename _Traits > int_type std::basic_streambuf<
_CharT, _Traits >::sbumpc () [inline], [inherited]
Getting the next character.
Returns
The next character, or eof.
If the input read position is available, returns that character and
increments the read pointer, otherwise calls and returns uflow().
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::pos_type std::basic_filebuf< _CharT, _Traits >::seekoff (off_type,
ios_base::seekdir, ios_base::openmode = ios_base::in | ios_base::out)
[protected], [virtual]
Alters the stream positions. Each derived class provides its own
appropriate behavior.
Note
Base class version does nothing, returns a pos_type that represents
an invalid stream position.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::cur.
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::pos_type std::basic_filebuf< _CharT, _Traits >::seekpos (pos_type,
ios_base::openmode = ios_base::in | ios_base::out) [protected],
[virtual]
Alters the stream positions. Each derived class provides its own
appropriate behavior.
Note
Base class version does nothing, returns a pos_type that represents
an invalid stream position.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::beg.
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::__streambuf_type * std::basic_filebuf< _CharT, _Traits >::setbuf
(char_type * __s, streamsize __n) [protected], [virtual]
Manipulates the buffer.
Parameters
__s Pointer to a buffer area.
__n Size of __s.
Returns
this
If no file has been opened, and both __s and __n are zero, then the
stream becomes unbuffered. Otherwise, __s is used as a buffer; see
https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering
for more.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
template<typename _CharT , typename _Traits > void std::basic_streambuf<
_CharT, _Traits >::setg (char_type * __gbeg, char_type * __gnext,
char_type * __gend) [inline], [protected], [inherited]
Setting the three read area pointers.
Parameters
__gbeg A pointer.
__gnext A pointer.
__gend A pointer.
Postcondition
__gbeg == eback(), __gnext == gptr(), and __gend == egptr()
Referenced by std::wbuffer_convert< _Codecvt, _Elem, _Tr
>::wbuffer_convert().
template<typename _CharT , typename _Traits > void std::basic_streambuf<
_CharT, _Traits >::setp (char_type * __pbeg, char_type * __pend)
[inline], [protected], [inherited]
Setting the three write area pointers.
Parameters
__pbeg A pointer.
__pend A pointer.
Postcondition
__pbeg == pbase(), __pbeg == pptr(), and __pend == epptr()
Referenced by std::wbuffer_convert< _Codecvt, _Elem, _Tr
>::wbuffer_convert().
template<typename _CharT , typename _Traits > int_type std::basic_streambuf<
_CharT, _Traits >::sgetc () [inline], [inherited]
Getting the next character.
Returns
The next character, or eof.
If the input read position is available, returns that character,
otherwise calls and returns underflow(). Does not move the read position
after fetching the character.
template<typename _CharT , typename _Traits > streamsize
std::basic_streambuf< _CharT, _Traits >::sgetn (char_type * __s,
streamsize __n) [inline], [inherited]
Entry point for xsgetn.
Parameters
__s A buffer area.
__n A count.
Returns xsgetn(__s,__n). The effect is to fill __s[0] through __s[__n-1]
with characters from the input sequence, if possible.
template<typename _CharT , typename _Traits > streamsize std::basic_filebuf<
_CharT, _Traits >::showmanyc () [protected], [virtual]
Investigating the data available.
Returns
An estimate of the number of characters available in the input
sequence, or -1.
If it returns a positive value, then successive calls to underflow()
will not return traits::eof() until at least that number of characters
have been supplied. If showmanyc() returns -1, then calls to underflow()
or uflow() will fail. [27.5.2.4.3]/1
Note
Base class version does nothing, returns zero.
The standard adds that the intention is not only that the calls [to
underflow or uflow] will not return eof() but that they will return
immediately.
The standard adds that the morphemes of showmanyc are es-how-many-
see, not show-manic.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::binary, and std::ios_base::in.
template<typename _CharT , typename _Traits > int_type std::basic_streambuf<
_CharT, _Traits >::snextc () [inline], [inherited]
Getting the next character.
Returns
The next character, or eof.
Calls sbumpc(), and if that function returns traits::eof(), so does this
function. Otherwise, sgetc().
template<typename _CharT , typename _Traits > int_type std::basic_streambuf<
_CharT, _Traits >::sputbackc (char_type __c) [inline], [inherited]
Pushing characters back into the input stream.
Parameters
__c The character to push back.
Returns
The previous character, if possible.
Similar to sungetc(), but __c is pushed onto the stream instead of the
previous character. If successful, the next character fetched from the
input stream will be __c.
template<typename _CharT , typename _Traits > int_type std::basic_streambuf<
_CharT, _Traits >::sputc (char_type __c) [inline], [inherited]
Entry point for all single-character output functions.
Parameters
__c A character to output.
Returns
__c, if possible.
One of two public output functions.
If a write position is available for the output sequence (i.e., the
buffer is not full), stores __c in that position, increments the
position, and returns traits::to_int_type(__c). If a write position is
not available, returns overflow(__c).
Referenced by std::wbuffer_convert< _Codecvt, _Elem, _Tr >::overflow().
template<typename _CharT , typename _Traits > streamsize
std::basic_streambuf< _CharT, _Traits >::sputn (const char_type * __s,
streamsize __n) [inline], [inherited]
Entry point for all single-character output functions.
Parameters
__s A buffer read area.
__n A count.
One of two public output functions.
Returns xsputn(__s,__n). The effect is to write __s[0] through
__s[__n-1] to the output sequence, if possible.
template<typename _CharT , typename _Traits > int_type std::basic_streambuf<
_CharT, _Traits >::sungetc () [inline], [inherited]
Moving backwards in the input stream.
Returns
The previous character, if possible.
If a putback position is available, this function decrements the input
pointer and returns that character. Otherwise, calls and returns
pbackfail(). The effect is to unget the last character gotten.
template<typename _CharT , typename _Traits > int std::basic_filebuf<
_CharT, _Traits >::sync () [protected], [virtual]
Synchronizes the buffer arrays with the controlled sequences.
Returns
-1 on failure.
Each derived class provides its own appropriate behavior, including the
definition of failure.
Note
Base class version does nothing, returns zero.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
template<typename _CharT , typename _Traits > virtual int_type
std::basic_streambuf< _CharT, _Traits >::uflow () [inline],
[protected], [virtual], [inherited]
Fetches more data from the controlled sequence.
Returns
The first character from the pending sequence.
Informally, this function does the same thing as underflow(), and in
fact is required to call that function. It also returns the new
character, like underflow() does. However, this function also moves the
read position forward by one.
Reimplemented in __gnu_cxx::stdio_sync_filebuf< _CharT, _Traits >.
template<typename _CharT , typename _Traits > basic_filebuf< _CharT, _Traits
>::int_type std::basic_filebuf< _CharT, _Traits >::underflow ()
[protected], [virtual]
Fetches more data from the controlled sequence.
Returns
The first character from the pending sequence.
Informally, this function is called when the input buffer is exhausted
(or does not exist, as buffering need not actually be done). If a buffer
exists, it is refilled. In either case, the next available character is
returned, or traits::eof() to indicate a null pending sequence.
For a formal definition of the pending sequence, see a good text such as
Langer & Kreft, or [27.5.2.4.3]/7-14.
A functioning input streambuf can be created by overriding only this
function (no buffer area will be used). For an example, see
https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html
Note
Base class version does nothing, returns eof().
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::in.
template<typename _CharT , typename _Traits > streamsize std::basic_filebuf<
_CharT, _Traits >::xsgetn (char_type * __s, streamsize __n) [protected],
[virtual]
Multiple character extraction.
Parameters
__s A buffer area.
__n Maximum number of characters to assign.
Returns
The number of characters assigned.
Fills __s[0] through __s[__n-1] with characters from the input sequence,
as if by sbumpc(). Stops when either __n characters have been copied, or
when traits::eof() would be copied.
It is expected that derived classes provide a more efficient
implementation by overriding this definition.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::in.
template<typename _CharT , typename _Traits > streamsize std::basic_filebuf<
_CharT, _Traits >::xsputn (const char_type * __s, streamsize __n)
[protected], [virtual]
Multiple character insertion.
Parameters
__s A buffer area.
__n Maximum number of characters to write.
Returns
The number of characters written.
Writes __s[0] through __s[__n-1] to the output sequence, as if by
sputc(). Stops when either n characters have been copied, or when
sputc() would return traits::eof().
It is expected that derived classes provide a more efficient
implementation by overriding this definition.
Reimplemented from std::basic_streambuf< _CharT, _Traits >.
References std::ios_base::app, and std::ios_base::out.
Member Data Documentation
template<typename _CharT , typename _Traits > char_type* std::basic_filebuf<
_CharT, _Traits >::_M_buf [protected]
Pointer to the beginning of internal buffer.
template<typename _CharT , typename _Traits > locale std::basic_streambuf<
_CharT, _Traits >::_M_buf_locale [protected], [inherited]
Current locale setting.
Referenced by std::basic_filebuf< _CharT, _Traits >::basic_filebuf().
template<typename _CharT , typename _Traits > size_t std::basic_filebuf<
_CharT, _Traits >::_M_buf_size [protected]
Actual size of internal buffer. This number is equal to the size of the
put area + 1 position, reserved for the overflow char of a full area.
template<typename _CharT , typename _Traits > char* std::basic_filebuf<
_CharT, _Traits >::_M_ext_buf [protected]
Buffer for external characters. Used for input when
codecvt::always_noconv() == false. When valid, this corresponds to
eback().
template<typename _CharT , typename _Traits > streamsize std::basic_filebuf<
_CharT, _Traits >::_M_ext_buf_size [protected]
Size of buffer held by _M_ext_buf.
template<typename _CharT , typename _Traits > const char*
std::basic_filebuf< _CharT, _Traits >::_M_ext_next [protected]
Pointers into the buffer held by _M_ext_buf that delimit a subsequence
of bytes that have been read but not yet converted. When valid,
_M_ext_next corresponds to egptr().
template<typename _CharT , typename _Traits > char_type*
std::basic_streambuf< _CharT, _Traits >::_M_in_beg [protected],
[inherited]
Start of get area.
template<typename _CharT , typename _Traits > char_type*
std::basic_streambuf< _CharT, _Traits >::_M_in_cur [protected],
[inherited]
Current read area.
template<typename _CharT , typename _Traits > char_type*
std::basic_streambuf< _CharT, _Traits >::_M_in_end [protected],
[inherited]
End of get area.
template<typename _CharT , typename _Traits > ios_base::openmode
std::basic_filebuf< _CharT, _Traits >::_M_mode [protected]
Place to stash in || out || in | out settings for current filebuf.
template<typename _CharT , typename _Traits > char_type*
std::basic_streambuf< _CharT, _Traits >::_M_out_beg [protected],
[inherited]
Start of put area.
template<typename _CharT , typename _Traits > char_type*
std::basic_streambuf< _CharT, _Traits >::_M_out_cur [protected],
[inherited]
Current put area.
template<typename _CharT , typename _Traits > char_type*
std::basic_streambuf< _CharT, _Traits >::_M_out_end [protected],
[inherited]
End of put area.
template<typename _CharT , typename _Traits > char_type std::basic_filebuf<
_CharT, _Traits >::_M_pback [protected]
Necessary bits for putback buffer management.
Note
pbacks of over one character are not currently supported.
template<typename _CharT , typename _Traits > char_type* std::basic_filebuf<
_CharT, _Traits >::_M_pback_cur_save [protected]
Necessary bits for putback buffer management.
Note
pbacks of over one character are not currently supported.
template<typename _CharT , typename _Traits > char_type* std::basic_filebuf<
_CharT, _Traits >::_M_pback_end_save [protected]
Necessary bits for putback buffer management.
Note
pbacks of over one character are not currently supported.
template<typename _CharT , typename _Traits > bool std::basic_filebuf<
_CharT, _Traits >::_M_pback_init [protected]
Necessary bits for putback buffer management.
Note
pbacks of over one character are not currently supported.
template<typename _CharT , typename _Traits > bool std::basic_filebuf<
_CharT, _Traits >::_M_reading [protected]
_M_reading == false && _M_writing == false for uncommitted mode;
_M_reading == true for read mode; _M_writing == true for write mode;
NB: _M_reading == true && _M_writing == true is unused.
Author
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