std::basic_filebuf - Man Page

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

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.

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.

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

class ios_base

class std::basic_filebuf< _CharT, _Traits >"The actual work of input and output (for files).

Template Parameters

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.

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.

The destructor closes the file first.

Initializes pback buffers, and moves normal buffers to safety. Assumptions: _M_in_cur has already been moved back

Deactivates pback buffer contents, and restores normal buffer. Assumptions: The pback buffer has only moved forward.

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.

Referenced by 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.

References std::basic_filebuf< _CharT, _Traits >::_M_mode, std::basic_filebuf< _CharT, _Traits >::_M_pback_init, std::basic_filebuf< _CharT, _Traits >::_M_reading, and std::basic_filebuf< _CharT, _Traits >::_M_set_buffer().

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

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().

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

Moving the read position.

Parameters

This just advances the read position without returning any data.

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.

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().

Changes translations.

Parameters

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.

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().

Returns true if the external file is open.

Opens an external file.

Parameters

Returns

this on success, NULL on failure

Opens an external file.

Parameters

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.

Opens an external file.

Parameters

Returns

this on success, NULL on failure

Consumes data from the buffer; writes to the controlled sequence.

Parameters

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.

Tries to back up the input sequence.

Parameters

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.

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

Moving the write position.

Parameters

This just advances the write position without returning any data.

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

Entry point for imbue().

Parameters

Returns

The previous locale.

Calls the derived imbue(__loc).

Alters the stream position.

Parameters

Calls virtual seekoff function.

Alters the stream position.

Parameters

Calls virtual seekpos function.

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.

Calls virtual sync function.

Referenced by std::basic_istream< _CharT, _Traits >::sync(), and std::wbuffer_convert< _Codecvt, _Elem, _Tr >::sync().

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().

Referenced by std::basic_istream< _CharT, char_traits< _CharT > >::get(), std::basic_istream< _CharT, _Traits >::ignore(), std::istreambuf_iterator< _CharT, _Traits >::operator++(), std::istreambuf_iterator< _CharT, _Traits >::operator++(), and std::basic_istream< _CharT, char_traits< _CharT > >::sync().

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.

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.

Manipulates the buffer.

Parameters

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 >.

Setting the three read area pointers.

Parameters

Postcondition

Referenced by std::wbuffer_convert< _Codecvt, _Elem, _Tr >::wbuffer_convert().

Setting the three write area pointers.

Parameters

Postcondition

Referenced by std::wbuffer_convert< _Codecvt, _Elem, _Tr >::wbuffer_convert().

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.

Referenced by std::basic_istream< _CharT, _Traits >::get(), std::basic_istream< _CharT, char_traits< _CharT > >::get(), std::basic_istream< _CharT, _Traits >::ignore(), std::istreambuf_iterator< _CharT, _Traits >::operator++(), std::istreambuf_iterator< _CharT, _Traits >::operator++(), and std::basic_istream< _CharT, char_traits< _CharT > >::readsome().

Entry point for xsgetn.

Parameters

Returns xsgetn(__s,__n). The effect is to fill __s[0] through __s[__n-1] with characters from the input sequence, if possible.

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.

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().

Referenced by std::basic_istream< _CharT, char_traits< _CharT > >::get(), std::basic_istream< _CharT, char_traits< _CharT > >::ignore(), std::basic_istream< _CharT, char_traits< _CharT > >::operator>>(), and std::basic_istream< _CharT, char_traits< _CharT > >::putback().

Pushing characters back into the input stream.

Parameters

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.

Referenced by std::basic_istream< _CharT, _Traits >::putback().

Entry point for all single-character output functions.

Parameters

Returns

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::ostreambuf_iterator< _CharT, _Traits >::operator=(), and std::wbuffer_convert< _Codecvt, _Elem, _Tr >::overflow().

Entry point for all single-character output functions.

Parameters

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.

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.

Synchronizes the buffer arrays with the controlled sequences.

Returns

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 >.

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 >.

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.

Multiple character extraction.

Parameters

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.

Multiple character insertion.

Parameters

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.

Pointer to the beginning of internal buffer.

Current locale setting.

Referenced by std::basic_filebuf< _CharT, _Traits >::basic_filebuf().

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.

Buffer for external characters. Used for input when codecvt::always_noconv() == false. When valid, this corresponds to eback().

Size of buffer held by _M_ext_buf.

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().

Start of get area.

Current read area.

End of get area.

Place to stash in || out || in | out settings for current filebuf.

Referenced by std::basic_filebuf< _CharT, _Traits >::close().

Start of put area.

Current put area.

End of put area.

Necessary bits for putback buffer management.

Note

pbacks of over one character are not currently supported.

Necessary bits for putback buffer management.

Note

pbacks of over one character are not currently supported.

Necessary bits for putback buffer management.

Note

pbacks of over one character are not currently supported.

Necessary bits for putback buffer management.

Note

pbacks of over one character are not currently supported.

Referenced by std::basic_filebuf< _CharT, _Traits >::close().

_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.

Referenced by std::basic_filebuf< _CharT, _Traits >::close().