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

       Generated automatically by Doxygen for libstdc++ from the source code.

                                                    libstdc++        std::basic_filebuf<_CharT,_Traits>(3cxx)

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>virtualstd::basic_filebuf<_CharT,_Traits>::~basic_filebuf()[inline],[virtual]
       The destructor closes the file first.

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

       TemplateParameters_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.

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>localestd::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_tstd::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>streamsizestd::basic_filebuf<_CharT,_Traits>::_M_ext_buf_size[protected]
       Size of buffer held by _M_ext_buf.

   template<typename_CharT,typename_Traits>constchar*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::openmodestd::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_typestd::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>boolstd::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>boolstd::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.

template<typename_CharT,typename_Traits>voidstd::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>voidstd::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>voidstd::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 putbufferarea 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>voidstd::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>localestd::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>voidstd::basic_filebuf<_CharT,_Traits>::imbue(constlocale&__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, Betweeninvocationsofthisfunctionaclassderivedfromstreambufcansafelycacheresultsofcallstolocalefunctionsandtomembersoffacetssoobtained.Note
           Base class version does nothing.

       Reimplemented from std::basic_streambuf<_CharT,_Traits>.

       References std::ios_base::cur.

   template<typename_CharT,typename_Traits>streamsizestd::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>boolstd::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(constchar*__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(conststd::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_typestd::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 someeffect 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_typestd::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, someothervalue 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>voidstd::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>localestd::basic_streambuf<_CharT,_Traits>::pubimbue(constlocale&__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_typestd::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_typestd::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>intstd::basic_streambuf<_CharT,_Traits>::pubsync()[inline],[inherited]
       Calls virtual sync function.

   template<typename_CharT,typename_Traits>int_typestd::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_typestd::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_typestd::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>voidstd::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>voidstd::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_typestd::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>streamsizestd::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>streamsizestd::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.

       Ifitreturnsapositivevalue,thensuccessivecallstounderflow()willnotreturntraits::eof()untilatleastthatnumberofcharactershavebeensupplied.Ifshowmanyc()returns-1,thencallstounderflow()oruflow()willfail.[27.5.2.4.3]/1Note
           Base class version does nothing, returns zero.

           The  standard  adds  that  theintentionisnotonlythatthecalls[tounderfloworuflow]willnotreturneof()butthattheywillreturnimmediately.

           The standard adds that themorphemesofshowmanycarees-how-many-see,notshow-manic.

       Reimplemented from std::basic_streambuf<_CharT,_Traits>.

       References std::ios_base::binary, and std::ios_base::in.

   template<typename_CharT,typename_Traits>int_typestd::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_typestd::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 thepreviouscharacter. If successful,
       the next character fetched from the input stream will be __c.

   template<typename_CharT,typename_Traits>int_typestd::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>streamsizestd::basic_streambuf<_CharT,_Traits>::sputn(constchar_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_typestd::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>intstd::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>virtualint_typestd::basic_streambuf<_CharT,_Traits>::uflow()[inline],[protected],[virtual],[inherited]
       Fetches more data from the controlled sequence.

       Returns
           The first character from the pendingsequence.

       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_typestd::basic_filebuf<_CharT,_Traits>::underflow()[protected],[virtual]
       Fetches more data from the controlled sequence.

       Returns
           The first character from the pendingsequence.

       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>streamsizestd::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>streamsizestd::basic_filebuf<_CharT,_Traits>::xsputn(constchar_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.

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

       #include <fstream>

       Inherits std::basic_streambuf<_CharT,_Traits>.

       Inherited by __gnu_cxx::stdio_filebuf<_CharT,_Traits>.

   PublicTypestypedefcodecvt< char_type, char, __state_type > __codecvt_typetypedef __basic_file< char > __file_typetypedefbasic_filebuf< char_type, traits_type > __filebuf_typetypedef traits_type::state_type __state_typetypedefbasic_streambuf< char_type, traits_type > __streambuf_typetypedef _CharT char_typetypedef traits_type::int_type int_typetypedef traits_type::off_type off_typetypedef traits_type::pos_type pos_typetypedef _Traits traits_typePublicMemberFunctionsbasic_filebuf ()
           Does not open any files.
       basic_filebuf (basic_filebuf &&)
       basic_filebuf (const basic_filebuf &)=deletevirtual~basic_filebuf ()
           The destructor closes the file first.
       __filebuf_type * close ()
           Closes the currently associated file.
       localegetloc () const
           Locale access.
       streamsizein_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 &)=deletelocalepubimbue (const locale &__loc)
           Entry point for imbue().
       int_type sbumpc ()
           Getting the next character.
       int_type sgetc ()
           Getting the next character.
       streamsizesgetn (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.
       streamsizesputn (const char_type *__s, streamsize __n)
           Entry point for all single-character output functions.
       int_type sungetc ()
           Moving backwards in the input stream.
       voidswap (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.

   ProtectedMemberFunctionsvoid__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 ()
       voidgbump (int __n)
           Moving the read position.
       virtualvoidimbue (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.
       voidpbump (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.
       voidsetg (char_type *__gbeg, char_type *__gnext, char_type *__gend)
           Setting the three read area pointers.
       voidsetp (char_type *__pbeg, char_type *__pend)
           Setting the three write area pointers.
       virtualstreamsizeshowmanyc ()
           Investigating the data available.
       voidswap (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.
       virtualstreamsizexsgetn (char_type *__s, streamsize __n)
           Multiple character extraction.
       virtualstreamsizexsputn (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.

   ProtectedAttributes
       char_type * _M_buf
           Pointer to the beginning of internal buffer.
       bool _M_buf_allocatedlocale_M_buf_locale
           Current locale setting.
       size_t _M_buf_size
       const __codecvt_type * _M_codecvt
       char * _M_ext_bufstreamsize_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_lockios_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_initFriendsclassios_base