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      1 // Stream buffer classes -*- C++ -*-
      2 
      3 // Copyright (C) 1997-2014 Free Software Foundation, Inc.
      4 //
      5 // This file is part of the GNU ISO C++ Library.  This library is free
      6 // software; you can redistribute it and/or modify it under the
      7 // terms of the GNU General Public License as published by the
      8 // Free Software Foundation; either version 3, or (at your option)
      9 // any later version.
     10 
     11 // This library is distributed in the hope that it will be useful,
     12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
     13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     14 // GNU General Public License for more details.
     15 
     16 // Under Section 7 of GPL version 3, you are granted additional
     17 // permissions described in the GCC Runtime Library Exception, version
     18 // 3.1, as published by the Free Software Foundation.
     19 
     20 // You should have received a copy of the GNU General Public License and
     21 // a copy of the GCC Runtime Library Exception along with this program;
     22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
     23 // <http://www.gnu.org/licenses/>.
     24 
     25 /** @file include/streambuf
     26  *  This is a Standard C++ Library header.
     27  */
     28 
     29 //
     30 // ISO C++ 14882: 27.5  Stream buffers
     31 //
     32 
     33 #ifndef _GLIBXX_STREAMBUF
     34 #define _GLIBXX_STREAMBUF 1
     35 
     36 #pragma GCC system_header
     37 
     38 #include <bits/c++config.h>
     39 #include <iosfwd>
     40 #include <bits/localefwd.h>
     41 #include <bits/ios_base.h>
     42 #include <bits/cpp_type_traits.h>
     43 #include <ext/type_traits.h>
     44 
     45 namespace std _GLIBCXX_VISIBILITY(default)
     46 {
     47 _GLIBCXX_BEGIN_NAMESPACE_VERSION
     48 
     49   template<typename _CharT, typename _Traits>
     50     streamsize
     51     __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
     52 			  basic_streambuf<_CharT, _Traits>*, bool&);
     53 
     54   /**
     55    *  @brief  The actual work of input and output (interface).
     56    *  @ingroup io
     57    *
     58    *  @tparam _CharT  Type of character stream.
     59    *  @tparam _Traits  Traits for character type, defaults to
     60    *                   char_traits<_CharT>.
     61    *
     62    *  This is a base class.  Derived stream buffers each control a
     63    *  pair of character sequences:  one for input, and one for output.
     64    *
     65    *  Section [27.5.1] of the standard describes the requirements and
     66    *  behavior of stream buffer classes.  That section (three paragraphs)
     67    *  is reproduced here, for simplicity and accuracy.
     68    *
     69    *  -# Stream buffers can impose various constraints on the sequences
     70    *     they control.  Some constraints are:
     71    *     - The controlled input sequence can be not readable.
     72    *     - The controlled output sequence can be not writable.
     73    *     - The controlled sequences can be associated with the contents of
     74    *       other representations for character sequences, such as external
     75    *       files.
     76    *     - The controlled sequences can support operations @e directly to or
     77    *       from associated sequences.
     78    *     - The controlled sequences can impose limitations on how the
     79    *       program can read characters from a sequence, write characters to
     80    *       a sequence, put characters back into an input sequence, or alter
     81    *       the stream position.
     82    *     .
     83    *  -# Each sequence is characterized by three pointers which, if non-null,
     84    *     all point into the same @c charT array object.  The array object
     85    *     represents, at any moment, a (sub)sequence of characters from the
     86    *     sequence.  Operations performed on a sequence alter the values
     87    *     stored in these pointers, perform reads and writes directly to or
     88    *     from associated sequences, and alter <em>the stream position</em> and
     89    *     conversion state as needed to maintain this subsequence relationship.
     90    *     The three pointers are:
     91    *     - the <em>beginning pointer</em>, or lowest element address in the
     92    *       array (called @e xbeg here);
     93    *     - the <em>next pointer</em>, or next element address that is a
     94    *       current candidate for reading or writing (called @e xnext here);
     95    *     - the <em>end pointer</em>, or first element address beyond the
     96    *       end of the array (called @e xend here).
     97    *     .
     98    *  -# The following semantic constraints shall always apply for any set
     99    *     of three pointers for a sequence, using the pointer names given
    100    *     immediately above:
    101    *     - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
    102    *       also be non-null pointers into the same @c charT array, as
    103    *       described above; otherwise, @e xbeg and @e xend shall also be null.
    104    *     - If @e xnext is not a null pointer and @e xnext < @e xend for an
    105    *       output sequence, then a <em>write position</em> is available.
    106    *       In this case, @e *xnext shall be assignable as the next element
    107    *       to write (to put, or to store a character value, into the sequence).
    108    *     - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
    109    *       input sequence, then a <em>putback position</em> is available.
    110    *       In this case, @e xnext[-1] shall have a defined value and is the
    111    *       next (preceding) element to store a character that is put back
    112    *       into the input sequence.
    113    *     - If @e xnext is not a null pointer and @e xnext< @e xend for an
    114    *       input sequence, then a <em>read position</em> is available.
    115    *       In this case, @e *xnext shall have a defined value and is the
    116    *       next element to read (to get, or to obtain a character value,
    117    *       from the sequence).
    118   */
    119   template<typename _CharT, typename _Traits>
    120     class basic_streambuf 
    121     {
    122     public:
    123       //@{
    124       /**
    125        *  These are standard types.  They permit a standardized way of
    126        *  referring to names of (or names dependent on) the template
    127        *  parameters, which are specific to the implementation.
    128       */
    129       typedef _CharT 					char_type;
    130       typedef _Traits 					traits_type;
    131       typedef typename traits_type::int_type 		int_type;
    132       typedef typename traits_type::pos_type 		pos_type;
    133       typedef typename traits_type::off_type 		off_type;
    134       //@}
    135 
    136       //@{
    137       /// This is a non-standard type.
    138       typedef basic_streambuf<char_type, traits_type>  	__streambuf_type;
    139       //@}
    140       
    141       friend class basic_ios<char_type, traits_type>;
    142       friend class basic_istream<char_type, traits_type>;
    143       friend class basic_ostream<char_type, traits_type>;
    144       friend class istreambuf_iterator<char_type, traits_type>;
    145       friend class ostreambuf_iterator<char_type, traits_type>;
    146 
    147       friend streamsize
    148       __copy_streambufs_eof<>(basic_streambuf*, basic_streambuf*, bool&);
    149 
    150       template<bool _IsMove, typename _CharT2>
    151         friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value, 
    152 					       _CharT2*>::__type
    153         __copy_move_a2(istreambuf_iterator<_CharT2>,
    154 		       istreambuf_iterator<_CharT2>, _CharT2*);
    155 
    156       template<typename _CharT2>
    157         friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
    158 				  istreambuf_iterator<_CharT2> >::__type
    159         find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
    160 	     const _CharT2&);
    161 
    162       template<typename _CharT2, typename _Traits2>
    163         friend basic_istream<_CharT2, _Traits2>&
    164         operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
    165 
    166       template<typename _CharT2, typename _Traits2, typename _Alloc>
    167         friend basic_istream<_CharT2, _Traits2>&
    168         operator>>(basic_istream<_CharT2, _Traits2>&,
    169 		   basic_string<_CharT2, _Traits2, _Alloc>&);
    170 
    171       template<typename _CharT2, typename _Traits2, typename _Alloc>
    172         friend basic_istream<_CharT2, _Traits2>&
    173         getline(basic_istream<_CharT2, _Traits2>&,
    174 		basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
    175 
    176     protected:
    177       /*
    178        *  This is based on _IO_FILE, just reordered to be more consistent,
    179        *  and is intended to be the most minimal abstraction for an
    180        *  internal buffer.
    181        *  -  get == input == read
    182        *  -  put == output == write
    183       */
    184       char_type* 		_M_in_beg;     ///< Start of get area.
    185       char_type* 		_M_in_cur;     ///< Current read area.
    186       char_type* 		_M_in_end;     ///< End of get area.
    187       char_type* 		_M_out_beg;    ///< Start of put area.
    188       char_type* 		_M_out_cur;    ///< Current put area.
    189       char_type* 		_M_out_end;    ///< End of put area.
    190 
    191       /// Current locale setting.
    192       locale 			_M_buf_locale;	
    193 
    194   public:
    195       /// Destructor deallocates no buffer space.
    196       virtual 
    197       ~basic_streambuf() 
    198       { }
    199 
    200       // [27.5.2.2.1] locales
    201       /**
    202        *  @brief  Entry point for imbue().
    203        *  @param  __loc  The new locale.
    204        *  @return  The previous locale.
    205        *
    206        *  Calls the derived imbue(__loc).
    207       */
    208       locale 
    209       pubimbue(const locale& __loc)
    210       {
    211 	locale __tmp(this->getloc());
    212 	this->imbue(__loc);
    213 	_M_buf_locale = __loc;
    214 	return __tmp;
    215       }
    216 
    217       /**
    218        *  @brief  Locale access.
    219        *  @return  The current locale in effect.
    220        *
    221        *  If pubimbue(loc) has been called, then the most recent @c loc
    222        *  is returned.  Otherwise the global locale in effect at the time
    223        *  of construction is returned.
    224       */
    225       locale   
    226       getloc() const
    227       { return _M_buf_locale; } 
    228 
    229       // [27.5.2.2.2] buffer management and positioning
    230       //@{
    231       /**
    232        *  @brief  Entry points for derived buffer functions.
    233        *
    234        *  The public versions of @c pubfoo dispatch to the protected
    235        *  derived @c foo member functions, passing the arguments (if any)
    236        *  and returning the result unchanged.
    237       */
    238       basic_streambuf*
    239       pubsetbuf(char_type* __s, streamsize __n) 
    240       { return this->setbuf(__s, __n); }
    241 
    242       /**
    243        *  @brief  Alters the stream position.
    244        *  @param  __off  Offset.
    245        *  @param  __way  Value for ios_base::seekdir.
    246        *  @param  __mode Value for ios_base::openmode.
    247        *
    248        *  Calls virtual seekoff function.
    249       */
    250       pos_type 
    251       pubseekoff(off_type __off, ios_base::seekdir __way, 
    252 		 ios_base::openmode __mode = ios_base::in | ios_base::out)
    253       { return this->seekoff(__off, __way, __mode); }
    254 
    255       /**
    256        *  @brief  Alters the stream position.
    257        *  @param  __sp  Position
    258        *  @param  __mode Value for ios_base::openmode.
    259        *
    260        *  Calls virtual seekpos function.
    261       */
    262       pos_type 
    263       pubseekpos(pos_type __sp,
    264 		 ios_base::openmode __mode = ios_base::in | ios_base::out)
    265       { return this->seekpos(__sp, __mode); }
    266 
    267       /**
    268        *  @brief  Calls virtual sync function.
    269       */
    270       int 
    271       pubsync() { return this->sync(); }
    272       //@}
    273 
    274       // [27.5.2.2.3] get area
    275       /**
    276        *  @brief  Looking ahead into the stream.
    277        *  @return  The number of characters available.
    278        *
    279        *  If a read position is available, returns the number of characters
    280        *  available for reading before the buffer must be refilled.
    281        *  Otherwise returns the derived @c showmanyc().
    282       */
    283       streamsize 
    284       in_avail() 
    285       { 
    286 	const streamsize __ret = this->egptr() - this->gptr();
    287 	return __ret ? __ret : this->showmanyc();
    288       }
    289 
    290       /**
    291        *  @brief  Getting the next character.
    292        *  @return  The next character, or eof.
    293        *
    294        *  Calls @c sbumpc(), and if that function returns
    295        *  @c traits::eof(), so does this function.  Otherwise, @c sgetc().
    296       */
    297       int_type 
    298       snextc()
    299       {
    300 	int_type __ret = traits_type::eof();
    301 	if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(), 
    302 						       __ret), true))
    303 	  __ret = this->sgetc();
    304 	return __ret;
    305       }
    306 
    307       /**
    308        *  @brief  Getting the next character.
    309        *  @return  The next character, or eof.
    310        *
    311        *  If the input read position is available, returns that character
    312        *  and increments the read pointer, otherwise calls and returns
    313        *  @c uflow().
    314       */
    315       int_type 
    316       sbumpc()
    317       {
    318 	int_type __ret;
    319 	if (__builtin_expect(this->gptr() < this->egptr(), true))
    320 	  {
    321 	    __ret = traits_type::to_int_type(*this->gptr());
    322 	    this->gbump(1);
    323 	  }
    324 	else 
    325 	  __ret = this->uflow();
    326 	return __ret;
    327       }
    328 
    329       /**
    330        *  @brief  Getting the next character.
    331        *  @return  The next character, or eof.
    332        *
    333        *  If the input read position is available, returns that character,
    334        *  otherwise calls and returns @c underflow().  Does not move the 
    335        *  read position after fetching the character.
    336       */
    337       int_type 
    338       sgetc()
    339       {
    340 	int_type __ret;
    341 	if (__builtin_expect(this->gptr() < this->egptr(), true))
    342 	  __ret = traits_type::to_int_type(*this->gptr());
    343 	else 
    344 	  __ret = this->underflow();
    345 	return __ret;
    346       }
    347 
    348       /**
    349        *  @brief  Entry point for xsgetn.
    350        *  @param  __s  A buffer area.
    351        *  @param  __n  A count.
    352        *
    353        *  Returns xsgetn(__s,__n).  The effect is to fill @a __s[0] through
    354        *  @a __s[__n-1] with characters from the input sequence, if possible.
    355       */
    356       streamsize 
    357       sgetn(char_type* __s, streamsize __n)
    358       { return this->xsgetn(__s, __n); }
    359 
    360       // [27.5.2.2.4] putback
    361       /**
    362        *  @brief  Pushing characters back into the input stream.
    363        *  @param  __c  The character to push back.
    364        *  @return  The previous character, if possible.
    365        *
    366        *  Similar to sungetc(), but @a __c is pushed onto the stream
    367        *  instead of <em>the previous character.</em> If successful,
    368        *  the next character fetched from the input stream will be @a
    369        *  __c.
    370       */
    371       int_type 
    372       sputbackc(char_type __c)
    373       {
    374 	int_type __ret;
    375 	const bool __testpos = this->eback() < this->gptr();
    376 	if (__builtin_expect(!__testpos || 
    377 			     !traits_type::eq(__c, this->gptr()[-1]), false))
    378 	  __ret = this->pbackfail(traits_type::to_int_type(__c));
    379 	else 
    380 	  {
    381 	    this->gbump(-1);
    382 	    __ret = traits_type::to_int_type(*this->gptr());
    383 	  }
    384 	return __ret;
    385       }
    386 
    387       /**
    388        *  @brief  Moving backwards in the input stream.
    389        *  @return  The previous character, if possible.
    390        *
    391        *  If a putback position is available, this function decrements
    392        *  the input pointer and returns that character.  Otherwise,
    393        *  calls and returns pbackfail().  The effect is to @a unget
    394        *  the last character @a gotten.
    395       */
    396       int_type 
    397       sungetc()
    398       {
    399 	int_type __ret;
    400 	if (__builtin_expect(this->eback() < this->gptr(), true))
    401 	  {
    402 	    this->gbump(-1);
    403 	    __ret = traits_type::to_int_type(*this->gptr());
    404 	  }
    405 	else 
    406 	  __ret = this->pbackfail();
    407 	return __ret;
    408       }
    409 
    410       // [27.5.2.2.5] put area
    411       /**
    412        *  @brief  Entry point for all single-character output functions.
    413        *  @param  __c  A character to output.
    414        *  @return  @a __c, if possible.
    415        *
    416        *  One of two public output functions.
    417        *
    418        *  If a write position is available for the output sequence (i.e.,
    419        *  the buffer is not full), stores @a __c in that position, increments
    420        *  the position, and returns @c traits::to_int_type(__c).  If a write
    421        *  position is not available, returns @c overflow(__c).
    422       */
    423       int_type 
    424       sputc(char_type __c)
    425       {
    426 	int_type __ret;
    427 	if (__builtin_expect(this->pptr() < this->epptr(), true))
    428 	  {
    429 	    *this->pptr() = __c;
    430 	    this->pbump(1);
    431 	    __ret = traits_type::to_int_type(__c);
    432 	  }
    433 	else
    434 	  __ret = this->overflow(traits_type::to_int_type(__c));
    435 	return __ret;
    436       }
    437 
    438       /**
    439        *  @brief  Entry point for all single-character output functions.
    440        *  @param  __s  A buffer read area.
    441        *  @param  __n  A count.
    442        *
    443        *  One of two public output functions.
    444        *
    445        *
    446        *  Returns xsputn(__s,__n).  The effect is to write @a __s[0] through
    447        *  @a __s[__n-1] to the output sequence, if possible.
    448       */
    449       streamsize 
    450       sputn(const char_type* __s, streamsize __n)
    451       { return this->xsputn(__s, __n); }
    452 
    453     protected:
    454       /**
    455        *  @brief  Base constructor.
    456        *
    457        *  Only called from derived constructors, and sets up all the
    458        *  buffer data to zero, including the pointers described in the
    459        *  basic_streambuf class description.  Note that, as a result,
    460        *  - the class starts with no read nor write positions available,
    461        *  - this is not an error
    462       */
    463       basic_streambuf()
    464       : _M_in_beg(0), _M_in_cur(0), _M_in_end(0), 
    465       _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
    466       _M_buf_locale(locale()) 
    467       { }
    468 
    469       // [27.5.2.3.1] get area access
    470       //@{
    471       /**
    472        *  @brief  Access to the get area.
    473        *
    474        *  These functions are only available to other protected functions,
    475        *  including derived classes.
    476        *
    477        *  - eback() returns the beginning pointer for the input sequence
    478        *  - gptr() returns the next pointer for the input sequence
    479        *  - egptr() returns the end pointer for the input sequence
    480       */
    481       char_type* 
    482       eback() const { return _M_in_beg; }
    483 
    484       char_type* 
    485       gptr()  const { return _M_in_cur;  }
    486 
    487       char_type* 
    488       egptr() const { return _M_in_end; }
    489       //@}
    490 
    491       /**
    492        *  @brief  Moving the read position.
    493        *  @param  __n  The delta by which to move.
    494        *
    495        *  This just advances the read position without returning any data.
    496       */
    497       void 
    498       gbump(int __n) { _M_in_cur += __n; }
    499 
    500       /**
    501        *  @brief  Setting the three read area pointers.
    502        *  @param  __gbeg  A pointer.
    503        *  @param  __gnext  A pointer.
    504        *  @param  __gend  A pointer.
    505        *  @post  @a __gbeg == @c eback(), @a __gnext == @c gptr(), and
    506        *         @a __gend == @c egptr()
    507       */
    508       void 
    509       setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
    510       {
    511 	_M_in_beg = __gbeg;
    512 	_M_in_cur = __gnext;
    513 	_M_in_end = __gend;
    514       }
    515 
    516       // [27.5.2.3.2] put area access
    517       //@{
    518       /**
    519        *  @brief  Access to the put area.
    520        *
    521        *  These functions are only available to other protected functions,
    522        *  including derived classes.
    523        *
    524        *  - pbase() returns the beginning pointer for the output sequence
    525        *  - pptr() returns the next pointer for the output sequence
    526        *  - epptr() returns the end pointer for the output sequence
    527       */
    528       char_type* 
    529       pbase() const { return _M_out_beg; }
    530 
    531       char_type* 
    532       pptr() const { return _M_out_cur; }
    533 
    534       char_type* 
    535       epptr() const { return _M_out_end; }
    536       //@}
    537 
    538       /**
    539        *  @brief  Moving the write position.
    540        *  @param  __n  The delta by which to move.
    541        *
    542        *  This just advances the write position without returning any data.
    543       */
    544       void 
    545       pbump(int __n) { _M_out_cur += __n; }
    546 
    547       /**
    548        *  @brief  Setting the three write area pointers.
    549        *  @param  __pbeg  A pointer.
    550        *  @param  __pend  A pointer.
    551        *  @post  @a __pbeg == @c pbase(), @a __pbeg == @c pptr(), and
    552        *         @a __pend == @c epptr()
    553       */
    554       void 
    555       setp(char_type* __pbeg, char_type* __pend)
    556       { 
    557 	_M_out_beg = _M_out_cur = __pbeg; 
    558 	_M_out_end = __pend;
    559       }
    560 
    561       // [27.5.2.4] virtual functions
    562       // [27.5.2.4.1] locales
    563       /**
    564        *  @brief  Changes translations.
    565        *  @param  __loc  A new locale.
    566        *
    567        *  Translations done during I/O which depend on the current
    568        *  locale are changed by this call.  The standard adds,
    569        *  <em>Between invocations of this function a class derived
    570        *  from streambuf can safely cache results of calls to locale
    571        *  functions and to members of facets so obtained.</em>
    572        *
    573        *  @note  Base class version does nothing.
    574       */
    575       virtual void 
    576       imbue(const locale& __loc) 
    577       { }
    578 
    579       // [27.5.2.4.2] buffer management and positioning
    580       /**
    581        *  @brief  Manipulates the buffer.
    582        *
    583        *  Each derived class provides its own appropriate behavior.  See
    584        *  the next-to-last paragraph of 
    585        *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25s02.html
    586        *  for more on this function.
    587        *
    588        *  @note  Base class version does nothing, returns @c this.
    589       */
    590       virtual basic_streambuf<char_type,_Traits>* 
    591       setbuf(char_type*, streamsize)
    592       {	return this; }
    593       
    594       /**
    595        *  @brief  Alters the stream positions.
    596        *
    597        *  Each derived class provides its own appropriate behavior.
    598        *  @note  Base class version does nothing, returns a @c pos_type
    599        *         that represents an invalid stream position.
    600       */
    601       virtual pos_type 
    602       seekoff(off_type, ios_base::seekdir,
    603 	      ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
    604       { return pos_type(off_type(-1)); } 
    605 
    606       /**
    607        *  @brief  Alters the stream positions.
    608        *
    609        *  Each derived class provides its own appropriate behavior.
    610        *  @note  Base class version does nothing, returns a @c pos_type
    611        *         that represents an invalid stream position.
    612       */
    613       virtual pos_type 
    614       seekpos(pos_type, 
    615 	      ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
    616       { return pos_type(off_type(-1)); } 
    617 
    618       /**
    619        *  @brief  Synchronizes the buffer arrays with the controlled sequences.
    620        *  @return  -1 on failure.
    621        *
    622        *  Each derived class provides its own appropriate behavior,
    623        *  including the definition of @a failure.
    624        *  @note  Base class version does nothing, returns zero.
    625       */
    626       virtual int 
    627       sync() { return 0; }
    628 
    629       // [27.5.2.4.3] get area
    630       /**
    631        *  @brief  Investigating the data available.
    632        *  @return  An estimate of the number of characters available in the
    633        *           input sequence, or -1.
    634        *
    635        *  <em>If it returns a positive value, then successive calls to
    636        *  @c underflow() will not return @c traits::eof() until at
    637        *  least that number of characters have been supplied.  If @c
    638        *  showmanyc() returns -1, then calls to @c underflow() or @c
    639        *  uflow() will fail.</em> [27.5.2.4.3]/1
    640        *
    641        *  @note  Base class version does nothing, returns zero.
    642        *  @note  The standard adds that <em>the intention is not only that the
    643        *         calls [to underflow or uflow] will not return @c eof() but
    644        *         that they will return immediately.</em>
    645        *  @note  The standard adds that <em>the morphemes of @c showmanyc are
    646        *         @b es-how-many-see, not @b show-manic.</em>
    647       */
    648       virtual streamsize 
    649       showmanyc() { return 0; }
    650 
    651       /**
    652        *  @brief  Multiple character extraction.
    653        *  @param  __s  A buffer area.
    654        *  @param  __n  Maximum number of characters to assign.
    655        *  @return  The number of characters assigned.
    656        *
    657        *  Fills @a __s[0] through @a __s[__n-1] with characters from the input
    658        *  sequence, as if by @c sbumpc().  Stops when either @a __n characters
    659        *  have been copied, or when @c traits::eof() would be copied.
    660        *
    661        *  It is expected that derived classes provide a more efficient
    662        *  implementation by overriding this definition.
    663       */
    664       virtual streamsize 
    665       xsgetn(char_type* __s, streamsize __n);
    666 
    667       /**
    668        *  @brief  Fetches more data from the controlled sequence.
    669        *  @return  The first character from the <em>pending sequence</em>.
    670        *
    671        *  Informally, this function is called when the input buffer is
    672        *  exhausted (or does not exist, as buffering need not actually be
    673        *  done).  If a buffer exists, it is @a refilled.  In either case, the
    674        *  next available character is returned, or @c traits::eof() to
    675        *  indicate a null pending sequence.
    676        *
    677        *  For a formal definition of the pending sequence, see a good text
    678        *  such as Langer & Kreft, or [27.5.2.4.3]/7-14.
    679        *
    680        *  A functioning input streambuf can be created by overriding only
    681        *  this function (no buffer area will be used).  For an example, see
    682        *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25.html
    683        *
    684        *  @note  Base class version does nothing, returns eof().
    685       */
    686       virtual int_type 
    687       underflow()
    688       { return traits_type::eof(); }
    689 
    690       /**
    691        *  @brief  Fetches more data from the controlled sequence.
    692        *  @return  The first character from the <em>pending sequence</em>.
    693        *
    694        *  Informally, this function does the same thing as @c underflow(),
    695        *  and in fact is required to call that function.  It also returns
    696        *  the new character, like @c underflow() does.  However, this
    697        *  function also moves the read position forward by one.
    698       */
    699       virtual int_type 
    700       uflow() 
    701       {
    702 	int_type __ret = traits_type::eof();
    703 	const bool __testeof = traits_type::eq_int_type(this->underflow(), 
    704 							__ret);
    705 	if (!__testeof)
    706 	  {
    707 	    __ret = traits_type::to_int_type(*this->gptr());
    708 	    this->gbump(1);
    709 	  }
    710 	return __ret;    
    711       }
    712 
    713       // [27.5.2.4.4] putback
    714       /**
    715        *  @brief  Tries to back up the input sequence.
    716        *  @param  __c  The character to be inserted back into the sequence.
    717        *  @return  eof() on failure, <em>some other value</em> on success
    718        *  @post  The constraints of @c gptr(), @c eback(), and @c pptr()
    719        *         are the same as for @c underflow().
    720        *
    721        *  @note  Base class version does nothing, returns eof().
    722       */
    723       virtual int_type 
    724       pbackfail(int_type __c  = traits_type::eof())
    725       { return traits_type::eof(); }
    726 
    727       // Put area:
    728       /**
    729        *  @brief  Multiple character insertion.
    730        *  @param  __s  A buffer area.
    731        *  @param  __n  Maximum number of characters to write.
    732        *  @return  The number of characters written.
    733        *
    734        *  Writes @a __s[0] through @a __s[__n-1] to the output sequence, as if
    735        *  by @c sputc().  Stops when either @a n characters have been
    736        *  copied, or when @c sputc() would return @c traits::eof().
    737        *
    738        *  It is expected that derived classes provide a more efficient
    739        *  implementation by overriding this definition.
    740       */
    741       virtual streamsize 
    742       xsputn(const char_type* __s, streamsize __n);
    743 
    744       /**
    745        *  @brief  Consumes data from the buffer; writes to the
    746        *          controlled sequence.
    747        *  @param  __c  An additional character to consume.
    748        *  @return  eof() to indicate failure, something else (usually
    749        *           @a __c, or not_eof())
    750        *
    751        *  Informally, this function is called when the output buffer
    752        *  is full (or does not exist, as buffering need not actually
    753        *  be done).  If a buffer exists, it is @a consumed, with
    754        *  <em>some effect</em> on the controlled sequence.
    755        *  (Typically, the buffer is written out to the sequence
    756        *  verbatim.)  In either case, the character @a c is also
    757        *  written out, if @a __c is not @c eof().
    758        *
    759        *  For a formal definition of this function, see a good text
    760        *  such as Langer & Kreft, or [27.5.2.4.5]/3-7.
    761        *
    762        *  A functioning output streambuf can be created by overriding only
    763        *  this function (no buffer area will be used).
    764        *
    765        *  @note  Base class version does nothing, returns eof().
    766       */
    767       virtual int_type 
    768       overflow(int_type __c  = traits_type::eof())
    769       { return traits_type::eof(); }
    770 
    771 #if _GLIBCXX_USE_DEPRECATED
    772     // Annex D.6
    773     public:
    774       /**
    775        *  @brief  Tosses a character.
    776        *
    777        *  Advances the read pointer, ignoring the character that would have
    778        *  been read.
    779        *
    780        *  See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
    781        */
    782       void 
    783       stossc() 
    784       {
    785 	if (this->gptr() < this->egptr()) 
    786 	  this->gbump(1);
    787 	else 
    788 	  this->uflow();
    789       }
    790 #endif
    791 
    792       // Also used by specializations for char and wchar_t in src.
    793       void 
    794       __safe_gbump(streamsize __n) { _M_in_cur += __n; }
    795 
    796       void
    797       __safe_pbump(streamsize __n) { _M_out_cur += __n; }
    798 
    799     private:
    800       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    801       // Side effect of DR 50. 
    802       basic_streambuf(const basic_streambuf& __sb)
    803       : _M_in_beg(__sb._M_in_beg), _M_in_cur(__sb._M_in_cur), 
    804       _M_in_end(__sb._M_in_end), _M_out_beg(__sb._M_out_beg), 
    805       _M_out_cur(__sb._M_out_cur), _M_out_end(__sb._M_out_cur),
    806       _M_buf_locale(__sb._M_buf_locale) 
    807       { }
    808 
    809       basic_streambuf&
    810       operator=(const basic_streambuf&) { return *this; };
    811     };
    812 
    813   // Explicit specialization declarations, defined in src/streambuf.cc.
    814   template<>
    815     streamsize
    816     __copy_streambufs_eof(basic_streambuf<char>* __sbin,
    817 			  basic_streambuf<char>* __sbout, bool& __ineof);
    818 #ifdef _GLIBCXX_USE_WCHAR_T
    819   template<>
    820     streamsize
    821     __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
    822 			  basic_streambuf<wchar_t>* __sbout, bool& __ineof);
    823 #endif
    824 
    825 _GLIBCXX_END_NAMESPACE_VERSION
    826 } // namespace
    827 
    828 #include <bits/streambuf.tcc>
    829 
    830 #endif /* _GLIBCXX_STREAMBUF */
    831