libstdc++
streambuf
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00001 // Stream buffer classes -*- C++ -*-
00002 
00003 // Copyright (C) 1997-2013 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file include/streambuf
00026  *  This is a Standard C++ Library header.
00027  */
00028 
00029 //
00030 // ISO C++ 14882: 27.5  Stream buffers
00031 //
00032 
00033 #ifndef _GLIBXX_STREAMBUF
00034 #define _GLIBXX_STREAMBUF 1
00035 
00036 #pragma GCC system_header
00037 
00038 #include <bits/c++config.h>
00039 #include <iosfwd>
00040 #include <bits/localefwd.h>
00041 #include <bits/ios_base.h>
00042 #include <bits/cpp_type_traits.h>
00043 #include <ext/type_traits.h>
00044 
00045 namespace std _GLIBCXX_VISIBILITY(default)
00046 {
00047 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00048 
00049   template<typename _CharT, typename _Traits>
00050     streamsize
00051     __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*,
00052               basic_streambuf<_CharT, _Traits>*, bool&);
00053 
00054   /**
00055    *  @brief  The actual work of input and output (interface).
00056    *  @ingroup io
00057    *
00058    *  @tparam _CharT  Type of character stream.
00059    *  @tparam _Traits  Traits for character type, defaults to
00060    *                   char_traits<_CharT>.
00061    *
00062    *  This is a base class.  Derived stream buffers each control a
00063    *  pair of character sequences:  one for input, and one for output.
00064    *
00065    *  Section [27.5.1] of the standard describes the requirements and
00066    *  behavior of stream buffer classes.  That section (three paragraphs)
00067    *  is reproduced here, for simplicity and accuracy.
00068    *
00069    *  -# Stream buffers can impose various constraints on the sequences
00070    *     they control.  Some constraints are:
00071    *     - The controlled input sequence can be not readable.
00072    *     - The controlled output sequence can be not writable.
00073    *     - The controlled sequences can be associated with the contents of
00074    *       other representations for character sequences, such as external
00075    *       files.
00076    *     - The controlled sequences can support operations @e directly to or
00077    *       from associated sequences.
00078    *     - The controlled sequences can impose limitations on how the
00079    *       program can read characters from a sequence, write characters to
00080    *       a sequence, put characters back into an input sequence, or alter
00081    *       the stream position.
00082    *     .
00083    *  -# Each sequence is characterized by three pointers which, if non-null,
00084    *     all point into the same @c charT array object.  The array object
00085    *     represents, at any moment, a (sub)sequence of characters from the
00086    *     sequence.  Operations performed on a sequence alter the values
00087    *     stored in these pointers, perform reads and writes directly to or
00088    *     from associated sequences, and alter <em>the stream position</em> and
00089    *     conversion state as needed to maintain this subsequence relationship.
00090    *     The three pointers are:
00091    *     - the <em>beginning pointer</em>, or lowest element address in the
00092    *       array (called @e xbeg here);
00093    *     - the <em>next pointer</em>, or next element address that is a
00094    *       current candidate for reading or writing (called @e xnext here);
00095    *     - the <em>end pointer</em>, or first element address beyond the
00096    *       end of the array (called @e xend here).
00097    *     .
00098    *  -# The following semantic constraints shall always apply for any set
00099    *     of three pointers for a sequence, using the pointer names given
00100    *     immediately above:
00101    *     - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
00102    *       also be non-null pointers into the same @c charT array, as
00103    *       described above; otherwise, @e xbeg and @e xend shall also be null.
00104    *     - If @e xnext is not a null pointer and @e xnext < @e xend for an
00105    *       output sequence, then a <em>write position</em> is available.
00106    *       In this case, @e *xnext shall be assignable as the next element
00107    *       to write (to put, or to store a character value, into the sequence).
00108    *     - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
00109    *       input sequence, then a <em>putback position</em> is available.
00110    *       In this case, @e xnext[-1] shall have a defined value and is the
00111    *       next (preceding) element to store a character that is put back
00112    *       into the input sequence.
00113    *     - If @e xnext is not a null pointer and @e xnext< @e xend for an
00114    *       input sequence, then a <em>read position</em> is available.
00115    *       In this case, @e *xnext shall have a defined value and is the
00116    *       next element to read (to get, or to obtain a character value,
00117    *       from the sequence).
00118   */
00119   template<typename _CharT, typename _Traits>
00120     class basic_streambuf 
00121     {
00122     public:
00123       //@{
00124       /**
00125        *  These are standard types.  They permit a standardized way of
00126        *  referring to names of (or names dependent on) the template
00127        *  parameters, which are specific to the implementation.
00128       */
00129       typedef _CharT                    char_type;
00130       typedef _Traits                   traits_type;
00131       typedef typename traits_type::int_type        int_type;
00132       typedef typename traits_type::pos_type        pos_type;
00133       typedef typename traits_type::off_type        off_type;
00134       //@}
00135 
00136       //@{
00137       /// This is a non-standard type.
00138       typedef basic_streambuf<char_type, traits_type>   __streambuf_type;
00139       //@}
00140       
00141       friend class basic_ios<char_type, traits_type>;
00142       friend class basic_istream<char_type, traits_type>;
00143       friend class basic_ostream<char_type, traits_type>;
00144       friend class istreambuf_iterator<char_type, traits_type>;
00145       friend class ostreambuf_iterator<char_type, traits_type>;
00146 
00147       friend streamsize
00148       __copy_streambufs_eof<>(basic_streambuf*, basic_streambuf*, bool&);
00149 
00150       template<bool _IsMove, typename _CharT2>
00151         friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value, 
00152                            _CharT2*>::__type
00153         __copy_move_a2(istreambuf_iterator<_CharT2>,
00154                istreambuf_iterator<_CharT2>, _CharT2*);
00155 
00156       template<typename _CharT2>
00157         friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
00158                   istreambuf_iterator<_CharT2> >::__type
00159         find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
00160          const _CharT2&);
00161 
00162       template<typename _CharT2, typename _Traits2>
00163         friend basic_istream<_CharT2, _Traits2>&
00164         operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
00165 
00166       template<typename _CharT2, typename _Traits2, typename _Alloc>
00167         friend basic_istream<_CharT2, _Traits2>&
00168         operator>>(basic_istream<_CharT2, _Traits2>&,
00169            basic_string<_CharT2, _Traits2, _Alloc>&);
00170 
00171       template<typename _CharT2, typename _Traits2, typename _Alloc>
00172         friend basic_istream<_CharT2, _Traits2>&
00173         getline(basic_istream<_CharT2, _Traits2>&,
00174         basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
00175 
00176     protected:
00177       /*
00178        *  This is based on _IO_FILE, just reordered to be more consistent,
00179        *  and is intended to be the most minimal abstraction for an
00180        *  internal buffer.
00181        *  -  get == input == read
00182        *  -  put == output == write
00183       */
00184       char_type*        _M_in_beg;     ///< Start of get area.
00185       char_type*        _M_in_cur;     ///< Current read area.
00186       char_type*        _M_in_end;     ///< End of get area.
00187       char_type*        _M_out_beg;    ///< Start of put area.
00188       char_type*        _M_out_cur;    ///< Current put area.
00189       char_type*        _M_out_end;    ///< End of put area.
00190 
00191       /// Current locale setting.
00192       locale            _M_buf_locale;  
00193 
00194   public:
00195       /// Destructor deallocates no buffer space.
00196       virtual 
00197       ~basic_streambuf() 
00198       { }
00199 
00200       // [27.5.2.2.1] locales
00201       /**
00202        *  @brief  Entry point for imbue().
00203        *  @param  __loc  The new locale.
00204        *  @return  The previous locale.
00205        *
00206        *  Calls the derived imbue(__loc).
00207       */
00208       locale 
00209       pubimbue(const locale& __loc)
00210       {
00211     locale __tmp(this->getloc());
00212     this->imbue(__loc);
00213     _M_buf_locale = __loc;
00214     return __tmp;
00215       }
00216 
00217       /**
00218        *  @brief  Locale access.
00219        *  @return  The current locale in effect.
00220        *
00221        *  If pubimbue(loc) has been called, then the most recent @c loc
00222        *  is returned.  Otherwise the global locale in effect at the time
00223        *  of construction is returned.
00224       */
00225       locale   
00226       getloc() const
00227       { return _M_buf_locale; } 
00228 
00229       // [27.5.2.2.2] buffer management and positioning
00230       //@{
00231       /**
00232        *  @brief  Entry points for derived buffer functions.
00233        *
00234        *  The public versions of @c pubfoo dispatch to the protected
00235        *  derived @c foo member functions, passing the arguments (if any)
00236        *  and returning the result unchanged.
00237       */
00238       basic_streambuf*
00239       pubsetbuf(char_type* __s, streamsize __n) 
00240       { return this->setbuf(__s, __n); }
00241 
00242       /**
00243        *  @brief  Alters the stream position.
00244        *  @param  __off  Offset.
00245        *  @param  __way  Value for ios_base::seekdir.
00246        *  @param  __mode Value for ios_base::openmode.
00247        *
00248        *  Calls virtual seekoff function.
00249       */
00250       pos_type 
00251       pubseekoff(off_type __off, ios_base::seekdir __way, 
00252          ios_base::openmode __mode = ios_base::in | ios_base::out)
00253       { return this->seekoff(__off, __way, __mode); }
00254 
00255       /**
00256        *  @brief  Alters the stream position.
00257        *  @param  __sp  Position
00258        *  @param  __mode Value for ios_base::openmode.
00259        *
00260        *  Calls virtual seekpos function.
00261       */
00262       pos_type 
00263       pubseekpos(pos_type __sp,
00264          ios_base::openmode __mode = ios_base::in | ios_base::out)
00265       { return this->seekpos(__sp, __mode); }
00266 
00267       /**
00268        *  @brief  Calls virtual sync function.
00269       */
00270       int 
00271       pubsync() { return this->sync(); }
00272       //@}
00273 
00274       // [27.5.2.2.3] get area
00275       /**
00276        *  @brief  Looking ahead into the stream.
00277        *  @return  The number of characters available.
00278        *
00279        *  If a read position is available, returns the number of characters
00280        *  available for reading before the buffer must be refilled.
00281        *  Otherwise returns the derived @c showmanyc().
00282       */
00283       streamsize 
00284       in_avail() 
00285       { 
00286     const streamsize __ret = this->egptr() - this->gptr();
00287     return __ret ? __ret : this->showmanyc();
00288       }
00289 
00290       /**
00291        *  @brief  Getting the next character.
00292        *  @return  The next character, or eof.
00293        *
00294        *  Calls @c sbumpc(), and if that function returns
00295        *  @c traits::eof(), so does this function.  Otherwise, @c sgetc().
00296       */
00297       int_type 
00298       snextc()
00299       {
00300     int_type __ret = traits_type::eof();
00301     if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(), 
00302                                __ret), true))
00303       __ret = this->sgetc();
00304     return __ret;
00305       }
00306 
00307       /**
00308        *  @brief  Getting the next character.
00309        *  @return  The next character, or eof.
00310        *
00311        *  If the input read position is available, returns that character
00312        *  and increments the read pointer, otherwise calls and returns
00313        *  @c uflow().
00314       */
00315       int_type 
00316       sbumpc()
00317       {
00318     int_type __ret;
00319     if (__builtin_expect(this->gptr() < this->egptr(), true))
00320       {
00321         __ret = traits_type::to_int_type(*this->gptr());
00322         this->gbump(1);
00323       }
00324     else 
00325       __ret = this->uflow();
00326     return __ret;
00327       }
00328 
00329       /**
00330        *  @brief  Getting the next character.
00331        *  @return  The next character, or eof.
00332        *
00333        *  If the input read position is available, returns that character,
00334        *  otherwise calls and returns @c underflow().  Does not move the 
00335        *  read position after fetching the character.
00336       */
00337       int_type 
00338       sgetc()
00339       {
00340     int_type __ret;
00341     if (__builtin_expect(this->gptr() < this->egptr(), true))
00342       __ret = traits_type::to_int_type(*this->gptr());
00343     else 
00344       __ret = this->underflow();
00345     return __ret;
00346       }
00347 
00348       /**
00349        *  @brief  Entry point for xsgetn.
00350        *  @param  __s  A buffer area.
00351        *  @param  __n  A count.
00352        *
00353        *  Returns xsgetn(__s,__n).  The effect is to fill @a __s[0] through
00354        *  @a __s[__n-1] with characters from the input sequence, if possible.
00355       */
00356       streamsize 
00357       sgetn(char_type* __s, streamsize __n)
00358       { return this->xsgetn(__s, __n); }
00359 
00360       // [27.5.2.2.4] putback
00361       /**
00362        *  @brief  Pushing characters back into the input stream.
00363        *  @param  __c  The character to push back.
00364        *  @return  The previous character, if possible.
00365        *
00366        *  Similar to sungetc(), but @a __c is pushed onto the stream
00367        *  instead of <em>the previous character.</em> If successful,
00368        *  the next character fetched from the input stream will be @a
00369        *  __c.
00370       */
00371       int_type 
00372       sputbackc(char_type __c)
00373       {
00374     int_type __ret;
00375     const bool __testpos = this->eback() < this->gptr();
00376     if (__builtin_expect(!__testpos || 
00377                  !traits_type::eq(__c, this->gptr()[-1]), false))
00378       __ret = this->pbackfail(traits_type::to_int_type(__c));
00379     else 
00380       {
00381         this->gbump(-1);
00382         __ret = traits_type::to_int_type(*this->gptr());
00383       }
00384     return __ret;
00385       }
00386 
00387       /**
00388        *  @brief  Moving backwards in the input stream.
00389        *  @return  The previous character, if possible.
00390        *
00391        *  If a putback position is available, this function decrements
00392        *  the input pointer and returns that character.  Otherwise,
00393        *  calls and returns pbackfail().  The effect is to @a unget
00394        *  the last character @a gotten.
00395       */
00396       int_type 
00397       sungetc()
00398       {
00399     int_type __ret;
00400     if (__builtin_expect(this->eback() < this->gptr(), true))
00401       {
00402         this->gbump(-1);
00403         __ret = traits_type::to_int_type(*this->gptr());
00404       }
00405     else 
00406       __ret = this->pbackfail();
00407     return __ret;
00408       }
00409 
00410       // [27.5.2.2.5] put area
00411       /**
00412        *  @brief  Entry point for all single-character output functions.
00413        *  @param  __c  A character to output.
00414        *  @return  @a __c, if possible.
00415        *
00416        *  One of two public output functions.
00417        *
00418        *  If a write position is available for the output sequence (i.e.,
00419        *  the buffer is not full), stores @a __c in that position, increments
00420        *  the position, and returns @c traits::to_int_type(__c).  If a write
00421        *  position is not available, returns @c overflow(__c).
00422       */
00423       int_type 
00424       sputc(char_type __c)
00425       {
00426     int_type __ret;
00427     if (__builtin_expect(this->pptr() < this->epptr(), true))
00428       {
00429         *this->pptr() = __c;
00430         this->pbump(1);
00431         __ret = traits_type::to_int_type(__c);
00432       }
00433     else
00434       __ret = this->overflow(traits_type::to_int_type(__c));
00435     return __ret;
00436       }
00437 
00438       /**
00439        *  @brief  Entry point for all single-character output functions.
00440        *  @param  __s  A buffer read area.
00441        *  @param  __n  A count.
00442        *
00443        *  One of two public output functions.
00444        *
00445        *
00446        *  Returns xsputn(__s,__n).  The effect is to write @a __s[0] through
00447        *  @a __s[__n-1] to the output sequence, if possible.
00448       */
00449       streamsize 
00450       sputn(const char_type* __s, streamsize __n)
00451       { return this->xsputn(__s, __n); }
00452 
00453     protected:
00454       /**
00455        *  @brief  Base constructor.
00456        *
00457        *  Only called from derived constructors, and sets up all the
00458        *  buffer data to zero, including the pointers described in the
00459        *  basic_streambuf class description.  Note that, as a result,
00460        *  - the class starts with no read nor write positions available,
00461        *  - this is not an error
00462       */
00463       basic_streambuf()
00464       : _M_in_beg(0), _M_in_cur(0), _M_in_end(0), 
00465       _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
00466       _M_buf_locale(locale()) 
00467       { }
00468 
00469       // [27.5.2.3.1] get area access
00470       //@{
00471       /**
00472        *  @brief  Access to the get area.
00473        *
00474        *  These functions are only available to other protected functions,
00475        *  including derived classes.
00476        *
00477        *  - eback() returns the beginning pointer for the input sequence
00478        *  - gptr() returns the next pointer for the input sequence
00479        *  - egptr() returns the end pointer for the input sequence
00480       */
00481       char_type* 
00482       eback() const { return _M_in_beg; }
00483 
00484       char_type* 
00485       gptr()  const { return _M_in_cur;  }
00486 
00487       char_type* 
00488       egptr() const { return _M_in_end; }
00489       //@}
00490 
00491       /**
00492        *  @brief  Moving the read position.
00493        *  @param  __n  The delta by which to move.
00494        *
00495        *  This just advances the read position without returning any data.
00496       */
00497       void 
00498       gbump(int __n) { _M_in_cur += __n; }
00499 
00500       /**
00501        *  @brief  Setting the three read area pointers.
00502        *  @param  __gbeg  A pointer.
00503        *  @param  __gnext  A pointer.
00504        *  @param  __gend  A pointer.
00505        *  @post  @a __gbeg == @c eback(), @a __gnext == @c gptr(), and
00506        *         @a __gend == @c egptr()
00507       */
00508       void 
00509       setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
00510       {
00511     _M_in_beg = __gbeg;
00512     _M_in_cur = __gnext;
00513     _M_in_end = __gend;
00514       }
00515 
00516       // [27.5.2.3.2] put area access
00517       //@{
00518       /**
00519        *  @brief  Access to the put area.
00520        *
00521        *  These functions are only available to other protected functions,
00522        *  including derived classes.
00523        *
00524        *  - pbase() returns the beginning pointer for the output sequence
00525        *  - pptr() returns the next pointer for the output sequence
00526        *  - epptr() returns the end pointer for the output sequence
00527       */
00528       char_type* 
00529       pbase() const { return _M_out_beg; }
00530 
00531       char_type* 
00532       pptr() const { return _M_out_cur; }
00533 
00534       char_type* 
00535       epptr() const { return _M_out_end; }
00536       //@}
00537 
00538       /**
00539        *  @brief  Moving the write position.
00540        *  @param  __n  The delta by which to move.
00541        *
00542        *  This just advances the write position without returning any data.
00543       */
00544       void 
00545       pbump(int __n) { _M_out_cur += __n; }
00546 
00547       /**
00548        *  @brief  Setting the three write area pointers.
00549        *  @param  __pbeg  A pointer.
00550        *  @param  __pend  A pointer.
00551        *  @post  @a __pbeg == @c pbase(), @a __pbeg == @c pptr(), and
00552        *         @a __pend == @c epptr()
00553       */
00554       void 
00555       setp(char_type* __pbeg, char_type* __pend)
00556       { 
00557     _M_out_beg = _M_out_cur = __pbeg; 
00558     _M_out_end = __pend;
00559       }
00560 
00561       // [27.5.2.4] virtual functions
00562       // [27.5.2.4.1] locales
00563       /**
00564        *  @brief  Changes translations.
00565        *  @param  __loc  A new locale.
00566        *
00567        *  Translations done during I/O which depend on the current
00568        *  locale are changed by this call.  The standard adds,
00569        *  <em>Between invocations of this function a class derived
00570        *  from streambuf can safely cache results of calls to locale
00571        *  functions and to members of facets so obtained.</em>
00572        *
00573        *  @note  Base class version does nothing.
00574       */
00575       virtual void 
00576       imbue(const locale& __loc) 
00577       { }
00578 
00579       // [27.5.2.4.2] buffer management and positioning
00580       /**
00581        *  @brief  Manipulates the buffer.
00582        *
00583        *  Each derived class provides its own appropriate behavior.  See
00584        *  the next-to-last paragraph of 
00585        *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25s02.html
00586        *  for more on this function.
00587        *
00588        *  @note  Base class version does nothing, returns @c this.
00589       */
00590       virtual basic_streambuf<char_type,_Traits>* 
00591       setbuf(char_type*, streamsize)
00592       { return this; }
00593       
00594       /**
00595        *  @brief  Alters the stream positions.
00596        *
00597        *  Each derived class provides its own appropriate behavior.
00598        *  @note  Base class version does nothing, returns a @c pos_type
00599        *         that represents an invalid stream position.
00600       */
00601       virtual pos_type 
00602       seekoff(off_type, ios_base::seekdir,
00603           ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
00604       { return pos_type(off_type(-1)); } 
00605 
00606       /**
00607        *  @brief  Alters the stream positions.
00608        *
00609        *  Each derived class provides its own appropriate behavior.
00610        *  @note  Base class version does nothing, returns a @c pos_type
00611        *         that represents an invalid stream position.
00612       */
00613       virtual pos_type 
00614       seekpos(pos_type, 
00615           ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
00616       { return pos_type(off_type(-1)); } 
00617 
00618       /**
00619        *  @brief  Synchronizes the buffer arrays with the controlled sequences.
00620        *  @return  -1 on failure.
00621        *
00622        *  Each derived class provides its own appropriate behavior,
00623        *  including the definition of @a failure.
00624        *  @note  Base class version does nothing, returns zero.
00625       */
00626       virtual int 
00627       sync() { return 0; }
00628 
00629       // [27.5.2.4.3] get area
00630       /**
00631        *  @brief  Investigating the data available.
00632        *  @return  An estimate of the number of characters available in the
00633        *           input sequence, or -1.
00634        *
00635        *  <em>If it returns a positive value, then successive calls to
00636        *  @c underflow() will not return @c traits::eof() until at
00637        *  least that number of characters have been supplied.  If @c
00638        *  showmanyc() returns -1, then calls to @c underflow() or @c
00639        *  uflow() will fail.</em> [27.5.2.4.3]/1
00640        *
00641        *  @note  Base class version does nothing, returns zero.
00642        *  @note  The standard adds that <em>the intention is not only that the
00643        *         calls [to underflow or uflow] will not return @c eof() but
00644        *         that they will return immediately.</em>
00645        *  @note  The standard adds that <em>the morphemes of @c showmanyc are
00646        *         @b es-how-many-see, not @b show-manic.</em>
00647       */
00648       virtual streamsize 
00649       showmanyc() { return 0; }
00650 
00651       /**
00652        *  @brief  Multiple character extraction.
00653        *  @param  __s  A buffer area.
00654        *  @param  __n  Maximum number of characters to assign.
00655        *  @return  The number of characters assigned.
00656        *
00657        *  Fills @a __s[0] through @a __s[__n-1] with characters from the input
00658        *  sequence, as if by @c sbumpc().  Stops when either @a __n characters
00659        *  have been copied, or when @c traits::eof() would be copied.
00660        *
00661        *  It is expected that derived classes provide a more efficient
00662        *  implementation by overriding this definition.
00663       */
00664       virtual streamsize 
00665       xsgetn(char_type* __s, streamsize __n);
00666 
00667       /**
00668        *  @brief  Fetches more data from the controlled sequence.
00669        *  @return  The first character from the <em>pending sequence</em>.
00670        *
00671        *  Informally, this function is called when the input buffer is
00672        *  exhausted (or does not exist, as buffering need not actually be
00673        *  done).  If a buffer exists, it is @a refilled.  In either case, the
00674        *  next available character is returned, or @c traits::eof() to
00675        *  indicate a null pending sequence.
00676        *
00677        *  For a formal definition of the pending sequence, see a good text
00678        *  such as Langer & Kreft, or [27.5.2.4.3]/7-14.
00679        *
00680        *  A functioning input streambuf can be created by overriding only
00681        *  this function (no buffer area will be used).  For an example, see
00682        *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25.html
00683        *
00684        *  @note  Base class version does nothing, returns eof().
00685       */
00686       virtual int_type 
00687       underflow()
00688       { return traits_type::eof(); }
00689 
00690       /**
00691        *  @brief  Fetches more data from the controlled sequence.
00692        *  @return  The first character from the <em>pending sequence</em>.
00693        *
00694        *  Informally, this function does the same thing as @c underflow(),
00695        *  and in fact is required to call that function.  It also returns
00696        *  the new character, like @c underflow() does.  However, this
00697        *  function also moves the read position forward by one.
00698       */
00699       virtual int_type 
00700       uflow() 
00701       {
00702     int_type __ret = traits_type::eof();
00703     const bool __testeof = traits_type::eq_int_type(this->underflow(), 
00704                             __ret);
00705     if (!__testeof)
00706       {
00707         __ret = traits_type::to_int_type(*this->gptr());
00708         this->gbump(1);
00709       }
00710     return __ret;    
00711       }
00712 
00713       // [27.5.2.4.4] putback
00714       /**
00715        *  @brief  Tries to back up the input sequence.
00716        *  @param  __c  The character to be inserted back into the sequence.
00717        *  @return  eof() on failure, <em>some other value</em> on success
00718        *  @post  The constraints of @c gptr(), @c eback(), and @c pptr()
00719        *         are the same as for @c underflow().
00720        *
00721        *  @note  Base class version does nothing, returns eof().
00722       */
00723       virtual int_type 
00724       pbackfail(int_type __c  = traits_type::eof())
00725       { return traits_type::eof(); }
00726 
00727       // Put area:
00728       /**
00729        *  @brief  Multiple character insertion.
00730        *  @param  __s  A buffer area.
00731        *  @param  __n  Maximum number of characters to write.
00732        *  @return  The number of characters written.
00733        *
00734        *  Writes @a __s[0] through @a __s[__n-1] to the output sequence, as if
00735        *  by @c sputc().  Stops when either @a n characters have been
00736        *  copied, or when @c sputc() would return @c traits::eof().
00737        *
00738        *  It is expected that derived classes provide a more efficient
00739        *  implementation by overriding this definition.
00740       */
00741       virtual streamsize 
00742       xsputn(const char_type* __s, streamsize __n);
00743 
00744       /**
00745        *  @brief  Consumes data from the buffer; writes to the
00746        *          controlled sequence.
00747        *  @param  __c  An additional character to consume.
00748        *  @return  eof() to indicate failure, something else (usually
00749        *           @a __c, or not_eof())
00750        *
00751        *  Informally, this function is called when the output buffer
00752        *  is full (or does not exist, as buffering need not actually
00753        *  be done).  If a buffer exists, it is @a consumed, with
00754        *  <em>some effect</em> on the controlled sequence.
00755        *  (Typically, the buffer is written out to the sequence
00756        *  verbatim.)  In either case, the character @a c is also
00757        *  written out, if @a __c is not @c eof().
00758        *
00759        *  For a formal definition of this function, see a good text
00760        *  such as Langer & Kreft, or [27.5.2.4.5]/3-7.
00761        *
00762        *  A functioning output streambuf can be created by overriding only
00763        *  this function (no buffer area will be used).
00764        *
00765        *  @note  Base class version does nothing, returns eof().
00766       */
00767       virtual int_type 
00768       overflow(int_type __c  = traits_type::eof())
00769       { return traits_type::eof(); }
00770 
00771 #if _GLIBCXX_USE_DEPRECATED
00772     // Annex D.6
00773     public:
00774       /**
00775        *  @brief  Tosses a character.
00776        *
00777        *  Advances the read pointer, ignoring the character that would have
00778        *  been read.
00779        *
00780        *  See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
00781        */
00782       void 
00783       stossc() 
00784       {
00785     if (this->gptr() < this->egptr()) 
00786       this->gbump(1);
00787     else 
00788       this->uflow();
00789       }
00790 #endif
00791 
00792       // Also used by specializations for char and wchar_t in src.
00793       void 
00794       __safe_gbump(streamsize __n) { _M_in_cur += __n; }
00795 
00796       void
00797       __safe_pbump(streamsize __n) { _M_out_cur += __n; }
00798 
00799     private:
00800       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00801       // Side effect of DR 50. 
00802       basic_streambuf(const basic_streambuf& __sb)
00803       : _M_in_beg(__sb._M_in_beg), _M_in_cur(__sb._M_in_cur), 
00804       _M_in_end(__sb._M_in_end), _M_out_beg(__sb._M_out_beg), 
00805       _M_out_cur(__sb._M_out_cur), _M_out_end(__sb._M_out_cur),
00806       _M_buf_locale(__sb._M_buf_locale) 
00807       { }
00808 
00809       basic_streambuf&
00810       operator=(const basic_streambuf&) { return *this; };
00811     };
00812 
00813   // Explicit specialization declarations, defined in src/streambuf.cc.
00814   template<>
00815     streamsize
00816     __copy_streambufs_eof(basic_streambuf<char>* __sbin,
00817               basic_streambuf<char>* __sbout, bool& __ineof);
00818 #ifdef _GLIBCXX_USE_WCHAR_T
00819   template<>
00820     streamsize
00821     __copy_streambufs_eof(basic_streambuf<wchar_t>* __sbin,
00822               basic_streambuf<wchar_t>* __sbout, bool& __ineof);
00823 #endif
00824 
00825 _GLIBCXX_END_NAMESPACE_VERSION
00826 } // namespace
00827 
00828 #include <bits/streambuf.tcc>
00829 
00830 #endif /* _GLIBCXX_STREAMBUF */