streambuf

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00001 // Stream buffer classes -*- C++ -*-
00002 
00003 // Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
00004 // Free Software Foundation, Inc.
00005 //
00006 // This file is part of the GNU ISO C++ Library.  This library is free
00007 // software; you can redistribute it and/or modify it under the
00008 // terms of the GNU General Public License as published by the
00009 // Free Software Foundation; either version 2, or (at your option)
00010 // any later version.
00011 
00012 // This library is distributed in the hope that it will be useful,
00013 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00014 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00015 // GNU General Public License for more details.
00016 
00017 // You should have received a copy of the GNU General Public License along
00018 // with this library; see the file COPYING.  If not, write to the Free
00019 // Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
00020 // USA.
00021 
00022 // As a special exception, you may use this file as part of a free software
00023 // library without restriction.  Specifically, if other files instantiate
00024 // templates or use macros or inline functions from this file, or you compile
00025 // this file and link it with other files to produce an executable, this
00026 // file does not by itself cause the resulting executable to be covered by
00027 // the GNU General Public License.  This exception does not however
00028 // invalidate any other reasons why the executable file might be covered by
00029 // the GNU General Public License.
00030 
00031 //
00032 // ISO C++ 14882: 27.5  Stream buffers
00033 //
00034 
00035 /** @file streambuf
00036  *  This is a Standard C++ Library header.
00037  */
00038 
00039 #ifndef _GLIBXX_STREAMBUF
00040 #define _GLIBXX_STREAMBUF 1
00041 
00042 #pragma GCC system_header
00043 
00044 #include <bits/c++config.h>
00045 #include <iosfwd>
00046 #include <bits/localefwd.h>
00047 #include <bits/ios_base.h>
00048 
00049 namespace std
00050 {
00051   /**
00052    *  @if maint
00053    *  Does stuff.
00054    *  @endif
00055   */
00056   template<typename _CharT, typename _Traits>
00057     streamsize
00058     __copy_streambufs(basic_streambuf<_CharT, _Traits>* __sbin,
00059               basic_streambuf<_CharT, _Traits>* __sbout);
00060   
00061   /**
00062    *  @brief  The actual work of input and output (interface).
00063    *
00064    *  This is a base class.  Derived stream buffers each control a
00065    *  pair of character sequences:  one for input, and one for output.
00066    *
00067    *  Section [27.5.1] of the standard describes the requirements and
00068    *  behavior of stream buffer classes.  That section (three paragraphs)
00069    *  is reproduced here, for simplicity and accuracy.
00070    *
00071    *  -# Stream buffers can impose various constraints on the sequences
00072    *     they control.  Some constraints are:
00073    *     - The controlled input sequence can be not readable.
00074    *     - The controlled output sequence can be not writable.
00075    *     - The controlled sequences can be associated with the contents of
00076    *       other representations for character sequences, such as external
00077    *       files.
00078    *     - The controlled sequences can support operations @e directly to or
00079    *       from associated sequences.
00080    *     - The controlled sequences can impose limitations on how the
00081    *       program can read characters from a sequence, write characters to
00082    *       a sequence, put characters back into an input sequence, or alter
00083    *       the stream position.
00084    *     .
00085    *  -# Each sequence is characterized by three pointers which, if non-null,
00086    *     all point into the same @c charT array object.  The array object
00087    *     represents, at any moment, a (sub)sequence of characters from the
00088    *     sequence.  Operations performed on a sequence alter the values
00089    *     stored in these pointers, perform reads and writes directly to or
00090    *     from associated sequences, and alter "the stream position" and
00091    *     conversion state as needed to maintain this subsequence relationship.
00092    *     The three pointers are:
00093    *     - the <em>beginning pointer</em>, or lowest element address in the
00094    *       array (called @e xbeg here);
00095    *     - the <em>next pointer</em>, or next element address that is a
00096    *       current candidate for reading or writing (called @e xnext here);
00097    *     - the <em>end pointer</em>, or first element address beyond the
00098    *       end of the array (called @e xend here).
00099    *     .
00100    *  -# The following semantic constraints shall always apply for any set
00101    *     of three pointers for a sequence, using the pointer names given
00102    *     immediately above:
00103    *     - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
00104    *       also be non-null pointers into the same @c charT array, as
00105    *       described above; otherwise, @e xbeg and @e xend shall also be null.
00106    *     - If @e xnext is not a null pointer and @e xnext < @e xend for an
00107    *       output sequence, then a <em>write position</em> is available.
00108    *       In this case, @e *xnext shall be assignable as the next element
00109    *       to write (to put, or to store a character value, into the sequence).
00110    *     - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
00111    *       input sequence, then a <em>putback position</em> is available.
00112    *       In this case, @e xnext[-1] shall have a defined value and is the
00113    *       next (preceding) element to store a character that is put back
00114    *       into the input sequence.
00115    *     - If @e xnext is not a null pointer and @e xnext< @e xend for an
00116    *       input sequence, then a <em>read position</em> is available.
00117    *       In this case, @e *xnext shall have a defined value and is the
00118    *       next element to read (to get, or to obtain a character value,
00119    *       from the sequence).
00120   */
00121   template<typename _CharT, typename _Traits>
00122     class basic_streambuf 
00123     {
00124     public:
00125       //@{
00126       /**
00127        *  These are standard types.  They permit a standardized way of
00128        *  referring to names of (or names dependant on) the template
00129        *  parameters, which are specific to the implementation.
00130       */
00131       typedef _CharT                    char_type;
00132       typedef _Traits                   traits_type;
00133       typedef typename traits_type::int_type        int_type;
00134       typedef typename traits_type::pos_type        pos_type;
00135       typedef typename traits_type::off_type        off_type;
00136       //@}
00137 
00138       //@{
00139       /**
00140        *  @if maint
00141        *  This is a non-standard type.
00142        *  @endif
00143       */
00144       typedef basic_streambuf<char_type, traits_type>   __streambuf_type;
00145       //@}
00146       
00147       friend class basic_ios<char_type, traits_type>;
00148       friend class basic_istream<char_type, traits_type>;
00149       friend class basic_ostream<char_type, traits_type>;
00150       friend class istreambuf_iterator<char_type, traits_type>;
00151       friend class ostreambuf_iterator<char_type, traits_type>;
00152 
00153       friend streamsize
00154       __copy_streambufs<>(__streambuf_type* __sbin,
00155               __streambuf_type* __sbout);
00156       
00157       template<typename _CharT2, typename _Traits2>
00158         friend basic_istream<_CharT2, _Traits2>&
00159         operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);
00160       
00161       template<typename _CharT2, typename _Traits2, typename _Alloc>
00162         friend basic_istream<_CharT2, _Traits2>&
00163         operator>>(basic_istream<_CharT2, _Traits2>&,
00164            basic_string<_CharT2, _Traits2, _Alloc>&);
00165       
00166       template<typename _CharT2, typename _Traits2, typename _Alloc>
00167         friend basic_istream<_CharT2, _Traits2>&
00168         getline(basic_istream<_CharT2, _Traits2>&,
00169         basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2);
00170 
00171     protected:
00172       //@{
00173       /**
00174        *  @if maint
00175        *  This is based on _IO_FILE, just reordered to be more consistent,
00176        *  and is intended to be the most minimal abstraction for an
00177        *  internal buffer.
00178        *  -  get == input == read
00179        *  -  put == output == write
00180        *  @endif
00181       */
00182       char_type*        _M_in_beg;     // Start of get area. 
00183       char_type*        _M_in_cur;     // Current read area. 
00184       char_type*        _M_in_end;     // End of get area. 
00185       char_type*        _M_out_beg;    // Start of put area. 
00186       char_type*        _M_out_cur;    // Current put area. 
00187       char_type*        _M_out_end;    // End of put area.
00188 
00189       /**
00190        *  @if maint
00191        *  Current locale setting.
00192        *  @endif
00193       */
00194       locale            _M_buf_locale;  
00195 
00196   public:
00197       /// Destructor deallocates no buffer space.
00198       virtual 
00199       ~basic_streambuf() 
00200       { }
00201 
00202       // [27.5.2.2.1] locales
00203       /**
00204        *  @brief  Entry point for imbue().
00205        *  @param  loc  The new locale.
00206        *  @return  The previous locale.
00207        *
00208        *  Calls the derived imbue(loc).
00209       */
00210       locale 
00211       pubimbue(const locale &__loc)
00212       {
00213     locale __tmp(this->getloc());
00214     this->imbue(__loc);
00215     _M_buf_locale = __loc;
00216     return __tmp;
00217       }
00218 
00219       /**
00220        *  @brief  Locale access.
00221        *  @return  The current locale in effect.
00222        *
00223        *  If pubimbue(loc) has been called, then the most recent @c loc
00224        *  is returned.  Otherwise the global locale in effect at the time
00225        *  of construction is returned.
00226       */
00227       locale   
00228       getloc() const
00229       { return _M_buf_locale; } 
00230 
00231       // [27.5.2.2.2] buffer management and positioning
00232       //@{
00233       /**
00234        *  @brief  Entry points for derived buffer functions.
00235        *
00236        *  The public versions of @c pubfoo dispatch to the protected
00237        *  derived @c foo member functions, passing the arguments (if any)
00238        *  and returning the result unchanged.
00239       */
00240       __streambuf_type* 
00241       pubsetbuf(char_type* __s, streamsize __n) 
00242       { return this->setbuf(__s, __n); }
00243 
00244       pos_type 
00245       pubseekoff(off_type __off, ios_base::seekdir __way, 
00246          ios_base::openmode __mode = ios_base::in | ios_base::out)
00247       { return this->seekoff(__off, __way, __mode); }
00248 
00249       pos_type 
00250       pubseekpos(pos_type __sp,
00251          ios_base::openmode __mode = ios_base::in | ios_base::out)
00252       { return this->seekpos(__sp, __mode); }
00253 
00254       int 
00255       pubsync() { return this->sync(); }
00256       //@}
00257 
00258       // [27.5.2.2.3] get area
00259       /**
00260        *  @brief  Looking ahead into the stream.
00261        *  @return  The number of characters available.
00262        *
00263        *  If a read position is available, returns the number of characters
00264        *  available for reading before the buffer must be refilled.
00265        *  Otherwise returns the derived @c showmanyc().
00266       */
00267       streamsize 
00268       in_avail() 
00269       { 
00270     const streamsize __ret = this->egptr() - this->gptr();
00271     return __ret ? __ret : this->showmanyc();
00272       }
00273 
00274       /**
00275        *  @brief  Getting the next character.
00276        *  @return  The next character, or eof.
00277        *
00278        *  Calls @c sbumpc(), and if that function returns
00279        *  @c traits::eof(), so does this function.  Otherwise, @c sgetc().
00280       */
00281       int_type 
00282       snextc()
00283       {
00284     int_type __ret = traits_type::eof();
00285     if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(), 
00286                                __ret), true))
00287       __ret = this->sgetc();
00288     return __ret;
00289       }
00290 
00291       /**
00292        *  @brief  Getting the next character.
00293        *  @return  The next character, or eof.
00294        *
00295        *  If the input read position is available, returns that character
00296        *  and increments the read pointer, otherwise calls and returns
00297        *  @c uflow().
00298       */
00299       int_type 
00300       sbumpc()
00301       {
00302     int_type __ret;
00303     if (__builtin_expect(this->gptr() < this->egptr(), true))
00304       {
00305         __ret = traits_type::to_int_type(*this->gptr());
00306         this->gbump(1);
00307       }
00308     else 
00309       __ret = this->uflow();
00310     return __ret;
00311       }
00312 
00313       /**
00314        *  @brief  Getting the next character.
00315        *  @return  The next character, or eof.
00316        *
00317        *  If the input read position is available, returns that character,
00318        *  otherwise calls and returns @c underflow().  Does not move the 
00319        *  read position after fetching the character.
00320       */
00321       int_type 
00322       sgetc()
00323       {
00324     int_type __ret;
00325     if (__builtin_expect(this->gptr() < this->egptr(), true))
00326       __ret = traits_type::to_int_type(*this->gptr());
00327     else 
00328       __ret = this->underflow();
00329     return __ret;
00330       }
00331 
00332       /**
00333        *  @brief  Entry point for xsgetn.
00334        *  @param  s  A buffer area.
00335        *  @param  n  A count.
00336        *
00337        *  Returns xsgetn(s,n).  The effect is to fill @a s[0] through
00338        *  @a s[n-1] with characters from the input sequence, if possible.
00339       */
00340       streamsize 
00341       sgetn(char_type* __s, streamsize __n)
00342       { return this->xsgetn(__s, __n); }
00343 
00344       // [27.5.2.2.4] putback
00345       /**
00346        *  @brief  Pushing characters back into the input stream.
00347        *  @param  c  The character to push back.
00348        *  @return  The previous character, if possible.
00349        *
00350        *  Similar to sungetc(), but @a c is pushed onto the stream instead
00351        *  of "the previous character".  If successful, the next character
00352        *  fetched from the input stream will be @a c.
00353       */
00354       int_type 
00355       sputbackc(char_type __c)
00356       {
00357     int_type __ret;
00358     const bool __testpos = this->eback() < this->gptr();
00359     if (__builtin_expect(!__testpos || 
00360                  !traits_type::eq(__c, this->gptr()[-1]), false))
00361       __ret = this->pbackfail(traits_type::to_int_type(__c));
00362     else 
00363       {
00364         this->gbump(-1);
00365         __ret = traits_type::to_int_type(*this->gptr());
00366       }
00367     return __ret;
00368       }
00369 
00370       /**
00371        *  @brief  Moving backwards in the input stream.
00372        *  @return  The previous character, if possible.
00373        *
00374        *  If a putback position is available, this function decrements the
00375        *  input pointer and returns that character.  Otherwise, calls and
00376        *  returns pbackfail().  The effect is to "unget" the last character
00377        *  "gotten".
00378       */
00379       int_type 
00380       sungetc()
00381       {
00382     int_type __ret;
00383     if (__builtin_expect(this->eback() < this->gptr(), true))
00384       {
00385         this->gbump(-1);
00386         __ret = traits_type::to_int_type(*this->gptr());
00387       }
00388     else 
00389       __ret = this->pbackfail();
00390     return __ret;
00391       }
00392 
00393       // [27.5.2.2.5] put area
00394       /**
00395        *  @brief  Entry point for all single-character output functions.
00396        *  @param  c  A character to output.
00397        *  @return  @a c, if possible.
00398        *
00399        *  One of two public output functions.
00400        *
00401        *  If a write position is available for the output sequence (i.e.,
00402        *  the buffer is not full), stores @a c in that position, increments
00403        *  the position, and returns @c traits::to_int_type(c).  If a write
00404        *  position is not available, returns @c overflow(c).
00405       */
00406       int_type 
00407       sputc(char_type __c)
00408       {
00409     int_type __ret;
00410     if (__builtin_expect(this->pptr() < this->epptr(), true))
00411       {
00412         *this->pptr() = __c;
00413         this->pbump(1);
00414         __ret = traits_type::to_int_type(__c);
00415       }
00416     else
00417       __ret = this->overflow(traits_type::to_int_type(__c));
00418     return __ret;
00419       }
00420 
00421       /**
00422        *  @brief  Entry point for all single-character output functions.
00423        *  @param  s  A buffer read area.
00424        *  @param  n  A count.
00425        *
00426        *  One of two public output functions.
00427        *
00428        *
00429        *  Returns xsputn(s,n).  The effect is to write @a s[0] through
00430        *  @a s[n-1] to the output sequence, if possible.
00431       */
00432       streamsize 
00433       sputn(const char_type* __s, streamsize __n)
00434       { return this->xsputn(__s, __n); }
00435 
00436     protected:
00437       /**
00438        *  @brief  Base constructor.
00439        *
00440        *  Only called from derived constructors, and sets up all the
00441        *  buffer data to zero, including the pointers described in the
00442        *  basic_streambuf class description.  Note that, as a result,
00443        *  - the class starts with no read nor write positions available,
00444        *  - this is not an error
00445       */
00446       basic_streambuf()
00447       : _M_in_beg(0), _M_in_cur(0), _M_in_end(0), 
00448       _M_out_beg(0), _M_out_cur(0), _M_out_end(0),
00449       _M_buf_locale(locale()) 
00450       { }
00451 
00452       // [27.5.2.3.1] get area access
00453       //@{
00454       /**
00455        *  @brief  Access to the get area.
00456        *
00457        *  These functions are only available to other protected functions,
00458        *  including derived classes.
00459        *
00460        *  - eback() returns the beginning pointer for the input sequence
00461        *  - gptr() returns the next pointer for the input sequence
00462        *  - egptr() returns the end pointer for the input sequence
00463       */
00464       char_type* 
00465       eback() const { return _M_in_beg; }
00466 
00467       char_type* 
00468       gptr()  const { return _M_in_cur;  }
00469 
00470       char_type* 
00471       egptr() const { return _M_in_end; }
00472       //@}
00473 
00474       /**
00475        *  @brief  Moving the read position.
00476        *  @param  n  The delta by which to move.
00477        *
00478        *  This just advances the read position without returning any data.
00479       */
00480       void 
00481       gbump(int __n) { _M_in_cur += __n; }
00482 
00483       /**
00484        *  @brief  Setting the three read area pointers.
00485        *  @param  gbeg  A pointer.
00486        *  @param  gnext  A pointer.
00487        *  @param  gend  A pointer.
00488        *  @post  @a gbeg == @c eback(), @a gnext == @c gptr(), and
00489        *         @a gend == @c egptr()
00490       */
00491       void 
00492       setg(char_type* __gbeg, char_type* __gnext, char_type* __gend)
00493       {
00494     _M_in_beg = __gbeg;
00495     _M_in_cur = __gnext;
00496     _M_in_end = __gend;
00497       }
00498 
00499       // [27.5.2.3.2] put area access
00500       //@{
00501       /**
00502        *  @brief  Access to the put area.
00503        *
00504        *  These functions are only available to other protected functions,
00505        *  including derived classes.
00506        *
00507        *  - pbase() returns the beginning pointer for the output sequence
00508        *  - pptr() returns the next pointer for the output sequence
00509        *  - epptr() returns the end pointer for the output sequence
00510       */
00511       char_type* 
00512       pbase() const { return _M_out_beg; }
00513 
00514       char_type* 
00515       pptr() const { return _M_out_cur; }
00516 
00517       char_type* 
00518       epptr() const { return _M_out_end; }
00519       //@}
00520 
00521       /**
00522        *  @brief  Moving the write position.
00523        *  @param  n  The delta by which to move.
00524        *
00525        *  This just advances the write position without returning any data.
00526       */
00527       void 
00528       pbump(int __n) { _M_out_cur += __n; }
00529 
00530       /**
00531        *  @brief  Setting the three write area pointers.
00532        *  @param  pbeg  A pointer.
00533        *  @param  pend  A pointer.
00534        *  @post  @a pbeg == @c pbase(), @a pbeg == @c pptr(), and
00535        *         @a pend == @c epptr()
00536       */
00537       void 
00538       setp(char_type* __pbeg, char_type* __pend)
00539       { 
00540     _M_out_beg = _M_out_cur = __pbeg; 
00541     _M_out_end = __pend;
00542       }
00543 
00544       // [27.5.2.4] virtual functions
00545       // [27.5.2.4.1] locales
00546       /**
00547        *  @brief  Changes translations.
00548        *  @param  loc  A new locale.
00549        *
00550        *  Translations done during I/O which depend on the current locale
00551        *  are changed by this call.  The standard adds, "Between invocations
00552        *  of this function a class derived from streambuf can safely cache
00553        *  results of calls to locale functions and to members of facets
00554        *  so obtained."
00555        *
00556        *  @note  Base class version does nothing.
00557       */
00558       virtual void 
00559       imbue(const locale&) 
00560       { }
00561 
00562       // [27.5.2.4.2] buffer management and positioning
00563       /**
00564        *  @brief  Maniuplates the buffer.
00565        *
00566        *  Each derived class provides its own appropriate behavior.  See
00567        *  the next-to-last paragraph of 
00568        *  http://gcc.gnu.org/onlinedocs/libstdc++/27_io/howto.html#2 for
00569        *  more on this function.
00570        *
00571        *  @note  Base class version does nothing, returns @c this.
00572       */
00573       virtual basic_streambuf<char_type,_Traits>* 
00574       setbuf(char_type*, streamsize)
00575       { return this; }
00576       
00577       /**
00578        *  @brief  Alters the stream positions.
00579        *
00580        *  Each derived class provides its own appropriate behavior.
00581        *  @note  Base class version does nothing, returns a @c pos_type
00582        *         that represents an invalid stream position.
00583       */
00584       virtual pos_type 
00585       seekoff(off_type, ios_base::seekdir,
00586           ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
00587       { return pos_type(off_type(-1)); } 
00588 
00589       /**
00590        *  @brief  Alters the stream positions.
00591        *
00592        *  Each derived class provides its own appropriate behavior.
00593        *  @note  Base class version does nothing, returns a @c pos_type
00594        *         that represents an invalid stream position.
00595       */
00596       virtual pos_type 
00597       seekpos(pos_type, 
00598           ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
00599       { return pos_type(off_type(-1)); } 
00600 
00601       /**
00602        *  @brief  Synchronizes the buffer arrays with the controlled sequences.
00603        *  @return  -1 on failure.
00604        *
00605        *  Each derived class provides its own appropriate behavior,
00606        *  including the definition of "failure".
00607        *  @note  Base class version does nothing, returns zero.
00608       */
00609       virtual int 
00610       sync() { return 0; }
00611 
00612       // [27.5.2.4.3] get area
00613       /**
00614        *  @brief  Investigating the data available.
00615        *  @return  An estimate of the number of characters available in the
00616        *           input sequence, or -1.
00617        *
00618        *  "If it returns a positive value, then successive calls to
00619        *  @c underflow() will not return @c traits::eof() until at least that
00620        *  number of characters have been supplied.  If @c showmanyc()
00621        *  returns -1, then calls to @c underflow() or @c uflow() will fail."
00622        *  [27.5.2.4.3]/1
00623        *
00624        *  @note  Base class version does nothing, returns zero.
00625        *  @note  The standard adds that "the intention is not only that the
00626        *         calls [to underflow or uflow] will not return @c eof() but
00627        *         that they will return "immediately".
00628        *  @note  The standard adds that "the morphemes of @c showmanyc are
00629        *         "es-how-many-see", not "show-manic".
00630       */
00631       virtual streamsize 
00632       showmanyc() { return 0; }
00633 
00634       /**
00635        *  @brief  Multiple character extraction.
00636        *  @param  s  A buffer area.
00637        *  @param  n  Maximum number of characters to assign.
00638        *  @return  The number of characters assigned.
00639        *
00640        *  Fills @a s[0] through @a s[n-1] with characters from the input
00641        *  sequence, as if by @c sbumpc().  Stops when either @a n characters
00642        *  have been copied, or when @c traits::eof() would be copied.
00643        *
00644        *  It is expected that derived classes provide a more efficient
00645        *  implementation by overriding this definition.
00646       */
00647       virtual streamsize 
00648       xsgetn(char_type* __s, streamsize __n);
00649 
00650       /**
00651        *  @brief  Fetches more data from the controlled sequence.
00652        *  @return  The first character from the <em>pending sequence</em>.
00653        *
00654        *  Informally, this function is called when the input buffer is
00655        *  exhausted (or does not exist, as buffering need not actually be
00656        *  done).  If a buffer exists, it is "refilled".  In either case, the
00657        *  next available character is returned, or @c traits::eof() to
00658        *  indicate a null pending sequence.
00659        *
00660        *  For a formal definiton of the pending sequence, see a good text
00661        *  such as Langer & Kreft, or [27.5.2.4.3]/7-14.
00662        *
00663        *  A functioning input streambuf can be created by overriding only
00664        *  this function (no buffer area will be used).  For an example, see
00665        *  http://gcc.gnu.org/onlinedocs/libstdc++/27_io/howto.html#6
00666        *
00667        *  @note  Base class version does nothing, returns eof().
00668       */
00669       virtual int_type 
00670       underflow()
00671       { return traits_type::eof(); }
00672 
00673       /**
00674        *  @brief  Fetches more data from the controlled sequence.
00675        *  @return  The first character from the <em>pending sequence</em>.
00676        *
00677        *  Informally, this function does the same thing as @c underflow(),
00678        *  and in fact is required to call that function.  It also returns
00679        *  the new character, like @c underflow() does.  However, this
00680        *  function also moves the read position forward by one.
00681       */
00682       virtual int_type 
00683       uflow() 
00684       {
00685     int_type __ret = traits_type::eof();
00686     const bool __testeof = traits_type::eq_int_type(this->underflow(), 
00687                             __ret);
00688     if (!__testeof)
00689       {
00690         __ret = traits_type::to_int_type(*this->gptr());
00691         this->gbump(1);
00692       }
00693     return __ret;    
00694       }
00695 
00696       // [27.5.2.4.4] putback
00697       /**
00698        *  @brief  Tries to back up the input sequence.
00699        *  @param  c  The character to be inserted back into the sequence.
00700        *  @return  eof() on failure, "some other value" on success
00701        *  @post  The constraints of @c gptr(), @c eback(), and @c pptr()
00702        *         are the same as for @c underflow().
00703        *
00704        *  @note  Base class version does nothing, returns eof().
00705       */
00706       virtual int_type 
00707       pbackfail(int_type /* __c */  = traits_type::eof())
00708       { return traits_type::eof(); }
00709 
00710       // Put area:
00711       /**
00712        *  @brief  Multiple character insertion.
00713        *  @param  s  A buffer area.
00714        *  @param  n  Maximum number of characters to write.
00715        *  @return  The number of characters written.
00716        *
00717        *  Writes @a s[0] through @a s[n-1] to the output sequence, as if
00718        *  by @c sputc().  Stops when either @a n characters have been
00719        *  copied, or when @c sputc() would return @c traits::eof().
00720        *
00721        *  It is expected that derived classes provide a more efficient
00722        *  implementation by overriding this definition.
00723       */
00724       virtual streamsize 
00725       xsputn(const char_type* __s, streamsize __n);
00726 
00727       /**
00728        *  @brief  Consumes data from the buffer; writes to the
00729        *          controlled sequence.
00730        *  @param  c  An additional character to consume.
00731        *  @return  eof() to indicate failure, something else (usually
00732        *           @a c, or not_eof())
00733        *
00734        *  Informally, this function is called when the output buffer is full
00735        *  (or does not exist, as buffering need not actually be done).  If a
00736        *  buffer exists, it is "consumed", with "some effect" on the
00737        *  controlled sequence.  (Typically, the buffer is written out to the
00738        *  sequence verbatim.)  In either case, the character @a c is also
00739        *  written out, if @a c is not @c eof().
00740        *
00741        *  For a formal definiton of this function, see a good text
00742        *  such as Langer & Kreft, or [27.5.2.4.5]/3-7.
00743        *
00744        *  A functioning output streambuf can be created by overriding only
00745        *  this function (no buffer area will be used).
00746        *
00747        *  @note  Base class version does nothing, returns eof().
00748       */
00749       virtual int_type 
00750       overflow(int_type /* __c */ = traits_type::eof())
00751       { return traits_type::eof(); }
00752 
00753 #ifdef _GLIBCXX_DEPRECATED
00754     // Annex D.6
00755     public:
00756       /**
00757        *  @brief  Tosses a character.
00758        *
00759        *  Advances the read pointer, ignoring the character that would have
00760        *  been read.
00761        *
00762        *  See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html
00763        *
00764        *  @note  This function has been deprecated by the standard.  You
00765        *         must define @c _GLIBCXX_DEPRECATED to make this visible; see
00766        *         c++config.h.
00767       */
00768       void 
00769       stossc() 
00770       {
00771     if (this->gptr() < this->egptr()) 
00772       this->gbump(1);
00773     else 
00774       this->uflow();
00775       }
00776 #endif
00777 
00778     private:
00779       // _GLIBCXX_RESOLVE_LIB_DEFECTS
00780       // Side effect of DR 50. 
00781       basic_streambuf(const __streambuf_type& __sb)
00782       : _M_in_beg(__sb._M_in_beg), _M_in_cur(__sb._M_in_cur), 
00783       _M_in_end(__sb._M_in_end), _M_out_beg(__sb._M_out_beg), 
00784       _M_out_cur(__sb._M_out_cur), _M_out_end(__sb._M_out_cur),
00785       _M_buf_locale(__sb._M_buf_locale) 
00786       { }
00787 
00788       __streambuf_type& 
00789       operator=(const __streambuf_type&) { return *this; };
00790     };
00791 
00792   // Explicit specialization declarations, defined in src/streambuf.cc.
00793   template<>
00794     streamsize
00795     __copy_streambufs(basic_streambuf<char>* __sbin,
00796               basic_streambuf<char>* __sbout);
00797 #ifdef _GLIBCXX_USE_WCHAR_T
00798   template<>
00799     streamsize
00800     __copy_streambufs(basic_streambuf<wchar_t>* __sbin,
00801               basic_streambuf<wchar_t>* __sbout);
00802 #endif
00803 } // namespace std
00804 
00805 #ifndef _GLIBCXX_EXPORT_TEMPLATE
00806 # include <bits/streambuf.tcc>
00807 #endif
00808 
00809 #endif /* _GLIBCXX_STREAMBUF */

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