std_streambuf.h

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// Stream buffer classes -*- C++ -*-

// Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003
// Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

//
// ISO C++ 14882: 27.5  Stream buffers
//

/** @file streambuf
 *  This is a Standard C++ Library header.  You should @c #include this header
 *  in your programs, rather than any of the "st[dl]_*.h" implementation files.
 */

#ifndef _CPP_STREAMBUF
#define _CPP_STREAMBUF	1

#pragma GCC system_header

#include <bits/c++config.h>
#include <iosfwd>
#include <cstdio> 	// For SEEK_SET, SEEK_CUR, SEEK_END
#include <bits/localefwd.h>
#include <bits/ios_base.h>

namespace std
{
  /**
   *  @if maint
   *  Does stuff.
   *  @endif
  */
  template<typename _CharT, typename _Traits>
    streamsize
    __copy_streambufs(basic_ios<_CharT, _Traits>& _ios,
		      basic_streambuf<_CharT, _Traits>* __sbin,
		      basic_streambuf<_CharT, _Traits>* __sbout);
  
  /**
   *  @brief  The actual work of input and output (interface).
   *
   *  This is a base class.  Derived stream buffers each control a
   *  pair of character sequences:  one for input, and one for output.
   *
   *  Section [27.5.1] of the standard describes the requirements and
   *  behavior of stream buffer classes.  That section (three paragraphs)
   *  is reproduced here, for simplicity and accuracy.
   *
   *  -# Stream buffers can impose various constraints on the sequences
   *     they control.  Some constraints are:
   *     - The controlled input sequence can be not readable.
   *     - The controlled output sequence can be not writable.
   *     - The controlled sequences can be associated with the contents of
   *       other representations for character sequences, such as external
   *       files.
   *     - The controlled sequences can support operations @e directly to or
   *       from associated sequences.
   *     - The controlled sequences can impose limitations on how the
   *       program can read characters from a sequence, write characters to
   *       a sequence, put characters back into an input sequence, or alter
   *       the stream position.
   *     .
   *  -# Each sequence is characterized by three pointers which, if non-null,
   *     all point into the same @c charT array object.  The array object
   *     represents, at any moment, a (sub)sequence of characters from the
   *     sequence.  Operations performed on a sequence alter the values
   *     stored in these pointers, perform reads and writes directly to or
   *     from associated sequences, and alter "the stream position" and
   *     conversion state as needed to maintain this subsequence relationship.
   *     The three pointers are:
   *     - the <em>beginning pointer</em>, or lowest element address in the
   *       array (called @e xbeg here);
   *     - the <em>next pointer</em>, or next element address that is a
   *       current candidate for reading or writing (called @e xnext here);
   *     - the <em>end pointer</em>, or first element address beyond the
   *       end of the array (called @e xend here).
   *     .
   *  -# The following semantic constraints shall always apply for any set
   *     of three pointers for a sequence, using the pointer names given
   *     immediately above:
   *     - If @e xnext is not a null pointer, then @e xbeg and @e xend shall
   *       also be non-null pointers into the same @c charT array, as
   *       described above; otherwise, @e xbeg and @e xend shall also be null.
   *     - If @e xnext is not a null pointer and @e xnext < @e xend for an
   *       output sequence, then a <em>write position</em> is available.
   *       In this case, @e *xnext shall be assignable as the next element
   *       to write (to put, or to store a character value, into the sequence).
   *     - If @e xnext is not a null pointer and @e xbeg < @e xnext for an
   *       input sequence, then a <em>putback position</em> is available.
   *       In this case, @e xnext[-1] shall have a defined value and is the
   *       next (preceding) element to store a character that is put back
   *       into the input sequence.
   *     - If @e xnext is not a null pointer and @e xnext< @e xend for an
   *       input sequence, then a <em>read position</em> is available.
   *       In this case, @e *xnext shall have a defined value and is the
   *       next element to read (to get, or to obtain a character value,
   *       from the sequence).
  */
  template<typename _CharT, typename _Traits>
    class basic_streambuf 
    {
    public:
      //@{
      /**
       *  These are standard types.  They permit a standardized way of
       *  referring to names of (or names dependant on) the template
       *  parameters, which are specific to the implementation.
      */
      typedef _CharT 					char_type;
      typedef _Traits 					traits_type;
      typedef typename traits_type::int_type 		int_type;
      typedef typename traits_type::pos_type 		pos_type;
      typedef typename traits_type::off_type 		off_type;
      //@}

      //@{
      /**
       *  @if maint
       *  These are non-standard types.
       *  @endif
      */
      typedef ctype<char_type>           		__ctype_type;
      typedef basic_streambuf<char_type, traits_type>  	__streambuf_type;
      typedef typename traits_type::state_type 		__state_type;
      //@}
      
      friend class basic_ios<char_type, traits_type>;
      friend class basic_istream<char_type, traits_type>;
      friend class basic_ostream<char_type, traits_type>;
      friend class istreambuf_iterator<char_type, traits_type>;
      friend class ostreambuf_iterator<char_type, traits_type>;

      friend streamsize
      __copy_streambufs<>(basic_ios<char_type, traits_type>& __ios,
			  __streambuf_type* __sbin,__streambuf_type* __sbout);
      
    protected:
      /**
       *  @if maint
       *  Pointer to the beginning of internally-allocated space.  Filebuf
       *  manually allocates/deallocates this, whereas stringstreams attempt
       *  to use the built-in intelligence of the string class.  If you are
       *  managing memory, set this.  If not, leave it NULL.
       *  @endif
      */
      char_type*		_M_buf; 	

      /**
       *  @if maint
       *  Actual size of allocated internal buffer, in bytes.
       *  @endif
      */
      size_t			_M_buf_size;

      /**
       *  @if maint
       *  Optimal or preferred size of internal buffer, in bytes.
       *  @endif
      */
      size_t			_M_buf_size_opt;

      /**
       *  @if maint
       *  True iff _M_in_* and _M_out_* buffers should always point to
       *  the same place.  True for fstreams, false for sstreams.
       *  @endif
      */
      bool 			_M_buf_unified;	

      //@{
      /**
       *  @if maint
       *  This is based on _IO_FILE, just reordered to be more consistent,
       *  and is intended to be the most minimal abstraction for an
       *  internal buffer.
       *  -  get == input == read
       *  -  put == output == write
       *  @endif
      */
      char_type* 		_M_in_beg;  	// Start of get area. 
      char_type* 		_M_in_cur;	// Current read area. 
      char_type* 		_M_in_end;	// End of get area. 
      char_type* 		_M_out_beg; 	// Start of put area. 
      char_type* 		_M_out_cur;  	// Current put area. 
      char_type* 		_M_out_end;  	// End of put area. 
      //@}

      /**
       *  @if maint
       *  Place to stash in || out || in | out settings for current streambuf.
       *  @endif
      */
      ios_base::openmode 	_M_mode;	

      /**
       *  @if maint
       *  Current locale setting.
       *  @endif
      */
      locale 			_M_buf_locale;	

      /**
       *  @if maint
       *  True iff locale is initialized.
       *  @endif
      */
      bool 			_M_buf_locale_init;

      //@{
      /**
       *  @if maint
       *  Necessary bits for putback buffer management. Only used in
       *  the basic_filebuf class, as necessary for the standard
       *  requirements. The only basic_streambuf member function that
       *  needs access to these data members is in_avail...
       *  
       *  @note pbacks of over one character are not currently supported.
       *  @endif
      */
      static const size_t   	_S_pback_size = 1; 
      char_type			_M_pback[_S_pback_size]; 
      char_type*		_M_pback_cur_save;
      char_type*		_M_pback_end_save;
      bool			_M_pback_init; 
      //@}

      /**
       *  @if maint
       *  Yet unused.
       *  @endif
      */
      fpos<__state_type>	_M_pos;

      // Initializes pback buffers, and moves normal buffers to safety.
      // Assumptions:
      // _M_in_cur has already been moved back
      void
      _M_pback_create()
      {
	if (!_M_pback_init)
	  {
	    size_t __dist = _M_in_end - _M_in_cur;
	    size_t __len = min(_S_pback_size, __dist);
	    traits_type::copy(_M_pback, _M_in_cur, __len);
	    _M_pback_cur_save = _M_in_cur;
	    _M_pback_end_save = _M_in_end;
	    this->setg(_M_pback, _M_pback, _M_pback + __len);
	    _M_pback_init = true;
	  }
      }

      // Deactivates pback buffer contents, and restores normal buffer.
      // Assumptions:
      // The pback buffer has only moved forward.
      void
      _M_pback_destroy() throw()
      {
	if (_M_pback_init)
	  {
	    // Length _M_in_cur moved in the pback buffer.
	    size_t __off_cur = _M_in_cur - _M_pback;
	    
	    // For in | out buffers, the end can be pushed back...
	    size_t __off_end = 0;
	    size_t __pback_len = _M_in_end - _M_pback;
	    size_t __save_len = _M_pback_end_save - _M_buf;
	    if (__pback_len > __save_len)
	      __off_end = __pback_len - __save_len;

	    this->setg(_M_buf, _M_pback_cur_save + __off_cur, 
		       _M_pback_end_save + __off_end);
	    _M_pback_cur_save = NULL;
	    _M_pback_end_save = NULL;
	    _M_pback_init = false;
	  }
      }

      // Correctly sets the _M_in_cur pointer, and bumps the
      // _M_out_cur pointer as well if necessary.
      void 
      _M_in_cur_move(off_type __n) // argument needs to be +-
      {
	bool __testout = _M_out_cur;
	_M_in_cur += __n;
	if (__testout && _M_buf_unified)
	  _M_out_cur += __n;
      }