fstream

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// File based streams -*- 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: 27.8  File-based streams
//

/** @file fstream
 *  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 _GLIBCXX_FSTREAM
#define _GLIBCXX_FSTREAM 1

#pragma GCC system_header

#include <istream>
#include <ostream>
#include <locale>	// For codecvt
#include <cstdio>       // For SEEK_SET, SEEK_CUR, SEEK_END, BUFSIZ     
#include <bits/basic_file.h>
#include <bits/gthr.h>

namespace std
{
  // [27.8.1.1] template class basic_filebuf
  /**
   *  @brief  The actual work of input and output (for files).
   *
   *  This class associates both its input and output sequence with an
   *  external disk file, and maintains a joint file position for both
   *  sequences.  Many of its sematics are described in terms of similar
   *  behavior in the Standard C Library's @c FILE streams.
  */
  // Requirements on traits_type, specific to this class:
  // traits_type::pos_type must be fpos<traits_type::state_type>
  // traits_type::off_type must be streamoff
  // traits_type::state_type must be Assignable and DefaultConstructable,
  // and traits_type::state_type() must be the initial state for codecvt.
  template<typename _CharT, typename _Traits>
    class basic_filebuf : public basic_streambuf<_CharT, _Traits>
    {
    public:
      // Types:
      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
       *  @doctodo
       *  @endif
      */
      typedef basic_streambuf<char_type, traits_type>  	__streambuf_type;
      typedef basic_filebuf<char_type, traits_type>     __filebuf_type;
      typedef __basic_file<char>		        __file_type;
      typedef typename traits_type::state_type          __state_type;
      typedef codecvt<char_type, char, __state_type>    __codecvt_type;
      //@}

      friend class ios_base; // For sync_with_stdio.

    protected:
      // Data Members:
      // MT lock inherited from libio or other low-level io library.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      __c_lock          	_M_lock;

      // External buffer.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      __file_type 		_M_file;

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

      // Beginning state type for codecvt.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      __state_type 		_M_state_beg;

      // During output, the state that corresponds to pptr(),
      // during input, the state that corresponds to egptr() and
      // _M_ext_next.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      __state_type		_M_state_cur;

      // Not used for output. During input, the state that corresponds
      // to eback() and _M_ext_buf.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      __state_type		_M_state_last;

      /**
       *  @if maint
       *  Pointer to the beginning of internal buffer.
       *  @endif
      */
      char_type*		_M_buf; 	

      /**
       *  @if maint
       *  Actual size of internal buffer. This number is equal to the size
       *  of the put area + 1 position, reserved for the overflow char of
       *  a full area.
       *  @endif
      */
      size_t			_M_buf_size;

      // Set iff _M_buf is allocated memory from _M_allocate_internal_buffer.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      bool			_M_buf_allocated;

      /**
       *  @if maint
       *  _M_reading == false && _M_writing == false for 'uncommitted' mode;  
       *  _M_reading == true for 'read' mode;
       *  _M_writing == true for 'write' mode;
       *
       *  NB: _M_reading == true && _M_writing == true is unused.
       *  @endif
      */ 
      bool                      _M_reading;
      bool                      _M_writing;

      //@{
      /**
       *  @if maint
       *  Necessary bits for putback buffer management.
       *
       *  @note pbacks of over one character are not currently supported.
       *  @endif
      */
      char_type			_M_pback; 
      char_type*		_M_pback_cur_save;
      char_type*		_M_pback_end_save;
      bool			_M_pback_init; 
      //@}

      // Cached codecvt facet.
      const __codecvt_type* 	_M_codecvt;

      /**
       *  @if maint
       *  Buffer for external characters. Used for input when
       *  codecvt::always_noconv() == false. When valid, this corresponds
       *  to eback().
       *  @endif
      */ 
      char*			_M_ext_buf;

      /**
       *  @if maint
       *  Size of buffer held by _M_ext_buf.
       *  @endif
      */ 
      streamsize		_M_ext_buf_size;

      /**
       *  @if maint
       *  Pointers into the buffer held by _M_ext_buf that delimit a
       *  subsequence of bytes that have been read but not yet converted.
       *  When valid, _M_ext_next corresponds to egptr().
       *  @endif
      */ 
      const char*		_M_ext_next;
      char*			_M_ext_end;

      /**
       *  @if maint
       *  Initializes pback buffers, and moves normal buffers to safety.
       *  Assumptions:
       *  _M_in_cur has already been moved back
       *  @endif
      */
      void
      _M_create_pback()
      {
	if (!_M_pback_init)
	  {
	    _M_pback_cur_save = this->gptr();
	    _M_pback_end_save = this->egptr();
	    this->setg(&_M_pback, &_M_pback, &_M_pback + 1);
	    _M_pback_init = true;
	  }
      }

      /**
       *  @if maint
       *  Deactivates pback buffer contents, and restores normal buffer.
       *  Assumptions:
       *  The pback buffer has only moved forward.
       *  @endif
      */ 
      void
      _M_destroy_pback() throw()
      {
	if (_M_pback_init)
	  {
	    // Length _M_in_cur moved in the pback buffer.
	    _M_pback_cur_save += this->gptr() != this->eback();
	    this->setg(this->_M_buf, _M_pback_cur_save, _M_pback_end_save);
	    _M_pback_init = false;
	  }
      }

    public:
      // Constructors/destructor:
      /**
       *  @brief  Does not open any files.
       *
       *  The default constructor initializes the parent class using its
       *  own default ctor.
      */
      basic_filebuf();

      /**
       *  @brief  The destructor closes the file first.
      */
      virtual
      ~basic_filebuf()
      { this->close(); }

      // Members:
      /**
       *  @brief  Returns true if the external file is open.
      */
      bool
      is_open() const throw() { return _M_file.is_open(); }

      /**
       *  @brief  Opens an external file.
       *  @param  s  The name of the file.
       *  @param  mode  The open mode flags.
       *  @return  @c this on success, NULL on failure
       *
       *  If a file is already open, this function immediately fails.
       *  Otherwise it tries to open the file named @a s using the flags
       *  given in @a mode.
       *
       *  [Table 92 gives the relation between openmode combinations and the
       *  equivalent fopen() flags, but the table has not been copied yet.]
      */
      __filebuf_type*
      open(const char* __s, ios_base::openmode __mode);

      /**
       *  @brief  Closes the currently associated file.
       *  @return  @c this on success, NULL on failure
       *
       *  If no file is currently open, this function immediately fails.
       *
       *  If a "put buffer area" exists, @c overflow(eof) is called to flush
       *  all the characters.  The file is then closed.
       *
       *  If any operations fail, this function also fails.
      */
      __filebuf_type*
      close() throw();

    protected:
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      void
      _M_allocate_internal_buffer();

      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      void
      _M_destroy_internal_buffer() throw();

      // [27.8.1.4] overridden virtual functions
      // [documentation is inherited]
      virtual streamsize
      showmanyc();

      // Stroustrup, 1998, p. 628
      // underflow() and uflow() functions are called to get the next
      // charater from the real input source when the buffer is empty.
      // Buffered input uses underflow()

      // [documentation is inherited]
      virtual int_type
      underflow();

      // [documentation is inherited]
      virtual int_type
      pbackfail(int_type __c = _Traits::eof());

      // Stroustrup, 1998, p 648
      // The overflow() function is called to transfer characters to the
      // real output destination when the buffer is full. A call to
      // overflow(c) outputs the contents of the buffer plus the
      // character c.
      // 27.5.2.4.5
      // Consume some sequence of the characters in the pending sequence.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      virtual int_type
      overflow(int_type __c = _Traits::eof());

      // Convert internal byte sequence to external, char-based
      // sequence via codecvt.
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      bool
      _M_convert_to_external(char_type*, streamsize);

      /**
       *  @brief  Manipulates the buffer.
       *  @param  s  Pointer to a buffer area.
       *  @param  n  Size of @a s.
       *  @return  @c this
       *
       *  If no file has been opened, and both @a s and @a n are zero, then
       *  the stream becomes unbuffered.  Otherwise, @c s is used as a
       *  buffer; see
       *  http://gcc.gnu.org/onlinedocs/libstdc++/27_io/howto.html#2
       *  for more.
      */
      virtual __streambuf_type*
      setbuf(char_type* __s, streamsize __n);

      // [documentation is inherited]
      virtual pos_type
      seekoff(off_type __off, ios_base::seekdir __way,
	      ios_base::openmode __mode = ios_base::in | ios_base::out);

      // [documentation is inherited]
      virtual pos_type
      seekpos(pos_type __pos,
	      ios_base::openmode __mode = ios_base::in | ios_base::out);

      // Common code for seekoff and seekpos
      /**
       *  @if maint
       *  @doctodo
       *  @endif
      */
      pos_type
      _M_seek(off_type __off, ios_base::seekdir __way, __state_type __state);

      // [documentation is inherited]
      virtual int
      sync();

      // [documentation is inherited]
      virtual void
      imbue(const locale& __loc);

      // [documentation is inherited]
      virtual streamsize
      xsgetn(char_type* __s, streamsize __n);