Date: Tue, 8 May 2001 09:52:38 +0300 (WET)
From: Andris Pavenis <pavenis AT lanet DOT lv>
To: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
Cc: djgpp-workers AT delorie DOT com
Subject: Re: libstdc++-v3: bug in handling text files for DJGPP
In-Reply-To: <3405-Mon07May2001211050+0300-eliz@is.elta.co.il>
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On Mon, 7 May 2001, Eli Zaretskii wrote:

> > From: pavenis AT lanet DOT lv
> > Date: Mon, 7 May 2001 19:45:18 +0300
> > 
> > basic_filebuf::sync() always advances file pointer by number of bytes 
> > stored in buffer for output (see seekoff at end of this procedure).
> > 
> > It's OK for example for Linux when there is no special format for text 
> > files. For DOS (and perhaps also Windows) we're getting problems as 
> > adding CR before LF is done by fwrite() and as result sync() 
> > incorrectly moves current pointer back.
> 
> DO I understand correctly that libstdc++ uses its own buffering (as
> opposed to the buffering code implemented in libc.a for stdio)?
> 
> If so, it should use code similar to what the DJGPP library does for
> buffered I/O functions.
> 


Here is source of basic_filebuf::sync()

virtual int 
      sync(void)
      {
	bool __testput = _M_out_cur && _M_out_beg < _M_out_end;
	if (__testput)
	  {
            // Make sure that libio resyncs its idea of the file position
            // with the external file.
            _M_file->sync();

	    // Need to restore current position. This interpreted as
	    // the position of the external byte sequence (_M_file)
	    // plus the offset in the current internal buffer
	    // (_M_out_beg - _M_out_cur)
	    streamoff __cur = _M_file->seekoff(0, ios_base::cur);
	    off_type __off = _M_out_cur - _M_out_beg;
	    _M_really_overflow();
	    _M_file->seekpos(__cur + __off);
	  }
	_M_last_overflowed = false;	
	return 0;
      }
      
_M_file->sync() is simply fflush(_M_file._M_cfile)

Andris