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backbuffer.h

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00001 #ifndef BACKBUFFER_H
00002 #define BACKBUFFER_H
00003 
00004 #include "zipios++/zipios-config.h"
00005 
00006 #include <algorithm>
00007 
00008 #include "zipios++/meta-iostreams.h"
00009 #include <vector>
00010 
00011 #include "zipios++/fcollexceptions.h"
00012 #include "zipios++/ziphead.h"
00013 #include "zipios++/zipheadio.h"
00014 #include "zipios++/virtualseeker.h"
00015 #include "zipios_common.h"
00016 
00017 namespace zipios {
00018 
00019 using std::ios ;
00020 using std::cerr ;
00021 using std::endl ;
00022 
00032 class BackBuffer : public vector< unsigned char > {
00033 public:
00042   inline explicit BackBuffer( istream &is, VirtualSeeker vs = VirtualSeeker(), 
00043                               int chunk_size = 1024 ) ;
00051   inline int readChunk( int &read_pointer ) ;
00052 
00053 private:
00054   VirtualSeeker _vs ;
00055   int _chunk_size ;
00056   istream &_is ;
00057   streampos _file_pos ;
00058   
00059 };
00060 
00061 BackBuffer::BackBuffer( istream &is, VirtualSeeker vs, int chunk_size ) 
00062   : _vs        ( vs         ),
00063     _chunk_size( chunk_size ),
00064     _is        ( is         ) 
00065 {
00066   _vs.vseekg( is, 0, ios::end ) ;
00067   _file_pos = _vs.vtellg( is ) ;
00068   // Only happens if _vs.startOffset() is a position
00069   // in the file that lies after _vs.endOffset(), which
00070   // is clearly not a valid situation.
00071   if ( _file_pos < 0 )
00072     throw FCollException( "Invalid virtual file endings" ) ;
00073 }
00074 
00075 int BackBuffer::readChunk( int &read_pointer ) {
00076   // Update chunk_size and file position
00077   _chunk_size = min<int> ( static_cast< int >( _file_pos ), _chunk_size ) ;
00078   _file_pos -= _chunk_size ;
00079   _vs.vseekg( _is, _file_pos, ios::beg ) ;
00080   // Make space for _chunk_size new bytes first in buffer
00081   insert ( begin(), _chunk_size, static_cast< char > ( 0 ) ) ; 
00082   // Read in the next _chunk_size of bytes
00083 
00084   readByteSeq ( _is, &( (*this)[ 0 ] ), _chunk_size ) ;
00085   read_pointer += _chunk_size ;
00086 
00087   if ( _is.good() )
00088     return _chunk_size ;
00089   else
00090     return 0 ;
00091 }
00092 
00093 }
00094 #endif
00095 
00100 /*
00101   Zipios++ - a small C++ library that provides easy access to .zip files.
00102   Copyright (C) 2000  Thomas Søndergaard
00103   
00104   This library is free software; you can redistribute it and/or
00105   modify it under the terms of the GNU Lesser General Public
00106   License as published by the Free Software Foundation; either
00107   version 2 of the License, or (at your option) any later version.
00108   
00109   This library is distributed in the hope that it will be useful,
00110   but WITHOUT ANY WARRANTY; without even the implied warranty of
00111   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00112   Lesser General Public License for more details.
00113   
00114   You should have received a copy of the GNU Lesser General Public
00115   License along with this library; if not, write to the Free Software
00116   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
00117 */

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