ReadBuffer.hpp

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/*==========================================================================
 * Copyright (c) 2003 University of Massachusetts.  All Rights Reserved.
 *
 * Use of the Lemur Toolkit for Language Modeling and Information Retrieval
 * is subject to the terms of the software license set forth in the LICENSE
 * file included with this software, and also available at
 * http://www.lemurproject.org/license.html
 *
 *==========================================================================
 */


//
// ReadBuffer
//
// tds - 13 November 2003
//

#ifndef LEMUR_READBUFFER_HPP
#define LEMUR_READBUFFER_HPP
#include "File.hpp"
namespace lemur 
{
  namespace file 
  {
    class ReadBuffer {
    private:
      File::offset_type _filePosition;
      char* _buffer;
      File& _file;
      size_t _bufferSize;
      size_t _bufferPosition;
      size_t _bufferDataLength;
      bool _gValid;
      bool _exclusiveAccess;

    public:
      // wrap <file> in a ReadBuffer with initial
      // buffer size <bufferSize>.  The buffer
      // may grow if necessary to support large
      // peek() and read() requests.
      // <exclusiveAccess> = true if the ReadBuffer is 
      // the only user of the underlying file, false otherwise.
      ReadBuffer( File& file, size_t bufferSize, bool exclusiveAccess = true );
      ~ReadBuffer();

      // standard read() semantics; will perform
      // an unbuffered read if the read size is
      // large enough
      void read( char* data, size_t length );

      // return a pointer to a buffer containing 
      // the next <length> bytes, but do not advance
      // the read pointer
      const char* peek( size_t length );

      // return a pointer to a buffer containing 
      // the next <length> bytes, and advance
      // the read pointer
      const char* read( size_t length );

      // move the internal read pointer
      // to <position>, which may be relative to the
      // beginning, end or current position of the file
      // as specified by <direction>.
      void seekg( File::offset_type position, std::fstream::seekdir direction );

      // return the read pointer location with
      // reference to the beginning of the file
      File::offset_type tellg();

      // return the current read state bits,
      // eofbit, badbit, etc. (same
      // semantics as std::ifstream::rdstate())
      int rdstate();

      // marks the underlying stream pointer
      // as invalid--call this if you seek
      // the underlying file to a new location
      void invalidateg();
    };
  }
}

#endif // LEMUR_READBUFFER_HPP

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