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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"

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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