WriteBuffer.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
 *
 *==========================================================================
 */


//
// WriteBuffer
//
// tds - 13 November 2003
//

#ifndef LEMUR_WRITEBUFFER_HPP
#define LEMUR_WRITEBUFFER_HPP

#include "File.hpp"
namespace lemur 
{
  namespace file 
  {
    
    class WriteBuffer {
    private:
      char* _buffer;
      size_t _bufferSize;
      File& _file;
      size_t _position;
      File::offset_type _filePos;
      bool _exclusiveAccess;

    public:
      // <exclusiveAccess> = true if the WriteBuffer is 
      // the only user of the underlying file, false otherwise.
      WriteBuffer( File& file, size_t bufferSize, bool exclusiveAccess = true  );
      ~WriteBuffer();

      // gives a memory pointer to the next <length>
      // bytes in the file.
      char* write( size_t length );

      // tells the WriteBuffer that <length> bytes
      // of the last write(size_t) call were not used
      // and should be returned as a part of the
      // next write(size_t) call.  This function cannot
      // be used in conjunction with the write(char*, size_t)
      // call.
      void unwrite( size_t length );
  
      // standard write semantics; will
      // perform an unbuffered write if
      // <length> is long enough to warrant it
      void write( const char* data, size_t length );

      // flushes the internal buffer out to 
      // the ofstream. does not explicitly
      // flush the ofstream.
      void flush();

      // returns the current write pointer
      // position
      File::offset_type tellp() ;
    };
  }
}

#endif // LEMUR_WRITEBUFFER_HPP

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