indexer.cs

// indexer.cs

// arguments: indexer.txt

using System;

using System.IO;



// Class to provide access to a large file

// as if it were a byte array.

public class FileByteArray

{

    Stream stream;      // Holds the underlying stream

                        // used to access the file.

// Create a new FileByteArray encapsulating a particular file.

    public FileByteArray(string fileName)

    {

        stream = new FileStream(fileName, FileMode.Open);

    }



    // Close the stream. This should be the last thing done

    // when you are finished.

    public void Close()

    {

        stream.Close();

        stream = null;

    }



    // Indexer to provide read/write access to the file.

    public byte this[long index]   // long is a 64-bit integer

    {

        // Read one byte at offset index and return it.

        get 

        {

            byte[] buffer = new byte[1];

            stream.Seek(index, SeekOrigin.Begin);

            stream.Read(buffer, 0, 1);

            return buffer[0];

        }

        // Write one byte at offset index and return it.

        set 

        {

            byte[] buffer = new byte[1] {value};

            stream.Seek(index, SeekOrigin.Begin);

            stream.Write(buffer, 0, 1);

        }

    }



    // Get the total length of the file.

    public long Length 

    {

        get 

        {

            return stream.Seek(0, SeekOrigin.End);

        }

    }

}



// Demonstrate the FileByteArray class.

// Reverses the bytes in a file.

public class Reverse 

{

    public static void Main(String[] args) 

    {

		// Check for arguments.

		if (args.Length != 1)

		{

			Console.WriteLine("Usage : Indexer ");

			return;

		}



		// Check for file existence

		if (!System.IO.File.Exists(args[0]))

		{

			Console.WriteLine("File " + args[0] + " not found.");

			return;

		}



		FileByteArray file = new FileByteArray(args[0]);

		long len = file.Length;



		// Swap bytes in the file to reverse it.

		for (long i = 0; i < len / 2; ++i) 

		{

			byte t;



			// Note that indexing the "file" variable invokes the

			// indexer on the FileByteStream class, which reads

			// and writes the bytes in the file.

			t = file[i];

			file[i] = file[len - i - 1];

			file[len - i - 1] = t;

		}



		file.Close();

    } 

}