Indexer

// 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();
}
}