How can I read/stream a file without loading the entire file into memory?

Question

How can I read an arbitrary file and process it \"piece by piece\" (meaning byte by byte or some other chunk size that would give the best read performance) without loading

Answer 1

   int fullfilesize = 0;// full size of file
    int DefaultReadValue = 10485760; //read 10 mb at a time
    int toRead = 10485760;
    int position =0;

  //  int 
 //   byte[] ByteReadFirst = new byte[10485760];

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        using (var fs = new FileStream(@"filepath", FileMode.Open, FileAccess.Read))
        {
            using (MemoryStream requestStream = new MemoryStream())
            {


                fs.Position = position;

                if (fs.Position >= fullfilesize)
                {
                    MessageBox.Show(" all done");
                    return;
                }
                System.Diagnostics.Debug.WriteLine("file position" + fs.Position);

                if (fullfilesize-position < toRead)
                {
                    toRead = fullfilesize - position;
                    MessageBox.Show("last time");
                }
                System.Diagnostics.Debug.WriteLine("toread" + toRead);
                int    bytesRead;
                byte[] buffer = new byte[toRead];
                int offset = 0;
                position += toRead;
                while (toRead > 0 && (bytesRead = fs.Read(buffer, offset, toRead)) > 0)
                {
                    toRead -= bytesRead;
                    offset += bytesRead;
                }

                toRead = DefaultReadValue;


            }
        }
    }

Copying Darin's , this method will read 10mb chunks till the end of the file