How do I read last 10 lines in a text file?

Question

I need to read last 10 lines in my file. File is about a 1MB, but I need code to be very efficient because of it will be running in a limited device.

PD: I've tested code in this post and no one is working for me.

EDIT This code is not working because of NETMF 4.1 does not have GetByteCount and GetString, do you know any other way to do this?

Answer 1

This is How I've finally solved. Anyway code is too slow so if any of you have any advice, please tell me:

    public static string ReadEndTokens(string filename, Int64 numberOfTokens, Encoding encoding, string tokenSeparator)
    {
        lock (typeof(SDAccess))
        {
            PersistentStorage sdPS = new PersistentStorage("SD");
            sdPS.MountFileSystem();
            string rootDirectory = VolumeInfo.GetVolumes()[0].RootDirectory;

            int sizeOfChar = 1;//The only encoding suppourted by NETMF4.1 is UTF8
            byte[] buffer = encoding.GetBytes(tokenSeparator);


            using (FileStream fs = new FileStream(rootDirectory + @"\" + filename, FileMode.Open, FileAccess.ReadWrite))
            {
                Int64 tokenCount = 0;
                Int64 endPosition = fs.Length / sizeOfChar;

                for (Int64 position = sizeOfChar; position < endPosition; position += sizeOfChar)
                {
                    fs.Seek(-position, SeekOrigin.End);
                    fs.Read(buffer, 0, buffer.Length);

                    encoding.GetChars(buffer);
                    if (encoding.GetChars(buffer)[0].ToString() + encoding.GetChars(buffer)[1].ToString() == tokenSeparator)
                    {
                        tokenCount++;
                        if (tokenCount == numberOfTokens)
                        {
                            byte[] returnBuffer = new byte[fs.Length - fs.Position];
                            fs.Read(returnBuffer, 0, returnBuffer.Length);                          
                            sdPS.UnmountFileSystem();// Unmount file system
                            sdPS.Dispose();
                            return GetString(returnBuffer);
                        }
                    }
                }

                // handle case where number of tokens in file is less than numberOfTokens
                fs.Seek(0, SeekOrigin.Begin);
                buffer = new byte[fs.Length];
                fs.Read(buffer, 0, buffer.Length);
                sdPS.UnmountFileSystem();// Unmount file system
                sdPS.Dispose();
                return GetString(buffer);
            }
        }
    }

    //As GetString is not implemented in NETMF4.1 I've done this method
    public static string GetString(byte[] bytes)
    {
        string cadena = "";
        for (int i = 0; i < bytes.Length; i++)
            cadena += Encoding.UTF8.GetChars(bytes)[i].ToString();
        return cadena;
    }

Answer 2

Try: File.ReadLines(myFilePath); and use Linq. http://msdn.microsoft.com/en-us/library/dd383503.aspx