How to split a text file into multiple files?

Question

In C#, what is the most efficient method to split a text file into multiple text files (the splitting delimiter being a blank line), while preserving the character encoding?

Answer 1

Purely for those who want to avoid thinking:

If you have a CSV (comma separated values) file and want to split the file when a field changes, identify/name the file by the change (without unnecessary quote marks), and strip out comments/certain lines (here identified by starting with "#)

Modified method:

public void Split(string inputfile, string outputfilesformat)
{

    System.IO.StreamWriter outfile = null;
    string line;
    string[] splitArray;
    string nameFromFile = "";
    try
    {
        using (var infile = new System.IO.StreamReader(inputfile))
        {
            while (!infile.EndOfStream)
            {
                line = infile.ReadLine();
                splitArray = line.Split(new char[] { ',' });
                if (!splitArray[0].StartsWith("\"#"))
                {
                    if (splitArray[4].Replace("\"", "") != nameFromFile.Replace("\"", ""))
                    {
                        if (outfile != null)
                        {
                            outfile.Dispose();
                            outfile = null;
                        }
                        nameFromFile = splitArray[4].Replace("\"", "");
                        continue;
                    }
                    if (outfile == null)
                    {
                        outfile = new System.IO.StreamWriter(
                            string.Format(outputfilesformat, nameFromFile),
                            false,
                            infile.CurrentEncoding);
                    }
                    outfile.WriteLine(line);
                }
            }
        }
    }
    finally
    {
        if (outfile != null)
            outfile.Dispose();
    }
}

Local path call:

    string strpath = Server.MapPath("~/Data/SPLIT/DATA.TXT");
    string newFile = Server.MapPath("~/Data/SPLIT");
    if (System.IO.File.Exists(@strpath))
    {
        Split(strpath, newFile+"\\{0}.CSV");
    }