using System.IO;

public void WriteTxt(string filepth, string str)
{
　　FileStream fs1 = new FileStream(filepth, FileMode.Create, FileAccess.ReadWrite);
　　StreamWriter sw = new StreamWriter(fs1);
　　sw.WriteLine(str);
　　sw.Close();
　　fs1.Close();
}

public string ReadTxt(string filepath)
{

    FileStream fs1 = new FileStream(filepath, FileMode.Open, FileAccess.Read);
    StreamReader sr = new StreamReader(fs1);

    var line = sr.ReadLine();
    sr.Close();
    fs1.Close();

    return line;
}