static private string logpathlog = AppDomain.CurrentDomain.BaseDirectory + "log.txt";

static public void writelog(string classname)
        {
string path = logpathlog;
if (!File.Exists(path))
            {
// Create a file to write to.
                using (File.Create(path)) { }
            }

            FileInfo fileinfo = new FileInfo(path);
if (fileinfo.Length > 1024 * 1024 * 2)
            {
                File.Move(path, AppDomain.CurrentDomain.BaseDirectory + DateTime.Now.ToString("yyyyMMddHHmmss") + "log.txt");

if (!File.Exists(path))
                {
using (File.Create(path)) { }
                }

            }

using (StreamWriter sw = File.AppendText(path))
            {
                sw.WriteLine(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") + "：" + "\t\n");
                sw.WriteLine(classname + "\t\n");
                sw.WriteLine("------------------------------------------------------------------------" + "\t\n");
                sw.Close();
            }

        }