using System.IO;
public static void WriteLog(string strLog)
{
  string sFilePath=\"d:\\\\\"+DateTime.Now.ToString(\"yyyyMM\");
  string sFileName = \"rizhi\" + DateTime.Now.ToString(\"dd\") + \".log\";
  sFileName = sFilePath+ \"\\\\\"+sFileName; //文件的绝对路径
  if (!Directory.Exists(sFilePath))//验证路径是否存在
  {
    Directory.CreateDirectory(sFilePath);
    //不存在则创建
  }
  FileStream fs;      
  StreamWriter sw;
  if (File.Exists(sFileName))
  //验证文件是否存在，有则追加，无则创建
  {
    fs = new FileStream(sFileName, FileMode.Append, FileAccess.Write);
  }
  else
  {
    fs = new FileStream(sFileName, FileMode.Create, FileAccess.Write);
  }
  sw = new StreamWriter(fs);
  sw.WriteLine(DateTime.Now.ToString(\"yyyy-MM-dd HH-mm-ss\") + \"   ---   \" + strLog);
  sw.Close();
  fs.Close();    
}