using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
CreateErrorLog("test");
}
private static string m_fileName = System.Web.HttpContext.Current.Server.MapPath("~/Error/" + DateTime.Now.ToString("yyyyMMdd") + ".log");
public static String FileName
{
get { return (m_fileName); }
set { if (value != null || value != "") { m_fileName = value; } }
}

public static void CreateErrorLog(string message)
{
if (File.Exists(m_fileName))
{
///如果日志文件已经存在，则直接写入日志文件
StreamWriter sr = File.AppendText(FileName);
sr.WriteLine("\n");
sr.WriteLine(DateTime.Now.ToString() + message);
sr.Close();
}
else
{
///创建日志文件
StreamWriter sr = File.CreateText(FileName);
sr.WriteLine("\n");
sr.WriteLine(DateTime.Now.ToString() + message);
sr.Close();
}
}
}
}

-------------------------------------------------------------------------

      string str;

             str = "sdds";

             string sPath = Application.StartupPath + "\\" + System.DateTime.Now.ToString("yyyy-MM-dd");

             if (!Directory.Exists(sPath))

             {

                 Directory.CreateDirectory(sPath);

             }

    string exstr = ex.ToString();

                                         StreamWriter sw = new StreamWriter(crefod() + "\\" + System.Guid.NewGuid().ToString() + ".txt", false);

                                         sw.WriteLine(exstr);

                                         sw.Close();//写入

             StreamWriter sw = new StreamWriter(sPath + "\\txtwrsssiter.txt", false);

             sw.WriteLine(str);

             sw.Close();//写入

   string str = ex.ToString();

                 StreamWriter sw = new StreamWriter("D:\\1111\\1.txt", false);

                 sw.WriteLine(str);

                 sw.Close();//写入