方法一：以日期为日志文件名，输出txt文件

public void WriteLog(string msg) 
{ 
    string filePath = AppDomain.CurrentDomain.BaseDirectory + "Log"; 
    if (!Directory.Exists(filePath)) 
    { 
        Directory.CreateDirectory(filePath); 
    } 
    string logPath = AppDomain.CurrentDomain.BaseDirectory + "Log\\" + DateTime.Now.ToString("yyyy-MM-dd") + ".txt"; 
    try 
    { 
        using (StreamWriter sw = File.AppendText(logPath)) 
        { 
            sw.WriteLine("消息：" + msg); 
            sw.WriteLine("时间：" + DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")); 
            sw.WriteLine("**************************************************"); 
            sw.WriteLine(); 
            sw.Flush(); 
            sw.Close(); 
            sw.Dispose(); 
        } 
    } 
    catch (IOException e) 
    { 
        using (StreamWriter sw = File.AppendText(logPath)) 
        { 
            sw.WriteLine("异常：" + e.Message); 
            sw.WriteLine("时间：" + DateTime.Now.ToString("yyy-MM-dd HH:mm:ss")); 
            sw.WriteLine("**************************************************"); 
            sw.WriteLine(); 
            sw.Flush(); 
            sw.Close(); 
            sw.Dispose(); 
        } 
    } 
}