如何在不使用第三方库的情况下登录 C # ？

I would rather not use any outside frameworks like log4j.net.

Why? Log4net would probably address most of your requirements. For example check this class: RollingFileAppender.

Log4net is well documented and there are thousand of resources and use cases on the web.

public void Logger(string lines)
{
//Write the string to a file.append mode is enabled so that the log
//lines get appended to  test.txt than wiping content and writing the log


using(System.IO.StreamWriter file = new System.IO.StreamWriter("c:\\test.txt", true))
{
file.WriteLine(lines);
}
}

For more information MSDN

I used to write my own error logging until I discovered ELMAH. I've never been able to get the emailing part down quite as perfectly as ELMAH does.

You can write directly to an event log. Check the following links:
http://support.microsoft.com/kb/307024
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx

And here's the sample from MSDN:

using System;
using System.Diagnostics;
using System.Threading;


class MySample{


public static void Main(){


// Create the source, if it does not already exist.
if(!EventLog.SourceExists("MySource"))
{
//An event log source should not be created and immediately used.
//There is a latency time to enable the source, it should be created
//prior to executing the application that uses the source.
//Execute this sample a second time to use the new source.
EventLog.CreateEventSource("MySource", "MyNewLog");
Console.WriteLine("CreatedEventSource");
Console.WriteLine("Exiting, execute the application a second time to use the source.");
// The source is created.  Exit the application to allow it to be registered.
return;
}


// Create an EventLog instance and assign its source.
EventLog myLog = new EventLog();
myLog.Source = "MySource";


// Write an informational entry to the event log.
myLog.WriteEntry("Writing to event log.");


}
}

If you want to stay close to .NET check out Enterprise Library Logging Application Block. Look here. Or for a quickstart tutorial check this. I have used the Validation application Block from the Enterprise Library and it really suits my needs and is very easy to "inherit" (install it and refrence it!) in your project.

If you want your own custom Error Logging you can easily write your own code. I'll give you a snippet from one of my projects.

public void SaveLogFile(object method, Exception exception)
{
string location = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) + @"\FolderName\";
try
{
//Opens a new file stream which allows asynchronous reading and writing
using (StreamWriter sw = new StreamWriter(new FileStream(location + @"log.txt", FileMode.Append, FileAccess.Write, FileShare.ReadWrite)))
{
//Writes the method name with the exception and writes the exception underneath
sw.WriteLine(String.Format("{0} ({1}) - Method: {2}", DateTime.Now.ToShortDateString(), DateTime.Now.ToShortTimeString(), method.ToString()));
sw.WriteLine(exception.ToString()); sw.WriteLine("");
}
}
catch (IOException)
{
if (!File.Exists(location + @"log.txt"))
{
File.Create(location + @"log.txt");
}
}
}

Then to actually write to the error log just write (q being the caught exception)

SaveLogFile(MethodBase.GetCurrentMethod(), `q`);

If you are looking for a real simple way to log, you can use this one liner. If the file doesn't exist, it's created.

System.IO.File.AppendAllText(@"c:\log.txt", "mymsg\n");