C#

<configuration>
  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net"/>
  </configSections>

  <log4net>
    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
      <file value="{0}.log"/>
      <appendToFile value="true"/>
      <rollingStyle value="Size"/>
      <maxSizeRollBackups value="5"/>
      <maximumFileSize value="100kb"/>
      <staticLogFileName value="true"/>
      <layout type="Oak.Common.Logger.MyPatternMatch">
        <conversionPattern value="%date [%thread] %level %logger - %message%newline"/>
      </layout>
    </appender>
    <root>
      <level value="ALL"></level>
      <appender-ref ref="RollingLogFileAppender"/>
    </root>
  </log4net>

string Path = Environment.GetFolderPath(System.Environment.SpecialFolder.ApplicationData)  + @"\Windows7Log4NetLogs\" + DateTime.Today.ToString("ddMMyyyy");
Logmanager.ChangeLogFile(Path);

public class Logmanager
{
    private static readonly Lazy<Logmanager> instance = new Lazy<Logmanager>(() => new Logmanager());

    private Logmanager() { }

    public static Logmanager Instance
    {
        get { return instance.Value; }
    }

    public ILog Logger(string LoggerName)
    {
        return log4net.LogManager.GetLogger(LoggerName);
    }


    /// <summary>
    /// This allows you to specify the log file name.
    /// </summary>
    public static void ChangeLogFile(string filename)
    {
        log4net.Repository.ILoggerRepository RootRep;
        RootRep = LogManager.GetRepository(Assembly.GetCallingAssembly());

        XmlElement section = ConfigurationManager.GetSection("log4net") as XmlElement;
        XPathNavigator navigator = section.CreateNavigator();
        XPathNodeIterator nodes = navigator.Select("appender/file");

        foreach (XPathNavigator appender in nodes)
        {
            appender.MoveToAttribute("value", string.Empty);
            appender.SetValue(string.Format(appender.Value, filename));
        }

        IXmlRepositoryConfigurator xmlCon = RootRep as IXmlRepositoryConfigurator;
        xmlCon.Configure(section);
    }
}