<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <section name="log4net" type="System.Configuration.IgnoreSectionHandler" />
    </configSections>
    <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup> 
    <appSettings>
        <!--压缩文件解压路径-->
        <add value="D:\FileCompare" key="FileCompare"/>
    </appSettings> 
    <log4net>
        <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
            <param name="File" value="Errorlogs\ErrorLog.txt"/>
            <param name="AppendToFile" value="true"/>
            <param name="MaxSizeRollBackups" value="30"/>
            <param name="MaximumFileSize" value="8096KB"/>
            <param name="RollingStyle" value="Size"/>
            <param name="StaticLogFileName" value="true"/>
            <layout type="log4net.Layout.PatternLayout">
                <!--<param name="Header" value="[Header]\r\n"/>
        <param name="Footer" value="[Footer]\r\n"/>-->
                <param name="ConversionPattern" value="%d %-5p %c  %m%n"/>
            </layout>
        </appender>
        <root>
            <level value="ALL"/>
            <appender-ref ref="RollingLogFileAppender"/>
        </root>
    </log4net>
</configuration>

 private void btnSelect_Click(object sender, EventArgs e)
        { 
            ILog log = LogManager.GetLogger("Error");
}