Config

<configuration>

<connectionStrings>
<add name="db_userConnectionString" connectionString="Data Source=WWW-C21CD4737E0;Initial Catalog=db_user;Integrated Security=True"
            providerName="System.Data.SqlClient" />
</connectionStrings>

<system.web>
<compilation debug="true" targetFramework="4.0" />
</system.web>

</configuration>

   <connectionStrings>
<add name="db_userConnectionString" connectionString="Data Source=WWW-C21CD4737E0;Initial Catalog=db_user;Integrated Security=True"
            providerName="System.Data.SqlClient" />
<!-- 简化 <add name ="123" connectionString =""/>

         另一种方法
<appSettings>
<add key="aa" value="Data Source=WWW-C21CD4737E0;Initial Catalog=db_user;Integrated Security=True"/>
</appSettings>-->
</connectionStrings>

前台调用 ： 加 using System.Configuration;

eg: string str = ConfigurationManager.ConnectionStrings["db_userConnectionString"].ToString();