cs中读取web.config中的数据库连接字符串（两种）

<appSettings> 
<add key="connectionStrings" value="Data Source =.;Initial Catalog =pubs;Integrated Security =True;
Persist Security Info =True;User ID=sa;Password=sa"/> 
</appSettings>

con.ConnectionString = System.Configuration.ConfigurationManager.AppSettings["connectionStrings"].ToString();

<connectionStrings> 
<add name="connectionStrings" connectionString="Data Source =.;Initial Catalog =pubs;Integrated Security =True;
Persist Security Info = True;User ID=sa;Password=sa"/> 
</connectionStrings>

con.ConnectionString = System.Web.Configuration.WebConfigurationManager.ConnectionStrings["connectionStrings"].ToString();