在web.config定义的数据库连接如何用在cs代码中

在web.config定义的数据库连接怎么用在cs代码中
用控件的话可以这样
ConnectionString= " <%$   ConnectionStrings:ConnectionString   %> "

那在cs代码中呢

------解决方案--------------------------------------------------------
ConfigurationManager.AppSettings[ " "];
ConfigurationManager.ConnectionStrings[ " "];
------解决方案--------------------------------------------------------

string ConnectionString = System.Configuration.ConfigurationSettings.AppSettings[ "connectionString "];
------解决方案--------------------------------------------------------
System.Configuration.ConfigurationManager.ConnectionStrings[ ".... "].ConnectionString;