配置文件是什么东西？

数据库 连接字符串 如果硬编在代码中，编译以后
想改的话不好改，所以最好放在配置文件中
Winform是app.config
webform是web.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
    </configSections>
    <connectionStrings>
        <add name="WindowsApplication11.Properties.Settings.MICA_SaleMgnConnectionString"
            connectionString="Data Source=MICA-SERVER;Initial Catalog=MICA_SaleMgn;User ID=sa"
            providerName="System.Data.SqlClient" />
    </connectionStrings>
</configuration>

那就可以用ConfigurationManager.ConnectionString["WindowsApplication11.Properties.Settings.MICA_SaleMgnConnectionString"].ConnectionString;

Sqlconnection conn=new Sqlconnection(中间是以上的字符串);

SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings
            ["WindowsFormsApplication3.Properties.Settings.testConnectionString"].ConnectionString);