// 配置文件
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
  <!-- 配置文件，连接数据库字符串 -->
      <add key="myconn" value="server=.;database=students; uid=sa;pwd=123456" />   
 </appSettings>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5"/>
    </startup>
</configuration>

// form文件
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Configuration;
using System.Data.SqlClient;

namespace myConfig
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void bt_Data_Click(object sender, EventArgs e)
        {      
            // 获取连接字符串信息
            string connstr = ConfigurationManager.AppSettings["myconn"];
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                string strcmd = "select * from stu;";
                DataSet ds = new DataSet();
                SqlDataAdapter da = new SqlDataAdapter(strcmd,connstr);
                da.Fill(ds,"MyTable");
                dgv_Data.DataSource = ds.Tables["MyTable"];      
            }
        }
    }
}