你必须在你的页面或类的顶部调用这个类:

using System.Configuration;

然后你可以使用这个返回连接字符串的方法来准备传递给sqlconnection对象，继续你的工作，如下所示:

    private string ReturnConnectionString()
    {
       // Put the name the Sqlconnection from WebConfig..
        return ConfigurationManager.ConnectionStrings["DBWebConfigString"].ConnectionString;
    }

简单说明一下，这是web配置中的值:

  <add name="DBWebConfigString" connectionString="....." />   </connectionStrings>

您需要向System添加一个引用。配置然后使用:

System.Configuration.ConfigurationManager.
    ConnectionStrings["connectionStringName"].ConnectionString;

首先加上这个:

using System.Configuration;

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.DataVisualization.Charting;
using System.Web.UI.WebControls;  

c#

string constring = ConfigurationManager.ConnectionStrings["ABCD"].ConnectionString;
                using (SqlConnection con = new SqlConnection(constring))

下面的网站。配置文件代码

<connectionStrings>
    <add name="ABCD" connectionString="Data Source=DESKTOP-SU3NKUU\MSSQLSERVER2016;Initial Catalog=TESTKISWRMIP;Integrated Security=True" providerName="System.Data.SqlClient"/>
  </connectionStrings>

在上面的代码中，ABCD是连接名称

C#

// Add a using directive at the top of your code file    
using System.Configuration;

// Within the code body set your variable    
string cs = ConfigurationManager.ConnectionStrings["connectionStringName"].ConnectionString;

VB

' Add an Imports statement at the top of your code file    
Imports System.Configuration

' Within the code body set your variable    
Dim cs as String = ConfigurationManager.ConnectionStrings("connectionStringName").ConnectionString

using System.Configuration;


string conn = ConfigurationManager.ConnectionStrings["ConStringName"].ToString();