//依据连接串名字connectionName返回数据连接字符串  public static string GetConnectionStringsConfig(string connectionName){//指定config文件读取string file = System.Windows.Forms.Application.ExecutablePath;System.Configuration.Configuration config = ConfigurationManager.OpenExeConfiguration(file);string connectionString =config.ConnectionStrings.ConnectionStrings[connectionName].ConnectionString.ToString();return connectionString;}

///<summary> ///更新连接字符串  ///</summary> ///<param name="newName">连接字符串名称</param> ///<param name="newConString">连接字符串内容</param> ///<param name="newProviderName">数据提供程序名称</param> public static void UpdateConnectionStringsConfig(string newName, string newConString, string newProviderName){//指定config文件读取string file = System.Windows.Forms.Application.ExecutablePath;Configuration config = ConfigurationManager.OpenExeConfiguration(file);bool exist = false; //记录该连接串是否已经存在  //如果要更改的连接串已经存在  if (config.ConnectionStrings.ConnectionStrings[newName] != null){exist = true;}// 如果连接串已存在，首先删除它  if (exist){config.ConnectionStrings.ConnectionStrings.Remove(newName);}//新建一个连接字符串实例  ConnectionStringSettings mySettings =new ConnectionStringSettings(newName, newConString, newProviderName);// 将新的连接串添加到配置文件中.  config.ConnectionStrings.ConnectionStrings.Add(mySettings);// 保存对配置文件所作的更改  config.Save(ConfigurationSaveMode.Modified);// 强制重新载入配置文件的ConnectionStrings配置节  ConfigurationManager.RefreshSection("connectionStrings");}

///<summary> ///返回*.exe.config文件中appSettings配置节的value项  ///</summary> ///<param name="strKey"></param> ///<returns></returns> public static string GetAppConfig(string strKey){string file = System.Windows.Forms.Application.ExecutablePath;Configuration config = ConfigurationManager.OpenExeConfiguration(file);foreach (string key in config.AppSettings.Settings.AllKeys){if (key == strKey){return config.AppSettings.Settings[strKey].Value.ToString();}}return null;}

///<summary>  ///在*.exe.config文件中appSettings配置节增加一对键值对  ///</summary>  ///<param name="newKey"></param>  ///<param name="newValue"></param>  public static void UpdateAppConfig(string newKey, string newValue){string file = System.Windows.Forms.Application.ExecutablePath;Configuration config = ConfigurationManager.OpenExeConfiguration(file);bool exist = false;foreach (string key in config.AppSettings.Settings.AllKeys){if (key == newKey){exist = true;}}if (exist){config.AppSettings.Settings.Remove(newKey);}config.AppSettings.Settings.Add(newKey, newValue);config.Save(ConfigurationSaveMode.Modified);ConfigurationManager.RefreshSection("appSettings");}

using System.Configuration;
//省略其他代码
public SalesOrderData(){string str = "";str = ConfigurationManager.ConnectionStrings["kyd"].ToString();conn = new SqlConnection(str);cmd = conn.CreateCommand();}