System.Data.SqlClient.SqlConnectionStringBuilder 链接字符串的问题

起先我是这么写的，只指定服务器地址，没有制定sql server 实例名，可以成功链接

            SqlConnectionStringBuilder sb = new SqlConnectionStringBuilder();
            sb.DataSource = @"localhost";
            sb.InitialCatalog = "Demon";
            sb.UserID = "sa";
            sb.Password = "sa";            

但是指定实例名后就无法链接了，报25的错：

           SqlConnectionStringBuilder sb = new SqlConnectionStringBuilder();
            sb.DataSource = @"localhostMSSQLSERVER";
            sb.InitialCatalog = "Demon";
            sb.UserID = "sa";
            sb.Password = "sa";

结果发现是指定实例名的时候必须要制定端口号的，原因不知道，猜测是当没有制定实例名时，微软会默认找，一旦指定实例名，微软便按程序员的连接串链接了。。。。、

            SqlConnectionStringBuilder sb = new SqlConnectionStringBuilder();
            sb.DataSource = @"localhostMSSQLSERVER,1433";
            sb.InitialCatalog = "Demon";
            sb.UserID = "sa";
            sb.Password = "sa";

不指定实例名，只指定端口号都是可以的。。。

            SqlConnectionStringBuilder sb = new SqlConnectionStringBuilder();
            sb.DataSource = @"localhostMSSQLSERVER,1433";
            sb.InitialCatalog = "Demon";
            sb.UserID = "sa";
            sb.Password = "sa";