ToString()的用法？

Question

using System;
using System.Threading;
using System.Globalization;class Class1
{
   static void Main()
   {
      Thread.CurrentThread.CurrentCulture = new CultureInfo("en-us");
         double MyDouble = 123456789;
     
      Console.WriteLine("The examples in en-US culture.\n");
      Console.WriteLine(MyDouble.ToString("C"));
      Console.WriteLine(MyDouble.ToString("E"));
      Console.WriteLine(MyDouble.ToString("P"));
      Console.WriteLine(MyDouble.ToString("N"));
      Console.WriteLine(MyDouble.ToString("F"));      Thread.CurrentThread.CurrentCulture = new CultureInfo("de-DE");
      Console.WriteLine("The examples in de-DE culture.\n");
      Console.WriteLine(MyDouble.ToString("C"));
      Console.WriteLine(MyDouble.ToString("E"));
      Console.WriteLine(MyDouble.ToString("P"));
      Console.WriteLine(MyDouble.ToString("N"));
      Console.WriteLine(MyDouble.ToString("F"));
   }
}
上述代码示例将下列内容显示到控制台。The examples in en-US culture:
$123,456,789.00
1.234568E+008
12,345,678,900.00%
123,456,789.00
123456789.00
The examples in de-DE culture:
123.456.789,00 DM
1,234568E+008
12,345,678,900.00%
123.456.789,00
123456789,00

Answer 1

string.Format("#,#",dr["字段名"].ToString());

Answer 2

数字的ToString才能按千分位处逗号：Int32.Parse(dr["字段名"].ToString()).Tostring("#,#");

Answer 3

应该是:
((decimal)dr["字段名"]).ToString("N0")