DateTime.Now.ToString 中的参数问题

DateTime.Now.ToString根据参数不同输出不同内容，功能很强的，总结一下。 [C#]
using System;
using System.Globalization; public class MainClass {
public static void Main(string[] args) {
DateTime dt = DateTime.Now;
String[] format = {
"d", "D",
"f", "F",
"g", "G",
"m",
"r",
"s",
"t", "T",
"u", "U",
"y",
"dddd, MMMM dd yyyy",
"ddd, MMM d \"'\"yy",
"dddd, MMMM dd",
"M/yy",
"dd-MM-yy",
};
String date;
for (int i = 0; i < format.Length; i++) {
date = dt.ToString(format[i], DateTimeFormatInfo.InvariantInfo);
Console.WriteLine(String.Concat(format[i], " :" , date));
}
/** Output.
*
* d :08/17/2000
* D :Thursday, August 17, 2000
* f :Thursday, August 17, 2000 16:32
* F :Thursday, August 17, 2000 16:32:32
* g :08/17/2000 16:32
* G :08/17/2000 16:32:32
* m :August 17
* r :Thu, 17 Aug 2000 23:32:32 GMT
* s :2000-08-17T16:32:32
* t :16:32
* T :16:32:32
* u :2000-08-17 23:32:32Z
* U :Thursday, August 17, 2000 23:32:32
* y :August, 2000
* dddd, MMMM dd yyyy :Thursday, August 17 2000
* ddd, MMM d "'"yy :Thu, Aug 17 '00
* dddd, MMMM dd :Thursday, August 17
* M/yy :8/00
* dd-MM-yy :17-08-00
*/
}
}