格式：DateTime.Compare(datetime1, datetime2)
参数为时间格式，为第一个参数比较第二个参数，返回小于0的值，等于0或大于0的值。
实例:
1 string st1 = "12:13"; 2 string st2 = "14:13"; 3 DateTime t1 = Convert.ToDateTime(st1); 4 Console.WriteLine(t1); //20186/6 下午 12:12:00
5 DateTime t2 = Convert.ToDateTime(st2); 6 Console.WriteLine(t2); //20186/6 下午 02:14:00
7 DateTime t3 = DateTime.Now; 8 Console.WriteLine(t3); 9 if (DateTime.Compare(t1, t2) > 0) Console.WriteLine(st1+">"+st2); 10 else if (DateTime.Compare(t1, t2) == 0) Console.WriteLine(st1+"="+st2); 11 else Console.WriteLine(st1+"<"+st2); 12
13 if (DateTime.Compare(t1, t3) > 0) Console.WriteLine("\r\n"+st1 + ">" + t3.ToString()); 14 else if (DateTime.Compare(t1, t3) == 0) Console.WriteLine("\r\n" + st1 + "=" + t3.ToString()); 15 else Console.WriteLine("\r\n" + st1 + "<" + t3.ToString());