集合|正则
简单实例：
string s = "2005-2-21";
Regex reg = new Regex("(?<y>\d{4})-(?<m>\d{1,2})-(?<d>\d{1,2})",RegexOptions.Compiled);
Match match = reg.Match(s);
int year = int.Parse(match.Groups["y"].Value);
int month = int.Parse(match.Groups["m"].Value);
int day = int .Parse(match.Groups["d"].Value);
DateTime time = new DateTime(year,month,day);
