正则表达式虽然学习起来非常的另人头痛和难过，但他也实在是非常的有效。
.NET Framework 正则表达式引擎是回溯的正则表达式匹配器，它并入了传统的非确定性有限自动机 (NFA) 引擎，虽然相比纯正则表达式确定性有限自动机 (DFA) 引擎来讲，速度上面有点慢，但功能更加强大了。
通过强大的正则表达式，可以作很多分析服务
//要求整个数字可以有－号，精度必须为22
string pattern = @"^-?\d+(\.\d{2})?$";3
System.Text.RegularExpressions.Regex rx = new System.Text.RegularExpressions.Regex(pattern);4
string[] patternTest ={ "-12.23", "+12.23", "22.3", "22", "=2.34", "2.34.45", "3242 ", "343.343", "" };
5
for (int i = 0; i <= patternTest.Length - 1; i++)6
{7
System.Console.WriteLine("{0} is {1}", patternTest[i], rx.IsMatch(patternTest[i]));8
}-12.23 is True
+12.23 is False
22.3 is False
22 is True
=2.34 is False
2.34.45 is False
3242 is False
343.343 is False
is False
修正了正则表达式，又可以对数据有其他的分析
string pattern = @"^[-|+]?\d+(\.\d{0,2})?$";2
System.Text.RegularExpressions.Regex rx = new System.Text.RegularExpressions.Regex(pattern);3
string[] patternTest ={ "-12.23", "+12.23", "22.3", "22", "=2.34", "2.34.45", "32. ","343.343", "" };4
for (int i = 0; i <= patternTest.Length - 1; i++)5
{6
System.Console.WriteLine("{0} is {1}", patternTest[i], rx.IsMatch(patternTest[i]));7
} 运行结果是
-12.23 is True
+12.23 is True
22.3 is True
22 is True
=2.34 is False
2.34.45 is False
32. is False
343.343 is False
is False
依据这个例子，可以作一个很有效的分析用户输入的程序了
以下是一个向远程请求http页面的，根据返回的结果，查找url连接的demo，可以根据这个demo了解象FlashGet之类的软件是如何快速有效的分析出可以下载的地址的。
string url = "Http://news.sina.com.cn";2
System.Net.WebRequest request = System.Net.WebRequest.Create(url);3
System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)request.GetResponse();4
System.IO.Stream httpStream = response.GetResponseStream();5
System.IO.StreamReader htmlRead = new System.IO.StreamReader(httpStream);6
string html = htmlRead.ReadToEnd();7
8
//System.Console.WriteLine(html); 9
10
11
string pattern = @"http://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?";12
System.Text.RegularExpressions.Regex rx = new System.Text.RegularExpressions.Regex(pattern);13
System.Text.RegularExpressions.MatchCollection matches = rx.Matches(html);14
15
for (int i = 0; i <= matches.Count - 1; i++)16
{17
System.Console.WriteLine(matches[i].Value);18
}
运行结果是，显示所有连接，大致如下
http://www.nen.com.cn/ target=_blank
http://www.tianshannet.com.cn/ target=_blank
http://www.nmgcb.com.cn/ target=_blank
http://www.jxcn.cn/ target=_blank
http://www.szed.com/ target=_blank
http://www.hljdaily.com.cn/ target=_blank
http://www.hifly.tv/ target=_blank
http://www.chinalegalnews.com.cn/ target=_blank
http://www.newssc.org
http://www.sconline.com.cn/ target=_blank
http://www.xawb.com/gb/news/node_2.htm target=_blank
http://www.anhuinews.com/ target=_blank
http://www.xinminweekly.com.cn/ target=_blank
http://news.cnhubei.com/ target=_blank
http://www.sdnews.com.cn/ target=_blank
http://www.qingdaonews.com/ target=_blank
http://www.dzwww.com/ target=_blank
http://www.66wz.com/cmsweb/webportal/ target=_blank
http://www.bjd.com.cn/ target=_blank
http://www.beijing.org.cn
http://news.sina.com.cn/media.html target=_blank
http://image2.sina.com.cn/c.gif width=1 height=1
http://tech.sina.com.cn/focus/sinahelp.shtml target=_blank
http://net.china.cn/chinese/index.htm target=_blank
http://corp.sina.com.cn/chn/ class=sinatail
http://corp.sina.com.cn/eng/ class=sinatail
http://ads.sina.com.cn/ class=sinatail
http://www.sina.com.cn/contactus.html class=sinatail
http://corp.sina.com.cn/chn/sina_job.html class=sinatail
http://www.sina.com.cn/intro/lawfirm.shtml class=sinatail
http://english.sina.com
http://members.sina.com.cn/apply/ class=sinatail
http://tech.sina.com.cn/focus/sinahelp.shtml class=sinatail
http://www.sina.com.cn/intro/copyright.shtml class=sinatail
http://ad4.sina.com.cn/200702/13/82610_news-couple-l.swf
http://ad4.sina.com.cn/200702/13/82609_news-couple-r.swf
http://ad4.sina.com.cn/sina/ae/ad_src/couplet/coupletv4.js
http://rm.sina.com.cn/icast/rotator.js
http://cast.icast.com.cn/a/4/4/1/9/1/389.js
http://image2.sina.com.cn/unipro/pub/getclickinfo_sinahome.js
