C#正则表达式

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有一段时间，正则表达式学习很火热很潮流，当时在CSDN一天就能看到好几个正则表达式的帖子，那段时间借助论坛以及Wrox Press出版的《C#字符串和正则表达式参考手册》学习了一些基础的知识，同时也为我在CSDN大概赚了1000分，今天想起来，去找《C#字符串和正则表达式参考手册》时，已经不知所踪了。现在用到正则的时候也比较少，把以前的笔记等整理一下，以志不忘。 
 
（1）“@”符号 
符下两ows表研究室的火热，当晨在“@”虽然并非C#正则表达式的“成员”，但是它经常与C#正则表达式出双入对。“@”表示，跟在它后面的字符串是个“逐字字符串”，不是很好理解，举个例子，以下两个声明是等效的： 
string x="D://My Huang//My Doc"; 
string y = @"D:/My Huang/My Doc"; 
事实上，如果按如下声明，C#将会报错，因为“/”在C#中用于实现转义，如“/n”换行： 
string x = "D:/My Huang/My Doc"; 
 
（2）基本的语法字符。 
/d  0-9的数字 
/D  /d的补集（以所以字符为全集，下同），即所有非数字的字符 
/w  单词字符，指大小写字母、0-9的数字、下划线 
/W  /w的补集 
/s  空白字符，包括换行符/n、回车符/r、制表符/t、垂直制表符/v、换页符/f 
/S  /s的补集 
.  除换行符/n外的任意字符 
[…]  匹配[]内所列出的所有字符 
[^…]  匹配非[]内所列出的字符 
下面提供一些简单的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_123529" onclick="this.style.display='none'; Code_Closed_Text_123529.style.display='none'; Code_Open_Image_123529.style.display='inline'; Code_Open_Text_123529.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_123529" style="display: none" onclick="this.style.display='none'; Code_Open_Text_123529.style.display='none'; Code_Closed_Image_123529.style.display='inline'; Code_Closed_Text_123529.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string i = "/n"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string m = "3"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"/D"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//同Regex r = new Regex("//D"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r.IsMatch(i)结果：true 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r.IsMatch(m)结果：false 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string i = "%"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string m = "3"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex("[a-z0-9]"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//匹配小写字母或数字字符 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r.IsMatch(i)结果：false 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r.IsMatch(m)结果：true 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
（3）定位字符 
“定位字符”所代表的是一个虚的字符，它代表一个位置，你也可以直观地认为“定位字符”所代表的是某个字符与字符间的那个微小间隙。 
^  表示其后的字符必须位于字符串的开始处 
$  表示其前面的字符必须位于字符串的结束处 
/b  匹配一个单词的边界 
/B  匹配一个非单词的边界 
另外，还包括：/A  前面的字符必须位于字符处的开始处，/z  前面的字符必须位于字符串的结束处，/Z  前面的字符必须位于字符串的结束处，或者位于换行符前 
下面提供一些简单的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_124003" onclick="this.style.display='none'; Code_Closed_Text_124003.style.display='none'; Code_Open_Image_124003.style.display='inline'; Code_Open_Text_124003.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_124003" style="display: none" onclick="this.style.display='none'; Code_Open_Text_124003.style.display='none'; Code_Closed_Image_124003.style.display='inline'; Code_Closed_Text_124003.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string i = "Live for nothing,die for something"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex("^Live for nothing,die for something$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r1.IsMatch(i) true 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex("^Live for nothing,die for some$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r2.IsMatch(i) false 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r3 = new Regex("^Live for nothing,die for some"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r3.IsMatch(i) true 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string i = @"Live for nothing, 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />die for something";//多行 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex("^Live for nothing,die for something$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r1 match count:" + r1.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex("^Live for nothing,die for something$", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r2 match count:" + r2.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r3 = new Regex("^Live for nothing,/r/ndie for something$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r3 match count:" + r3.Matches(i).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r4 = new Regex("^Live for nothing,$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r4 match count:" + r4.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r5 = new Regex("^Live for nothing,$", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r5 match count:" + r5.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r6 = new Regex("^Live for nothing,/r/n$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r6 match count:" + r6.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r7 = new Regex("^Live for nothing,/r/n$", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r7 match count:" + r7.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r8 = new Regex("^Live for nothing,/r$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r8 match count:" + r8.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r9 = new Regex("^Live for nothing,/r$", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r9 match count:" + r9.Matches(i).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r10 = new Regex("^die for something$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r10 match count:" + r10.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r11 = new Regex("^die for something$", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r11 match count:" + r11.Matches(i).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r12 = new Regex("^"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r12 match count:" + r12.Matches(i).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r13 = new Regex("$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r13 match count:" + r13.Matches(i).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r14 = new Regex("^", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r14 match count:" + r14.Matches(i).Count);//2 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r15 = new Regex("$", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r15 match count:" + r15.Matches(i).Count);//2 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r16 = new Regex("^Live for nothing,/r$/n^die for something$", RegexOptions.Multiline); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r16 match count:" + r16.Matches(i).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//对于一个多行字符串，在设置了Multiline选项之后，^和$将出现多次匹配。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string i = "Live for nothing,die for something"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string m = "Live for nothing,die for some thing"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex(@"/bthing/b"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r1 match count:" + r1.Matches(i).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex(@"thing/b"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r2 match count:" + r2.Matches(i).Count);//2 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r3 = new Regex(@"/bthing/b"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r3 match count:" + r3.Matches(m).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r4 = new Regex(@"/bfor something/b"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r4 match count:" + r4.Matches(i).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />///b通常用于约束一个完整的单词 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
 （4）重复描述字符 
“重复描述字符”是体现C#正则表达式“很好很强大”的地方之一： 
{n}  匹配前面的字符n次 
{n,}  匹配前面的字符n次或多于n次 
{n,m}  匹配前面的字符n到m次 
?  匹配前面的字符0或1次 
+  匹配前面的字符1次或多于1次 
*  匹配前面的字符0次或式于0次 
以下提供一些简单的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_124300" onclick="this.style.display='none'; Code_Closed_Text_124300.style.display='none'; Code_Open_Image_124300.style.display='inline'; Code_Open_Text_124300.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_124300" style="display: none" onclick="this.style.display='none'; Code_Open_Text_124300.style.display='none'; Code_Closed_Image_124300.style.display='inline'; Code_Closed_Text_124300.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "1024"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string y = "+1024"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string z = "1,024"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string a = "1"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string b="-1024"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string c = "10000"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"^/+?[1-9],?/d{3}$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("x match count:" + r.Matches(x).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("y match count:" + r.Matches(y).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("z match count:" + r.Matches(z).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("a match count:" + r.Matches(a).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("b match count:" + r.Matches(b).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("c match count:" + r.Matches(c).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//匹配1000到9999的整数。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
 （5）择一匹配 
C#正则表达式中的 (|) 符号似乎没有一个专门的称谓，姑且称之为“择一匹配”吧。事实上，像[a-z]也是一种择一匹配，只不过它只能匹配单个字符，而(|)则提供了更大的范围，(ab|xy)表示匹配ab或匹配xy。注意“|”与“()”在此是一个整体。下面提供一些简单的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_124433" onclick="this.style.display='none'; Code_Closed_Text_124433.style.display='none'; Code_Open_Image_124433.style.display='inline'; Code_Open_Text_124433.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_124433" style="display: none" onclick="this.style.display='none'; Code_Open_Text_124433.style.display='none'; Code_Closed_Image_124433.style.display='inline'; Code_Closed_Text_124433.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "0"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string y = "0.23"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string z = "100"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string a = "100.01"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string b = "9.9"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string c = "99.9"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string d = "99."; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string e = "00.1"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"^/+?((100(.0+)*)|([1-9]?[0-9])(/./d+)*)$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("x match count:" + r.Matches(x).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("y match count:" + r.Matches(y).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("z match count:" + r.Matches(z).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("a match count:" + r.Matches(a).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("b match count:" + r.Matches(b).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("c match count:" + r.Matches(c).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("d match count:" + r.Matches(d).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("e match count:" + r.Matches(e).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//匹配0到100的数。最外层的括号内包含两部分“(100(.0+)*)”，“([1-9]?[0-9])(/./d+)*”，这两部分是“OR”的关系，即正则表达式引擎会先尝试匹配100，如果失败，则尝试匹配后一个表达式（表示[0,100)范围中的数字）。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
（6）特殊字符的匹配 
下面提供一些简单的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_124558" onclick="this.style.display='none'; Code_Closed_Text_124558.style.display='none'; Code_Open_Image_124558.style.display='inline'; Code_Open_Text_124558.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_124558" style="display: none" onclick="this.style.display='none'; Code_Open_Text_124558.style.display='none'; Code_Closed_Image_124558.style.display='inline'; Code_Closed_Text_124558.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "//"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex("^////$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r1 match count:" + r1.Matches(x).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex(@"^//$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r2 match count:" + r2.Matches(x).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r3 = new Regex("^//$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r3 match count:" + r3.Matches(x).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//匹配“/” 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "/""; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex("^/"$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r1 match count:" + r1.Matches(x).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex(@"^""$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("r2 match count:" + r2.Matches(x).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//匹配双引号 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
 （7）组与非捕获组 
以下提供一些简单的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_124857" onclick="this.style.display='none'; Code_Closed_Text_124857.style.display='none'; Code_Open_Image_124857.style.display='inline'; Code_Open_Text_124857.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_124857" style="display: none" onclick="this.style.display='none'; Code_Open_Text_124857.style.display='none'; Code_Closed_Image_124857.style.display='inline'; Code_Closed_Text_124857.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing,die for something"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string y = "Live for nothing,die for somebody"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"^Live ([a-z]{3}) no([a-z]{5}),die /1 some/2$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("x match count:" + r.Matches(x).Count);//1 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Console.WriteLine("y match count:" + r.Matches(y).Count);//0 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//正则表达式引擎会记忆“()”中匹配到的内容，作为一个“组”，并且可以通过索引的方式进行引用。表达式中的“/1”，用于反向引用表达式中出现的第一个组，即粗体标识的第一个括号内容，“/2”则依此类推。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing,die for something"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"^Live for no([a-z]{5}),die for some/1$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r.IsMatch(x)) 
<img id="Codehighlighter1_527_609_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_527_609_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_527_609_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_527_609_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_527_609_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_527_609_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_527_609_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_527_609_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_527_609_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("group1 value:" + r.Match(x).Groups[1].Value);//输出：thing 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//获取组中的内容。注意，此处是Groups[1]，因为Groups[0]是整个匹配的字符串，即整个变量x的内容。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing,die for something"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"^Live for no(?<g1>[a-z]{5}),die for some/1$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r.IsMatch(x)) 
<img id="Codehighlighter1_806_891_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_806_891_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_806_891_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_806_891_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_806_891_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_806_891_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_806_891_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_806_891_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_806_891_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("group1 value:" + r.Match(x).Groups["g1"].Value);//输出：thing 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//可根据组名进行索引。使用以下格式为标识一个组的名称(?<groupname>…)。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing nothing"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"([a-z]+) /1"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r.IsMatch(x)) 
<img id="Codehighlighter1_1032_1121_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_1032_1121_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_1032_1121_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_1032_1121_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_1032_1121_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_1032_1121_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_1032_1121_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_1032_1121_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_1032_1121_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    x = r.Replace(x, "$1"); 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("var x:" + x);//输出：Live for nothing 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//删除原字符串中重复出现的“nothing”。在表达式之外，使用“$1”来引用第一个组，下面则是通过组名来引用： 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing nothing"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"(?<g1>[a-z]+) /1"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r.IsMatch(x)) 
<img id="Codehighlighter1_1280_1372_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_1280_1372_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_1280_1372_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_1280_1372_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_1280_1372_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_1280_1372_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_1280_1372_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_1280_1372_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_1280_1372_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    x = r.Replace(x, "${g1}"); 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("var x:" + x);//输出：Live for nothing 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /> 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"^Live for no(?:[a-z]{5})$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r.IsMatch(x)) 
<img id="Codehighlighter1_1474_1554_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_1474_1554_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_1474_1554_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_1474_1554_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_1474_1554_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_1474_1554_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_1474_1554_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_1474_1554_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_1474_1554_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("group1 value:" + r.Match(x).Groups[1].Value);//输出：(空) 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//在组前加上“?:”表示这是个“非捕获组”，即引擎将不保存该组的内容。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
 （8）贪婪与非贪婪 
正则表达式的引擎是贪婪，只要模式允许，它将匹配尽可能多的字符。通过在“重复描述字符”（*,+）后面添加“?”，可以将匹配模式改成非贪婪。请看以下示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_125011" onclick="this.style.display='none'; Code_Closed_Text_125011.style.display='none'; Code_Open_Image_125011.style.display='inline'; Code_Open_Text_125011.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_125011" style="display: none" onclick="this.style.display='none'; Code_Open_Text_125011.style.display='none'; Code_Closed_Image_125011.style.display='inline'; Code_Closed_Text_125011.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing,die for something"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex(@".*thing"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r1.IsMatch(x)) 
<img id="Codehighlighter1_102_197_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_102_197_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_102_197_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_102_197_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_102_197_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_102_197_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_102_197_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_102_197_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_102_197_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("match:" + r1.Match(x).Value);//输出：Live for nothing,die for something 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex(@".*?thing"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r2.IsMatch(x)) 
<img id="Codehighlighter1_252_329_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_252_329_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_252_329_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_252_329_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_252_329_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_252_329_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_252_329_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_252_329_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_252_329_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("match:" + r2.Match(x).Value);//输出：Live for nothing 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
（9）回溯与非回溯 
使用“(?>…)”方式进行非回溯声明。由于正则表达式引擎的贪婪特性，导致它在某些情况下，将进行回溯以获得匹配，请看下面的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_125137" onclick="this.style.display='none'; Code_Closed_Text_125137.style.display='none'; Code_Open_Image_125137.style.display='inline'; Code_Open_Text_125137.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_125137" style="display: none" onclick="this.style.display='none'; Code_Open_Text_125137.style.display='none'; Code_Closed_Image_125137.style.display='inline'; Code_Closed_Text_125137.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "Live for nothing,die for something"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex(@".*thing,"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r1.IsMatch(x)) 
<img id="Codehighlighter1_103_181_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_103_181_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_103_181_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_103_181_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_103_181_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_103_181_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_103_181_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_103_181_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_103_181_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("match:" + r1.Match(x).Value);//输出：Live for nothing, 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex(@"(?>.*)thing,"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r2.IsMatch(x))//不匹配 
<img id="Codehighlighter1_245_301_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_245_301_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_245_301_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_245_301_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_245_301_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_245_301_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_245_301_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_245_301_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_245_301_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("match:" + r2.Match(x).Value); 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//在r1中，“.*”由于其贪婪特性，将一直匹配到字符串的最后，随后匹配“thing”，但在匹配“,”时失败，此时引擎将回溯，并在“thing,”处匹配成功。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />在r2中，由于强制非回溯，所以整个表达式匹配失败。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
（10）正向预搜索、反向预搜索 
正向预搜索声明格式：正声明 “(?=…)”，负声明 “(?!...)” ，声明本身不作为最终匹配结果的一部分，请看下面的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_125258" onclick="this.style.display='none'; Code_Closed_Text_125258.style.display='none'; Code_Open_Image_125258.style.display='inline'; Code_Open_Text_125258.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_125258" style="display: none" onclick="this.style.display='none'; Code_Open_Text_125258.style.display='none'; Code_Closed_Image_125258.style.display='inline'; Code_Closed_Text_125258.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "1024 used 2048 free"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex(@"/d{4}(?= used)"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r1.Matches(x).Count==1) 
<img id="Codehighlighter1_104_172_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_104_172_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_104_172_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_104_172_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_104_172_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_104_172_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_104_172_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_104_172_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_104_172_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("r1 match:" + r1.Match(x).Value);//输出：1024 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex(@"/d{4}(?! used)"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r2.Matches(x).Count==1) 
<img id="Codehighlighter1_243_312_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_243_312_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_243_312_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_243_312_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_243_312_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_243_312_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_243_312_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_243_312_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_243_312_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("r2 match:" + r2.Match(x).Value); //输出：2048 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r1中的正声明表示必须保证在四位数字的后面必须紧跟着“ used”，r2中的负声明表示四位数字之后不能跟有“ used”。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
反向预搜索声明格式：正声明“(?<=)”，负声明“(?<!)”，声明本身不作为最终匹配结果的一部分，请看下面的示例：
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_125410" onclick="this.style.display='none'; Code_Closed_Text_125410.style.display='none'; Code_Open_Image_125410.style.display='inline'; Code_Open_Text_125410.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_125410" style="display: none" onclick="this.style.display='none'; Code_Open_Text_125410.style.display='none'; Code_Closed_Image_125410.style.display='inline'; Code_Closed_Text_125410.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = "used:1024 free:2048"; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r1 = new Regex(@"(?<=used:)/d{4}"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r1.Matches(x).Count==1) 
<img id="Codehighlighter1_105_173_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_105_173_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_105_173_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_105_173_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_105_173_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_105_173_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_105_173_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_105_173_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_105_173_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("r1 match:" + r1.Match(x).Value);//输出：1024 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r2 = new Regex(@"(?<!used:)/d{4}"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />if (r2.Matches(x).Count==1) 
<img id="Codehighlighter1_245_313_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_245_313_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_245_313_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_245_313_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_245_313_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_245_313_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_245_313_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_245_313_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_245_313_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    Console.WriteLine("r2 match:" + r2.Match(x).Value);//输出：2048 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />//r1中的反向正声明表示在4位数字之前必须紧跟着“used:”，r2中的反向负声明表示在4位数字之前必须紧跟着除“used:”之外的字符串。 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
（11）十六进制字符范围 
正则表达式中，可以使用 "/xXX" 和 "/uXXXX" 表示一个字符（"X" 表示一个十六进制数）形式字符范围： 
/xXX       编号在 0到255 范围的字符，比如：空格可以使用 "/x20" 表示。 
/uXXXX   任何字符可以使用 "/u" 再加上其编号的4位十六进制数表示，比如：汉字可以使用“[/u4e00-/u9fa5]”表示。

 
（12）对[0,100]的比较完备的匹配 
下面是一个比较综合的示例，对于匹配[0,100]，需要特殊考虑的地方包括 
*00合法，00.合法，00.00合法，001.100合法 
*空字符串不合法，仅小数点不合法，大于100不合法 
*数值是可带后缀的，如“1.07f”表示该值为一个float类型（未考虑）
<div style="border-right: #cccccc 1px solid; padding-right: 5px; border-top: #cccccc 1px solid; padding-left: 4px; font-size: 13px; padding-bottom: 4px; border-left: #cccccc 1px solid; width: 98%; word-break: break-all; padding-top: 4px; border-bottom: #cccccc 1px solid; background-color: #eeeeee"><img id="Code_Closed_Image_125638" onclick="this.style.display='none'; Code_Closed_Text_125638.style.display='none'; Code_Open_Image_125638.style.display='inline'; Code_Open_Text_125638.style.display='inline';" height="16" src="/Images/OutliningIndicators/ContractedBlock.gif" width="11" align="top" alt="" /><img id="Code_Open_Image_125638" style="display: none" onclick="this.style.display='none'; Code_Open_Text_125638.style.display='none'; Code_Closed_Image_125638.style.display='inline'; Code_Closed_Text_125638.style.display='inline';" height="16" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" width="11" align="top" alt="" />Code 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />Regex r = new Regex(@"^/+?0*(?:100(/.0*)?|(/d{0,2}(?=/./d)|/d{1,2}(?=($|/.$)))(/./d*)?)$"); 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />string x = ""; 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" />while (true) 
<img id="Codehighlighter1_129_403_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_129_403_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_129_403_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_129_403_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_129_403_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_129_403_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_129_403_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_129_403_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedBlock.gif" align="top" alt="" /><span id="Codehighlighter1_129_403_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    x = Console.ReadLine(); 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    if (x != "exit") 
<img id="Codehighlighter1_184_365_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_184_365_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_184_365_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_184_365_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedSubBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_184_365_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_184_365_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_184_365_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_184_365_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedSubBlock.gif" align="top" alt="" />    <span id="Codehighlighter1_184_365_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />        if (r.IsMatch(x)) 
<img id="Codehighlighter1_220_279_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_220_279_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_220_279_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_220_279_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedSubBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_220_279_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_220_279_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_220_279_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_220_279_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedSubBlock.gif" align="top" alt="" />        <span id="Codehighlighter1_220_279_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />            Console.WriteLine(x + " succeed!"); 
<img src="/Images/OutliningIndicators/ExpandedSubBlockEnd.gif" align="top" alt="" />        } 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />        else 
<img id="Codehighlighter1_301_359_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_301_359_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_301_359_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_301_359_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedSubBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_301_359_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_301_359_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_301_359_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_301_359_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedSubBlock.gif" align="top" alt="" />        <span id="Codehighlighter1_301_359_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />            Console.WriteLine(x + " failed!"); 
<img src="/Images/OutliningIndicators/ExpandedSubBlockEnd.gif" align="top" alt="" />        } 
<img src="/Images/OutliningIndicators/ExpandedSubBlockEnd.gif" align="top" alt="" />    } 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />    else 
<img id="Codehighlighter1_379_401_Open_Image" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_379_401_Open_Text').style.display='none'; document.getElementById('Codehighlighter1_379_401_Closed_Image').style.display='inline'; document.getElementById('Codehighlighter1_379_401_Closed_Text').style.display='inline';" src="/Images/OutliningIndicators/ExpandedSubBlockStart.gif" align="top" alt="" /><img id="Codehighlighter1_379_401_Closed_Image" style="display: none" onclick="this.style.display='none'; document.getElementById('Codehighlighter1_379_401_Closed_Text').style.display='none'; document.getElementById('Codehighlighter1_379_401_Open_Image').style.display='inline'; document.getElementById('Codehighlighter1_379_401_Open_Text').style.display='inline';" src="/Images/OutliningIndicators/ContractedSubBlock.gif" align="top" alt="" />    <span id="Codehighlighter1_379_401_Closed_Text" style="border-right: #808080 1px solid; border-top: #808080 1px solid; display: none; border-left: #808080 1px solid; border-bottom: #808080 1px solid; background-color: #ffffff"><img src="http://www.cnblogs.com/Images/dot.gif" alt="" />{ 
<img src="/Images/OutliningIndicators/InBlock.gif" align="top" alt="" />        break; 
<img src="/Images/OutliningIndicators/ExpandedSubBlockEnd.gif" align="top" alt="" />    } 
<img src="/Images/OutliningIndicators/ExpandedBlockEnd.gif" align="top" alt="" />} 
<img src="/Images/OutliningIndicators/None.gif" align="top" alt="" /></div>
（13）精确匹配有时候是困难的 
有些需求要做到精确匹配比较困难，例如：日期、Url、Email地址等，其中一些你甚至需要研究一些专门的文档写出精确完备的表达式，对于这种情况，只能退而求其次，保证比较精确的匹配。例如对于日期，可以基于应用系统的实际情况考虑一段较短的时间，或者对于像Email的匹配，可以只考虑最常见的形式。