限定符

2008-09-04

更新： 2008 年 7 月

限定符指定在输入中必须存在前导元素（可以是字符、组或字符类）的多少个实例才能找到匹配项。

.NET Framework 正则表达式中的限定符

下表列出了 .NET Framework 正则表达式支持的限定符。数量 n 和 m 是整数常数。有关贪婪限定符与惰性限定符之间差别的描述，请参见表后面的“贪婪限定符与惰性限定符”一节。

限定符	说明
*	匹配前导元素零次或零次以上。该限定符等效于 {0,}。* 是贪婪限定符，对应的非贪婪限定符是 ?。例如，正则表达式 \b919\b 尝试匹配字边界后面的数字 9。9 后面可以是数字 1 的零个或零个以上的实例，而数字 1 后面又可跟数字 9 的零个或零个以上的实例。下面的示例演示了此正则表达式。在输入字符串内的 9 个数字中，有 5 个与模式匹配，有 4 个（95、929、9129 和 9919）不匹配。 `Dim pattern As String = "\b919\b" Dim input As String = "99 95 919 929 9119 9219 999 9919 91119" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '99' found at position 0. ' '919' found at position 6. ' '9119' found at position 14. ' '999' found at position 24. ' '91119' found at position 33.` `string pattern = "\b919*\b"; string input = "99 95 919 929 9119 9219 999 9919 91119"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '99' found at position 0. // '919' found at position 6. // '9119' found at position 14. // '999' found at position 24. // '91119' found at position 33.`
+	匹配前导元素一次或多次。它等效于 {1,}。+ 是贪婪限定符，对应的非贪婪限定符是 +?。例如，正则表达式 \ba(n)+\w?\b 尝试匹配以字母 a 开头且后跟字母 n 的一个或多个实例的完整单词。下面的示例演示了此正则表达式。该正则表达式匹配单词 an、annual、announcement 和 antique，但不匹配 autumn 和 all。 `Dim pattern As String = "\ba(n)+\w?\b" Dim input As String = "Autumn is a great time for an annual announcement to all antique collectors." For Each match As Match In Regex.Matches(input, pattern, RegexOptions.IgnoreCase) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'an' found at position 27. ' 'annual' found at position 30. ' 'announcement' found at position 37. ' 'antique' found at position 57.` `string pattern = @"\ba(n)+\w*?\b"; string input = "Autumn is a great time for an annual announcement to all antique collectors."; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnoreCase)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'an' found at position 27. // 'annual' found at position 30. // 'announcement' found at position 37. // 'antique' found at position 57.`
?	匹配前导元素零次或一次。它等效于 {0,1}。? 是贪婪限定符，对应的非贪婪限定符是 ??。例如，正则表达式 \ban?\b 尝试匹配以字母 a 开头且后跟字母 n 的零个或一个实例的完整单词。换言之，它尝试匹配单词 a 和 an。下面的示例演示了此正则表达式。 `Dim pattern As String = "\ban?\b" Dim input As String = "An amiable animal with a large snount and an animated nose." For Each match As Match In Regex.Matches(input, pattern, RegexOptions.IgnoreCase) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'An' found at position 0. ' 'a' found at position 23. ' 'an' found at position 42.` `string pattern = @"\ban?\b"; string input = "An amiable animal with a large snount and an animated nose."; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnoreCase)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'An' found at position 0. // 'a' found at position 23. // 'an' found at position 42.`
{n}	匹配前导元素恰好 n 次。{n} 是贪婪限定符，对应的非贪婪限定符为 {n}?。例如，正则表达式 \b\d+\,\d{3}\b 尝试匹配如下字符串：先是一个字边界，然后是一个或多个十进制数字，后面再跟 3 个十进制数字，最后又是一个字边界。下面的示例演示了此正则表达式。 `Dim pattern As String = "\b\d+\,\d{3}\b" Dim input As String = "Sales totaled 103,524 million in January, " + _ "106,971 million in February, but only " + _ "943 million in March." For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '103,524' found at position 14. ' '106,971' found at position 45.` `string pattern = @"\b\d+\,\d{3}\b"; string input = "Sales totaled 103,524 million in January, " + "106,971 million in February, but only " + "943 million in March."; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '103,524' found at position 14. // '106,971' found at position 45.`
{n,}	匹配前导元素至少 n 次。{n,} 是贪婪限定符，对应的非贪婪限定符为 {n}?。例如，正则表达式 \b\d{2,}\b\D+ 尝试匹配如下字符串：先是一个字边界，然后是至少 2 个数字，然后再跟一个字边界和一个非数字字符。下面的示例演示了此正则表达式。该正则表达式不能匹配短语 7 days，原因是该短语只包含一个十进制数字；但该表达式可成功匹配短语 10 weeks 和 300 years。 `Dim pattern As String = "\b\d{2,}\b\D+" Dim input As String = "7 days, 10 weeks, 300 years" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '10 weeks, ' found at position 8. ' '300 years' found at position 18.` `string pattern = @"\b\d{2,}\b\D+"; string input = "7 days, 10 weeks, 300 years"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '10 weeks, ' found at position 8. // '300 years' found at position 18.`
{n,m}	匹配前导元素至少 n 次，但不超过 m 次。{n,m} 是贪婪限定符，对应的非贪婪限定符为 {n,m}?。例如，正则表达式 (00\s){2,4} 尝试匹配两个相连的零和一个紧随的空格，且匹配 2 到 4 个实例。下面的示例演示了此正则表达式。注意输入字符串的最后包含此模式 5 次，而不是最大的 4 次。但是，此字符串的开头（一直到空格和第五对 0）与该正则表达式模式匹配。 `Dim pattern As String = "(00\s){2,4}" Dim input As String = "0x00 FF 00 00 18 17 FF 00 00 00 21 00 00 00 00 00" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '00 00 ' found at position 8. ' '00 00 00 ' found at position 23. ' '00 00 00 00 ' found at position 35.` `string pattern = @"(00\s){2,4}"; string input = "0x00 FF 00 00 18 17 FF 00 00 00 21 00 00 00 00 00"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '00 00 ' found at position 8. // '00 00 00 ' found at position 23. // '00 00 00 00 ' found at position 35.`
*?	匹配前导元素零次或零次以上，但次数尽可能少。它是与贪婪限定符 * 相对的惰性限定符。例如，正则表达式 \b\w?oo\w?\b 匹配包含字符串 oo 的所有单词。下面的示例演示了此正则表达式。 `Dim pattern As String = "\b\w?oo\w?\b" Dim input As String = "woof root root rob oof woo woe" For Each match As Match In Regex.Matches(input, pattern, RegexOptions.IgnoreCase) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'woof' found at position 0. ' 'root' found at position 5. ' 'root' found at position 10. ' 'oof' found at position 19. ' 'woo' found at position 23.` `string pattern = @"\b\w?oo\w?\b"; string input = "woof root root rob oof woo woe"; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnoreCase)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'woof' found at position 0. // 'root' found at position 5. // 'root' found at position 10. // 'oof' found at position 19. // 'woo' found at position 23.`
+?	匹配前导元素一次或多次，但次数尽可能少。它是与贪婪限定符 + 相对的惰性限定符。例如，正则表达式 \b\w+?\b 匹配由字边界分隔的一个或多个字符。下面的示例演示了此正则表达式。 `Dim pattern As String = "\b\w+?\b" Dim input As String = "Aa Bb Cc Dd Ee Ff" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'Aa' found at position 0. ' 'Bb' found at position 3. ' 'Cc' found at position 6. ' 'Dd' found at position 9. ' 'Ee' found at position 12. ' 'Ff' found at position 15.` `string pattern = @"\b\w+?\b"; string input = "Aa Bb Cc Dd Ee Ff"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'Aa' found at position 0. // 'Bb' found at position 3. // 'Cc' found at position 6. // 'Dd' found at position 9. // 'Ee' found at position 12. // 'Ff' found at position 15.`
??	匹配前导元素零次或一次，但次数尽可能少。它是与贪婪限定符 ? 相对的惰性限定符。例如，正则表达式 ^(\s)(System.)??Console.Write(Line)??\(?? 尝试匹配字符串 Console.Write 或 Console.WriteLine。该字符串还可在 Console 之前包含 System.，并且后面可跟一个左括号。该字符串必须位于一行的开头，不过它的前面可以有空白。下面的示例演示了此正则表达式。 Dim pattern As String = "^(\s)(System.)??Console.Write(Line)??\(??" Dim input As String = "System.Console.WriteLine(""Hello!"")" + vbCrLf + _ "Console.Write(""Hello!"")" + vbCrLf + _ "Console.WriteLine(""Hello!"")" + vbCrLf + _ "Console.ReadLine()" + vbCrLf + _ " Console.WriteLine" For Each match As Match In Regex.Matches(input, pattern, _ RegexOptions.IgnorePatternWhitespace Or RegexOptions.IgnoreCase Or RegexOptions.MultiLine) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'System.Console.Write' found at position 0. ' 'Console.Write' found at position 36. ' 'Console.Write' found at position 61. ' ' Console.Write' found at position 110. string pattern = @"^(\s)*(System.)??Console.Write(Line)??\(??"; string input = "System.Console.WriteLine(\"Hello!\")\n" + "Console.Write(\"Hello!\")\n" + "Console.WriteLine(\"Hello!\")\n" + "Console.ReadLine()\n" + " Console.WriteLine"; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnorePatternWhitespace \| RegexOptions.IgnoreCase \| RegexOptions.Multiline)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'System.Console.Write' found at position 0. // 'Console.Write' found at position 36. // 'Console.Write' found at position 61. // ' Console.Write' found at position 110.
{n}?	匹配前导元素恰好 n 次。它是与贪婪限定符 {n}+ 相对的惰性限定符。例如，正则表达式 \b(\w{3,}?\.){2}?\w{3,}?\b 匹配恰好两组字符，且每组字符后面跟一个位于字边界的句点。然后，后面再跟另一组字符和一个字边界。此正则表达式标识的应该是一个网站地址。下面的示例演示了该正则表达式。请注意，它匹配 www.microsoft.com 和 mdsn.microsoft.com，但不匹配 mywebsite 或 mycompany.com。 `Dim pattern As String = "\b(\w{3,}?\.){2}?\w{3,}?\b" Dim input As String = "www.microsoft.com msdn.microsoft.com mywebsite mycompany.com" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'www.microsoft.com' found at position 0. ' 'msdn.microsoft.com' found at position 18.` `string pattern = @"\b(\w{3,}?\.){2}?\w{3,}?\b"; string input = "www.microsoft.com msdn.microsoft.com mywebsite mycompany.com"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'www.microsoft.com' found at position 0. // 'msdn.microsoft.com' found at position 18.`
{n,}?	匹配前导元素至少 n 次，但次数尽可能少。它是与贪婪限定符 {n,} 相对的惰性限定符。请参见演示 {n}? 限定符的示例。该例中的正则表达式使用 {n,} 限定符来匹配含有至少 3 个字符且这些字符后面跟有句点的字符串。
{n,m}?	匹配前导元素 n 到 m 次，但次数尽可能少。它是与贪婪限定符 {n,m} 相对的惰性限定符。例如，正则表达式 \b[A-Z](\w?\s?){1,10}[.!?] 匹配包含一到十个词的句子。它所匹配的是一个字边界后跟一个大写字母，大写字母后面跟一到十个单词字符组合，每个组合可有零个或零个以上的单词字符和一个空格字符（空格可选）。然后该匹配项由一个句点、一个惊叹号或一个问号结束。下面的示例演示了此正则表达式。该示例匹配输入字符串中除了包含 18 个单词那个句子之外的所有句子。 Dim pattern As String = "\b[A-Z](\w?\s?){1,10}[.!?]" Dim input As String = "Hi. I am writing a short note. Its purpose is " + _ "to test a regular expression that attempts to find " + _ "sentences with ten or fewer words. Most sentences " + _ "in this note are short." For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'Hi.' found at position 0. ' 'I am writing a short note.' found at position 4. ' 'Most sentences in this note are short.' found at position 132. string pattern = @"\b[A-Z](\w?\s?){1,10}[.!?]"; string input = "Hi. I am writing a short note. Its purpose is " + "to test a regular expression that attempts to find " + "sentences with ten or fewer words. Most sentences " + "in this note are short."; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'Hi.' found at position 0. // 'I am writing a short note.' found at position 4. // 'Most sentences in this note are short.' found at position 132.

贪婪限定符与惰性限定符

一些限定符有两种版本：

贪婪版本。

贪婪限定符尝试尽可能多地匹配它所应用到的元素。
非贪婪（惰性）版本。

非贪婪限定符尝试尽可能少地匹配它所应用到的元素。

为了演示两者之间的差别，请考虑一个非常简单的正则表达式，它用于从信用卡号之类的数字串中提取最后四位数。使用 * 贪婪限定符的正则表达式版本为 \b.*([0-9]{4})\b。但是，如果有一个字符串包含两个卡号，那么该正则表达式只成功显示第二个卡号的最后四位数，如下面的示例所示。

Dim greedyPattern As String = "\b.*([0-9]{4})\b"
Dim input1 As String = "1112223333 3992991999"
For Each match As Match In Regex.Matches(input1, greedypattern)
   Console.WriteLine("Account ending in ******{0}.", match.Groups(1).Value)
Next
' The example displays the following output:
'       Account ending in ******1999.

string greedyPattern = @"\b.*([0-9]{4})\b";
string input1 = "1112223333 3992991999";
foreach (Match match in Regex.Matches(input1, greedyPattern))
   Console.WriteLine("Account ending in ******{0}.", match.Groups[1].Value);

// The example displays the following output:
//       Account ending in ******1999.

这不是所需要的行为。该正则表达式未能匹配第一个卡号，因为 * 限定符尝试在整个字符串中尽可能多地匹配前面的元素，因此它在字符串的末尾找到了匹配项。

但是采用 *? 惰性限定符的对应正则表达式可产生期望的行为，如下面的示例所示。

Dim lazyPattern As String = "\b.*?([0-9]{4})\b"
Dim input2 As String = "1112223333 3992991999"
For Each match As Match In Regex.Matches(input2, lazypattern)
   Console.WriteLine("Account ending in ******{0}.", match.Groups(1).Value)
Next     
' The example displays the following output:
'       Account ending in ******3333.
'       Account ending in ******1999.

string lazyPattern = @"\b.*?([0-9]{4})\b";
string input2 = "1112223333 3992991999";
foreach (Match match in Regex.Matches(input2, lazyPattern))
   Console.WriteLine("Account ending in ******{0}.", match.Groups[1].Value);

// The example displays the following output:
//       Account ending in ******3333.
//       Account ending in ******1999.

在大多数情况下，带有贪婪限定符和惰性限定符的正则表达式将返回相同的匹配项。在与句点 (. ) 元字符（该元字符匹配任何字符）一起使用时，它们多数情况下会返回不同的结果。

请参见

其他资源

正则表达式语言元素

修订记录

日期	修订记录	原因
2008 年 7 月	大幅修订。	内容 Bug 修复

限定符	说明
*	匹配前导元素零次或零次以上。该限定符等效于 {0,}。* 是贪婪限定符，对应的非贪婪限定符是 ?。例如，正则表达式 \b919\b 尝试匹配字边界后面的数字 9。9 后面可以是数字 1 的零个或零个以上的实例，而数字 1 后面又可跟数字 9 的零个或零个以上的实例。下面的示例演示了此正则表达式。在输入字符串内的 9 个数字中，有 5 个与模式匹配，有 4 个（95、929、9129 和 9919）不匹配。 `Dim pattern As String = "\b919\b" Dim input As String = "99 95 919 929 9119 9219 999 9919 91119" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '99' found at position 0. ' '919' found at position 6. ' '9119' found at position 14. ' '999' found at position 24. ' '91119' found at position 33.` `string pattern = "\b919*\b"; string input = "99 95 919 929 9119 9219 999 9919 91119"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '99' found at position 0. // '919' found at position 6. // '9119' found at position 14. // '999' found at position 24. // '91119' found at position 33.`
+	匹配前导元素一次或多次。它等效于 {1,}。+ 是贪婪限定符，对应的非贪婪限定符是 +?。例如，正则表达式 \ba(n)+\w?\b 尝试匹配以字母 a 开头且后跟字母 n 的一个或多个实例的完整单词。下面的示例演示了此正则表达式。该正则表达式匹配单词 an、annual、announcement 和 antique，但不匹配 autumn 和 all。 `Dim pattern As String = "\ba(n)+\w?\b" Dim input As String = "Autumn is a great time for an annual announcement to all antique collectors." For Each match As Match In Regex.Matches(input, pattern, RegexOptions.IgnoreCase) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'an' found at position 27. ' 'annual' found at position 30. ' 'announcement' found at position 37. ' 'antique' found at position 57.` `string pattern = @"\ba(n)+\w*?\b"; string input = "Autumn is a great time for an annual announcement to all antique collectors."; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnoreCase)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'an' found at position 27. // 'annual' found at position 30. // 'announcement' found at position 37. // 'antique' found at position 57.`
?	匹配前导元素零次或一次。它等效于 {0,1}。? 是贪婪限定符，对应的非贪婪限定符是 ??。例如，正则表达式 \ban?\b 尝试匹配以字母 a 开头且后跟字母 n 的零个或一个实例的完整单词。换言之，它尝试匹配单词 a 和 an。下面的示例演示了此正则表达式。 `Dim pattern As String = "\ban?\b" Dim input As String = "An amiable animal with a large snount and an animated nose." For Each match As Match In Regex.Matches(input, pattern, RegexOptions.IgnoreCase) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'An' found at position 0. ' 'a' found at position 23. ' 'an' found at position 42.` `string pattern = @"\ban?\b"; string input = "An amiable animal with a large snount and an animated nose."; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnoreCase)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'An' found at position 0. // 'a' found at position 23. // 'an' found at position 42.`
{n}	匹配前导元素恰好 n 次。{n} 是贪婪限定符，对应的非贪婪限定符为 {n}?。例如，正则表达式 \b\d+\,\d{3}\b 尝试匹配如下字符串：先是一个字边界，然后是一个或多个十进制数字，后面再跟 3 个十进制数字，最后又是一个字边界。下面的示例演示了此正则表达式。 `Dim pattern As String = "\b\d+\,\d{3}\b" Dim input As String = "Sales totaled 103,524 million in January, " + _ "106,971 million in February, but only " + _ "943 million in March." For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '103,524' found at position 14. ' '106,971' found at position 45.` `string pattern = @"\b\d+\,\d{3}\b"; string input = "Sales totaled 103,524 million in January, " + "106,971 million in February, but only " + "943 million in March."; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '103,524' found at position 14. // '106,971' found at position 45.`
{n,}	匹配前导元素至少 n 次。{n,} 是贪婪限定符，对应的非贪婪限定符为 {n}?。例如，正则表达式 \b\d{2,}\b\D+ 尝试匹配如下字符串：先是一个字边界，然后是至少 2 个数字，然后再跟一个字边界和一个非数字字符。下面的示例演示了此正则表达式。该正则表达式不能匹配短语 7 days，原因是该短语只包含一个十进制数字；但该表达式可成功匹配短语 10 weeks 和 300 years。 `Dim pattern As String = "\b\d{2,}\b\D+" Dim input As String = "7 days, 10 weeks, 300 years" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '10 weeks, ' found at position 8. ' '300 years' found at position 18.` `string pattern = @"\b\d{2,}\b\D+"; string input = "7 days, 10 weeks, 300 years"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '10 weeks, ' found at position 8. // '300 years' found at position 18.`
{n,m}	匹配前导元素至少 n 次，但不超过 m 次。{n,m} 是贪婪限定符，对应的非贪婪限定符为 {n,m}?。例如，正则表达式 (00\s){2,4} 尝试匹配两个相连的零和一个紧随的空格，且匹配 2 到 4 个实例。下面的示例演示了此正则表达式。注意输入字符串的最后包含此模式 5 次，而不是最大的 4 次。但是，此字符串的开头（一直到空格和第五对 0）与该正则表达式模式匹配。 `Dim pattern As String = "(00\s){2,4}" Dim input As String = "0x00 FF 00 00 18 17 FF 00 00 00 21 00 00 00 00 00" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' '00 00 ' found at position 8. ' '00 00 00 ' found at position 23. ' '00 00 00 00 ' found at position 35.` `string pattern = @"(00\s){2,4}"; string input = "0x00 FF 00 00 18 17 FF 00 00 00 21 00 00 00 00 00"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // '00 00 ' found at position 8. // '00 00 00 ' found at position 23. // '00 00 00 00 ' found at position 35.`
*?	匹配前导元素零次或零次以上，但次数尽可能少。它是与贪婪限定符 * 相对的惰性限定符。例如，正则表达式 \b\w?oo\w?\b 匹配包含字符串 oo 的所有单词。下面的示例演示了此正则表达式。 `Dim pattern As String = "\b\w?oo\w?\b" Dim input As String = "woof root root rob oof woo woe" For Each match As Match In Regex.Matches(input, pattern, RegexOptions.IgnoreCase) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'woof' found at position 0. ' 'root' found at position 5. ' 'root' found at position 10. ' 'oof' found at position 19. ' 'woo' found at position 23.` `string pattern = @"\b\w?oo\w?\b"; string input = "woof root root rob oof woo woe"; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnoreCase)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'woof' found at position 0. // 'root' found at position 5. // 'root' found at position 10. // 'oof' found at position 19. // 'woo' found at position 23.`
+?	匹配前导元素一次或多次，但次数尽可能少。它是与贪婪限定符 + 相对的惰性限定符。例如，正则表达式 \b\w+?\b 匹配由字边界分隔的一个或多个字符。下面的示例演示了此正则表达式。 `Dim pattern As String = "\b\w+?\b" Dim input As String = "Aa Bb Cc Dd Ee Ff" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'Aa' found at position 0. ' 'Bb' found at position 3. ' 'Cc' found at position 6. ' 'Dd' found at position 9. ' 'Ee' found at position 12. ' 'Ff' found at position 15.` `string pattern = @"\b\w+?\b"; string input = "Aa Bb Cc Dd Ee Ff"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'Aa' found at position 0. // 'Bb' found at position 3. // 'Cc' found at position 6. // 'Dd' found at position 9. // 'Ee' found at position 12. // 'Ff' found at position 15.`
??	匹配前导元素零次或一次，但次数尽可能少。它是与贪婪限定符 ? 相对的惰性限定符。例如，正则表达式 ^(\s)(System.)??Console.Write(Line)??\(?? 尝试匹配字符串 Console.Write 或 Console.WriteLine。该字符串还可在 Console 之前包含 System.，并且后面可跟一个左括号。该字符串必须位于一行的开头，不过它的前面可以有空白。下面的示例演示了此正则表达式。 Dim pattern As String = "^(\s)(System.)??Console.Write(Line)??\(??" Dim input As String = "System.Console.WriteLine(""Hello!"")" + vbCrLf + _ "Console.Write(""Hello!"")" + vbCrLf + _ "Console.WriteLine(""Hello!"")" + vbCrLf + _ "Console.ReadLine()" + vbCrLf + _ " Console.WriteLine" For Each match As Match In Regex.Matches(input, pattern, _ RegexOptions.IgnorePatternWhitespace Or RegexOptions.IgnoreCase Or RegexOptions.MultiLine) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'System.Console.Write' found at position 0. ' 'Console.Write' found at position 36. ' 'Console.Write' found at position 61. ' ' Console.Write' found at position 110. string pattern = @"^(\s)*(System.)??Console.Write(Line)??\(??"; string input = "System.Console.WriteLine(\"Hello!\")\n" + "Console.Write(\"Hello!\")\n" + "Console.WriteLine(\"Hello!\")\n" + "Console.ReadLine()\n" + " Console.WriteLine"; foreach (Match match in Regex.Matches(input, pattern, RegexOptions.IgnorePatternWhitespace \| RegexOptions.IgnoreCase \| RegexOptions.Multiline)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'System.Console.Write' found at position 0. // 'Console.Write' found at position 36. // 'Console.Write' found at position 61. // ' Console.Write' found at position 110.
{n}?	匹配前导元素恰好 n 次。它是与贪婪限定符 {n}+ 相对的惰性限定符。例如，正则表达式 \b(\w{3,}?\.){2}?\w{3,}?\b 匹配恰好两组字符，且每组字符后面跟一个位于字边界的句点。然后，后面再跟另一组字符和一个字边界。此正则表达式标识的应该是一个网站地址。下面的示例演示了该正则表达式。请注意，它匹配 www.microsoft.com 和 mdsn.microsoft.com，但不匹配 mywebsite 或 mycompany.com。 `Dim pattern As String = "\b(\w{3,}?\.){2}?\w{3,}?\b" Dim input As String = "www.microsoft.com msdn.microsoft.com mywebsite mycompany.com" For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'www.microsoft.com' found at position 0. ' 'msdn.microsoft.com' found at position 18.` `string pattern = @"\b(\w{3,}?\.){2}?\w{3,}?\b"; string input = "www.microsoft.com msdn.microsoft.com mywebsite mycompany.com"; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'www.microsoft.com' found at position 0. // 'msdn.microsoft.com' found at position 18.`
{n,}?	匹配前导元素至少 n 次，但次数尽可能少。它是与贪婪限定符 {n,} 相对的惰性限定符。请参见演示 {n}? 限定符的示例。该例中的正则表达式使用 {n,} 限定符来匹配含有至少 3 个字符且这些字符后面跟有句点的字符串。
{n,m}?	匹配前导元素 n 到 m 次，但次数尽可能少。它是与贪婪限定符 {n,m} 相对的惰性限定符。例如，正则表达式 \b[A-Z](\w?\s?){1,10}[.!?] 匹配包含一到十个词的句子。它所匹配的是一个字边界后跟一个大写字母，大写字母后面跟一到十个单词字符组合，每个组合可有零个或零个以上的单词字符和一个空格字符（空格可选）。然后该匹配项由一个句点、一个惊叹号或一个问号结束。下面的示例演示了此正则表达式。该示例匹配输入字符串中除了包含 18 个单词那个句子之外的所有句子。 Dim pattern As String = "\b[A-Z](\w?\s?){1,10}[.!?]" Dim input As String = "Hi. I am writing a short note. Its purpose is " + _ "to test a regular expression that attempts to find " + _ "sentences with ten or fewer words. Most sentences " + _ "in this note are short." For Each match As Match In Regex.Matches(input, pattern) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index) Next ' The example displays the following output: ' 'Hi.' found at position 0. ' 'I am writing a short note.' found at position 4. ' 'Most sentences in this note are short.' found at position 132. string pattern = @"\b[A-Z](\w?\s?){1,10}[.!?]"; string input = "Hi. I am writing a short note. Its purpose is " + "to test a regular expression that attempts to find " + "sentences with ten or fewer words. Most sentences " + "in this note are short."; foreach (Match match in Regex.Matches(input, pattern)) Console.WriteLine("'{0}' found at position {1}.", match.Value, match.Index); // The example displays the following output: // 'Hi.' found at position 0. // 'I am writing a short note.' found at position 4. // 'Most sentences in this note are short.' found at position 132.

通过

限定符

.NET Framework 正则表达式中的限定符

贪婪限定符与惰性限定符

请参见

其他资源

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其他资源