正则表达式 (?的用法

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http://msdn.microsoft.com/en-us/library/e347654k.aspx

It also allows the engine to verify that a substring exists at the end of the match without including the substring in the matched text. The following example uses positive lookahead to extract the words in a sentence that are not followed by punctuation symbols.

C#
VB
using System;
using System.Text.RegularExpressions;

publicclass Example
{
   publicstaticvoid Main()
   {
      string pattern = @"\b[A-Z]+\b(?=\P{P})";
      string input = "If so,what comes next?";
      foreach (Match match in Regex.Matches(input,pattern,RegexOptions.IgnoreCase))
         Console.WriteLine(match.Value);
   }
}
// The example displays the following output:
//       If
//       what
//       comes

The regular expression\b[A-Z]+\b(?=\P{P})is defined as shown in the following table.

Pattern

Description

\b

Begin the match at a word boundary.

[A-Z]+

Match any alphabetic character one or more times. Because theRegex.Matchesmethod is called with theRegexOptions.IgnoreCaseoption,the comparison is case-insensitive.

End the match at a word boundary.

(?=\P{P})

Look ahead to determine whether the next character is a punctuation symbol. If it is not,the match succeeds.

原文链接:https://www.f2er.com/regex/362698.html

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