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.
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. |
