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To summarize, we recommend that you use interpreted regular expressions when you call regular expression methods with a specific regular expression relatively infrequently. ]" Dim sw As Stopwatch Dim match As Match Dim ctr As Integer Dim in File As New Stream Reader(".\Dreiser_The Financier.txt") Dim input As String = in File. Close() ' Read first ten sentences with interpreted regex. Write Line("10 Sentences with Interpreted Regex:") sw = Stopwatch. Success Then ' Do nothing with the match except get the next match. If you determine that backtracking is not necessary, you can disable it by using the Imports System. Regular Expressions Module Example Public Sub Main() Dim input As String = "This this word Sentence name Capital" Dim pattern As String = "\b\p\w*\b" For Each match As Match In Regex. Any additional characters can consist of an alphanumeric character, a hyphen, an underscore, or a period, though the last character must be alphanumeric. In some cases, this regular expression pattern can exhibit extremely poor performance because quantifiers are nested, and because the subexpression . Length 1 End If Catch e As Regex Match Timeout Exception If e. Total Milliseconds Back to top Regular expressions in .
This topic outlines some of the best practices that developers can adopt to ensure that their regular expressions achieve optimal performance.
It contains the following sections: In general, regular expressions can accept two types of input: constrained or unconstrained.
Regular Expressions Module Example Public Sub Main() Dim sw As Stopwatch Dim addresses() As String = ' The following regular expression should not actually be used to ' validate an email address.
Write Line() Next End Sub End Module ' The example displays output similar to the following: ' 1.
Developers then determine whether this pattern requires correction or further elaboration by testing it with multiple valid input items. Matched ' AAAAAAAAAAA' in .0000045 // // 1.
When the pattern matches all presumed valid inputs, it is declared to be production-ready and can be included in a released application. Warning The following example uses a regular expression that is prone to excessive backtracking and that is likely to reject valid email addresses. You should not use it in an email validation routine. To match unconstrained input, a regular expression must be able to efficiently handle three kinds of text: The last text type is especially problematic for a regular expression that has been written to handle constrained input. If that regular expression also relies on extensive backtracking, the regular expression engine can spend an inordinate amount of time (in some cases, many hours or days) processing seemingly innocuous text. If you would like a regular expression that validates email addresses, see How to: Verify that Strings Are in Valid Email Format.