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LIKE operator fails with multiple occurance of string in pattern?

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Ed Brown

I'm working on a VB.Net application that needs to do quite a bit of string
pattern matching, and am having problems using the "LIKE" operator to match
the same string twice in the pattern. For example, in the following code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim theString As String
theString = "1234 TEST 5432 TEST ABCD"
If theString Like "*TEST*TEST*" Then
MessageBox.Show("Matches!")
Else
MessageBox.Show("No Match!")
End If
End Sub

I would expect the LIKE operator in this test to return true, since
theString matches the pattern "*TEST*TEST*", specifying zero-or-more
characters followed by "TEST" followed by zero-or-more characters followed
by "TEST" followed by zero-or-more characters. However, when I run the above
code, the LIKE operator returns false. If I change the pattern to
"*TEST*ABC*", the LIKE operator returns true. If I alter the pattern to
something like "*TEST*TEST A*", it again returns false. It seems that LIKE
won't match a pattern that contains the same string of characters twice. Can
anyone explain why the operator behaves this way?

Thanks in advance for any replies.

Reply to this message...

Jay B. Harlow [MVP - Outlook] (VIP)

Ed,
I cannot explain the Like operator as I don't use it very much, I use the
System.Test.RegularExpressions.RegEx class instead. As the patterns
supported by RegEx far exceeds the patterns allowed in the Like operator.

Something like:

Dim theRegex As New
System.Text.RegularExpressions.Regex(".*TEST.*TEST.*")
Dim theString As String
theString = "1234 TEST 5432 TEST ABCD"
If theRegex.IsMatch(theString) Then
MessageBox.Show("Matches!")
Else
MessageBox.Show("No Match!")
End If

I will normally define my Regex variables as Shared within a class, or
Static within a routine, with the RegExOptions.Compiled option if the regex
is used a lot within my program.

Something like:

Imports System.Text.RegularExpressions

Static theRegex As New Regex(".*TEST.*TEST.*",
RegexOptions.Compiled)

The following site provides a good overview of regular expressions:

http://www.regular-expressions.info/

While this site provides the syntax specifically supported by .NET:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpgenref/html/cpconRegularExpressionsLanguageElements.asp

Hope this helps
Jay

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Ed Brown

Thanks Jay, using the RegEx class did the trick.

"Jay B. Harlow [MVP - Outlook]" <Click here to reveal e-mail address> wrote in message
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	System.EventArgs
	System.Object
	System.Text.RegularExpressions.Regex
	System.Text.RegularExpressions.RegexOptions
	System.Windows.Forms.MessageBox

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