Case (in)sensitive comparison with VB.NET LIKE operator in runtime (without Option Compare)

Question

Is there anyway to use LIKE operator in VB.NET as case sensitive or insensitive during runtime? For example use a flag to do case sensitive or insensitive comparisons.

Obviously this can be done by simple converting them into lower case and forcing application to Option Compare Binary but maybe there is a better way to do this?

score 2 · Answer 1 · edited Aug 15 '13 at 03:35

2

I don't think so. However, you should probably not use the Like operator anyways if case-insensitivity is important - instead, use regular expressions.

Dim re As New System.Text.RegularExpressions.Regex("^.+ough$", System.Text.RegularExpressions.RegexOptions.IgnoreCase)

re.IsMatch("rough") ' True
re.IsMatch("tough") ' True
re.IsMatch("rOUGH") ' True
re.IsMatch("ough")  ' False

There's a lot to learn, but basically . is equivalent to ?, .* is equivalent to *, and \d is equivalent to #. You have to wrap it in ^ and $ for equivalency, too. Regular expressions are much more powerful and will do what you need.

You should probably add Imports System.Text.RegularExpressions if you plan to use them a lot. They can be compiled and reused for efficiency, too.

edited Aug 15 '13 at 03:35

dreamlax

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answered Jun 24 '11 at 23:35

Ry-

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That's the problem I don't need much powerful, I need less powerful :) – dr. evil Jun 25 '11 at 00:47
@dr. evil: Can you give us an example of the pattern in question, and in what situation it will be used? – Ry- Jun 25 '11 at 18:14
It'll be entered by user as normal users can't write regex it'll be quite dirty to convert their wildcards into regex, still doable though. – dr. evil Jun 26 '11 at 11:21
@dr. evil: Not really; I found an article online that talks about using Like in C#, and you can apply the same principles. Just make the replacements of `*`, `?`, and `#`, escape the whole thing, and surround it in `^` and `$`. It does sound complicated, but here's a pre-made one for you (and if you can't read C#, there's an online conversion tool too): http://social.msdn.microsoft.com/forums/en-US/csharpgeneral/thread/bce145b8-95d4-4be4-8b07-e8adee7286f1/ – Ry- Jun 26 '11 at 18:29
@minitech Yes that's the approach but I guess you also know that LIKE syntax is not just * and ? – dr. evil Jun 27 '11 at 12:58
@dr. evil: Yes, but the other types are equivalent to regex, e.g. `[aeiou]` in `Like` is equivalent to `[aeiou]` in regex. – Ry- Jun 27 '11 at 15:41
Oh. Well, add exceptions: `.Replace("\[", "[").Replace("\]", "]").Replace("!", "^")` – Ry- Jun 27 '11 at 19:57

score 0 · Answer 2 · answered May 20 '15 at 09:38

You could provide a custom class to ensure that you get case case-insensitive comparison even if the default settings is Compare Binary(case sensitive). You can specify the Option Compare in a code-file:

Option Compare Text

Public Class CaseInsensitiveLikeOperator
    Public Shared Function IsLike(str As String, pattern As String) As Boolean
        Return str Like pattern
    End Function
End Class

Now this works:

Dim isSame = CaseInsensitiveLikeOperator.IsLike("foo", "Fo?") ' True

If your default is Option Compare Text you could provide two classes to be on the safe side.

Maybe the best option is to learn regex ;-)

Case (in)sensitive comparison with VB.NET LIKE operator in runtime (without Option Compare)

2 Answers2