Regex not working in .NET

Question

So I'm trying to match up a regex and I'm fairly new at this. I used a validator and it works when I paste the code but not when it's placed in the codebehind of a .NET2.0 C# page.

The offending code is supposed to be able to split on a single semi-colon but not on a double semi-colon. However, when I used the string

"entry;entry2;entry3;entry4;"

I get a nonsense array that contains empty values, the last letter of the previous entry, and the semi-colons themselves. The online javascript validator splits it correctly. Please help!

My regex:

((;;|[^;])+)

Can you remove the javascript tag as this is a .NET question... — t0mm13b
– t0mm13b, Commented Jan 29, 2010 at 15:58
nregex.com/nregex/default.aspx is useful for checking regexes easily online, and so is sourceforge.net/projects/regulator on the desktop. The second is also very useful for learning them. — Sam Holder
– Sam Holder, Commented Jan 29, 2010 at 16:00
I had used a javascript validator to validate my original regex. The difference between c# and javascript regex is apparently my problem, hence why I tagged it javascript. — C Bauer
– C Bauer, Commented Jan 29, 2010 at 16:04

Greg Bacon · Accepted Answer · 2010-01-29 16:24:51Z

5

Split on the following regular expression:

(?<!;);(?!;)

It means match semicolons that are neither preceded nor succeeded by another semicolon.

For example, this code

var input = "entry;entry2;entry3;entry4;";
foreach (var s in Regex.Split(input, @"(?<!;);(?!;)"))
    Console.WriteLine("[{0}]", s);

produces the following output:

[entry]
[entry2]
[entry3]
[entry4]
[]

The final empty field is a result of the semicolon on the end of the input.

If the semicolon is a terminator at the end of each field rather than a separator between consecutive fields, then use Regex.Matches instead

foreach (Match m in Regex.Matches(input, @"(.+?)(?<!;);(?!;)"))
    Console.WriteLine("[{0}]", m.Groups[1].Value);

to get

[entry]
[entry2]
[entry3]
[entry4]

edited Jan 29, 2010 at 16:24

answered Jan 29, 2010 at 15:52

Greg Bacon

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1 Comment

C Bauer Over a year ago

Thanks! Too bad I was so far off with my original. This one leaves a trailing empty entry, any thoughts on how to get rid of that one?

t0mm13b · Accepted Answer · 2010-01-29 15:55:07Z

1

Why not use String.Split on the semicolon?

string sInput = "Entry1;entry2;entry3;entry4";
string[] sEntries = sInput.Split(';');
// Do what you have to do with the entries in the array...

Hope this helps, Best regards, Tom.

answered Jan 29, 2010 at 15:55

t0mm13b

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5 Comments

Austin Salonen Over a year ago

The "but not on double semicolons" requirement makes this kind of ugly.

Mkkt Bkkt Over a year ago

the problem is that he doesn't want to split on double-semicolon (;;) hence String.Split() is inadequate for him.

C Bauer Over a year ago

Sorry Tom, this would not work because it would split on ALL semicolons and I need it to skip over double semi-colons, as stated in the original question.

t0mm13b Over a year ago

@DrJokepu: If you look at his sample input, there is no double semicolon...and anyway if there was there would be an empty element in the offset in the array

thijs Over a year ago

You can tell split not to return empty values, use the msdn.microsoft.com/en-us/library/system.stringsplitoptions.aspx

nemke · Accepted Answer · 2010-01-29 16:51:54Z

1

As tommieb75 wrote, you can use String.Split with StringSplitOptions Enumeration so you can control your output of newly created splitting array

string input = "entry1;;entry2;;;entry3;entry4;;";
char[] charSeparators = new char[] {';'};
// Split a string delimited by characters and return all non-empty elements.
result = input.Split(charSeparators, StringSplitOptions.RemoveEmptyEntries);

The result would contain only 4 elements like this:

<entry1><entry2><entry3><entry4>

answered Jan 29, 2010 at 16:51

nemke

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2 Comments

C Bauer Over a year ago

Please read the original question to see why this does not work. I knew only regex would work before I asked the question.

nemke Over a year ago

So you would like to split a;b;c;;d to [a][b][c;;d] or [a][b][c][d]. If it's the second, you can still use Split, but if it's the first I will delete my answer.

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