Regular Expression Worst Situation

Question

1.00/5 (1 vote)

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Hello, I am blasting my head off with one reg exp and can't get it working on C#

the text it this

HTML

<span class="css-truncate-target">0.1.1.0</span>

I want to get the Version: 0.1.1.0

And the C# is:

C#

Match match = Regex.Match(releasesString, @"<span class=""css - truncate - target"">(?:[0-9].[0-9].[0-9].[0-9])<\/span>",
            RegexOptions.IgnoreCase);

            if (match.Success)
            {
                Console.WriteLine(match.Groups[1].Value);
            }

And the Success is always false

Posted 7-Dec-15 12:51pm

Zhivko Kabaivanov

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Comments

PIEBALDconsult 7-Dec-15 20:57pm

You must be ready for a shot of Expresso
http://www.ultrapico.com/Expresso.htm

PIEBALDconsult 7-Dec-15 21:08pm

You have SPACEs surrounding the HYPHENs in your Expression but not in the sample text -- so it can't succeed.
Oh, and the ?: in your group instructs the engine _not_ to capture, so you will still have trouble trying to access Groups[1] .
And why did you escape the SLASH?

2 solutions

Solution 1

You have too many problems here, even though the problem is extremely simple. First of all, '.' is a special Regular Expression notation. So, escape it: '\.'.
Take each '[0-9]' term in round brackets, it will help you to get set of matches and later parse each of the matches into integer. And finally, do you really want to have only one digit in each version component? I doubt it. Add multiplicity: '+' (which means 1 or more). Oh, and I almost forgot: add ^ at the beginning and $ at the end.
I hope after I described all your mistakes, you can easily solve the problem.

See also:
https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex%28v=vs.110%29.aspx[^],
https://msdn.microsoft.com/en-us/library/e7sf90t3(v=vs.110).aspx[^],
https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.matchcollection%28v=vs.110%29.aspx[^].

Note that I referenced the method Matches, not Match. This is what you really want, because you need to match each part of the version separately and parse all matches separately.

But I would solve the problem much simpler:

C#

string[] versionParts = versionString.Split('.');
//and then use int.TryParse for each element of the array versionParts

—SA

Posted 7-Dec-15 13:16pm

Sergey Alexandrovich Kryukov

Updated 7-Dec-15 13:19pm

v3

Comments

BillWoodruff 8-Dec-15 1:27am

My vote of #4: seems to me this answer has good suggestions on the RegEx, and, since I prefer to write code rather than use RegEx, I go for the idea of splitting the string, and then parsing the numbers as suggested here.

If you did split with the code shown here, element #0 would be:

<span class=\"css-truncate-target:">0

and the last element would be: 0</span>

char[] split = new[] {'.', '<', '>'}; // better split with this

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Peter Leow · Accepted Answer · 2015-12-07T17:10:00

Solution 2

Try this:

(?<=\<span.*\>)\d\.\d\.\d.\d(?=\</span\>)

The keys lie in:

(?<=exp) // zero-width positive lookahead assertion

and

(?=exp) // zero-width positive lookbehind assertion

Google and find out more about them.

Posted 7-Dec-15 17:10pm

Peter Leow

Comments

BillWoodruff 8-Dec-15 1:27am

+5

Peter Leow 8-Dec-15 1:46am

Thank you, BillWoodruff.

Matt T Heffron 8-Dec-15 13:17pm

+5

Peter Leow 8-Dec-15 20:44pm

Thank you, Matt T Heffron.