regex pattern in c# doesn't return result

Question

I have a pattern (?<=.*?\*)([\-\+])(.\d{0,2})(?=(d)) which will return -45 in a string *-45d using http://regexstorm.net/tester when I use this pattern in my c# code it doesn't return anything.

string text= "*-4d";
string pattern = @"(<?<=.*?\*)([\-\+])(.\d{0,2})(?=(d))";
var result= Regex.Match(text, pattern);

any ideas why this is?

dotNetFiddle

Your pattern in C# code different for the first line one. First is correct. — Hamlet Hakobyan
– Hamlet Hakobyan, Commented Jan 5, 2015 at 22:53
may be you have already tried this, but are you looking for something like this: [-+]\d{0,2}d? -> returns (+/- with two digits and an optional 'd') your pattern doesn't return anything — SZT
– SZT, Commented Jan 5, 2015 at 22:55
Thanks Yorye your suggestion worked in the .NET code. Grant, I tried my pattern in regexstorm.net/tester and it worked — user3421997
– user3421997, Commented Jan 5, 2015 at 22:59

Mike Dinescu · Accepted Answer · 2015-01-05 22:50:27Z

1

I'm not sure what you thought the regex was supposed to match but most likely the problem is here:

 (<?<=.*?\*)

That will match something like this: <?<=some_arbitary_text_followed_by_a_*

If you want to do a negative look-behind, the syntax should be ?<= but there is also the problem of the .*? which is incompatible with a look-behind. Something like this should work though:

string pattern = @"(?<=\*)([\-\+])(.\d{0,2})(?=(d))";

answered Jan 5, 2015 at 22:50

Mike Dinescu

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