Regex expression not working in objective c

Question

//string
NSString *haystack = @".test {test:test} .test2{dasf:asdF}";
//pattern
 NSString *needle = @"[^{}]*{[^{}]*}";

What I want from this is .test {test:test} and .test2{dasf:asdF} in an array (rest of the code handles this) but for some reason this regexp is not working correctly because no results are found.

If

NSString *needle = @"[^{}]*";

I get the following

(
".test ",
"",
"test:test",
"",
" .test2",
"",
"dasf:asdF",
"",
""
)

which is expected. After a lot of fiddling it seems to be a problem with { and } in the regex but I can't think why.

Incidently, if anyone can explain why I get these empty elements in the array above that would be useful to know as well.

Thanks!

disjunction · Accepted Answer · 2012-06-16 09:17:03Z

1

Did you try [^{}]+ (with plus) instead of [^{}]*? Just because * matches also zero chars

answered Jun 16, 2012 at 9:17

disjunction

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2 Comments

neutrino Over a year ago

Ah nice! answers my ancillary question at the end.. any ideas for my main problem? Thanks.

disjunction Over a year ago

Well, because {} are special chars in regex - you specify quantity of matches with them. So a{17} means "a" 17 times. You just need to escape them, i.e. [^{}]+\{[^{}]+\}

sergio · Accepted Answer · 2012-06-16 09:21:04Z

0

Would you try using:

 NSString *needle = @"[^{}]*\{[^{}]*\}";

indeed, { and } have special meaning in regexs (but they are sort of "automatically" escaped when used within [])

answered Jun 16, 2012 at 9:21

sergio

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5 Comments

neutrino Over a year ago

Hmm.. no luck, don't think } requires escaping. It throughs up this : warning: unknown escape sequence '\}'. Thanks anyway!

sergio Over a year ago

what about: NSString *needle = @"[^{}]+[{][^{}]+[}]";

neutrino Over a year ago

Yes!! Thanks! Now why on earth does it need that? [] around {}'s? Is it a way of escaping without \?

sergio Over a year ago

well, I don't know what are you using to match the regex (and it could be a fault in that library), but it is sure that {} are modifiers, so you cannot use them freely; on the other hand [] have the property of escaping their content, so it does the trick. The problem is why \{ and \} are rejected... that's why I think of a problem with the regex engine...

neutrino Over a year ago

I'm using NSRegularExpression which is in the cocoa framework I think - I haven't used any external libraries.... Interesting I guess.

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