What's wrong with this Objective-C regex?

Question

I'm trying to detect any words between asterisks:

NSString *questionString = @"hello *world*";
NSMutableAttributedString *goodText = [[NSMutableAttributedString alloc] initWithString:questionString]; //should turn the word "world" blue

    NSRange range = [questionString rangeOfString:@"\\b\\*(.+?)\\*\\b" options:NSRegularExpressionSearch|NSCaseInsensitiveSearch];
    if (range.location != NSNotFound) {
        DLog(@"found a word within asterisks - this never happens");
        [goodText addAttribute:NSForegroundColorAttributeName value:[UIColor blueColor] range:range];
    }

But I never get a positive result. What's wrong with the regex?

There is no word boundary there. Try adding a search for zero or more whitespace characters. — borrrden, Nov 08 '13 at 04:21
check this link it's helps to you. http://stackoverflow.com/questions/2753956/string-contains-string-in-objective-c — Muralikrishna, Nov 08 '13 at 04:21
Nevermind about the whitespace, but still there is no word boundary as far as I can tell. — borrrden, Nov 08 '13 at 04:23
@borrrden how would I change the regex to include a word boundary? — soleil, Nov 08 '13 at 04:35

score 3 · Accepted Answer · edited May 23 '17 at 12:03

3

@"\\B\\*([^*]+)\\*\\B"

should achieve what you expect.

You have to use \B in place of \b for word boundaries, as per Difference between \b and \B in regex.

Finally, using [^*]+ matches each pair of asterisks, instead of the outermost only.

For instance, in the string

Hello *world* how *are* you

it will correctly match world and are, instead of world how are.

Another way for achieving the same is using ? which will make the + non-greedy.

@"\\B\\*(.+?)\\*\\B"

Also it's worth noting that rangeOfString:options returns the range of the first match, whereas if you are interested in all the matches you have to use build a NSRegularExpression instance with that pattern and use its matchesInString:options:range: method.

edited May 23 '17 at 12:03

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answered Nov 08 '13 at 05:00

Gabriele Petronella

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This works. But if the string is "hello \*world\* how \*are\* you", "how" also turns blue. – soleil Nov 08 '13 at 05:07
No it doesn't. The rest of your code does, since you are using `rangeOfString` which will return the range of the first match. – Gabriele Petronella Nov 08 '13 at 05:15
If you want to retrieve all the matches, you have to use the ` matchesInString:options:range:` method of `NSRegularExpression`. – Gabriele Petronella Nov 08 '13 at 05:16
Thanks. Any idea how I can remove the asterisks after I do the regex test? I just want to turn the word blue. The asterisks shouldn't be displayed. I can't do stringByReplacingOccurrencesOfString on goodText because it is an NSMutableAttributedString. – soleil Nov 08 '13 at 05:25
I'm afraid you will have to break down the string in `NSString` instances, remove the asterisks, and compose the attributed string again. – Gabriele Petronella Nov 08 '13 at 05:28
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P.S. in this case `?` doesn't mean "optional", it means "non-greedy" right? – borrrden Nov 08 '13 at 05:37

What's wrong with this Objective-C regex?

1 Answers1