Get substring using regex in Objective-C?

Question

Context

I've been going back & forth for a couple of hours trying to solve something and am still not satisfied with the result.

I want to get the username of an iPhone from UIDevice both in English and Spanish. So I've come up with a regex to get ("Andres's iPhone" > "Andres") and ("iPhone de Andres" > "Andres").

The magic is something like:

Problem

When trying to get the substring from [[UIDevice currentDevice] name] the user name can be matched by one of the two alternatives in the regex.

This causes that the actual name might be obtained by:

[[regEx firstMatchInString:str options:0 range:NSMakeRange(0, [str length])] rangeAtIndex:1]

if the first alternative matched; but if the second alternative performs the match, then it is:

[[regEx firstMatchInString:str options:0 range:NSMakeRange(0, [str length])] rangeAtIndex:2]

Notice that, according to the alternative matching, I have to get the first index or the second. For the moment I've worked around this with:

+ (NSString *)getSubstringInString:(NSString *)str matchedByRegEx:(NSRegularExpression *)regEx
{
  NSString * result = nil;

  NSTextCheckingResult * match = [regEx firstMatchInString:str options:0 range:NSMakeRange(0, [str length])];
  for (int i=1; i<[match numberOfRanges]; i++) {
    NSRange matchRange = [match rangeAtIndex:i];
    if (!NSEqualRanges(matchRange, NSMakeRange(NSNotFound, 0))) {
      result = [str substringWithRange:matchRange];
    }
  }

  return result;
}

Actual question

But is there a better way to get the matching substring, disregarding what was the alternative from the regex used ?

Hope I've made myself clear, thanks in advance for any possible help!

Dalorzo · Accepted Answer · 2016-08-26 15:45:44Z

1

I will get to your question shortly but first some enhancements by using:

options: .CaseInsensitive

with NSRegularExpression you avoid using expression with and without casing.

So this

(?:iPhone|iphone|phone|iPad|ipad|pad|iPod|ipod|pod)

becomes

(?:iphone|phone|ipad|pad|ipod|pod)

Next by enhancement is i as optional you could still match the other options like:

[i]*(phone|pad|pod)

The expression you need may look like this now:

(?>[i]*(?:phone|pad|pod)\s*de\s)(.+)|(.+)(?='s\s[i]*phone|pad|pod)

The final touch is:

let sample:String = "Andres's iPhone"

let regex = try! NSRegularExpression(pattern: "(?>[i]*(?:phone|pad|pod)\\s*de\\s)(.+)|(.+)(?='s\\s[i]*phone|pad|pod)"
 , options: NSRegularExpressionOptions.CaseInsensitive)

let match = regex.firstMatchInString(sample, options: [], range: NSRange(location: 0, length: sample.characters.count))

print((sample as NSString).substringWithRange(match!.range))

edited Aug 26, 2016 at 15:45

answered Jan 13, 2016 at 18:26

Dalorzo

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2 Comments

Andres C Over a year ago

Thanks for the improvements. I totally overlooked the caps thing: I do set the caseinsensitive option but forgot to update the expression. Good catch!

Andres C Over a year ago

Regarding the question though, if I do match!.range ([match range] in objc) I get the full range of the string, not the matching expression.

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