iOS provides a NSRegularExpression class for working with regular expressions. Here's how to run a regex against a string and iterate through the matches:

NSError* error;
NSRegularExpression* regex = [NSRegularExpression regularExpressionWithPattern:@"XXX" options:NSRegularExpressionCaseInsensitive error:&error];
NSString* string = @"HelloXXXworldXXXXXX";
__block NSUInteger count = 0;
[regex enumerateMatchesInString:string options:0 range:NSMakeRange(0, [string length]) usingBlock:^(NSTextCheckingResult* match, NSMatchingFlags flags, BOOL* stop) {
    NSRange matchRange = [match range];
    NSRange range = [match rangeAtIndex:0];
    NSLog(@"range (%@, %@)", @(range.location), @(range.length));
    NSLog(@"string: %@", [string substringWithRange:range]);
}];

What's also interesting is iOS provides NSDataDetector, as a subclass of NSRegularExpression.

NSError* error;
NSDataDetector* detector = [NSDataDetector dataDetectorWithTypes:NSTextCheckingTypeLink|NSTextCheckingTypePhoneNumber error:&error];
NSString* string = @"My homepage is at https://hboon.com and my phone number is 391-165-8164";
__block NSUInteger count = 0;
[detector enumerateMatchesInString:string options:0 range:NSMakeRange(0, [string length]) usingBlock:^(NSTextCheckingResult* match, NSMatchingFlags flags, BOOL* stop){
    NSRange matchRange = [match range];
    if ([match resultType] == NSTextCheckingTypeLink) {
        NSURL* url = [match URL];
        NSLog(@"matched URL: %@", url);
    } else if ([match resultType] == NSTextCheckingTypePhoneNumber) {
        NSString* phoneNumber = [match phoneNumber];
        NSLog(@"matched phone number: %@", phoneNumber);
    }
}];

NSDataDetector comes with pre-built matching capability for dates, addresses, links, and phone numbers, so you don't have to build your own regex for them.

PS: If you want to build more complicated regular expressions, check out my app Regex for OS X that includes tools to help build and test regular expressions.

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