Regular expressions in an Objective-C Cocoa application

Question

I noticed that as of iOS 4.0 Apple provides a NSRegularExpression class. Additionally, as of 10.7, the class is available under OS X.

1. Yes, there's no regex support in Cocoa. If you're only interested in boolean matching, you can use NSPredicate which supports ICU regex syntax. But usually you're interested in the position of the match or position of subexpressions, and you cannot get it with NSPredicate.
2. As mentioned you can use regex POSIX functions. But they are considered slow, and the regex syntax is limited compared to other solutions (ICU/pcre).
3. There are many OSS libraries, CocoaDev has an extensive list.

4. RegExKitLite for example doesn't requires any libraries, just add the .m and .h to your project.

   (My complaint against RegExKitLite is that it extends NSString via category, but it can be considered as a feature too. Also it uses the nonpublic ICU libraries shipped with the OS, which isn't recommended by Apple.)

RegexKit is the best I've found yet. Very Cocoa:y. I'm using the "Lite" version in several of our iPhone apps:

sourceforge

lingonikorg

You can use the POSIX Regular Expressions library (Yay for a POSIX compliant OS). Try

man 3 regex

The cheap and dirty hack solution that I use to solve REGEX and JSON parsing issues is to create a UIWebView object and inject Javascript function(s) to do the parsing. The javascript function then returns a string of the value (or list of values) I care about. In fact, you can store a small library set of functions customized for particular tasks and then just call them as needed.

I don't know if it this technique scales to huge volumes of repeated parsing requests, but for quick transactional stuff it gets the job done without depending on any extra external resources or code you might not understand.

I like the AGRegex framework which uses PCRE, handy if you are used to the PCRE syntax. The best version of this framework is the one in the Colloquy IRC client as it has been upgraded to use PCRE 6.7:

http://colloquy.info/project/browser/trunk/Frameworks/AGRegex

It's very lightweight, much more so than RegExKit (although not as capable of course).