Fraction: Does not recognize selector forward::

If you’re crazy like me you love reading really good primers on programming. Not just to learn about a particular language but to enjoy well written technical prose. (Yeah, I said I was crazy). Yesterday, I started reading Stephen Kochan’s classic Programming in Objective-C (original edition), which was published in 2003. What I like about Kochan is how he presents the principles of object oriented programming and the syntax of Objective-C without jumping into writing a fancy application. Kochan takes his time to teach each component of the language and the paradigm instead of glossing over the details to quickly get to a utilitarian example.

If you want to understand how a great tutorial is written you can’t do much better than Kochan. Unfortunately a lot has changed in the Mac OS X world since 2003 and the code examples don’t compile. The code is fine. It’s the default compiler setting that have changed. A Google search on the compile error brought me to a a good discussion on the problem on Apple’s developer support forum. You have to dig but the fix is pretty trivial if you know gcc complier flags (which the target audience of a primer are unlikely to know).

My advice to students and armchair time travelers who want to follow the original book is to resist the urge to change the source code examples to inherit from NSObject. Instead use the  -arch i386 flag as suggested by very helpful forum user Constantino. (Mysteriously Constantino’s forum name is spelled with a K.)

In other words instead of compiling with

gcc ClassName.m -o ProgramName -l objc


gcc -arch i386 -o ProgramName ClassName.m -lobjc

To compile and run the OOP first example of the book from the terminal you can copy and paste the following 2 lines:

gcc -arch i386 -o Fraction Fraction.m -lobjc

And for the full experience, don’t use Xcode or a fancy text editor. VI is fun, old school, and Apple’s Terminal a joy to work with.


  • There is a third edition that probably addressed this issue. But what fun is that if you only have the original edition? I would love to set up an old Mac with a vintage version of the Mac OS X to really immerse  myself in the experience!
  • There is also also a Programming in Objective-C 2.0 3rd Edition which looks like a lot of fun to read and which might actually be more relevant if you have an urgent need to write a modern Mac application.






One response to “Fraction: Does not recognize selector forward::”

  1. gertrude Avatar

    thanks for this! 🙂