What Are Some Quirks/Surprises with Using .mm Files in Objective-C?

Question

I want to use some C++ STL collections in my Objective-C iPhone app. Apparently this is possible by giving files the extension ".mm" . What are some of the quirks/surprises associated with this?

I want to use the basic containers that I'm familiar with (vector, queue, set, ...)

Cheers!

Answer 1

See Using C++ With Objective-C for a detailed list of what you can and can't do. You can do most things that you would expect. You just can't do things like have a C++ class inherit from an Objective-C class or vice-versa, you can't mix C++ exceptions with Objective-C exceptions, and C++ introduces several new keywords not present in Objective-C.

Answer 2

The major quirk of Objective-C++ is that if you don't pass -fobjc-call-cxx-cdtors to g++, it won't call the constructor and destructor of C++ instance variables in of ObjC objects. So remember to turn that option on and you should be good.

Answer 3

The files will be compiled with the Objective-C++ compiler, so things will behave more like g++ than gcc, but since that's what you want it probably doesn't count as a surprise. From the Objective-C side, I'm not aware of any gotchas, and I've worked on several large projects that made significant used of Objective-C++. Just keep in mind that Objective-C reserved words are reserved in Objective-C++ as well, so you can occasionally run into issues with third-party C++ libraries (e.g., if they use "id" as a parameter in a public interface).

Answer 4

You'd be surprised how well it works. I haven't really gotten into any problems intermixing Obj-C and C++ in a .mm file.