Recommend way to use a large C++ library in a Cocoa application?

Question

I'm trying to develop an application that can "stack" FITS images. To read FITS images I can either use CCFits (a C++ library) or CFITSIO (AC library) - there is no native Objective-C library.

I would prefer to use CCFits as it allows object-oriented design which I'm hoping will allow me to organize the program better. I've already tried to use CFITSIO but it gets rather unwieldy after a while (of course, this could be because of my inexperience in developing large applications).

So overall, what's the best way to approach this? Should I write wrappers for the CFITSIO functions and write my own classes? Is there a way to use C++ classes in Objective-C - the library contains quite a few classes and I know I can use opaque pointers to wrap around the classes, but how would things like class inheritance be preserved? Will I have to subclass a class in Objective-C manually and wrap the subclass there?

Answer 1

You can easily mix C++ and Objective-C using Objective-C++. In XCode just rename your .m files to .mm and it will recognize the files as Objective-C++. Then you can use the C++ classes in your Objective-C code ( some restrictions apply , but not many).

Since Objective-C is an extension to C you can use C libraries in any Objective-C program easily.

Answer 2

Mixing C++ and Objective-C is easy, as @myrkos says. However do make sure you read up carefully how the two languages interact. In particular you cannot inherit an Objective-C class from a C++ class, or vice-versa (which you seem to allude to in your question).

That's not usually an issue in practice.

They compose very nicely, however (that is you can have an Objective-C object as a member of a C++ class and vice-versa - as long as it's all in a .mm file). If you hold a C++ object as an ivar of an Objective-C class by value then constructors and destructors will be called for you automatically.

Answer 3

So overall, what's the best way to approach this?

Use the variant you are comfortable with (CCFits).

Should I write wrappers for the CFITSIO functions and write my own classes?

No.

Is there a way to use C++ classes in Objective-C - the library contains quite a few classes and I know I can use opaque pointers to wrap around the classes, but how would things like class inheritance be preserved?

Objective-C++ allows you to use C, Objective-C, and C++ programs in the same translation with very few issues. Therefore, your implementations can mix Cocoa and C++ as needed. C++ classes can hold ObjC types, and ObjC types can hold C++ types.

Will I have to subclass a class in Objective-C manually and wrap the subclass there?

Just use the CCFits library as-is. There is little to gain by wrapping it in ObjC types, and a lot of time to lose.

If you want to stick with strict ObjC in some areas, then you will need to learn how to hide C++ types behind ObjC interfaces (not a wrapper interface -- just a high level interface for your app's usage of CCFits).