Re: Using C++ classes from Objective C

FROM : Christopher Nebel
DATE : Thu Mar 20 19:33:51 2008

On Mar 20, 2008, at 10:32 AM, Rob Napier wrote:

> Say you have a C++ object called MyObject in the namespace myapp 
> that you want to access through your ObjC. What I tend to do is 
> create an ObjC++ object called MyObjectWrapper that owns a 
> myapp::MyObject and presents a pure ObjC interface to its methods. 
> Users of MyObjectWrapper don't have to include MyObject.h. The trick 
> is that you need to use void* rather than a real class type in 
> MyObjectWrapper.h like this:
>
> typedef void* MyObjectPtr
>
> @interterface MyObjectWrapper : NSObject
> {
>  MyObjectPtr myObject;
> }
>
> That will get you around having C++ class definitions in your header.


Actually, you don't need the "void" typedef -- you can exploit the 
fact that "class" and "struct" are (almost) synonymous in C++:

   struct MyObject; // forward declaration.
   typedef struct MyObject MyObject; // this is Objective-C, after all...

   @interterface MyObjectWrapper : NSObject
   {
       MyObject *myObject;
   }

Compiles fine in Objective-C or Objective-C++.  In your 
implementation, you give the real definition of MyObject:

   class MyObject {
       ...
   };

C++ (or at least gcc) doesn't mind that it was forward-declared using 
"struct", since the only difference between "class" and "struct" is 
the default access privilege.


--Chris N.