Objective C member in C++ class

Question

Hi. Is it possible to have a objective c member in a c++ class

@interface ObjectiveCClass : UIViewController  {

    int someVarialbe;

}
- (void)someFunction;

@end


class CPlusPlusClass{
      ObjectiveCClass obj;          // have a objective c member

      void doSomething(){
           obj.someFunction;        // and call a objective c method
       }
};

Any guidance would really be appreciated.

Cheers

Answer 1

To create header files that can be shared between obj-c and cpp code, you could use the compiler predefined macros to do something like:

// A .h file defining a objc class and a paired cpp class
// The implementation for both the objective C class and CPP class
// MUST be in a paired .mm file
#pragma once

#ifdef __OBJC__
#import <CoreFoundation/CoreFoundation.h>
#else
#include <objc/objc.h>
#endif

#ifdef __OBJC__

@interface ObjectiveCClass :
...

typedef ObjectiveCClass* ObjectiveCClassRef;

#else

typedef id ObjectiveCClassRef;

#endif

#ifdef __cplusplus

class CPlusPlusClass {
  ObjectiveCClassRef obj;

  void doSomethind();
};

#endif

Im not 100% sure its legal to have ObjectiveCClassRef change type like that between c/cpp and obj-c builds. But id is a c/cpp compatible type defined in the objective C header files as capable of storing an objective C class pointer, and, when used in .m or .mm files, allows you to call the object directly using objective C syntax.

Answer 2

There's a dialect of Objective-C called Objective-C++ that is interoperable with C++ the same way that Objective-C is interoperable with C. You can either change the setting for the file to be Objective-C++ or change the extension to ".mm". You'll still need to access Objective-C objects through pointers and do the alloc-init dance and all that, of course.