How to use Objective-C in C++ header?

Question

I tried to do the following in the A.h file:

#include "Bar.hpp"

#import <Foundation/Foundation.h>

namespace foo 
{
  struct A : Bar::B
  {
    public:

    A() : Bar::B() {}

    id delegate;

    virtual void OnEvent(...);
  };
}

But I get zillion of errors like 'I dont know what NSString is'. How do I do it correctly?

What kind of source are you including it from? It will only work if the language is Objective C++ (not C, Objective C or plain C++). — Mike Seymour
– Mike Seymour, Commented Aug 28, 2012 at 16:13
The source, which is shown above, is from an .h file, which has a corresponding .mm implementation. — fspirit
– fspirit, Commented Aug 29, 2012 at 7:16
Presumably, you're also including it from other files. Are they all Objective C++ too? If you include it from any source files of other languages, then you'll get errors. — Mike Seymour
– Mike Seymour, Commented Aug 29, 2012 at 8:20

Farcaller · Accepted Answer · 2012-08-28 16:12:27Z

5

You're including it in a .cpp file? Rename it to .mm (that's the correct file extension for Objective-C++).

answered Aug 28, 2012 at 16:12

Farcaller

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3 Comments

Hot Licks Over a year ago

Or one can set the file type under "Get Info".

fspirit Over a year ago

No, it's a .h file. That .h file has a corresponding .mm impl.

Farcaller Over a year ago

Make sure that all files that #include/#import this one header are .mm

Sergey Kalinichenko · Accepted Answer · 2012-08-28 16:17:15Z

3

If you would like to use one of your Objective C classes inside your "regular" C++ class (as opposed to Objective C++) you could use the trick described in this article, which boils down to including <objc/objc-runtime.h> instead of <Foundation/Foundation.h>, and using a wrapped struct objc_object in place of a "real" Objective C object.

#ifdef __OBJC__
@class ABCWidget;
#else
typedef struct objc_object ABCWidget;
#endif

namespace abc
{
  class Widget
  {
    ABCWidget* wrapped;
  public:
    Widget();
    ~Widget();
    void Reticulate();
  };
}

answered Aug 28, 2012 at 16:17

Sergey Kalinichenko

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