Re: Objective-C++ Instance Variables

In article <woody-33200E.17164003072008@[EMAIL PROTECTED]
>,
 William Woody <woody@[EMAIL PROTECTED]
> wrote:

> > I'm trying to bridge between my Cocoa App and my C++ framework via
> > Objective-C++. Apparently I can't have C++ objects as instance
> > variables in my ObjC class because they contain virtual methods. Also,
> > I don't appear to be able to include my C++ header files in by ObjC
> > header file; they work fine if I include them in my implementation
> > file (.mm).
> > 
> > How should I create my C++ objects and use them within my ObjC class
> > (over it's lifetime)?  Perhaps I should be doing this a different way?
> > What I have is a C++ framework compiled into a dylib. I include the
> > headers in my .mm and link in the dylib.
> 
> 
> What I've done is create a pointer in my Objective C class which points 
> to my C++ class:
> 
> @[EMAIL PROTECTED]
 ObjCClass : NSObject
> {
>    CPPClass *fPtr;
> }
> 
> - (id)init;
> - (void)dealloc;
> 
> @[EMAIL PROTECTED]
> 
> ...
> 
> @[EMAIL PROTECTED]
 ObjCClass
> 
> - (id)init
> {
>    self = [super init];
>    if (self) {
>       fPtr = new CPPClass;
>    }
>    return self;
> }
> 
> - (void)dealloc
> {
>    if (fPtr) delete fPtr;
>    [super dealloc];
> }
> 
> @[EMAIL PROTECTED]
> 
> 
> Note that this implies that you either #include the C++ header in your 
> Objective C header, or you need to declare the CPPClass in the Objective

> C header as a anonymous C++ class. In either case, this means you can 
> only #im****t your Objective C header in a .mm file.

Not So! Remember that in C++ 'struct' is the same as 'class' except in a 
'struct' all the members default to public.  So, you can forward declare 
in your Obj-C.h file:

typedef struct CPPClass CPPClass;

this lets you include your .h file in a .c file just fine.

 
> There are some places where things can get a little mind-bending, by the

> way; in a few places in my code I've written things like:
> 
>    std::map<int32_t,MyStruct> array;
>    ...
>    return array[[myObjC count]];
> 
> Where the outer [] is the C++ operator [] call, and the inner [] is an 
> Objective C method call.

this is a good place to introduce a tem****ary variable.


Here is a tested example of using the header from a .mm file in a .m:

// main.h
#im****t <Foundation/Foundation.h>

#ifdef __cplusplus
extern "C" {
#endif

typedef struct CPPClass CPPClass;

@[EMAIL PROTECTED]
 ObjCClass : NSObject {
    CPPClass *fPtr;
 }
 
- (id)init;
- (void)dealloc;
@[EMAIL PROTECTED]
 *MakeObjCClass(void);

#ifdef __cplusplus
}
#endif

//main.mm
#im****t "main.h"
#im****t "cpp.h"

@[EMAIL PROTECTED]
 ObjCClass

- (id)init {
  self = [super init];
  if (self) {
    fPtr = new CPPClass;
  }
  return self;
}

- (void)dealloc {
  if (fPtr) delete fPtr;
  [super dealloc];
}

@[EMAIL PROTECTED]
 main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    ObjCClass *obj = MakeObjCClass();
    if (obj) {
    }
    // insert code here...
    NSLog(@[EMAIL PROTECTED]
"Hello, World!");
    [pool release];
    return 0;
}

// cpp.h

struct CPPClass {
public:
  CPPClass();
  ~CPPClass();
private:
  int g;
};

// cpp.cpp

#include "cpp.h"

CPPClass::CPPClass() : g(1){
}

CPPClass::~CPPClass() {
}

// m.m
#include "main.h"

ObjCClass *MakeObjCClass(void) {
  return [[[ObjCClass alloc] init] autorelease];
}


To summarize: 
m.m is straight Obj-C. It has no trouble with main.h.

main.mm is Obj-C++, It has no trouble with the forward declared C++ 
cl***** in main.h, that are fully declared in cpp.h.

cpp.cpp is straight C++. It only sees cpp.h, so everything is cool.