Adding c++ object in the NSMutableArray

Question

I have MeetingUser C++ class; new_meetingUser is its object.

I want to add it to the NSMutableArray meetingUsersList, which I did using NSValue. However, I can't make out how to handle the memory of the object and the ownership of NSMutableArray.

MeetingUser *new_meetingUser = new MeetingUser(userName, dispName );
[meetingUsersList addObject:[NSValue valueWithPointer:new_meetingUser]];

Tom Dalling · Accepted Answer · 2012-06-07 05:57:32Z

3

You can add the C++ object to the array like that, but the array will not take ownership of the object. You will have to ensure that the object is not deleted while it's in the array, otherwise it will become a dangling pointer. Then you have to delete the object manually later, when you know it is safe to do so.

If you want the array to take ownership of the object, then you will have to use a CFMutableArray. CFMutableArray allows you to specify functions that called when objects are removed from the array, or when the array is deallocated. In your case, you want to set the CFMutableArray to call delete on the objects.

answered Jun 7, 2012 at 5:57

Tom Dalling

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4 Comments

Chuck Over a year ago

Caveat: Having the array delete the objects could be dangerous if there could be other references to them. It depends on if this is the only way objects could ever be added to the array.

user149341 Over a year ago

Caveat II: delete isn't a function, so you'd have to write an itty bitty callback function to wrap it.

Tom Dalling Over a year ago

Yep. If you want the C++ object to be reference counted like a normal NSObject, you'll probably need to make a wrapper class that deletes the object in dealloc, then add the wrapper object to the NSMutableArray.

Chuck Over a year ago

@Saraswati: NSValue does absolutely nothing to manage the memory for you. It literally just holds a pointer.

Chuck · Accepted Answer · 2012-06-07 05:58:04Z

1

Essentially, you can't. C++ objects and Objective-C objects are totally different things, despite both being called "objects." NSArray can only hold Objective-C objects. It can't hold primitives, structs, C++ objects or anything else that is not an Objective-C object. The best workaround is to create an Objective-C class that wraps your C++ class and store that in the array.

answered Jun 7, 2012 at 5:58

Chuck

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Comments

user149341 · Accepted Answer · 2012-06-07 05:58:49Z

1

One approach would be to write a small ObjC class to wrap your C++ object. This can be as simple or as complex as you want -- the only major thing it needs to do is store the C++ object in a field, and delete it in dealloc.

answered Jun 7, 2012 at 5:58

user149341

Comments

Prashant Tukadiya · Accepted Answer · 2022-03-03 13:03:55Z

0

Similar problem I had

Create Objective C Wrapper class MeshHolder.hh

#import <Foundation/Foundation.h>


#include "Sculpt.h"

NS_ASSUME_NONNULL_BEGIN

@interface MeshHolder : NSObject

-(void) setupMesh:(Mesh_CPP *)mesh;
-(Mesh_CPP *)getMesh;

@end

NS_ASSUME_NONNULL_END

and .MM file

#import "MeshHolder.hh"



@implementation MeshHolder

Mesh_CPP * meshTEMP_;


-(void) setupMesh:(Mesh_CPP *)mesh {
    meshTEMP_ = mesh;
}

-(Mesh_CPP *)getMesh {
    return meshTEMP_;
}

@end

How to use it

@property(strong,nonatomic) NSMutableArray<MeshHolder*>  *arrMeshes;

 MeshHolder *meshH = [MeshHolder new];
 [meshH setupMesh:meshTemp];
 [_arrMeshes addObject:meshH];

Hope it is helpful as a quick example

answered Mar 3, 2022 at 13:03

Prashant Tukadiya

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