acces c++ datamember in objective-c class - objective-c

Question

What I'm trying to do is quite simple but I probably have the syntax wrong.
I have an Objective-C Interface with a Note class parameter. Note.h is a C++ class that basically looks like this:
#include <string>
using namespace std;
class Note {
public:
string name;
Note(string name){
this->name = name; // ERROR: Cannot find interface declaration for 'Note'
}
};
This is my controller where is using Note. I changed the file extension to .mm
#class Note;
#interface InstrumentGridViewController : UIViewController {
#public
Note* note;
}
#property (nonatomic, retain) Note* note;
And this is how I'm using it:
#implementation InstrumentGridViewController
#synthesize note;
- (void)buttonPressed:(id)sender {
note = Note("fa"); // ERROR: Cannot convert 'Note' to 'Note*' in assignment
NSLog(#"naam van de noot is %s", note->name); // ERROR: Cannot find interface declaration for 'Note'
}
I'm getting these three errors though (I've added them as comments on the right lines)
Any idea how what I'm doing wrong?

Answer 1

You need to allocate the Note object using new:
- (void)buttonPressed:(id)sender
{
if (note != 0)
delete note;
note = new Note("fa");
NSLog(#"naam van de noot is %s", note->name.c_str());
}
However it doesn't seem right to be doing that in the button press action method...
Also don't forget to delete it in your object's dealloc method:
- (void)dealloc
{
delete note;
[super dealloc];
}
Lastly your #property attribute retain is wrong as it's not an Objective-C object; instead use assign and better still make it readonly.
A better way to initialise most objects is by using a const reference to them rather than a copy:
Note(const string &name)
{
this->name = name;
}

Answer 2

Your Note C++ class is not valid. Change its declaration to be instead:
class Note {
public:
string name;
Note(string aName) {
name = aName;
}
};
Also change your InstrumentGridViewController:
- (void)buttonPressed:(id)sender {
note = new Note("fa");
NSLog(#"naam van de noot is %s", note->name);
}
- (void)dealloc {
delete note;
[super dealloc]; // Use this only if not using ARC
}

Answer 3

The Cannot find interface declaration for 'Note' error was caused because of #class Note in my Obj-C controller .h file. It's strange because I have a working sample project where #class is used and it works fine.
I fixed it using forward declarations the way they are described here and here.
// used typedef struct <classname> <classname>
typedef struct Note Note;
// instead of
#class Note
The above goes in the Obj-C header file. In the .mm file goes the #import "Note.h" statement