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;
}