Question

This is a simple class ive created in C++ for a musical application im creating for an iOS device which will store some values of notes and their timings :

class info {
public:
    float attackTime;
    Note noteStriked;

    void setData(float timeOfAttack, Note nameOfStrikeNote){
        attackTime = timeOfAttack;
        noteStriked = nameOfStrikeNote;
    }
};

above… Note is a struct which can only contain default values such as {SNARE, DRUM, HIHAT} and so on. The idea is to create a Note object and store those objects in a NSMutableArray for later access.

Then in my main .h file i have a NSMutableArray sequenceOfNotes; and in my .m file i am trying to add an object to my mutablearray… but i dont know how to do this. Ive tried various things but with fail it does not work!

//Create one instance of the class
NoteData *currentNoteData;

// Update the instance of the class.. its two variables: attackTime and noteStriked
currentNoteData->attackTime = timeHit;
currentNoteData->noteStriked = SNARE;

//Then im trying to add the above instance to my mutableArray below
[sequenceOfNotes addObject:currentNoteData];

The error produced on that line is
Cannot initialise a parameter of type ‘id’ with an lvalue of type ‘NoteData *’

what id then like to do after the error is fixed is to be able to retrieve my object at any position of the array i choose and then be able to choose an attribute variable from that object at that specific index.

//PsuedoCode
array {
  position 0: NoteData object {
                attackTime = 45.34,
                noteStriked = HIHAT
              }
  position 1: NoteData object {
                attackTime = 65.32,
                noteStriked = SNARE
              }
  position 2: NoteData object {
                attackTime = 78.53,
                noteStriked = HIHAT
              }
  position 3: NoteData object {
                attackTime = 98.44,
                noteStriked = KICK
              }
  etc etc

}

//and then convert NSObject to normal c++ object something like this... 
NoteData temp = [noteSequence objectAtIndex:0];

//so that i can then do this:
float currentTime = temp.attackTime;
Note currentNote = temp.noteStriked;

Obviously theres a conversion issue.. if anyone can help me with this that would be awesome

Answer 1

You have to wrap your C++ object pointer into a NSValue:

[MyArray addObject:[NSValue valueWithPointer:new MyCPPObject()]];

...

MyCPPObject *obj = [[MyArray objectAtIndex:index] pointerValue];

Alternatively, why don’t you just use a vector<MyCPPObject> or a list<MyCPPObject>?