CODEWITHSUNDEEP
objective-carraysmultidimensional-array
MrHappyAsthma
MrHappyAsthma

Reputation: 6522

2D Array Declaration - Objective C

Is there a way to declare a 2D array of integers in two steps? I am having an issue with scope. This is what I am trying to do:

//I know Java, so this is an example of what I am trying to replicate:

int Array[][];
Array = new int[10][10];

Now, in OBJ-C I want to do something similar, but I cant get the syntax right. Right now I have it in one step, but I cannot use it outside of the If-Statement in which I currently have it:

int Array[10][10]; //This is based on an example I found online, but I need 
                   //to define the size on a seperate line than the allocation

Can anyone help me out with this? I know its probably a more basic question, but you can't use the keyword "new" outside of a message (to my knowledge) and you cant send messages to ints. :(

*EDIT 1:**

My problem is scope related.

//Declare Array Somehow
Array[][] //i know this isn't valid, but I need it without size

//if statement
if(condition)
Array[1][2]
else
Array[3][4]

//I need to access it outside of those IFs

//... later in code
Array[0][0] = 5;

Upvotes: 1

Views: 3149

Answers (2)

Richard J. Ross III
Richard J. Ross III

Reputation: 55533

This is my preferred way of creating a 2D array, if you know the size of one of the boundaries:

int (*myArray)[dim2];

myArray = calloc(dim1, sizeof(*myArray));

And it can be freed in one call:

free(myArray);

Unfortunately, one of the bounds MUST be fixed for this to work.

However, if you don't know either of the boundaries, this should work too:

static inline int **create2dArray(int w, int h)
{
    size_t size = sizeof(int) * 2 + w * sizeof(int *);
    int **arr = malloc(size);
    int *sizes = (int *) arr;
    sizes[0] = w;
    sizes[1] = h; 
    arr = (int **) (sizes + 2);

    for (int i = 0; i < w; i++)
    {
        arr[i] = calloc(h, sizeof(**arr));
    }

    return arr;
}

static inline void free2dArray(int **arr)
{
     int *sizes = (int *) arr;
     int w = sizes[-2];
     int h = sizes[-1];

     for (int i = 0; i < w; i++)
         free(arr[i]);

     free(&sizes[-2]);
}

Upvotes: 4

MByD
MByD

Reputation: 137272

The declaration you showed (e.g. int Array[10][10];) is OK, and will be valid for the scope it was declared to, if you do it in a class scope, then it will be valid for the whole class.

If the size of the array varies, either use dynamic allocation (e.g. malloc and friends) or use NSMutableArray (for non-primitive data types)

Upvotes: 0

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