How can I define an array in my Objective-C header file?

Question

I have this code in my main file:

int grid[] = { 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 ,
               1 , 2 , 3 , 2 , 3 , 2 , 3 , 1 , 
               1 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 
               1 , 0 , 1 , 0 , 1 , 0 , 1 , 1 , 
               1 , 0 , 1 , 0 , 0 , 0 , 0 , 1 , 
               1 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 
               1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 };

How do I define it in my header so that I can access the variable throughout my class?

Answer 1

extern int grid[];

Let's suppose you had some code like this:

int grid[] = { 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 ,
        1 , 2 , 3 , 2 , 3 , 2 , 3 , 1 , 
        1 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 
        1 , 0 , 1 , 0 , 1 , 0 , 1 , 1 , 
        1 , 0 , 1 , 0 , 0 , 0 , 0 , 1 , 
        1 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 
        1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 };

int arr_sum(int* arr, int len)
{
    int sum = 0;
    for (int i = 0; i < len; i++) {
            sum += arr[i];
    }
    return sum;
}

int main(int argc, char** argv)
{
    printf("%d\n", arr_sum(grid, sizeof(grid)/sizeof(int) ));
    return 0;
}

If you wanted to separate this out into two different files, say, you could have the following, for example:

in grid.c:

int grid[] = { 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 ,
        1 , 2 , 3 , 2 , 3 , 2 , 3 , 1 , 
        1 , 0 , 0 , 0 , 0 , 0 , 0 , 1 , 
        1 , 0 , 1 , 0 , 1 , 0 , 1 , 1 , 
        1 , 0 , 1 , 0 , 0 , 0 , 0 , 1 , 
        1 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 
        1 , 1 , 1 , 1 , 1 , 1 , 1 , 0 };

In main.c:

extern grid[];

int arr_sum(int* arr, int len)
{
    int sum = 0;
    for (int i = 0; i < len; i++) {
            sum += arr[i];
    }
    return sum;
}

int main(int argc, char** argv)
{
    printf("%d\n", arr_sum(grid, sizeof(grid)/sizeof(int) ));
    return 0;
}

Answer 2

You can't define it in your header. You have to declare it in your header and define it in a source (.m) file:

// In MyClass.h
extern int grid[];

// In MyClass.m
int grid[] = {...};