Question

tI have the following code:

 #define FIRST_COUNT 100
 #define X_COUNT 250
 #define Y_COUNT 310
 #define z_COUNT 40

struct s_tsp {

     short abc[FIRST_COUNT][X_COUNT][Y_COUNT][Z_COUNT];
};

struct s_tsp xyz;

I need to run through the data like this:

for (int i = 0; i < FIRST_COUNT; ++i)
    for (int j = 0; j < X_COUNT; ++j)
          for (int k = 0; k < Y_COUNT; ++k)
                for (int n = 0; n < Z_COUNT; ++n)
                      doSomething(xyz, i, j, k, n);

I’ve tried to think of a more elegant, less brain-dead approach. ( I know that this sort of multidimensional array is inefficient in terms of cpu usage, but that is irrelevant in this case.) Is there a better approach to the way I’ve structured things here?

Answer 1

If you need a 4D array, then that’s what you need. It’s possible to ‘flatten’ it into a single dimensional malloc()ed ‘array’, however that is not quite as clean:

abc = malloc(sizeof(short)*FIRST_COUNT*X_COUNT*Y_COUNT*Z_COUNT);

Accesses are also more difficult:

*(abc + FIRST_COUNT*X_COUNT*Y_COUNT*i + FIRST_COUNT*X_COUNT*j + FIRST_COUNT*k + n)

So that’s obviously a bit of a pain.

But you do have the advantage that if you need to simply iterate over every single element, you can do:

for (int i = 0; i < FIRST_COUNT*X_COUNT*Y_COUNT*Z_COUNT; i++) {
    doWhateverWith *(abc+i);
}

Clearly this method is terribly ugly for most uses, and is a bit neater for one type of access. It’s also a bit more memory-conservative and only requires one pointer-dereference rather than 4.