function to get 2d-arrays from stack and heap

Question

Consider a simple struct, Foo, which contains a pointer to some other strucrt, Baz. and a two-dimensional array, (stack-allocated):
Foo arr[ARR_SIZE][ARR_SIZE];

Next, consider a function which mallocs (in the heap, obviously) a memory for a new 2d-array of Foos. A code snippet:

Foo** arr_copy = malloc(sizeof(Foo*) * ARR_SIZE);
for (int i = 0; i < ARR_SIZE; i++)
{
    arr_copy[i] = malloc(sizeof(Foo) * ARR_SIZE);
}

for (int i = 0; i < ARR_SIZE; i++)
{
        for (int j = 0; j < ARR_SIZE; j++)
        {
            arr_copy[i][j].baz = malloc_baz();
        }
}

Now, in my project I have various of functions which need to handle both the original array (stack allocated) and the copy (which is heap-allocated)

Problem is, things got quirky (memory looks corrupted) when I passed the copy to some function which iterate the 2d-array and print some info.

Basically, I know that there should not be a difference between: void fun(Foo** arr) to void fun(Foo arr[ARR_SIZE][ARR_SIZE]) but both ways were problematic.

So my question is, how can a function handle both arrays, stack/heap allocated?

Thanks.

Answer 1

If you try to do this in c or c++:

 int test[][];

you will get this error:

error: declaration of 'test' as multidimensional array must have bounds for all dimensions except the first

This is because test is not in fact a double ponter as you'd expect. But the compiler converts it into a single block of data. And this: int test[XSIZE][YSIZE]; int n = test[x][y];

will be converted into something like this:

int test[XSIZE*YSIZE];
n = test[YSIZE*x + y];

For solving this, i think @BLUEPIXY already put a solution in the comments. Also, have a look at this question.