Indexing into std::array of std::array

Question

I have some confusion about indexing of an array of arrays in C++:

I have:

array<array<int, SIZE_INNER>, SIZE_OUTER> arr;

When I do indexing, I assume the following:

arr[outer_index][inner_index]

So, outer_index into the array with SIZE_OUTER comes first, and the inner index then comes second.

Is that true?

Answer 1

Yes. Think like this: arr[o] accesses the o-th element of arr . The fact that the element is an array too doesn't change much.

Subsequent calls to operator [] access elements returned by previous calls.

Answer 2

Yes. Let break it down a little

array<int, SIZE_INNER>

Is going to create an array of size SIZE_INNER. Now you wrap that array in

array<array<int, SIZE_INNER>, SIZE_OUTER> arr;

So the inner array is your "column" and the outer array is your "row". Just like with plain 2d arrays.

When working with the [] operator the one farthest to the right is for the inner most array.