Question

I wrote the following code In c just to check whether the code would break or not:

int main(void)
{
    int A [5] [2] [3];
    printf("%d\n\n", A[6]);
    printf("%d\n\n", &A[6][0][0]);
    system("pause");
}

Now, the code does not break which was something I was not expecting. When we declare a multidimensional array: int A [5][2][3], doesn’t that conceptually mean that A in its first level is a one-dimensional array of 5 elements ( 0 – 4 ) and every element of that array is itself a one-dimensional array of 2 elements and every element of that array is a one-dimensional array of 3 elements? If that concept is correct, how can
A[6][0][0] even exist – since in the first level we only have 5 elements ( 0 based ) .

Any help, would be greatly appreciated.

Answer 1

You are accessing a position outside the array, there is no A[6]. That’s undefined behavior, and anything could happen.

Note that A[5] is a well defined location (past the end of the array), so getting a pointer to it is legal but trying to access that pointer is not. However, getting a pointer to A[6] or any other greater index is completely undefined.