assign int[][] to int** [duplicate]

Question

As far as I know, in some contexts, an array is converted into a pointer to its first element:

int a[5];
int * p;

p = a;

Following this approach and considering I can assign an array to a pointer, why can't I assign a bidimensional array to a pointer to a pointer?

int a[5][5];
int ** q;

q = a;

However, I can assign an array of pointers to a pointer to a pointer:

int * p[5];
int ** q;

q = p;

If an array is converted into a pointer to its first element, when q = a happens in the second example, a should be a pointer to a[0] and a[0] should be a pointer to a[0][0], right?

Besides, I don't get an error if I do:

cout << **a;

Thanks in advance and I hope you can help me to understand.

Answer 1

The problem is that an array int a[5][5]; stores 25 consecutive int.

A pointer to arrays/pointers like int **q; expects to find an array of consecutive pointers to int.

This is why the assignment you want to do is not possible.

Answer 2

a multi-dimensional array can be assigned to a single pointer

int a[5][5];
int *p = a;

because the memory is allocated as a single block organized by row.

a = a11 a12 a13
    a21 a22 a23    

a = a11 a12 a13 a21 a22 a23