Consider following declaration:

int a[M][N]; // M and N are known compile-time

Would it be legal to treat it like as it was declared as:

int a[N][M];

or even:

int a[A][B]; // where A * B = M * N

in C without breaking its rules (badly)?

I found that it can be acomplished without any cast:

#include <stdio.h>

void print_array(int a[][2], int n);

int main(void)
{
    int a[2][3] = {{1, 2, 3}, {4, 5, 6}};

    //int (*p1)[2] = a; // compile error

    int (*ptr_temp)[] = a; // pointer to array of incomplete type
    int (*p2)[2] = ptr_temp; // compiles without any warning

    print_array(p2, 3);
}

void print_array(int a[][2], int n)
{
    for (int i = 0; i < n; i++)
        for (int j = 0; j < 2; j++)
            printf("a[%d][%d] = %d\n", i, j, a[i][j]);
}

Notice that we cannot assign a to p1 pointer directly. However compiler does not complain when p2 is assigned with ptr_temp even if it seems to be potentially dangerous (it does not require any cast for that). Is it really sanitized? If so, then why it disallows the first assignmment?