why does this pointer arithmetic on a 2D array work?

Question

I wrote the following code:

#include <iostream>
using namespace std;

int main()
{
    int a[10][10];
    for (int i = 0; i < 10; i++)
        for (int j = 0; j < 10; j++)
            a[i][j] = i * j;
    cout << *(*(a + 3) + 4) << endl;
    return 0;
}

I was expecting it to print some garbage data, or a segmentation fault. What I got was 12. I tested it both in c and c++ (using gcc and g++ respectively), and I herd this works the same on VS although I haven't tested this. Why does this work, and is there a official documentation of this behavior?

Answer 1

*(a + b)=a[b] you take the address of a, move it by b and take the value at the corresponding address

So *(*(a + 3) + 4)means *(a[3]+4) which mean a[3][4]=12