c++ aliasing pointer of dynamic dimensional array

Question

I am working on multidimensional arrays. The matrix's data and dimensions are given during runtime, and I tried to access the data with type alias pointer such as below.

It worked well with my code, but I am not sure if it's within c++ standard.

Can I use type alias like this: unknown-dimensional array pointer?

    cin >> a; //1
    cin >> b; //2
    cin >> c; //3

    int* buf = new int[100]; //just to allocate some memory for test

    using arr_t = int (*)[a][b][c]; //type alias of pointer of array
    arr_t arr = reinterpret_cast<arr_t>(buf);

    buf[3] = 1;
    cout << arr[0][1][0] << endl; // 1 (It's easier than buf[b*c*0 + c*1 + 0])

    cout << (void*)&buf[3] << endl; //0x18b8e78
    cout << (void*)&(*arr)[0][1][0] << endl; //0x18b8e78

Answer 1

int (*)[a][b][c] with runtime values uses VLA (Variable Length Array) extension, and so, is not standard C++.

And even with that extension, your cast breaks strict aliasing rules.