c++ dynamic array initialization with declaration

Question

I have function like this:

void findScarf1(bool ** matrix, int m, int n, int radius, int connectivity); 

and in main function I create 2d dynamic array to pass in this function

    bool matrix[6][7] = {
    {0, 0, 1, 1, 1, 0, 0},
    {0, 0, 1, 1, 1, 0, 0},
    {0, 0, 1, 1, 1, 0, 0},
    {0, 0, 1, 1, 1, 0, 0},
    {0, 0, 1, 1, 1, 0, 0},
    {0, 0, 1, 1, 1, 0, 0}
};

The problem is:

findScarf1(matrix, 6, 7, 3, 4);

causes error C2664: 'findScarf1' : cannot convert parameter 1 from 'bool [6][7]' to 'bool **'

How to initialize array compactly(simultaneously with declaration)?

p.s. sorry if it's duplicate question but I've spent 1.5 hours figuring it out

Answer 1

If you look at how your array is laid out in memory, and compare it how a pointer-to-pointer "matrix" is laid out, you will understand why you can't pass the matrix as a pointer to pointer.

You matrix is like this:

[ matrix[0][0] | matrix[0][1] | ... | matrix[0][6] | matrix[1][0] | matrix[1][1] | ... ]

A matrix in pointer-to-pointer is like this:

[ matrix[0] | matrix[1] | ... ]
  |           |
  |           v
  |           [ matrix[1][0] | matrix[1][1] | ... ]
  v
  [ matrix[0][0] | matrix[0][1] | ... ]

You can solve this by changing the function argument:

bool (*matrix)[7]

That makes the argument matrix a pointer to an array, which will work.

---

And by the way, the matrix variable you have is not dynamic, it's fully declared and initialized by the compiler, there's nothing dynamic about it.

Answer 2

Technically, a 2D array is an array of 1D arrays. So it cannot convert into pointer to pointer. It can convert into pointer to array, though.

So this should work:

void findScarf1(bool (*matrix)[7], int m, int n, int radius, int connectivity); 

Here bool (*matrix)[7] declares a pointer to array of 7 bool.

Hope that helps.