Question

I’ve a 3×3 2D dynamic array allocated as below:

int** matrix = new int* [3];
matrix[0] = new int [3*3];
for (int i = 1; i < 3; ++i)
    matrix[i] = matrix[i-1] + 3;

How should I deallocate it? Is this correct:

delete [] matrix;

delete [] matrix[0];

Or should I also delete matrix[1], [2]

Answer 1

The way you have it, you should :

delete [] matrix[0];
delete [] matrix;

But this is a very unconventional way of allocating a dynamic 2D array. Normally you allocate an array of pointers, and then you allocate an array of your actual type for every row (column).

// allocate
int **matrix = new int*[3];
for(int i = 0; i &lt 3; ++i)
  matrix[i] = new int[3];

// deallocate
for(int i = 0; i &lt 3; ++i)
  delete [] matrix[i];

delete [] matrix;