段故障动态分配的二维数组

Question

I have a homework assignment where I have to dynamically allocate a 2d array and i am getting seg faults when my arrays are long and skinny, such as 2x8, and the problem only occurs when certain values are in the array. here is my code for making the array and then deleting it.

int main()
{
  int **p;
  int w, h;

  cin >> w >> h;

  p= new int *[w];
  for (int k=0; k<w; k++)
    p[k]= new int[h];
  for (int i=0; i<h; i++)
  {
    for(int k=0; k<w; k++)
    {
      cin >> p[i][k];
    }
  }


  for (int k=0; k < w; k++)
    delete []p[k];
  delete []p;
  return 0;
}

example input that causes seg fault: 
8 2
5 4 2 3 0 1 2 5
2 0 1 0 9 6 3 2

Using gdb I found it is segfaulting right after the first delete in the loop.

Answer 1

You have mixed up your indexes. You allocate w pointers, but your loop runs i through h elements.

Answer 2

The loops for assigning values have their boundaries swapped.

p is given an array of length w , but then the iterator i which loops up to h is used to index it.

p= new int *[w];

....

cin >> p[i][k];

p[i][k] is read as p[i] then indexed by [k] .