Question

I am trying to write a very simple piece of code to create a 3×2 matrix using STL vectors.
This is what I have:

#include <vector>
using namespace std;

int main ()
{

  int i;

  vector<int> * x = new vector<int> [3];

  for (i = 0; i < 3; i++)
       x[i] = vector<int> (2); 

  delete x;

  return 0;

}

The problem is that every time I run the program, it crashes. If I remove the delete x then it works fine, but will probably result in memory leaks.

I know that this is probably not the best way to create a matrix and there is a battalion of choices out there, but I would just like to know why the above program crashes every time.

Also, replacing every occurrence of vector<int> with say int, then all work fine again.

Answer 1

To destroy dynamically allocated arrays you must use delete[], not delete.

While that will make the code work, it is a suboptimal solution. The following program does the same thing, but is much more succint, and safer.

#include <vector>

int main ()
{
  std::vector<std::vector<int>> x(3, std::vector<int>(2));
}