How pointer is still able to read data even after 'delete' operator? [duplicate]

manpreet Best Answer 3 years ago

I'm trying to understand Pointers to class. I also ran it on CodeBlocks. foo pointer.

// pointer to classes example
#include 
using namespace std;

class Rectangle {
  int width, height;
public:
  Rectangle(int x, int y) : width(x), height(y) {}
  int area(void) { return width * height; }
};


int main() {
  Rectangle obj (3, 4);
  Rectangle * foo, * bar, * baz;
  foo = &obj;
  bar = new Rectangle (5, 6);
  baz = new Rectangle[2] { {2,5}, {3,6} };
  cout << "obj's area: " << obj.area() << '\n';
  cout << "*foo's area: " << foo->area() << '\n';
  cout << "*bar's area: " << bar->area() << '\n';
  cout << "baz[0]'s area:" << baz[0].area() << '\n';
  cout << "baz[1]'s area:" << baz[1].area() << '\n';
  delete bar;
  delete[] baz;
  delete foo;
   cout << "Try: ";
   cout << foo->area();
  return 0;
}

Actual Result: obj's area: 12 *foo's area: 12 *bar's area: 30 baz[0]'s area:10 baz[1]'s area:18 Try: 12

manpreet 3 years ago

The pointer is invalidated by the delete expression.

The behaviour of indirecting through an invalid pointer is undefined. Your program indirects through foo after it has been deleted. The behaviour of your program is undefined.

How pointer is still able to read data even after 'delete' operator?

Because the behaviour is undefined.