What does 'has virtual method … but non-virtual destructor' warning mean during C++ compilation?

Question

#include 
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    virtual int area ()
      { return (0); }
  };

cl         


        

Answer 1

It merely means that a code like

CPolygon* p = new CRectangle;
delete p;

... or whatever wrapping into whatever smart pointer, will essentially not behave correctly since CPolygon is not polymorphic on deletion, and the CRectange part will not be destroyed properly.

If you're not going to delete CRectangle and CPolygon polymorphicaly, that warning is not meaningful.