C ++中的new，delete和subclasses

TextItem

XObject

  TextItem *textItem = new TextItem();
  XObject *xItem = textItem;
  delete textItem;

  TextItem *textItem = new TextItem();
  XObject *xItem = textItem;
  delete xItem;

delete

_BLOCK_TYPE_IS_VALID

XObject *xItem = textItem;
delete xItem;

class XObject
{
    public:
       virtual ~XObject();
     //^^^^^^ this makes virtual destructor
};

XObject

virtual

struct XObject
{
    // now deleting derived classes
    // through this base class is okay
    virtual ~XObject() {}
};

struct TextItem : XObject {};