Casting a CRect object/pointer to a CObject pointer

I am trying to use the following line of code to cast a CRect to a CCbject:


CObject* pHint=DYNAMIC_DOWNCAST(CObject, mRects[x][y]);

but I get an error stating "none of the two overloads can convert parameter 2 from type 'Class CRect*'"

I need this to use in CView OnUpdate so that I only redraw part of the screen.

CRect is not derived from CObject.
But you can use brute pointer casting:
UpdateAllViews(NULL, 0L, reinterpret_cast<CObject*>(&rcUpdate));

Just remember to cast it back in OnUpdate.

A tip: if you're ever going to use a selfmade struct UPDATE_PARAMS (or something like that), you may want to add a CObject* operator to the struct:

Code:

---

struct UpdateParams
{
  int type;
  CRect rcUpdate;
  long id;
  operator CObject*() { return reinterpret_cast<CObject*>this; };
};

// somewhere:
UpdateParams up;
// set members
UpdateAllViews(this, 0L, up);

---

This makes it easier to write and read, and since you don't use UpdateParams anywhere else (hopefully), it isn't a type safety hazard IMO.