Question

I have an array that stores pointers to some objects and I want to know if it’s possible to free an object if you have only a pointer to it.
For example:

var test_form :Tform;
    p: Pointer;
vartest := Tform.create(nil);
p:=@vartest;

and if at runtime I only have p is it possible to free vartest?

Answer 1

The pointer p points to a TObject variable. That is, p is a pointer to a reference to an object. Therefore you need to de-reference p. Like this: p^. Because p is un-typed you need to cast it before calling the Free method.

So, putting this together, you can free the object like this:

TObject(p^).Free;

This will not modify the vartest variable though. It will merely destroy the object. If you want to set vartest to nil as well then you can do it like this:

FreeAndNil(p^);

FreeAndNil is an odd beast because it takes an un-typed parameter. That’s why you don’t need to cast to TObject.

To avoid all this casting it would be preferable to declare p as a typed pointer, e.g. ^TObject or ^TForm.