Test if memory pointer is valid?

Is there a way or technique for knowing if a pointer points to memory that
has been freed ?

The example is a little silly, in reality, P & Q might fields in instances
of disparate classes

P: Pointer;
Q: Pointer;
BuffSize: Integer;

BuffSize := 32000;
GetMem(P, BuffSize);
F.Read(P^,BuffSize);
....
Q := P;
....
if ...
FreeMem(P,BuffSize)
....

if [ Q points to memory that has not been freed ] // what technique, if
any, can test this?
FreeMem (Q,BuffSize);

end;

--
Richard A. DeVenezia


.

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