Fwd: crashing while killing list - Gpc

11 Jul 2001


      *Groan*  once again, programing is primarily a lesson in humility.
rpewing@lbl.gov wrote:
...
I just upgraded to a more recent version of GPC, 2001something.  I don't
know if that's the root cause, but I'm having trouble killing a linked
list.  I get a page fault or a GPF (I'm running under win98) when trying
to delete the last or next to last record.  I've marked the line named
in the call traceback.
..
I forgot to initialize the pointer to Nil.  I think BP did this for me, so I got 
out of the habit.  A corrected version is below.
Toby
...

Program ListTest;
type
  PRec   = ^Rec;
  Rec    = record
    ri   : integer;
    Next : PRec;
  end;
var
  Root   : PRec;
  i      : integer;
{----------}
Procedure LWipe(var Root : PRec);
var point : PRec;
begin
  while (Root <> Nil) do begin
    write('deleting ', root^.ri, ' ');
    point := Root;
    Root := Root^.next;
    Dispose(point);
  end;
end;
{----------}
Procedure LInsert(var num  : integer;
                  var Root : PRec);
{insert a new record at the *front* of the list}
var
  Site        : Rec;
  temp        : PRec;
begin
  with Site do begin
    ri := num;
    next := Nil;
  end;
  if Root = Nil then begin                     {starting the list}
    New(Root);
    Root^ := Site;
  end else begin                               {list already exists}
    New(temp);                                 {get new memory}
    temp^ := Site;                             {move memory}
    temp^.next := Root;                        {repoint pointers}
    Root := temp;
  end;
end;                                           {LInsert}
{----------}
Begin
Root := Nil;       {<< the line I forgot}
...
for i := 1 to 100 do LInsert(i, Root);
  LWipe(Root);
End.