Category : Pascal Source Code
Archive   : P_PASCAL.ZIP
Filename : LISTTEST.PAS

(*$c+*)
PROGRAM listtest;
TYPE List_ptr = ^Node;
Node = RECORD
Number : Integer;
Next : List_ptr
END;
VAR First, Current : List_ptr;
i : Integer;
Marker : ^Integer;
BEGIN
{ NOTE: UPPERCASE IS NOT NECESSARY; I JUST LIKE TO USE IT. }
{ --------------------------------------------------------- }
{ In this system, whole blocks of memory are allocated }
{ and deallocated by MARK(^Integer) and RELEASE(^Integer). }
{ MARK() saves the heap state as an Integer pointer BEFORE }
{ allocation using NEW() begins, and RELEASE() restores the }
{ heap to that state after the memory allocated by NEW() is }
{ no longer needed. Note that MARK() and RELEASE() do not }
{ have to appear in the same procedure. All that is needed }
{ is for them to have the same Integer pointer parameter. }
{ ---------------------------------------------------------- }
{ Save the heap address in Marker: }
MARK(Marker);
{ Initialize the list and its pointers: }
NEW(First); First^.Next := NIL;
Current := First;
FOR i := 1 TO 30 DO
BEGIN
{ Add each number to the list; then add a node: }
Current^.Number := i;
NEW(Current^.Next);
Current := Current^.Next;
Current^.Next := NIL
END;
Current := First;
WHILE Current^.Next <> NIL DO
BEGIN
{ Write out the node value: }
WRITE('Current Number: ', Current^.Number : 2,
'; Current^.Next ','is ');
First := Current^.Next;
IF Current^.Next <> NIL THEN WRITE('not ');
WRITE('nil. Current^.Next^.Next is ');
IF Current^.Next^.Next <> NIL THEN WRITE('not ');
WRITELN('nil.');
{ USE OF RELEASE() BELOW MAKES THIS INSTANCE }
{ OF DISPOSE() UNNECESSARY, BUT NOT WRONG: }
DISPOSE(Current);
Current := First
END;
{ RETURN ALL OF THE NEW() NODES TO THE HEAP IN ONE }
{ OPERATION. DISPOSE() ABOVE HAS ALREADY DONE THIS }
{ WORK ONE NODE AT A TIME. IN THIS EXAMPLE, EITHER }
{ DISPOSE() OR RELEASE() IS REDUNDANT, BUT NOT BOTH: }
RELEASE(Marker)
END.