peterhi@syma.sussex.ac.uk (Peter Hickman) (01/31/91)
I've got this problem with my Metrowerks Start Pak for the Macintosh, other
than the one I mentioned before. The example program below works fine, not the
best code in the world but then I am just a beginner.
MODULE test;
FROM Storage IMPORT ALLOCATE, DEALLOCATE;
FROM InOut IMPORT Write, WriteLn, WriteCard, WriteString, HoldScreen;
CONST
Start = 1;
Finish = 10;
TYPE
String = ARRAY [0..1] OF CHAR;
PtEl = POINTER TO Element;
Element = RECORD
Name : String;
Rank : CARDINAL;
Next : PtEl;
END;
VAR
First : PtEl;
i : CARDINAL;
PROCEDURE Insert( Rank : CARDINAL );
VAR
Ptr, Previous, q : PtEl;
BEGIN
ALLOCATE( q, SIZE( PtEl ) );
q^.Name[0] := 'f';
q^.Name[1] := 'F';
q^.Rank := Rank;
q^.Next := NIL;
Ptr := First;
WHILE (Ptr#NIL) AND (Ptr^.Rank<Rank) DO
Previous := Ptr;
Ptr := Ptr^.Next;
END;
IF First=NIL THEN
First := q;
ELSIF First=Ptr THEN
First := q;
q^.Next := Ptr;
ELSIF Ptr=NIL THEN
Previous^.Next := q;
ELSE
Previous^.Next := q;
q^.Next := Ptr;
END;
END Insert;
PROCEDURE Delete( Rank : CARDINAL );
VAR
Ptr, Previous : PtEl;
BEGIN
Ptr := First;
IF Ptr#NIL THEN
WHILE (Ptr#NIL) AND (Ptr^.Rank#Rank) DO
Previous := Ptr;
Ptr := Ptr^.Next;
END;
IF Ptr=First THEN
First := Ptr^.Next;
DEALLOCATE( Ptr, SIZE( PtEl ) );
ELSIF Ptr=NIL THEN
WriteString( " Rank not found" );
ELSE
Previous^.Next := Ptr^.Next;
DEALLOCATE( Ptr, SIZE( PtEl ) );
END;
END;
END Delete;
PROCEDURE WriteList;
VAR
Ptr : PtEl;
BEGIN
Ptr := First;
WHILE Ptr#NIL DO
Write( Ptr^.Name[0] );
Write( Ptr^.Name[1] );
Write( ' ' );
WriteCard( Ptr^.Rank, 4 );
WriteLn;
Ptr := Ptr^.Next;
END;
END WriteList;
BEGIN
First := NIL;
FOR i := Start TO Finish BY 2 DO
Insert( i );
END;
WriteList;
FOR i := Start+1 TO Finish BY 2 DO
Insert( i );
END;
WriteList;
FOR i := Finish TO Start BY -3 DO
Delete( i );
END;
WriteList;
HoldScreen;
END test.
So nothing execpected happens when it is run. Now make 3 small changes, first
to the String TYPE...
String : ARRAY [0..2] OF CHAR;
and add the following to Insert...
q^.Name[2] := 'x';
and this to WriteList...
Write( Ptr^.Name[2] );
It will compile Ok, but when it runs!!! The output characters, the Writes in
WriteList, print out junk and the CARDINAL Rank eventually ( even with in the
first three lines ) starts to contain incorrect values. 5423 for example.
Well what have I done wrong? I cant tell and I strongly suspect the compiler.
There are better PD compilers for the IBM than this if it is a bug. Also I was
thinking of upgrading to the next ( expensive ) version, the PSE. With this as
a track record I am mightily tempted to stick with C. Any comments on the PSE
version?
Peter Hi
Peter "You're doing computing as an ARTS degree!" Hickman
COGS U/G PH, University of Sussex, Falmer, Brighton, BN1 9QH
--------------------------------------- peterhi@uk.ac.sussex.syma ------------
"Lego is the Mechano of the intellectual cripple" - Aaron Sloman
--------------------------------------- peterhi@uk.ac.sussex.tsuna -----------
"More beer, more shouting, resistance is useless" - USTA barsldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University) (01/31/91)
ALLOCATE( q, SIZE( PtEl ) ); ^^^^ Aha! Try the following: ALLOCATE(q, SIZE(Element)); ^^^^^^^ I made this change and got the program to work just fine, both in its original form and with the changes you described. *Without* this fix, the program completely hung up my Mac. On breaking into MacsBug, it told me that the application heap had suffered major damage. No wonder... By the way, I use the MPW version of the Metrowerks compiler. I've only been using it for about four months, but so far it looks like the most bug-free of the various Mac compilers I've used. Lawrence D'Oliveiro fone: +64-71-562-889 Computer Services Dept fax: +64-71-384-066 University of Waikato electric mail: ldo@waikato.ac.nz Hamilton, New Zealand 37^ 47' 26" S, 175^ 19' 7" E, GMT+13:00
BJ020000@NDSUVM1.BITNET (Dave Mueller) (01/31/91)
This is a spool of what happens when it is run under Waterloo Mod-2.. The reason you start getting junk output could be 'cause you have wandered into unallocated territory.. Dave Ready; T=0.01/0.01 09:45:35 mw tst mod Waterloo Modula-2 (version 2) File 'TST MOD A0': 109 lines, modules imported 2, no errors fF 1 fF 3 fF 5 fF 7 fF 9 fF 1 fF 2 fF 3 fF 4 fF 5 fF 6 fF 7 fF 8 fF 9 fF 10 Bad free list. Traceback started for machine address 02ee28 Base Return Activation Register Address Record 02edda 02ee28 0ab7dc An 'addressing' exception has occurred Traceback started for machine address 02246a Base Return Activation Register Address Record 0a78a4 0a7998 0ab9e4 07e9c8 07ea26 0ab944 07e920 07e9a4 0ab90c 05fde4 05fe2a 0ab8e4 02343e 023466 0ab89c 023360 0233aa 0ab85c 028840 028872 0ab80c 02edda 02ee28 0ab7dc 05f01e 05f03a 0ab7b4 0d530c 0d556e 0ab784 TST.Delete at line 71 0d575a 0d58a8 0ab75c TST.Main at line 106 Traceback ended Ready; T=0.25/0.29 09:45:48 cons get
peterhi@syma.sussex.ac.uk (Peter Hickman) (02/01/91)
Thank you, and all those other people, for pointing out the cause of the problem. I have been staring vainly for many days at the code. I think that the problem was that the first program actually worked ( honest it did ) and I thus assumed it was the changes that introduced the error not just make them manifest. Thanks again. Peter 'Wally' Hi