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> -----Original Message-----
> From: blackbox{([at]})nowhere.xy> Behalf Of Rex Couture
> Sent: Wednesday, 10 October 2007 12:44 AM
> To: BlackBox Mailing List
> Subject: [BlackBox] - Why does this compile?
>
>
> At 01:42 AM 10/9/2007, Bernhard Treutwein wrote:
> >it compiles for the same reason why the following
> >compiles:
> >
> >PROCEDURE Crash*;
> >VAR i: INTEGER; a: ARRAY 4 OF REAL;
> >BEGIN
> > i:= -800;
> > a[i]:= i
> >END Crash;
>
>
> Yes, thanks. It just came as a surprise that it does
> not even attempt to check array bounds at compile time.
>
> Rex Couture
>
I am not surprised that the compiler would find it difficult to check
array bounds when the index value is a *variable*.
However, I would have been surprised if the compiler did not check the
array bounds when the index value is a *constant* as it should be able
to evaluate the value of the constant at compile time. e.g.
PROCEDURE Crash*;
CONST i: -800;
VAR a: ARRAY 4 OF REAL;
BEGIN
a[i]:= i
END Crash;
Fortunately, BlackBox *does* report this as an error at compile time.
If you need some more insight into what the compiler can be / can't be
expected to be able to do when checking array bounds, refer to Chapter
10.3 'Index Variables and Record Fields' of Niklaus Wirth's Compiler
Construction book. You can download a copy from:
http://www.oberon.ethz.ch/books.html
Regards,
Chris Burrows
CFB Software
http://www.cfbsoftware.com/gpcp
--- BlackBox
--- send subject HELP or UNSUBSCRIBE to blackbox{([at]})nowhere.xy
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Received on Wed Oct 10 2007 - 04:38:49 UTC