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From: Russell Whitaker
Subject: (gpc-20060215) fillchar bug
Date: 2 Apr 2006, 12:36:14

On Sun, 2 Apr 2006, Waldek Hebisch wrote:

> Russell Whitaker wrote:
>> hi
>>
>> The following compiles but no longer works:
>>
>> program fill;
>> var
>>    s: string(10);
>> begin
>>    fillchar(s[1], s.capacity, ' ');
>>    writeln("ok");
>> end.
>>
>
> Do you get a message about out of range value? If yes then strictly
> speaking the compiler is right: s is uninitialized, so its length
> is set to 0, hence access to s[1] is illegal (out of range). In fact,
> I see another problem with the code above: s[1] is a single char,
> but fillchar acceses also s[2],... which strictly speaking is another
> out of bound access (but ATM compiler can not detect this problem).
>
> I would say that fillchar is incompatible with range checking (at least
> now). ATM you can say:
>
>  setlength(s, 10);
>  fillchar(s[1], s.capacity, ' ');

Thanks. Adding setlength did the job.

> and I will work. However, I think that the correct way is:
>
>  setlength(s, s.capacity);
>  fillchar(s[1..length(s)], length(s), ' ');

shouldn't that be
    fillchar(s[1], length(s), ' ');  ?

> In the future we may teach the compiler that fillchar is special, so
> it applies to it relaxed range checking rules, but that would
> require non-trivial changes in the compiler.
>
perhaps something like:
   if ( start+count ) GT s.capacity then out-of-range-error
   if ( start+count ) GT length(s) then setlength( s, start+count)

Also, if the fillchar line is written as
   fillchar( s, count, Afillchar );
it should default to
   fillchar( s[1], count, Afillchar );

current behavior fillchar( s, ... overwrites length (and capacity?) 
fields.

   Russ

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