Re: Empty String confusion; Positive and Natural

["J-P. Rosen" <rosen@adalog.fr>]

Le 30/11/2021 à 13:17, Kevin Chadwick a écrit :
> I have a create function that returns a type RunOutput
> 
> I always get range check failed even with a string of multiple characters.
> 
> type RunOutput(LogLen, OutputLen : Natural) is record
>             LogStr : String(0..LogLen);
>             Output : String(0..OutputLen);
> ...
> end record;
> 
> I did have the following which works, so long as the string is not empty
> 
> type RunOutput(LogLen, OutputLen : Positive) is record
>             LogStr : String(1..LogLen);
>             Output : String(1..OutputLen);
> ...
> end record;
> 
> 
> P.s. I am not using exceptions with messages for log strings because I would rather use features that work with the zero footprint runtime as much as possible, where it makes sense.
> 
Since String is indexed by Positive (not Natural), the lower bound 
cannot be 0. OTOH, there is no check for bounds of empty arrays, 
therefore the following would work:

type RunOutput(LogLen, OutputLen : Natural) is record
              LogStr : String(1..LogLen);
              Output : String(1..OutputLen);

and you can have empty strings if Loglen or Outputlen is 0, without 
Constraint_Error. (It's precisely for that reason that there is no check 
of bounds of empty arrays).
-- 
J-P. Rosen
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