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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: ADA.STRINGS.INDEX_ERROR : a-strunb.adb:782
Date: Mon, 15 Jan 2018 09:29:39 +0100
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Date: 2018-01-15T09:29:39+01:00
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On 15/01/2018 02:18, Mehdi Saada wrote:
> This if statement exactly, seems to raise
> "ADA.STRINGS.INDEX_ERROR : a-strunb.adb:782"(No indication of line, so I can't know more).

There is a list of funny numbers following the exception message. Pass 
that list to

    addr2line --exe=<program-name> <funny-numbers>

That will give you the stack trace.

> What does this exception means ? You can see there's no string type variable to be accessed, here.
> CHAINE is of UNBOUNDED_STRING type. LA_PILE is a stack of characters, EMPILER means "putting on the stack's top" in french.
> 
> if IS_BASIC(ELEMENT(CHAINE,IND)) then
>     EMPILER(LA_PILE,ELEMENT(CHAINE,IND));
> else DELETE(CHAINE, IND,IND);
> end if;
> 
> It's enclosed in:
> for Ind in 1..Length(CHAINE) loop
>          begin
>              if IS_BASIC(ELEMENT(CHAINE,IND)) then
>                      EMPILER(LA_PILE,ELEMENT(CHAINE,IND));
>              else DELETE(CHAINE, IND,IND);
>              end if;
>           end;
> end loop;

When deleting elements of a list by position the loop must run positions 
in reverse:

    for Ind in reverse 1 .. Length (CHAINE) loop
       ...
       delete at Ind
       ...
    end loop;

That will keep the positions straight. Position /= index, BTW.

However, deleting characters from a string almost never has sense. You 
probably should reconsider the algorithm.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de