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From: prichtmyer@yahoo.com (Peter Richtmyer)
Newsgroups: comp.lang.ada
Subject: Re: In case statment? (was Re: is exception when others => null;
 smart?)
Date: 30 Oct 2002 11:57:08 -0800
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"Anders Wirzenius" <anders.wirzenius@pp.qnet.fi> wrote in message news:<CaNv9.103$eX2.5358@read2.inet.fi>...
> "Peter Richtmyer" <prichtmyer@yahoo.com> wrote in message
> news:1b585154.0210291023.70af4929@posting.google.com...
> 
> > As the following example illustrates, it really depends upon
> > the compiler too. A "bad" value is handled differently as
> > shown:
> > -----------------------------------------------------------
> > with system;
> > with text_io;
> > procedure test is
> >
> >      a : character := character'val(2#11111111#);
> >      for a'size use 8;
> >      b : boolean;
> >      for b'address use a'address;
> >      for b'size use 8;
> >
> > begin
> >
> >    case b is
> >       when true =>
> >         text_io.put_line ("b is true");
> >       when false =>
> >         text_io.put_line ("b is false");
> >       when others =>
> >         text_io.put_line ("ObjectAda for Windows V7.1.105 "    &
> >                           "professional " edition gets here, " &
> >                           "and so does Rational Apex Ada 95 v. 4.0.0b");
> >    end case;
> >
> > exception
> >    when others =>
> >       text_io.put_line ("Gnat 3.14P gets here ");
> > end test;
> > ---------------------------------------------------------------
> 
> But if you move the assignment to after begin, the Gnat behaviour changes:
> ...
>      a : character;
>      for a'size use 8;
>      b : boolean := false;
>      for b'address use a'address;
>      for b'size use 8;
> 
> begin
>    a := character'val(2#11111111#);
> ...
> and the program execution ends up under when others =>
> 
> Anders

Were you using Gnat ? 

I tried it your way and still got the exception (which is the 
behavior I like). I also tried it your way, but with the 'a'
data definition of null char:

         a : character := character'val(0);
         for a'size use 8;
         b : boolean;
         for b'address use a'address;
         for b'size use 8;
    
     begin 
         a := character'val(2#11111111#); 

and still got the exception on Gnat. Which is what I would
expect (on Gnat).

Peter