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From: "Anders Wirzenius" <anders.wirzenius@pp.qnet.fi>
Newsgroups: comp.lang.ada
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Subject: Re: In case statment? (was Re: is exception when others => null;
 smart?)
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Date: Wed, 30 Oct 2002 08:58:10 GMT
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"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