Re: CONSTRAINT_ERROR - why?

["James S. Rogers" <jimmaureenrogers@worldnet.att.net>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message
news:wccof7obef4.fsf@shell01.TheWorld.com...
> "James S. Rogers" <jimmaureenrogers@worldnet.att.net> writes:
>
> > "Alfred Hilscher" <Alfred.Hilscher@t-online.de> wrote in message
> > news:3DFB7841.F898C02@t-online.de...
> > > This program raises exception CONSTRAINT_ERROR for the second
> > > assignment. It happens with GNAT 3.13p and 3.14p (on windows).
> > >
> > > Can someone explain why? Is this a compiler error or do I
misunderstand
> > > something?
> > >
> > > I would expect that the computation is done first and then the result
> > > (33 which is successfully assigned the statement before) is assigned.
> > > But it seems that the size (=264) is assigned before the division is
> > > executed.
>
> The 'Size is implicitly converted to BYTE, and then the "/" operator of
> type BYTE is used.  You want to do the division in, say, Integer,
> and then explicitly convert to BYTE, like:

This is what I expected.
I checked GNAT 3.15p just as a sanity check.

>
>     ... := BYTE(Integer'(Fac_Conf_Struct'Size / 8));
>
> > > with Interfaces.C; use Interfaces.C;
> > >
> > > with Text_IO; use Text_IO;
> > >
> > > procedure Test is
> > >
> > >     type    BYTE       is new Interfaces.C.Unsigned_Char;
> > >
> > >     type Fac_Conf_Struct is
> > >       record
> > >         Struct_Length     : BYTE;
> > >         Filler            : String (1..32);
> > >       end record;
> > >
> > >
> > >   X : Fac_Conf_Struct;
> > > begin
> > >   Put_Line ("Struct_Length=" & Integer'Image (Fac_Conf_Struct'Size /
> > > 8));
> > >   X.Struct_Length := 33;
> > >   X.Struct_Length := (Fac_Conf_Struct'Size / 8);  -- Value is 33, too.
> > > But - constraint_error is raised
> > > end Test;
> >
> > It compiles and runs without exception using GNAT 3.15p.
>
> Perhaps checking is turned off?
>
I checked that too. Nope.
Checking was not turned off.

Jim Rogers