Re: CONSTRAINT_ERROR - why?

[Robert A Duff <bobduff@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:

    ... := 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?

- Bob