Re: Size and pack

[byhoe@greenlime.com (Adrian Hoe)]

tmoran@acm.org wrote in message news:<_umC7.74983$gT6.38373531@news1.rdc1.sfba.home.com>...
> > >           Log_Num      at 5 range 0 .. 31;
> > >           End_Byte     at 9 range 0 .. 7;
> > >           LRC          at 10 range 0 .. 7;
> > >        end record;
> > >     for Rx_Header_Data'size use 8*11;
> >
> > The problem was that this rep clause will not work, because Log_Num must
> > be aligned to a 4-byte boundary.  Some compilers will silently ignore your
> > rep clause, I believe GNAT will tell you it can't do it.
>   I tested it on Gnat 3.13p on Windows before posting, and Gnat was
> perfectly happy with it.  And ARM 13.5.1(23) says that "If component
> clauses are given for all components, the record representation clause
> completely specifies the representation of the type and will be obeyed
> exactly by the implementation."  That seems pretty unambiguous to me.

I tested the code on GNAT 3.13p-7 on Linux and it works!

Is having, "for Rx_Header_Data'size use 8*11;" better than pragma
pack? What is the rational? I suppose the former tells the compiler
exactly how many bytes/bits to be allocated for Rx_Header_Data.

Adrian Hoe