Re: Problem using Ada.Text_IO.Modular_IO

[Adam Beneschan <adam@irvine.com>]

On Jul 9, 9:52 am, jujo...@googlemail.com wrote:
> Dear All,
>
> I'm tying to print variables of a defined modular type to the standard
> io and a file.
> The type I'm working with is: type Unsigned is mod 2**64;
>
> Therefore I define a modular_io package to do this:
> package mio is new ada.text_io.modular_io(usigned);
>
> However, when compile my little test program (using gnatmake -gnato),
> the compiler tells me that a "Constraint Error" will be raised at
> runtime. So I tried it with only 63 bit (mod 2**63), which works fine
> with the GNAT 4.3.1 (20080420) on a 32bit Ubuntu-Linux machine.
>
> ----------- test program -----------
> with ada.text_io; use ada.text_io;
> procedure test is
>         type Unsigned is mod 2**64;
>         package M_IO is new Ada.Text_IO.Modular_IO (Unsigned);
>         u : Unsigned := -1;
> begin
>         m_io.put(Item =>  u, Width =>  20, Base  => 16);
> end;
> -----------------------------------------
>
> I guess that this is a bug. However, what can I do instead of this, to
> get 64 bit words printed as hex, octal and binary?

Here's an even simpler workaround than my last suggestion: After the
declaration of "u", just add this:

  pragma Volatile (u);

This prevents the compiler from thinking it knows what "u" is going to
hold, and everything works fine.  Of course, in real-life code, you're
a lot more likely to using "put" on a value that the compiler won't be
able to determine at compile time, so the above bug isn't going to
appear anyway and you don't need a workaround.

                               -- Adam