Re: How to access this package written in C?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

resander <kresander@gmail.com> writes:

> On Apr 22, 10:12�pm, Keith Thompson <ks...@mib.org> wrote:
>> There is no guarantee that an int can hold the value of an address,
>> and there are common systems (including Linux systems) where it
>> can't. �Worse, you're not likely to get a warning if you convert
>> a pointer to int, even if there's a loss of information.

Why?  I'd think if int is smaller than whatever*, then
a cast to int clearly deserves a warning.

>> The right type for this parameter is void* (which is roughly
>> analogous to Ada's System.Address).

Yeah, roughly.  System.Address is somewhat lower level than
C's void*.

> Thank you all for your concerns about using an int for passing an
> address. The interface actually uses a void * (could also be char * as
> that is what is needed), but I changed it for the post because I
> thought an all-int interface would be easier to handle at the Ada-to-C
> boundary. That seems to have backfired!

You should look at section B (especially B.3) of the Ada RM.
There's a type char_star you can use.

There's no void_star.  I'm not sure why -- probably this
part of Ada predates void* in C, and nobody bothered
to upgrade Ada to match the new C.

> Q1.
> Addresses are not negative. How do I output a System.Address?

In GNAT, there is a function System.Address_Image.
Look at the file s-addima.ads in your GNAT
distribution.

Beware: this is not portable to other Ada compilers.

- Bob