Re: Ada array vs C pointer (call by reference)

[Adrian Hoe <abyhoe@gmail.com>]

On Jun 28, 6:54 am, "Jeffrey R. Carter"
<spam.jrcarter....@spam.acm.org> wrote:
> Adrian Hoe wrote:
>
> > Can I use Float instead of Interfaces.C.C_Float?
>
> You can use anything you want: Boolean, Duration, a task type, ...
>
> But if you want to be sure it will work, you'll use Interfaces.C.C_Float.
>
> > Why use Interfaces.C.Int, Interfaces.C.C_Float since they are all new
> > declaration of Ada types.
>
> > I know it is for readability and maintainability but the question is
> > logical as the declaration in Interfaces.C is just merely creating a
> > new Ada type with a new name, unless there is pragma Convention
> > statement after every such declaration in Interfaces.C.
>
> I suggest you read ARM B.3. There you'll find, "Each of the types declared in
> Interfaces.C is C-compatible."
>
> > Wouldn't it be better to write as such?
>
> > type C_Data is array (Positive range <>) of Float;
> > pragma Convention (C, C_Data);
>
> Not if you want to be sure it will work.
>
> > Is PWM_Data passed as pointer to pwmRead?
>
> B.3 also contains, "An Ada parameter of an array type with component type T, of
> any mode, is passed as a t* argument to a C function, where t is the C type
> corresponding to the Ada type T."


Ok. Ada somewhat guarantees a safe environment of its own. The
ultimate concern is how Ada (or we) can guarantee a safe interfacing
to C?

Like those previous posts in this thread (by Maciej, Keith, et al), it
depends on compiler implementation. The question is, the C library
(which I am interfacing with) is compiled by unknown C compiler with
unknown switches and the author cannot be contacted. The only
documentation I have is the C header file. Can Ada safe implementation
guarantee a safe interface in this case? Or rather, how Ada can
guarantee a safe interface?

This does not limit to float * but can be anything else. The reason I/
we ask this (stupid) question is that I want to eliminate undesired
results because the results returned will be difficult to trace/prove
for correctness.
--
Adrian Hoe
http://adrianhoe.com