Re: Calling Ada from C

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Hannibal Holm writes:
> I have a slight problem trying to call an Ada function from a C
> function. I need to pass in an unconstrained array to the Ada
> function. The problem is how I specify the size.
>
> This is probably very simple, but I am more or less just getting
> started with Ada, comming from a C-background.
>
> My code yealds warnings like this (when compiled with GNAT):
>
> foo.ads:50:23: warning: type of argument "Insert_C.Packet" is
> unconstrained array
> foo.ads:50:23: warning: foreign caller must pass bounds explicitly
>
> I have been searching a lot in order to figure out what to do about
> this, but all the FFI documentation is for calling C-functions from
> Ada, and some very simple examples of how to call ada functions that
> take primitive arguments (ints, and similar items).
>
> Anyone who know how to pass in the bounds explicitly?

You have three options:
- pass two extra parameters, First and Last
- pass the length
- declare that the lower bound is some fixed "known" value and pass the
  upper bound (this is subtly different than the above...)

-- 
Ludovic Brenta.