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

["Peter C. Chapin" <pchapin@sover.net>]

Maciej Sobczak wrote:

>> No, Ada can't guarantee it directly.  Instead, Ada requires the
>> implementation to guarantee it.
> 
> And how the implementation can guarantee it without mandating the
> representation on the C compiler?

My understanding is that the interfacing to C is only really meaningful 
if the Ada compiler is in some way associated with a corresponding C 
compiler (for example, created by the same vendor). In such a case, the 
Ada side selects appropriate types in Interfaces.C to match the types 
used by the *associated* C compiler. If the C compiler supports multiple 
representations of its basic types, well, that's interesting... the Ada 
side could do the same (compiler option?). The point is that the two 
compilers are working together.

I never assumed that Interfaces.C could somehow magically allow any Ada 
compiler to work with any C compiler. I'm surprised that some people 
seem to expect that. However, when I call C code compiled with gcc using 
GNAT, I would expect Interfaces.C to specify the right types because gcc 
and GNAT are closely related compilers. Furthermore if I then move my 
Ada/C program to another Ada/C compiler suite, I would expect it to 
continue to work (if I'm using Interfaces.C properly, etc, of course).

Peter