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

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 27 Cze, 18:11, Keith Thompson <ks...@mib.org> wrote:

> > Ada *cannot* guarantee that Interfaces.C.C_Float is the *right* float,
> > because it does not verify how the C code was compiled and there is a
> > lot of freedom given to C implementers in this area.
> > Same for all other types.
>
> 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?

Consider a C compiler that has a switch that selects the
representation for fundamental types. It is not uncommon.
I can have *the same* program compiled twice by *the same* compiler
and the two versions will differ in representation of their
fundamental types.

How Ada implementation can guarantee anything in this area?

> Look at it this way.  You have the choice of using
> Interfaces.C.C_Float, which (assuming the Ada implementation gets it
> right), is guaranteed to match C's float

There is no way to guarantee that. The only way is to name two
compilers and say that *they* are compatible with this and that
switches. But then - there is no added value from Interfaces.C.XXX.

> Why would you even
> consider using Float?

Because the amount of magic and handwaving in interfacing is the same
as with Interfaces.C.C_float, but it is less typing. :-)

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com