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

[Keith Thompson <kst-u@mib.org>]

Robert A Duff <bobduff@shell01.TheWorld.com> writes:
> Keith Thompson <kst-u@mib.org> writes:
> > Interfaces.C.C_Float, which (assuming the Ada implementation gets it
> > right), is guaranteed to match C's float, or of using Float, which has
> > no such guarantee (but saves a little typing).  Why would you even
> > consider using Float?
> 
> You might have a program that uses Float all over the place,
> and you want to add some interface to C in one tiny corner
> of that program.  You might be tempted to use Float at the
> interface to C in order to avoid a lot of type conversions.
> 
> It's a pretty good bet that Ada's Float and Ada's Interfaces.C.C_Float,
> and C's float are all represented the same.  If you're using GNAT,
> I think the documentation guarantees that.
> 
> But you're right -- the "right" way to interface to C is to use the
> types in Interfaces.C, and use pragma Convention when you declare
> your own types.

And if you take the shortcut of assuming that Float and C_Float are
the same, and your program is later compiled on a system where they're
not, you're not likely to get an error message.  In the worst case,
you'll just get subtly wrong answers.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"