Re: Interfacing to C library...

["Eric G. Miller" <egm2@jps-nospam.net>]

In <wcck7jwuf3v.fsf@shell01.TheWorld.com>, Robert A Duff wrote:

> "Eric G. Miller" <egm2@jps-nospam.net> writes:
> 
>> Seems Ada always passes records via C pointers. So, the above
>> doesn't work. Surely, there's a way!  Or do I need a C wrapper for
>> my Ada wrapper ;-(
> 
> This is a bug in the Ada 95 language, which, I must admit, is partly my
> fault.  It has since been "fixed" by adding pragma C_Pass_By_Copy.
> See AI-131.  This AI is approved by WG9, and is part of Corrigendum 1.
> 
> Perhaps "fixed" is an overstatement.  The bug has been patched with a
> kludgy pragma.

Missed that addition since I was looking at a copy of original RM...

Anyway, I don't think the C_Pass_By_Copy semantics quite work the way I
want them too (or, it's "kludgy").  All the "Set" routines of this C
library take C structs by copy while all the "Get" routines take pointers
and all routines return (in the function sense) a long integer status
code.  I've found if I use access types for the "Get" routines, then I 
have to worry about aliasing and need to use T'Unchecked_Access or I
need to dynamically create the objects via "new".  I think I like the
GNAT Import_Function()/Import_Procedure() pragmas a little better, 
since they facilitate finer control over the parameter passing method.
However, I'd rather not use compiler specific capabilities...