Mixed languages and frustration.

Mixed languages and frustration.

[Freejack]

Alright, so I'm sitting here trying to juggle between C pointers and Ada
access types/allocators, with moderate success. And I start wondering to
myself "How many people on comp.lang.ada nearly blow a fuse when doing
the same thing?"

So I'm curious, are juggling the two types(pun intended) as chaffing for
you as it is for me? Maybe I just dont know enough about the Interfaces
libs yet.

Also, I'm gonna post up my project to a hosting site once it looks
remotely sane. Then you'll see just how crummy a developer I really
am.(Something which is becoming abundantly clear to me as I progress.)

Hope nobody barfs. Heh.

Freejack

Re: Mixed languages and frustration.

[Robert I. Eachus]

Freejack wrote:
> Alright, so I'm sitting here trying to juggle between C pointers and Ada
> access types/allocators, with moderate success. And I start wondering to
> myself "How many people on comp.lang.ada nearly blow a fuse when doing
> the same thing?"
> 
> So I'm curious, are juggling the two types(pun intended) as chaffing for
> you as it is for me? Maybe I just dont know enough about the Interfaces
> libs yet.

No, eventually you will learn to do it the way we do.  Create a package 
that contains all the C cruft and hides it from anyone using the 
package.  The basic rule is that if you are using C pointers, the 
visible Ada abstraction should be a private--or limited private type. 
That way all the headaches are confined to one section of code.

Oh, and don't forget that you can have several Ada subprograms (usually 
with the same name) that correspond to a single C function.  Also often 
you want to have the Ada "wrapper" subprogram translate -1, etc. return 
values as exceptions.  This is expecially true with those C functions 
that either use the storage your pass them, or allocate storage if the 
pointer passed is null.  Treating that on the Ada side as a procedure 
and a function that happen to have the same name is often the right 
binding.  (And even then, the wrapper function may copy the return value 
when the C function does the allocation into an Ada structure, free the 
pointer than return the structure.  Sounds a lot more complex than it is.)

-- 
                                                     Robert I. Eachus

"Quality is the Buddha. Quality is scientific reality. Quality is the 
goal of Art. It remains to work these concepts into a practical, 
down-to-earth context, and for this there is nothing more practical or 
down-to-earth than what I have been talking about all along...the repair 
of an old motorcycle."  -- from Zen and the Art of Motorcycle 
Maintenance by Robert Pirsig

Re: Mixed languages and frustration.

[sk]

Freejack <user@nospam.net>:

 > Alright, so I'm sitting here trying to juggle between C '
 > pointers and Ada access types/allocators, with moderate
 > success ...

What exactly do you mean by "juggling" between C-pointers and
Ada access types ?

Are you :

1) Using Ada and trying to apply your C pointer knowledge ?

2) Using Ada bindings to "C" interfaces ?

Once you describe what you are trying to do, you might get
some useful responses from cla.

-- 
-------------------------------------------------
-- Merge vertically for real address
--
--     s n p @ t . o
--      k i e k c c m
-------------------------------------------------

Re: Mixed languages and frustration.

[Wes Groleau]

If you _really_ want to to pass an Ada access value
directly to a C pointer, without the precautions
and engineering suggested by others...

   If XYZ is an Ada access type, then

   the C pointer to the heap object is  XYZ.all'Address

-- 
Wes Groleau
   ----
   The man who reads nothing at all is better educated
   than the man who reads nothing but newspapers.
                             -- Thomas Jefferson

Re: Mixed languages and frustration.

[Freejack]

On Tue, 14 Oct 2003 17:53:13 -0400, Wes Groleau wrote:


> If you _really_ want to to pass an Ada access value directly to a C
> pointer, without the precautions and engineering suggested by others...
> 
>    If XYZ is an Ada access type, then
> 
>    the C pointer to the heap object is  XYZ.all'Address
 
I dont mind the precautions. I was just ranting. I'm actually making
pretty good headway. I just sometimes get tripped up from time to time.

Freejack

Re: Mixed languages and frustration.

[Jeffrey Carter]

Wes Groleau wrote:
> 
>   If XYZ is an Ada access type, then
> 
>   the C pointer to the heap object is  XYZ.all'Address

This will usually work, but is not guaranteed to. System.Address is a 
private type because there are systems where an address doesn't map 
neatly to an integer, as a C pointer must.

-- 
Jeff Carter
"Death awaits you all, with nasty, big, pointy teeth!"
Monty Python & the Holy Grail
20

Re: Mixed languages and frustration.

[Wes Groleau]

Jeffrey Carter wrote:
> Wes Groleau wrote:
>>   If XYZ is an Ada access type, then
>>
>>   the C pointer to the heap object is  XYZ.all'Address
> 
> This will usually work, but is not guaranteed to. System.Address is a 
> private type because there are systems where an address doesn't map 
> neatly to an integer, as a C pointer must.

However, contrary to a popular belief among
Ada programmers, unchecked conversion from
access to address will usually NOT work on
most systems.

-- 
Wes Groleau
   "Grant me the serenity to accept those I cannot change;
    the courage to change the one I can;
    and the wisdom to know it's me."
                                -- unknown

Re: Mixed languages and frustration.

[Steve]

"Freejack" <user@nospam.net> wrote in message
news:pan.2003.10.14.20.30.30.107171.1209@nospam.net...
> Alright, so I'm sitting here trying to juggle between C pointers and Ada
> access types/allocators, with moderate success. And I start wondering to
> myself "How many people on comp.lang.ada nearly blow a fuse when doing
> the same thing?"
>
> So I'm curious, are juggling the two types(pun intended) as chaffing for
> you as it is for me? Maybe I just dont know enough about the Interfaces
> libs yet.

I too find it frustrating at times dealing with interfaces.  This is not
unique to interfacing between Ada and C.  I have the same frustrations
interfacing with Delphi.

My greatest frustration usually comes from poorly documented interfaces
where some behaviour is presumed.  Sometimes it gets really ugly when
tasking (or multiple threads) is involved.

Steve
(The Duck)

> Also, I'm gonna post up my project to a hosting site once it looks
> remotely sane. Then you'll see just how crummy a developer I really
> am.(Something which is becoming abundantly clear to me as I progress.)
>
> Hope nobody barfs. Heh.
>
> Freejack

Re: Mixed languages and frustration.

[Stephen Leake]

Freejack <user@nospam.net> writes:

> Alright, so I'm sitting here trying to juggle between C pointers and Ada
> access types/allocators, with moderate success. And I start wondering to
> myself "How many people on comp.lang.ada nearly blow a fuse when doing
> the same thing?"

I try to avoid code in C at all costs.

When I do need to pass pointers to C, I just use 'Address on the Ada
side. It's not guarantteed portable, but neither is the C code, so
it's good enough. And it's far easier to get right, and usually more
efficient, than messing with Interfaces.C pointer stuff.

-- 
-- Stephe

Re: Mixed languages and frustration.

[Ole-Hjalmar Kristensen]

>>>>> "SL" == Stephen Leake <Stephe.Leake@nasa.gov> writes:

    SL> Freejack <user@nospam.net> writes:
    >> Alright, so I'm sitting here trying to juggle between C pointers and Ada
    >> access types/allocators, with moderate success. And I start wondering to
    >> myself "How many people on comp.lang.ada nearly blow a fuse when doing
    >> the same thing?"

    SL> I try to avoid code in C at all costs.

    SL> When I do need to pass pointers to C, I just use 'Address on the Ada
    SL> side. It's not guarantteed portable, but neither is the C code, so
    SL> it's good enough. And it's far easier to get right, and usually more
    SL> efficient, than messing with Interfaces.C pointer stuff.

    SL> -- 
    SL> -- Stephe

Yes. And in the same spirit, to go in the opposite direction, if you
have got a C pointer, just declare an Ada object and use an address
rep clause to put it where the pointer points. Same caveats apply.

-- 
If you are going to shoot, shoot, don't talk.
Il Brutto