C binding issue

C binding issue

[kat-Zygfryd]

I want to write a binding for Lua 5.0
but I encountered a problem:

in lua.h we have this definition:

typedef const char * (*lua_Chunkreader) (lua_State *L, void *ud, size_t
*sz);

question:
how do I define such a callback in Ada, so that I could set
the value of *sz from within it.

Zygfryd

Re: C binding issue

[David Holm]

Something like this if I'm not mistaken (been a while since I used callbacks in Ada):

type size_t_ptr is access all Interfaces.C.size_t;
type Lua_Chunkreader_Proc is access function
   (L : Lua_State_Type; Ptr : System.Address; Sz : size_t_ptr) return
   Interfaces.C.Strings.chars_ptr;


//David Holm

On Sat, 10 May 2003 22:30:40 +0200
"kat-Zygfryd" <6667@wp.pl> wrote:

> I want to write a binding for Lua 5.0
> but I encountered a problem:
> 
> in lua.h we have this definition:
> 
> typedef const char * (*lua_Chunkreader) (lua_State *L, void *ud, size_t
> *sz);
> 
> question:
> how do I define such a callback in Ada, so that I could set
> the value of *sz from within it.
> 
> Zygfryd
> 
> 

Re: C binding issue

[kat-Zygfryd]

Thanks, I just thought that access types and C pointers
are incompatible.

Zygfryd

Re: C binding issue

[David C. Hoos]

"kat-Zygfryd" <6667@wp.pl> wrote in message
news:b9k0rv$bls$1@news.onet.pl...
> Thanks, I just thought that access types and C pointers
> are incompatible.

Questions of this type are answered in the Ada Reference manual.

This particular case is covered in B.3 (68), viz.:

An Ada access T parameter, or an Ada out or in out parameter of an
elementary type T, is passed as a t* argument to a C function, where t is
the C type corresponding to the Ada type T. In the case of an elementary out
or in out parameter, a pointer to a temporary copy is used to preserve
by-copy semantics.
>
> Zygfryd
>
>
> _______________________________________________
> comp.lang.ada mailing list
> comp.lang.ada@ada.eu.org
> http://ada.eu.org/mailman/listinfo/comp.lang.ada
>
>

Re: C binding issue

[Jeffrey Carter]

David C. Hoos wrote:
 > "kat-Zygfryd" <6667@wp.pl> wrote in message
 > news:b9k0rv$bls$1@news.onet.pl...
 >
 >> Thanks, I just thought that access types and C pointers are
 >> incompatible.
 >
 > Questions of this type are answered in the Ada Reference manual.
 >
 > This particular case is covered in B.3 (68), viz.:
 >
 > An Ada access T parameter, or an Ada out or in out parameter of an
 > elementary type T, is passed as a t* argument to a C function, where
 > t is the C type corresponding to the Ada type T. In the case of an
 > elementary out or in out parameter, a pointer to a temporary copy is
 > used to preserve by-copy semantics.

This refers to access parameters; the example used a named access type.
These can be made C-compatible by applying pragma Convention to them:

type Void_Ptr is access all Integer;
pragma Convention (C, Void_Ptr);

-- 
Jeff Carter
"Beyond 100,000 lines of code you
should probably be coding in Ada."
P. J. Plauger

Re: C binding issue

[Sergey Koshcheyev]

"David Holm" <david@realityrift.com> wrote in message
news:20030511004621.63e7fbd9.david@realityrift.com...
> Something like this if I'm not mistaken (been a while since I used
callbacks in Ada):
>
> type size_t_ptr is access all Interfaces.C.size_t;
> type Lua_Chunkreader_Proc is access function
>    (L : Lua_State_Type; Ptr : System.Address; Sz : size_t_ptr) return
>    Interfaces.C.Strings.chars_ptr;
>
>
> //David Holm

I think it is possible to just use an out parameter of type size_t, instead
of complicating matters with pointers. Or is there some subtle problem with
this approach?

Sergey.

Re: C binding issue

[kat-Zygfryd]

"Sergey Koshcheyev" <serko84@hotmail.com> wrote in message
news:b9lolp$1mnf$1@ns.felk.cvut.cz...
> I think it is possible to just use an out parameter of type size_t,
instead
> of complicating matters with pointers. Or is there some subtle problem
with
> this approach?
>
> Sergey.

It's a function not a procedure.

Zygfryd
>

Re: C binding issue

[David C. Hoos]

"Sergey Koshcheyev" <serko84@hotmail.com> wrote in message
news:b9lolp$1mnf$1@ns.felk.cvut.cz...
>
> "David Holm" <david@realityrift.com> wrote in message
> news:20030511004621.63e7fbd9.david@realityrift.com...
> > Something like this if I'm not mistaken (been a while since I used
> callbacks in Ada):
> >
> > type size_t_ptr is access all Interfaces.C.size_t;
> > type Lua_Chunkreader_Proc is access function
> >    (L : Lua_State_Type; Ptr : System.Address; Sz : size_t_ptr) return
> >    Interfaces.C.Strings.chars_ptr;
> >
> >
> > //David Holm
>
> I think it is possible to just use an out parameter of type size_t,
instead
> of complicating matters with pointers. Or is there some subtle problem
with
> this approach?
Out mode parameters are not allowed for functions.
>
> Sergey.
>
>
> _______________________________________________
> comp.lang.ada mailing list
> comp.lang.ada@ada.eu.org
> http://ada.eu.org/mailman/listinfo/comp.lang.ada
>
>

Re: C binding issue

[Antonio Vargas]

Hi

I was thinking in a similar project. Do you intend to make the binding
public under GNU?

"kat-Zygfryd" <6667@wp.pl> wrote in message news:<b9jni3$mh0$1@news.onet.pl>...
> I want to write a binding for Lua 5.0
> ...
> Zygfryd

Antonio Vargas
Barcelos - Portugal