Re: Ada equivalent for C-pointer?

[Niklas Holsti <nobody@nowhere.fi>]

Martin Krischik wrote:
> Pascal Obry wrote:
> 
> 
>>Nick Roberts <nick.roberts@acm.org> writes:
>>
>>
>>>For example, if there is a C function defined thus:
>>>
>>>   int wibble(int *n);
>>>
>>>then in Ada you can declare:
>>>
>>>   function Wibble (Number: in out Interfaces.C.int);
>>>   pragma Import(C,Wibble,"wibble");
>>>
>>>and it should work. (Obviously, you must link the C functions in
>>>somehow.)
>>
>>I don't think so. Here Number will be passed by value, no? And you also
>>need the returned value ;)
> 
> 
> No all out and in out parameter are passed as pointer when pragma Import(C
> is used - thats unless you use C_Pass_By_Copy. I have written quite a lot
> of code interfaceing with C.

But according to LRM B.3(68), for an "in out" parameter of an 
*elementary* type (as here) the pointer that is passed to the C function 
is a pointer to a *temporary copy* of the parameter (here Number), not a 
pointer to the parameter itself. This may not be what the C function 
expects. For example, it would not make sense for "wibble" to save the 
pointer for later use.

(Perhaps this detail is explained in the Wiki page that was referenced. 
For some reason, I couldn't reach that page to read it.)

-- 
Niklas Holsti
Tidorum Ltd

niklas holsti tidorum fi
       .      @       .