Re: [slang-users] Re: How to handle a variable reference passed to a C function?

["John E. Davis" <jed@xxxxxxxxxxx>]

Hi Sebastian,

In the C API, SLang_Ref_Type is mainly there to support callback
functions and to assign values to references.  It was never designed
as a mechanism for passing data into C functions.

Also, Mike Noble created slirp, so he deserves full credit for it.

I am happy that you were able to find a solution.

Thanks,
--John

Sebastian Gniazdowski <sgniazdowski@xxxxxxxxx> wrote:
> I couldn't resolve the problem and I've found following mention in
> slirp-…/examples/kitchensink/test.sl (line 80) that C-side fetching of an
> input reference variables is not supported:
>
> % The next call attempts a NULL ptr reference, since the public S-Lang C api
> % doesn't provide a way of dereferencing (obtaining the value of) a S-Lang
> ref
>
> So I've went a different path – #argmap(out) one parameter so that the
> function returns 2 values, and also use a normal (not reference) parameter
> pass in value. So the call now looks like:
>
> variable start_search_pos = 5;
> (str, position) = afunc(start_search_pos, DIRECTION_LEFT);
>
> and it's a better solution than the original, because the "start_search_pos"
> isn't exactly the same as the "start_pos" that's being returned – the
> function looks for a adjacent word at given position and in given
> direction, and it returns the starting position of the found word.
>
> So the API is now cleaner :)
>
> BTW. thanks for creating Slirp and S-Lang :)
>
>
> On Thu, 22 Jul 2021 at 09:42, Sebastian Gniazdowski <sgniazdowski@xxxxxxxxx>
> wrote:
>
>> Hi,
>> I want to have additional out parameters for a function, so I do:
>>
>> variable in1=1, in2=2, in3out = 3'
>> afunc(in1,in2,&in3out);
>>
>> Then, on the C side I do:
>>
>> void afunc(long in1, long in2, long *in3out)
>> {
>>     log("inout parameter holds value %li", *in3out);
>> }
>>
>> And generate the glue code via slirp.
>>
>> However, the value printed by log() function / passed to the function by
>> the third, pointer parameter is 0. Why?
>>
>> --
>> Best regards,
>> Sebastian Gniazdowski
>>
>
>
> -- 
> Best regards,
> Sebastian Gniazdowski
_______________________________________________
For list information, visit <http://jedsoft.org/slang/mailinglists.html>.