Le mercredi 08 juillet 2015 à 04:56 -0700, Panagiotis Mamatsis a écrit
:
> On Wednesday, July 8, 2015 at 2:45:17 PM UTC+3, Milan Bouchet-Valat
> wrote:
> > Le mercredi 08 juillet 2015 à 03:28 -0700, Panagiotis Mamatsis a
> > écrit
> > :
> > > Hello to everyone,
> > > i am a n00b in Julia language and i am trying to understand
> > the
> > > way to call code written in C via shared libraries. I have
> > started
> > > with a 'small scale' case into which i am trying to call a
> > function
> > > which returns void but accepts a pointer to an Integer. When i
> > > perform the call from a Julia script the number returned back is
> > "0"
> > > and not the one i am expecting...when i am calling the C function
> > the
> > > argument i am supplying is Ptr{Cint}. Can somebody please explain
> >
> > > what i am missing ?
> > Showing the code you tried would be helpful.
> >
> > Anyway, this precise case is documented. Let us know whether that's
> >
> > enough to fix your problem. For 0.3:
> > http://docs.julialang.org/en/release-0.3/manual/calling-c-and
> > -fortran
> > -code/#passing-pointers-for-modifying-inputs
> >
> > For 0.4 (a bit different):
> > http://docs.julialang.org/en/latest/manual/calling-c-and-fortran
> > -code/#passing-pointers-for-modifying-inputs
> >
> >
> > Regards
> Hi Milan and thank you so much for your quick response. I didn't
> keyed in my source code because i don't want to burden people by
> reading source code. :)
> Anyway...here is my little Julia script:
>
> mynumber=convert(Cint, 0)
> ccall((:funct1, "./libtest.so"), Void, (Ptr{Cint},), &mynumber)
> println(mynumber)
>
> My C code:
> void funct1(int *i){
> *i=5;
> }
>
> The environment i am using is Linux (Ubuntu flavor) and the version
> of Julia is 0.3.10.
>
> I have read the documentation of Julia for callign external functions
> of C and Fortran but it seems that i am missing something !
You probably missed the interesting part in the middle of the long
docs. In the link I gave you, you'll see that something like this
should work:
mynumber = Cint[0]
ccall((:funct1, "./libtest.so"), Void, (Ptr{Cint},), &mynumber)
The reason is that an immutable (like an Int) has no 'individual'
existence nor storage: 5 is always equal to 5, and it doesn't make
sense to change it to be equal to 3. So you need to create a one
-element array and modify this location.
Regards
