Daniel,
I tried your code and could reproduce the problem: I have to suggestions:
-- Julia is 1-based, so drop the 0 in your unsafe_load. The default
parameter is 1, which is what you want in this case.
-- I can't really understand what your function is supposed to do (and my C
is a bit rusty), but this simpler version works for me.
I suggest to start there and add the additional functionality of
particles_add bit by bit.
Good luck.
#include <stdio.h>
#include <stdlib.h>
int N = 7;
int Nmax = 9;
struct particle {
double x;
double y;
double z;
};
struct particle* particles = NULL;
void particles_add(struct particle pt){
printf("%.2f\t%.2f\t%.2f\n", pt.x, pt.y, pt.z);
}
On Sunday, June 21, 2015 at 11:42:06 PM UTC+9, Daniel Carrera wrote:
>
> Hello,
>
> I'm trying to learn how to call C libraries from Julia. So I wrote a
> simple C library that does nothing in particular and I am having trouble
> talking to that library from Julia. Here is my library:
>
> ---------------------------------------------
> % cat foo.c
> #include <stdio.h>
> #include <stdlib.h>
>
> int N = 7;
> int Nmax = 9;
>
> struct particle {
> double x;
> double y;
> double z;
> };
>
> struct particle* particles = NULL;
>
> void particles_add(struct particle pt){
> while (Nmax <= N){
> Nmax += 128;
> particles = realloc(particles,sizeof(struct particle)*Nmax);
> }
> particles[N] = pt;
> N++;
> }
>
> ---------------------------------------------
> % make
> gcc -Wall -std=c99 -Wpointer-arith -c -fPIC foo.c
> gcc -Wall -std=c99 -Wpointer-arith -shared -o libfoo.so foo.o
> ---------------------------------------------
>
>
> So, there are two things I would like to do from Julia: I'd like to read
> the variable "N" and I'd like to create a "particle" struct and pass it to
> the "particles_add()" function. I used the documentation on this page:
>
> http://julia.readthedocs.org/en/latest/manual/calling-c-and-fortran-code/
>
> Based on what I read, this is what I came up with:
>
> ---------------------------------------------
> % cat foo.jl
> const lib = "./libfoo.so"
>
> N() = unsafe_load(cglobal(("N" ,lib), Cint), 0)
> Nmax() = unsafe_load(cglobal(("Nmax",lib), Cint), 0)
>
> immutable Particle
> x ::Cdouble
> y ::Cdouble
> z ::Cdouble
> end
>
> function add(pt::Particle)
> ccall(("particles_add", lib), Void, (Particle,), pt)
> end
>
> function add(;x=0,y=0,z=0)
> add(Particle(x,y,z))
> end
> ---------------------------------------------
>
>
> However, nothing here works: I cannot read "N" (I get gibberish) and I
> cannot call "particles_add()" (I get a segfault):
>
> ---------------------------------------------
> % julia
> ...
> julia> include("foo.jl")
> add (generic function with 2 methods)
>
> julia> N()
> 32570
>
> julia> Nmax()
> 7
>
> julia> add(x=0)
>
> signal (11): Segmentation fault
> particles_add at ./libfoo.so (unknown line)
> julia_add_20314 at (unknown line)
> jlcall_add_20314 at (unknown line)
> unknown function (ip: -490800184)
> unknown function (ip: -490804016)
> unknown function (ip: -490736582)
> jl_f_top_eval at /usr/bin/../lib/x86_64-linux-gnu/julia/libjulia.so
> (unknown line)
> eval_user_input at REPL.jl:53
> jlcall_eval_user_input_20278 at (unknown line)
> jl_apply_generic at /usr/bin/../lib/x86_64-linux-gnu/julia/libjulia.so
> (unknown line)
> anonymous at task.jl:95
> jl_handle_stack_switch at
> /usr/bin/../lib/x86_64-linux-gnu/julia/libjulia.so (unknown line)
> julia_trampoline at /usr/bin/../lib/x86_64-linux-gnu/julia/libjulia.so
> (unknown line)
> unknown function (ip: 4199613)
> __libc_start_main at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
> unknown function (ip: 4199667)
> unknown function (ip: 0)
> zsh: segmentation fault (core dumped) julia
> ---------------------------------------------
>
>
> So, at this point I am really stuck. Clearly I have missed a lot of
> fundamental issues in either my C code, or my Julia code, or both. Can
> anyone figure out what I'm doing wrong?
>
>
> Cheers,
> Daniel.
>
