How to use a julia compiled object from within a C program

New to Julia
,
1

Hi all !

I need to develop an interface to use an existing Julia project from within a C porgram.
As I am VERY newbie in Julia, I started creating a VERY simple Julia script to better understand the operation mode.

The steps I need to achieve are (I guess) :

  • Write a simple julia script
  • Create an object (using output-o compilation option)
  • Create a shared object (by gcc -share)
  • Create a .h header to use this library from C
  • Use the Julia library from C
    But I am experiencing problems with the last step :frowning: I just don’t know (and don’t find in Julia doc) how to write the .h file compatible with julia-native library. Thus, when I try to compile my C program I obtain “undefined reference” to my julia function.

Here’s my julia script “MULT.ji” :

module MULT

   export doubler

   function doubler(x)
      x*2
   end

   function tripler(x)
      x*3
   end

   function quadrupler(x)
      x*4
   end
end

Here’s my header “mult.h” :

int doubler(int x);
int tripler(int x);
int quadrupler(int x);

Here’s my C file “intcjulia.c”

#include "mult.h"
#include <stdio.h>

int main(){
  printf("double de 2 : %u ", doubler(2));
}

And here’s how I compiled :

#creation du .JI et du .O

./bin/julia --output-ji testji.ji --output-o testo.o MULT.jl

#creation du .SO

gcc -shared -o libmult.so testo.o

compilation du C

gcc -L. -Llib/ intcjulia.c -lmult -ljulia

What am I doing wrong ? Where can I find some doc about this issue ? Does anybody can help me ?
Thank you in advance.

Nextor

1 Like
2

If I had to guess I’d say that the name mangling in Julia is different from C, so the linker is looking for the wrong mangled name

3

Thank you for your response Philip, but I don’t really understand. You mean that the name mangling (such as Upper or lower case or underscores) is incorrect ?
Which is the correct way ?
In you opinion, my .H file, and mainly my .C file are correct ?
Is it the right way to make julia code visible ?
Thanks

4

In your Julia code, you don’t specify any types, but in your C header, you assume everything is int?

I’m not an expert myself, but in a recent article by @sdanisch, he uses a line like this to compile a specific function method:

precompile(foo, (Float64, Float64))

Maybe this is what you need, to?

5

Have a look at static-julia.

2 Likes
6

If it is feasible to compile/refactor your C program as a library, it is much easier to call C from Julia (or any other high level language) than the other way around.

1 Like
7

Please vote for my feature request:
https://github.com/JuliaComputing/static-julia/issues/42

8

Please vote for my feature request:

This is typically counter-productive. Recruit someone to work on your feature instead.

1 Like
9

Why should this be counter-productive?
Other open source projects use “stars” of github issues and feature requests to prioritize what to implement in the next release, for example the Python IDE Spyder.
See:
https://github.com/spyder-ide/spyder/issues?q=is%3Aopen+is%3Aissue+label%3A"11–20+stars"

10

Thank you for your response stev, but i my case, the existing pattern it is not possible to invert dependencies. It is the existing C program that needs to call functions of the existing Julia module.