CODEWITHSUNDEEP
juliamethod-call
Antonello
Antonello

Reputation: 6423

How to specify a relative library path in Julia ccall?

to ccall a custom made library, I need to write down the library full path on the system:

j = ccall((:add3, "[FULL_PATH]/libmylib.so"), Float32, (Float32,), 2)

I am trying to use instead a relative path with:

j = ccall((:add3, "$(pwd())/libmylib.so"), Float32, (Float32,), 2)

but, while "$(pwd())/libmylib.so" returns the right path for the library, ccall with pwd returns a TypeError: in ccall: first argument not a pointer or valid constant expression, expected Ptr, got Tuple{Symbol,String}.

So, how to ccall a library that is in the same folder than the Julia script/current working directory ?

I am puzzled, as according to this thread in Windows seems to work, even if the doc for ccall specify:

Note that the argument type tuple must be a literal tuple, and not a tuple-valued variable or expression.

For info, I'm in Ubuntu 18.04 and the library has been implemented with

mylib.c:

float add3 (float i){
 return i+3;
}

mylib.h:

#ifndef _MYLIB_H_
#define _MYLIB_H_

extern float get2 ();
extern float add3 (float i);

Compilation (gcc):

gcc -o mylib.o -c mylib.c
gcc -shared -o libmylib.so mylib.o -lm -fPIC

Upvotes: 2

Views: 600

Answers (2)

fredrikekre
fredrikekre

Reputation: 10984

As far as I know this is the most used pattern:

const mylib = joinpath(pwd(), "libmylib.so")
j = ccall((:add3, mylib), Cfloat, (Cfloat,), 2)

Note that pwd can be a bit more in "flux" than you want for a library path, it is probably better to relate it to the file, e.g.

const mylib = joinpath(@__DIR__, "libmylib.so")

where @__DIR__ expands to the directory of the file itself.

Upvotes: 2

Antonello
Antonello

Reputation: 6423

As often, I found the solution only after posting on SO.. it seems setting the question helps defining better the problem..

Any how, the solution is to first get the function pointer with cglobal - where I can use pwd() - and then use the ccall method with the function pointer:

f = cglobal((:add3, "$(pwd())/libmylib.so"))
j = ccall(f, Float32, (Float32,), i)

Upvotes: 0

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