access dll function on C project from Ruby

Question

I have a project written in C controlling hardware devices. I'm trying to access DLL functions in my projects from a Ruby app in order to control the hardware from the Ruby web app. I'm failing in loading the dll project files using FFI and Fiddle. Does anyone have an example I can use to share of a similar case?

Thanks.

@shadowsheep SWIG is used for creating extensions though and I'm looking to just load a dll file into my Ruby app and use the functions in it. Am I missing something here? — Yof, Jan 30 '18 at 22:38
Nope! You can use swig to auto generate ruby wrapoer for your dll like that http://web.mit.edu/svn/src/swig-1.3.25/Examples/ruby/class/index.html — shadowsheep, Jan 30 '18 at 22:40
See at the tutorial http://www.swig.org/tutorial.html sorry I don’t answer with a live example ‘cause are on my mobile right now. — shadowsheep, Jan 30 '18 at 22:45
So if it answers your question, could you flag it as the accepted one? — shadowsheep, Jan 31 '18 at 17:46

shadowsheep · Accepted Answer · 2018-01-31T17:35:32.603

I suggest using SWIG (http://swig.org)

I'll give you an example on OSX but you could find the equivalent on Windows as well.

Let's say you have a library (in my case hello.bundle or in your case hello.DLL) with this header file hello.h

#ifndef __HELLO__
#define __HELLO__

extern void say_hello(void); 

#endif

and you wanna call say_hello from a ruby program like that run.rb:

# file: run.rb
require 'hello'

# Call a c function
Hello.say_hello

(Pay attention here that the module name is Capitalised)

what you have to do is to create a file hello.i like that:

%module hello
 %{
 #include "hello.h"
 %}

 // Parse the original header file
 %include "hello.h"

And then run the command:

swig -ruby hello.i

This will generate a file .c that is a wrapper that will be installed as a wrapper module for your ruby environment: hello_wrap.c.

Then you need to create a file extconf.rb with this content:

require 'mkmf'
create_makefile('hello')

Pay attention that here "hello" is the name of our module in the file .i.

Then you must run ruby extconf.rb that will generate a Makefile.

ruby extconf.rb    
creating Makefile

Then you must type make that will compile the _wrap.c file against the library (in my case .bundle in your case .DLL).

make
compiling hello_wrap.c
linking shared-object hello.bundle

Now you must type make install (or sudo make install on Unix/Osx)

sudo make install
Password:
/usr/bin/install -c -m 0755 hello.bundle /Library/Ruby/Site/2.3.0/universal-darwin17

Then you can run your program run.rb

ruby run.rb 
Hello, world!

I'll paste here below the .c file used to generate the library hello.bundle

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

void say_hello(void) {
    printf("Hello, world!\n");
    return;
}

If you leave this file along with it's .h file the Makefile will build the library for you

make
compiling hello.c
compiling hello_wrap.c
linking shared-object hello.bundle

access dll function on C project from Ruby

1 Answers1