I’ve recently taken an interest in extending Ruby in C, and thought I’d share a quick demo. (I don’t know how to do anything truly fancy yet, so this is going to be the tried-and-true “Hello, world!” example.) The below is adapted from this RubyGems tutorial.
I’ll start with the Ruby script to build the extension:
mkmf generates the Makefile that will compile and link the C extension. dir_config() allows configuration with the various “with” options (which I won’t be using here, since we’re not going to have to look anywhere else for libraries or include files); create_makefile() builds the Makefile.
Next up, the C file:
The first two lines pull in the appropriate header files (which contain all sorts of necessary constant and function definitions). Lines 4 through 8 define a world() method that just prints “Hello, world!” and returns nil; lines 10 through 14 use the built-in Init_ function (which is called when the file is required in). Inside this function, the “Hello” class is defined (line 12) and the world() method is attached as a singleton method (line 13).
These are the only files we need. Now all we’ve got to do is generate the Makefile, compile and link the extension, and test it out. YMMV on this next bit, but if you’re working with OSX, you should get the results shown here. (I’ll try to mention anything specific to my machine or setup that would cause a difference.)
In the directory containing your two files (extconf.rb and hello.c), type the following commands (and you should see the associated output):
If all’s well, you should notice the addition of a Makefile, an object file (hello.o), and a shared object (hello.bundle on my machine, but you’ll see hello.so if you’re working with Linux or Windows):
Finally, we’re ready to fire up IRB and test out our new Hello class and its accompanying world method. Note that some older tutorials that teach Ruby pre-1.9.2 may show the use of the file name without the prepended “./”, which will not work in Ruby 1.9.2 and later. The reason for this is that in 1.9.2, a change was introduced that removed the working directory from the Ruby path ($:). The good news is that this was replaced by the awesomeness that is require_relative; the bad news is that require_relative relies on being called from a file, and since the IRB session isn’t treated as a file in the current directory, require_relative doesn’t work with it. All this to say: you gotta type require './hello'. Them’s the breaks.
Voilà—your (and my) very first C extension for Ruby!