From: Aaron Patterson <aaron@...>
Date: 2010-01-26T04:59:46+09:00
Subject: Re: Compiling multiple C source files into a single library

On Tue, Jan 26, 2010 at 04:46:37AM +0900, Daniel Berger wrote:
> Hi,
> 
> In the past I've always put all my code into a single source file and
> built it that way. However, I'd like to split out my C source files
> into a "one class per file" arrangement for a particular project, but
> I'm not sure how to do it. I'm using rake-compiler on Snow Leopard,
> btw.
> 
> Here's the layout I have:
> 
> my_project
>   Rakefile
>   ext/
>     foo/
>       extconf.rb
>       foo.c
>       bar.c
> 
> foo.c and bar.c are pretty basic C source files:
> 
> // foo.c
> #include <ruby.h>
> 
> void Init_foo(){
>   VALUE cFoo = rb_define_class("Foo", rb_cObject);
>   rb_define_const(cFoo, "VERSION", rb_str_new2("0.0.1"));
> }

Call Init_bar() from Init_foo().  Ruby will only call one function when
your extension loads.  The "Init_*" function maps to the name of the
shared object you build.  So if you build "foo.bundle", ruby will call
"Init_foo", and only "Init_foo".  Other initialization is up to you.

> // bar.c
> #include <ruby.h>
> 
> // I also tried Init_foo here, but that lead to a compiler error
> void Init_bar(){
>   VALUE cBar = rb_define_class("Bar", rb_cObject);
>   rb_define_const(cBar, "VERSION", rb_str_new2("0.0.1"));
> }
> 
> The extconf.rb file is just "require 'mkmf'; create_makefile('foo')".

The create_makefile() call determines the name of the shared object
built.  Since you're building "foo.bundle", *only* Init_foo will be
called.

> The Rake task is simply "Rake::ExtensionTask.new('foo')".
> 
> Running "rake compile:stuff" builds like so:
> 
> gcc -I. -I/opt/ree/lib/ruby/1.8/i686-darwin10.2.0 -I/opt/ree/lib/ruby/
> 1.8/i686-darwin10.2.0 -I../../../../ext/foo -D_XOPEN_SOURCE -
> D_DARWIN_C_SOURCE   -fno-common -g -Os -fno-strict-aliasing  -pipe -
> fno-common   -c ../../../../ext/foo/bar.c
> gcc -I. -I/opt/ree/lib/ruby/1.8/i686-darwin10.2.0 -I/opt/ree/lib/ruby/
> 1.8/i686-darwin10.2.0 -I../../../../ext/foo -D_XOPEN_SOURCE -
> D_DARWIN_C_SOURCE   -fno-common -g -Os -fno-strict-aliasing  -pipe -
> fno-common   -c ../../../../ext/foo/foo.c
> cc -dynamic -bundle -undefined suppress -flat_namespace -o foo.bundle
> bar.o foo.o -L. -L/opt/ree/lib -L.     -ldl -lobjc
> cd -
> cp tmp/i686-darwin10.2.0/foo/1.8.7/foo.bundle lib/foo.bundle
> 
> But, if I run the following test.rb program it fails:
> 
> $:.unshift 'lib'
> require 'stuff' # ok
> p Foo::VERSION # ok
> p Bar::VERSION # fail, uninitialized constant Bar
> 
> Why isn't Bar visible? What's the right way to do what I'm attempting?

Just call Init_bar() from inside Init_foo().

Hope that helps!

-- 
Aaron Patterson
http://tenderlovemaking.com/