# Re: Ruby extension issue **URL:** \ **Category:** Ruby\ **Created:** [December 28, 2006, 10:47pm UTC](https://www.ruby-forum.com/t/re-ruby-extension-issue/80586 "2006-12-28T22:47:52Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Wim\_Vander\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/13edae/32.png) [@Wim\_Vander\_S](https://www.ruby-forum.com/u/Wim_Vander_S)\ **Post date:** [December 28, 2006, 10:47pm UTC](https://www.ruby-forum.com/t/re-ruby-extension-issue/80586/1 "2006-12-28T22:47:52Z")
I was able to fix the problem by changing my extconf.rb to: ``` require 'mkmf' dir_config('gamer') have_library("SDL", "SDL_Init") have_header("SDL/SDL.h") pkg_config("sdl") create_makefile('gamer') ``` However, I don’t know _WHY_ it works. The pkg\_config seems to be the crucial line. I just went through other people’s extconf.rb files and guessed the “sdl” value. Any help would be appreciated, since there seems to be no documentation about pkg\_config… Wim – Wim Vander S. Bachelor Computer Science, University Ghent [http://nanoblog.ath.cx](http://nanoblog.ath.cx) My weblog, powered by Ruby and BSD licensed. ---
**Author:** ![Wim\_Vander\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/13edae/32.png) [@Wim\_Vander\_S](https://www.ruby-forum.com/u/Wim_Vander_S)\ **Post date:** [December 28, 2006, 11:37pm UTC](https://www.ruby-forum.com/t/re-ruby-extension-issue/80586/2 "2006-12-28T23:37:57Z")
On Dec 28, 2006, at 13:45, Wim Vander S. wrote: > However, I don’t know _WHY_ it works. The pkg\_config seems to be > the crucial line. > I just went through other people’s extconf.rb files and guessed the > “sdl” value. > Any help would be appreciated, since there seems to be no > documentation about > pkg\_config… $ ruby extconf.rb checking for SDL\_Init() in -lSDL… no checking for SDL/SDL.h… no creating Makefile $ You should never call create\_makefile makefile when required libraries and headers can’t be found. – Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net) I LIT YOUR GEM ON FIRE! ---
**Author:** ![Wim\_Vander\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/13edae/32.png) [@Wim\_Vander\_S](https://www.ruby-forum.com/u/Wim_Vander_S)\ **Post date:** [December 28, 2006, 11:39pm UTC](https://www.ruby-forum.com/t/re-ruby-extension-issue/80586/3 "2006-12-28T23:39:57Z")
Eric H. wrote: > > create\_makefile(‘gamer’) > > checking for SDL\_Init() in -lSDL… no Ok thanks 🙂 Could you also explain what these methods do exactly? Wim – Wim Vander S. Bachelor Computer Science, University Ghent [http://nanoblog.ath.cx](http://nanoblog.ath.cx) My weblog, powered by Ruby and BSD licensed. ---
**Author:** ![Wim\_Vander\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/13edae/32.png) [@Wim\_Vander\_S](https://www.ruby-forum.com/u/Wim_Vander_S)\ **Post date:** [December 29, 2006, 12:44am UTC](https://www.ruby-forum.com/t/re-ruby-extension-issue/80586/4 "2006-12-29T00:44:05Z")
On Dec 28, 2006, at 14:39, Wim Vander S. wrote: > > > documentation about > > Ok thanks 🙂 Could you also explain what these methods do exactly? > require ‘mkmf’ > > dir\_config(‘gamer’) dunno > have\_library(“SDL”, “SDL\_Init”) Do we have an SDL\_Init() declared in libSDL.so (platform dependent)? Returns true or false if it was found or not. Check the return value and abort if false and you need this library. > have\_header(“SDL/SDL.h”) Do we have an SDL/SDL.h file lying around somewhere? Returns true or false if it was found or not. Check the return value and abort if false and you need this library. > pkg\_config(“sdl”) dunno > create\_makefile(‘gamer’) creates a Makefile that will build gamer.so – Eric H. - removed\_email\_address@domain.invalid - [http://blog.segment7.net](http://blog.segment7.net) I LIT YOUR GEM ON FIRE! ---
**Author:** ![Wim\_Vander\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/13edae/32.png) [@Wim\_Vander\_S](https://www.ruby-forum.com/u/Wim_Vander_S)\ **Post date:** [December 29, 2006, 3:34pm UTC](https://www.ruby-forum.com/t/re-ruby-extension-issue/80586/5 "2006-12-29T15:34:14Z")
On Fri, 2006-12-29 at 18:13 +0900, Wim Vander S. wrote: > Thank you, but my main problem is the pkg\_config ☹ pkg\_config calls the Gnome utility pkg-config to get information about the libraries that are installed. For example: $ pkg-config --libs libebook-1.2 -pthread -L/lib -lebook-1.2 -lgnome-2 -lpopt -ledataserver-1.2 -lgnomevfs-2 -lgobject-2.0 -lxml2 -lz -lgconf-2 -lbonobo-2 -lbonobo-activation -lORBit-2 -lm -lgmodule-2.0 -ldl -lgthread-2.0 -lglib-2.0 The nice thing about using the extconf.rb pkg\_config method is that you don’t have to explicitly list all of those libraries to compile/link your extension. One thing that confused me at first was that the extconf.rb method is “pkg\_config” (with an underscore) and the Gnome utility program is “pkg-config” (with a dash). But anyhow, it’s very handy and it can make your extconf.rb files much shorter. Yours, Tom ---
**Author:** ![Wim\_Vander\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/13edae/32.png) [@Wim\_Vander\_S](https://www.ruby-forum.com/u/Wim_Vander_S)\ **Post date:** [December 29, 2006, 10:15am UTC](https://www.ruby-forum.com/t/re-ruby-extension-issue/80586/6 "2006-12-29T10:15:17Z")
Eric H. wrote: > > > > Any help would be appreciated, since there seems to be no > > > > libraries and headers can’t be found. > > > pkg\_config(“sdl”) Thank you, but my main problem is the pkg\_config ☹ Well for now I’ll just be happy that it works 🙂 Wim – Wim Vander S. Bachelor Computer Science, University Ghent [http://nanoblog.ath.cx](http://nanoblog.ath.cx) My weblog, powered by Ruby and BSD licensed.