devkit DevKit-tdm-32-4.5.2-20111229-1559-sfx をインストールした後、ruby 1.9.3 をインストールした後
gem install json --platform=ruby を実行すると、次のように表示されます。
Temporarily enhancing PATH to include DevKit...
Building native extensions. This could take a while...
Impossibile trovare il percorso specificato.
ERROR: Error installing json:
ERROR: Failed to build gem native extension.
C:/Ruby193/bin/ruby.exe extconf.rb
creating Makefile
Gem files will remain installed in C:/Ruby193/lib/ruby/gems/1.9.1/gems/json-1.8.0 for inspection.
Results logged to C:/Ruby193/lib/ruby/gems/1.9.1/gems/json-1.8.0/ext/json/ext/generator/gem_make.out