Cannot install JSON gem in rails using windows
Solution 1:
You are working with Windows, so the RubyInstaller Development Kit may help you: http://rubyinstaller.org/add-ons/devkit/
The devkit installs a C-compiler (and some other stuff) to compile C-written parts.
Install it and try again to install the gem - perhaps with option --platform=ruby.
Details can be found at https://github.com/oneclick/rubyinstaller/wiki/Development-Kit
Solution 2:
That's because this gem using a piece of code written on C. For working properly you need c compiler installed on your machine. As a way, try to use json_pure written on pure Ruby