gem install rmagick error - ruby-on-rails

Question

I know there are many questions about this error but I read several tutorials and SO discussions without coming to a solution.
I'm trying to install rmagick (I want to install Spree ecommerce for Ruby on Rails which requires ImageMagick and rmagick).
I'm working on Windows 7 (64 bit), Ruby version is: 2.1.5, Rails version is 4.2.1. and I downloaded and installed (in C:\ImageMagick) ImageMagick-6.9.1-2-Q16-x64-dll.exe and I also installed Dev-Kit.
I followed the steps that Sumit Munot suggested here ImageMagick Install Windows but when I follow the step 6 I get this errors.
C:\Sites>gem install rmagick
Temporarily enhancing PATH to include DevKit...
Building native extensions. This could take a while...
ERROR: Error installing rmagick:
ERROR: Failed to build gem native extension.
C:/RailsInstaller/Ruby2.1.0/bin/ruby.exe extconf.rb
checking for Ruby version >= 1.8.5... yes
checking for stdint.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=C:/RailsInstaller/Ruby2.1.0/bin/ruby
C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:456:in `try_do': The compiler
failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:587:in `try_cpp'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:1067:in `block i
n have_header'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:918:in `block in
checking_for'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:351:in `block (2
levels) in postpone'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:321:in `open'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:351:in `block in
postpone'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:321:in `open'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:347:in `postpone
'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:917:in `checking
_for'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:1066:in `have_he
ader'
from extconf.rb:37:in `configure_headers'
from extconf.rb:17:in `initialize'
from extconf.rb:474:in `new'
from extconf.rb:474:in `<main>'
extconf failed, exit code 1
Gem files will remain installed in C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1
.0/gems/rmagick-2.15.0 for inspection.
Results logged to C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/extensions/x86
-mingw32/2.1.0/rmagick-2.15.0/gem_make.out
C:\Sites>gem install rmagick
Temporarily enhancing PATH to include DevKit...
Building native extensions. This could take a while...
ERROR: Error installing rmagick:
ERROR: Failed to build gem native extension.
C:/RailsInstaller/Ruby2.1.0/bin/ruby.exe extconf.rb
checking for Ruby version >= 1.8.5... yes
checking for stdint.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=C:/RailsInstaller/Ruby2.1.0/bin/ruby
C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:456:in `try_do': The compiler
failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:587:in `try_cpp'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:1067:in `block i
n have_header'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:918:in `block in
checking_for'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:351:in `block (2
levels) in postpone'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:321:in `open'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:351:in `block in
postpone'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:321:in `open'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:347:in `postpone
'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:917:in `checking
_for'
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/2.1.0/mkmf.rb:1066:in `have_he
ader'
from extconf.rb:37:in `configure_headers'
from extconf.rb:17:in `initialize'
from extconf.rb:474:in `new'
from extconf.rb:474:in `<main>'
extconf failed, exit code 1
Gem files will remain installed in C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1
.0/gems/rmagick-2.15.0 for inspection.
Results logged to C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/extensions/x86
-mingw32/2.1.0/rmagick-2.15.0/gem_make.out
This is my path: C:\RailsInstaller\Git\cmd;C:\RailsInstaller\Ruby2.1.0\bin;C:\Ruby21\bin;
Do I have to add something to the path?

Answer 1

Yeah, had the same trouble and gave it a second shot.
Remove your current ImageMagic folder and rmagick gem
Install ImageMagick-6.7.9-3-Q16-windows-dll.exe from here and ImageMagick-6.7.9-2-Q8-windows-static.exe in the same folder (these worked while the most recent ones don't)
in your console window set path=d:\ImageMagick;%path%
gem install rmagick -- '--with-opt-dir="d:\ImageMagick"'
I installed ImageMagick obviously in d:\ImageMagick, so adapt for your situation.
This worked for my Ruby 1.9.3 under Windows 7, success !

Answer 2

Set %DEVKIT_HOME%\bin in your %PATH% in the System Variables: