gem install iconv

我的结果：

Temporarily enhancing Path to include DevKit...
Building native extensions. This could take a while...
Error : Error installing iconv:
    ERROR: Failed to build gem native extension.

C:/Ruby/Ruby200/bin/ruby.exe -r ./siteconf20150217-3212-i8hzmh.rb extconf.rb
checking for rb_enc_get() in ruby/encoding.h... yes
checking for rb_sys_fail_str() in ruby.h... yes
checking for iconv() in iconv.h... no
checking for iconv() in -liconv... no
*** 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:/Ruby/Ruby200/bin/ruby
    --with-iconv-dir
    --without-iconv-dir
    --with-iconv-include
    --without-iconv-include=${iconv-dir}/include
    --with-iconv-lib
    --without-iconv-lib=${iconv-dir}/
    --enable-config-charset
    --disable-config-charset
    --with-config-charset
    --without-config-charset
    --with-iconvlib
    --without-iconvlib

extconf Failed,exit code 1

请帮帮我！！！！
谢谢.