mac os gem安装json出现error failed的解决办法

升级到最新的mac os mavericks。装json出现错误：

gem install json -v '1.8.1'

building native extensions.  this could take a while...
error:  error installing json:
  error: failed to build gem native extension.

    /usr/local/var/rbenv/versions/2.0.0-p247/bin/ruby extconf.rb
creating makefile

make "destdir="
compiling generator.c
in file included from /usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby.h:33,
                 from ../fbuffer/fbuffer.h:5,
                 from generator.c:1:
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:51:21: error: string.h: no such file or directory
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:61:21: error: stdint.h: no such file or directory
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:64:23: error: inttypes.h: no such file or directory
/usr/local/var/rbenv/versions/2.0.0-p247/include/ruby-2.0.0/ruby/ruby.h:68:19: error: stdio.h: no such file or directory

解决办法：

xcode-select --install

需要重新安装command line developer tools

如果这个办法还是不行，mac下需要安装下apple-gcc42

brew install apple-gcc42

注意brew 0.9.4应该是不带apple-gcc42的源的，可以使用brew doctor检查下是否和mavericks兼容，这里需要升级

brew update