Installing gcc and g++ on Mac Lion 10.7.3

1. Install Xcode 4.3 by clicking "View in Mac Apple Store"
          If you want to get an Apple account without a credit card, follow this.

2. Get "Command Line Tools for Xcode" inside Xcode
           Xcode --> Open Developer Tool --> Command Line Tools for Xcode.dmg

3. You now have gcc and g++
          Type which gcc you should see /usr/bin/gcc, and which g++ you should see /usr/bin/g++

Extra notes:
- At first I cannot not find gcc in /usr/bin. Google points me to install Xcode
- After I have Xcode, gcc does not work either. I could not find /Developer. Then I read "/Developer No Longer Exists" in Xcode 4.3

solution to "error: unordered_map: No such file or directory"

#include <unordered_map>
-->
#include <tr1/unordered_map>