http://stackoverflow.com/questions/7832892/how-to-change-the-default-gcc-compiler-in-ubuntu

To figure out the current priorities of gcc,type in the command pointed out by @tripleee's comment:

查看当前的可切换的版本： update-alternatives --query gcc

设置为4.5
update-alternatives --set g++ /usrbing++-4.5update gcc gcc- cppbin cpp4.5
Here,4.6 is still the default (aka "auto mode"),but I explicitly switch to 4.5 temporarily (manual mode). To go back to 4.6:
方法二：例如有 4.6 4.5 两个版本updateinstall /usrbing++ g ++-4.6 100 update4.550gcc gcc gcc-cpp cppbin cpp50--auto gcc update cppbin

echo 'export CXX=/usr/bin/gcc-4.5'>>~/.bashrc

移除当前的选择可以这样

First erased the current update-alternatives setup for gcc and g++:

 
 

  
  
 
   
 
    
 
     
 
      
Install Packages
 
      
It seems that both gcc-4.3 and gcc-4.4 are installed after install build-essential. However,we can explicitly install the following packages:
 
      
 
     
 
   
 
  
 
 

sudo update-alternatives --remove-all gcc 
sudo update-alternatives --remove-all g++sudo apt-get install gcc-4.3 gcc-4.4 g++-4.3 g++-4.4

sudo update-alternatives --remove-all gcc 
sudo update-alternatives --remove-all g++