How to install a specific version of g++?

Download the g++-4.1 version from here. g++-4.1 is not available in the recent Ubuntu repositories. So you need to download the package from the link provided.

Install/compile the download package alongside with the current version of g++.

Then use update-alternatives to switch version

sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.3 10

Change the default version by choosing the appropriate version:

sudo update-alternatives --config g++