The gcc package coming with Knoppix V 6.2.1 CD is newer than the one in the stable branch. I think that the easiest solution would be to install the g++ package from the testing branch.

I would suggest that you boot your Knoppix Live CD, connect to the internet, kill the screensaver daemon and execute the following commands in a terminal.
Code:
sudo apt-get update
sudo apt-get -t testing install g++
mkdir /home/knoppix/test
cd /home/knoppix/test
wget http://download.savannah.gnu.org/releases/ddrescue/ddrescue-1.8.tar.bz2
tar xjf ddrescue-1.8.tar.bz2
cd ddrescue-1.8
./configure
make
sudo make install
You have to install the GNU info program if you like to read the documentation.
Code:
sudo apt-get -t testing install info
info -f /usr/local/share/info/ddrescue.info