POSTIN

/bin/sh

update-alternatives --install /usr/bin/cpp cpp /usr/bin/cpp-3.4.0 200304 --slave /lib/cpp lib_cpp /usr/bin/cpp-3.4.0
[ -e /usr/bin/cpp ] || update-alternatives --auto cpp

POSTUN

/bin/sh

if [ ! -f /usr/bin/cpp-3.4.0 ]; then
  update-alternatives --remove cpp /usr/bin/cpp-3.4.0
fi