On EasyPeasy 1.1 (for mini notebooks) derived from Ubuntu I installed g++ using apt-get:
$ apt-get install g++
One of the lines displayed was:
Setting up g++ (4:4.3.1-1ubuntu2) ...
What the does "4:" mean?
$ g++ --version
g++ (Ubuntu 4.3.2-1ubuntu12) 4.3.2
What is the relationship of the "4.3.1" in apt-get to the "4.3.2" g++ version?
It is an epoch. According to the debian policy manual,
the purpose of epochs is to allow us to leave behind mistakes in version numbering, and to cope with situations where the version numbering scheme changes
IIRC gcc 3.4.x introduced ABI-incompatible changes from the 3.3.x series, and this epoch may have been introduced by debian maintainers at that time.