Cannot install g++ on 12.10

Question

sudo apt-get install g++

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 g++ : Depends: g++-4.7 (>= 4.7.0-1~) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Answer 1

Seems like you have some broken packages or dependencies. Try doing sudo apt-get update, if you get some error updating, try following:

sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.backup
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update

and then try installing g++.

Answer 2

Always run sudo apt-get update then sudo apt-get install g++. The sudo apt-get clean command is optional. My install worked just fine without it.

Answer 3

Rather than just installing g++ or gcc it is more recommended to install the build-essential package.

You should install it with the following commands:

sudo apt-get update
sudo apt-get install build-essential

Those two commands should install all the basics needed by the system to build things.