The past few weeks I have been using the great eclim, and the corresponding emacs–eclim package. It allows you to use many of Eclipse’s features in your favourite editor. The installation of emacs-eclim is rather easy, and the one for eclim is even easier, since it comes with a simple clickety-click-installer.
I use emacs-eclim for Java development, and it works rather well. I use the two functions ac-complete-emacs-eclim and ac-complete-eclim-c-dot for auto-completion, which is the most important aspect when using such heavily object oriented languages and when developing large projects. Also useful are the functions eclim-java-import-missing, and eclim-java-remove-unused-imports. The current project can be compiled by calling eclim-project-build.
In theory, you can also use eclim with CDT for C++ development and auto-completion, but I rather stick with my earlier clang based solution, which is very fast and accurate.