This is very strange.
I just installed CB from source on my Ubuntu box. Compiled it and so. It still didnt gave me any codecompletion on the standard and STL libraries. I went totally out of control, hitting and opening all of the Settings -> sub menues. I ran into the Settings->Compiler and debugger menu, and started a flamewar against Search directories (Compiler and resource compiler), typing in /usr/include/c++/4.2.3. It didnt help either. I closed the IDE, and reopened it again, reopened my test project, and then, finally, like lightning from a blue sky, I finally had codecompletion on the SL and STL. YES!!!
Till this minute I still dont know if it was this that did the job because I have been trying so many things in the gap between the reopening of the project and placing of the search directories.