This problem stems from changes they made starting with 12.04 where the path to the include folders is different. Netbeans hasn't been updated to automatically find this new path system, so you're code assistance and project paths need to be changed.
To do this as late as 14.04, open Netbeans, go to the preferences dialog, and the C/C++ tab. There you will find a code assistance tab with a list of absolute paths to certain folders. Add /usr/include/c++/4.8 to the list, finalize that and close preferences.
Then, on the project you are working on, right click on the project icon in the side bar and go to the very bottom to find properties. Click that, then on the C or C++ Compiler option, which ever one you're using, and there should be an Include Directories line. Click the ellipsis on that line, and add the same path there.
Once you have that all closed up, your project should have proper code completion and compile correctly. I hope this helps.