I'm currently using UltraEdit, which is armed with Ctags, to edit C++ files (.cpp). Its Ctags support automatically autocompletes symbols while I'm typing—but it can't correctly confine itself to only the members of a class, which is so blind. How to make UltraEdit smarter like Vim+ctags+cppcomplete? So far, I can't find any plugins on web.
UltraEdit doesn't do a great job of auto complete when compared to an IDE like Eclipse etc. because it doesn't know how to parse tokens in a language specific way - i.e. it has no way of knowing what your variable/method names are and listing just those for auto complete.
However, UltraEdit does have a default auto-complete feature built in (control+space) - UltraEdit will search back 50K in the active file from the cursor location for words that match a partially typed word and show these. Go to Advanced > Configuration > Editor > Auto-complete and you can tick the option to "show auto-complete dialog automatically" after X number of chars.
Also, you can set language specific auto-complete files (and UtlraEdit's website has a few predefined ones you can download). So for example you can fill this file with a bunch of class names or other common words/tokens and they will always appear in the auto-complete dialog for that file type too. Link a specific auto-complete file to a file type through preferences:
Lastly, as of UltraEdit 18, the editor got a lot better with templates. While you have a c file open, display the template view: View > Views/Lists > Template List. You should see in that template list a bunch of smart template for common c structures such as IF, DO etc etc. You can also create your own here too.
Note that all these things (search tokens 50k back in the file; list tokens in the autocomplete file; list templates) will all show up on control+space.