Turn VIM omni completion ON

Turn omni completion feature by put this in vimrc.

autocmd FileType python set omnifunc=pythoncomplete#Complete
autocmd FileType javascript set omnifunc=javascriptcomplete#CompleteJS
autocmd FileType html set omnifunc=htmlcomplete#CompleteTags
autocmd FileType css set omnifunc=csscomplete#CompleteCSS
autocmd FileType xml set omnifunc=xmlcomplete#CompleteTags
autocmd FileType php set omnifunc=phpcomplete#CompletePHP
autocmd FileType c set omnifunc=ccomplete#Complete

Default vim turn off this feature. And here to set ctags

ctags -R -f ~/.vim/qttags /usr/include/qt3

:set tags +=~/.vim/qttags