How to i show omnicomplete's autocomplete list without autocompleting current text

Question

I am learning vim with omnicomplete. I am wondering whether I can show the omnicomplete list without autocompleting current text. For example,

If I type "str.c" and then invoke omnicomplete, it will show a list containing possible words starting with "c", and autocomplete the current text to, say "capitalize".

If, for example, the method I am looking for is count, I have to scroll all the way down the list to find it, or delete the "apitalize" part, and then type o, etc. Is it possible to just show the list, so that if I invoke it after c, it will show the list without autocompleting to capitalize? For example to something like below, where I can still type o to quickly go to count

Answer 1

Thanks to @romainl comment, I looked up completeopt, and I found the answer Make Vim completion popup menu work just like in an IDE. It has a bunch of other related tips. To make the behaviour as described in the question,

:set completeopt=longest,menuone