I just started using Eclipse Oxygen for C development and I'm facing a problem with Content Assist which is not working on Ctrl+Space. I've tried all solutions posted around but none of them work. It seems there is a bug concerning key schemes. There should be three predefined schemes - Default, Emacs and Microsoft Visual Studio, but I also have another one called default. It is empty, I can use Restore Defaults which populates the key bindings, but it can't be either stored (next time I open it it is empty again) nor selected as active scheme.
Going to C/C++ -> Editor -> Content Assist -> Advanced shows that all proposal kinds are bound to that problematic default key scheme which is empty and can't be selected as active.
When I select Default (notice capital D) key scheme and add key binding for the Content Assist (Basic Proposals), then go to editor, start typing for example a function name and then press the newly assigned key shortcut I get the following dialog:
attachment: eclipse dialog. PNG
When I click on Advanced Content Assist preference page link and from there just click Cancel I suddenly get the list of proposals in the editor. To get the proposals list again I have to repeat the above steps.
My C/C++ -> Editor -> Content Assist -> Advanced preferences look like this:
I had the same problem and was able to solve it building on your analysis. In the "Default" key scheme, I unassigned Ctrl-Space from "Content Assist" and assigned it to "C/C++ Content Assist (Parsing-based proposals)". This now shows up as the key binding for parsing-based proposals in C/C++ -> Editor -> Content Assist -> Advanced. Of course now I get only parsing-based proposals, but that's OK for me; if I want others, I can bind another key to them. I haven't been able to figure out how to properly bind the entire Content Assist to a key.