Typically by setting the "dict" variable appropriately, one can autocomplete english words, but what about C/C++ code?
One fine morning, I had an epiphany. Why don't people use the ctags/etags database to autocomplete. The database already has lots of semantic information about the code and it would have all the project specific keywords too. Now, I am not a guy who has too many epiphanies, so I was sure someone had implemented it even before I could spell "vim". With this in mind, I googled the specific terms "vim autocomplete using ctags". The first stackoverflow result had a brilliant suggestion: omniautocomplete.
Before I go into what omniautocomplete (a plug-in for vim) does, let me first list down my requirements from an autocomplete tool
1) Autocomplete sensibly: Use the knowledge that I am editing "c++" code and give sensible suggestions.
2) It should *not* be enabled by default when I run vim i.e. do not blindly putt crao in my .vim. The reason is that I work on multiple projects at the same time and I don't want suggestions from one project to be mixed with other.
3) No lag in autocompleting.
4) Provide a quick way to update the autocomplete "database".
Some vim scripting + omnicomplete provides all that and more. What more, you might ask. Well, it provides an eclipse-like pop-up when asked to autocomplete. It can also fire when I enter a "." or "->". It also has an option to show "function prototypes" alongwith autocomplete suggestions. This is awesome!!!
To get you excited, here is a screenshot. It looks exactly the same.
Setting up omnicomplete is super-easy. Installation instructions are outlined here. All it involves is unzipping a zip file to ~/.vim
The next part is more interesting:
Since ctags database is used, ctags needs to be compiled with some specific options. The commandline I picked up from their documentation is this:
$ ctags -R --c++-kinds=+p --fields=+iaS --extra=+q .
Now, the "tags" variable in vim needs to point to the tags of your project. Setting this up each time you open vim can be irritating. Very irritating. So, I wrote the following vim function to alleviate the issue:
if a:proj == "mythread"
map <C-F12> :!ctags -R --c++-kinds=+p --fields=+iaS --extra=+q -f /home/jitesh/repos/mythread_lib/tags /home/jitesh/repos/mythread_lib<CR>
let OmniCpp_ShowPrototypeInAbbr = 1
let OmniCpp_MayCompleteDot = 1
Now, when I open vim, all I have to do is:
Note - Re-generating the ctags database is also pretty easy, Just press Ctrl+F12. Notice the keymapping in the vim function above.
So, when I define a new function in my code, I just do a Ctrl+F12 and the tags are updated and ready to be auto-completed.
Pressing ctrl+P or ctrl+N invokes the autocompletion.
When I start vim, none of this stuff is loaded, so there is no load-time penalty/bloat + I can work on multiple projects just by calling "SetProj" with the appropriate parameter.
I sign-off a happy user! vim FTW