YCM Autocomplete Fix

I’ll get straight to the point here, if you’ve installed the YouCompleteMe plugin for Vim and/or Neovim, you might’ve run into a problem with C and/or C++ auto-completion suggestions. The big issue you may have run into just like me and a bunch of other people is that you’re not getting standard library suggestions and language syntax suggestions. I’ve found a way to fix it.

The Fix

The fix itself is really simple. Put this snippet of code into your .vimrc or your init.vim file if you use Neovim:

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let g:ycm_semantic_triggers = {
	\ 'c': [
	\	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
	\	'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',
	\	'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
	\	'y', 'z'],
\}

This might be a bit of a hacky way to do it. So what this does is sets all the lexicographic characters to trigger ycm. By default for C and C++ has the dot (.) and arrow (->) operators as the semantic triggers. As these are the default for the languages, you don’t need to add them to our list. Now I’m not sure if this is the best way to get the auto-completion to work but I found this way it actually suggests standard library functions and primative types and functions I’ve already declared. It’ll also show function arguments instead of just showing the function name.

If you want this to work with C and C++ you just have to add C++ like this:

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let g:ycm_semantic_triggers = {
	\ 'c,cpp': [
	\	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
	\	'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',
	\	'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
	\	'y', 'z'],
\}

There is one thing that you need to make sure you have. For ycm to work for a project, it requires you to have a .ycm_extra_conf.py file for each project. I don’t do this, I have a config file for each langauge in a config directory and source that when I edit a file based on its extension, like so:

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augroup filetype_c
	autocmd!

	let g:ycm_global_ycm_extra_conf = '~/.config/nvim/config/.ycm_c_conf.py'

	...
augroup END

I won’t go over the setup of a ycm conf file here but there’s an exmaple on the ycm GitHub. I’ve also based my config off this config on GitHub. You do have to change some things in the flags list and that’s the ’-std’ and ’x’ flags. These change depending on which version of C and C++ you’re using. Here’s what I have for C:

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BASE_FLAGS = [
        '-Wall',
        '-Wextra',
        '-Werror',
        '-Wno-long-long',
        '-Wno-variadic-macros',
        '-fexceptions',
        '-ferror-limit=10000',
        '-DNDEBUG',
        '-std=c99',
        '-xc',
        '-DUSE_CLANG_COMPLETER',
        '-I/usr/include/'
        ]

Here’s what I currently have for C++:

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BASE_FLAGS = [
    '-Wall',
    '-Wextra',
    '-Werror',
    '-Wno-long-long',
    '-Wno-variadic-macros',
    '-fexceptions',
    '-ferror-limit=10000',
    '-DNDEBUG',
    '-std=c++11',
    '-xc++',
    '-DUSE_CLANG_COMPLETER',
    '-I/usr/include/'
    ]

Hopefully that has fixed the problem for you as it did for me. I’ve seen a few posts online and a few videos on YouTube of people saying they haven’t been able to get ycm to work for C and C++. Again I don’t know if this is the best way to get this to work but it can stay as a workaround for now until someone finds a better way to do so.