adding semantic trigger value for ycm when writing C++

init.vim

@@ -159,9 +159,11 @@ let g:gutentags_enabled = 0
     au FileType c,cpp,javascript,python,java,scala,sh,groovy,vim let g:gutentags_enabled=1
   augroup plug#end
 
-    Plug 'bfrg/vim-cpp-modern'
+Plug 'bfrg/vim-cpp-modern'
 Plug 'octol/vim-cpp-enhanced-highlight'
 
+let g:ycm_semantic_triggers = { 'cpp': ['re!(?=[a-zA-Z_]{1})'] }
+
 autocmd FileType c,cpp,h,hpp ClangFormatAutoEnable
 set encoding=UTF-8