How can I fold GNU C style functions in Vim correctly?

Question

When writing C code, I use a mixture of GNU and K&R style. This means that the return value, each parameter and the opening body curly brace of a function is on its own line. I would also like to use Vim's folding feature but with foldmethod=syntax, the folding looks like this:

bad-folding

Is it possible to see the function name in the fold summary without any special fold markers or foldexprs?

http://stackoverflow.com/questions/762310/how-can-i-automatically-fold-a-long-c-code-in-vim — manav m-n, Dec 04 '12 at 12:18
@matthias find you some solution for the correct folding in C? — JuanPablo, Nov 16 '16 at 13:33
No unfortunately not. And because of that I do not fold C code except manually :-( — matthias, Nov 16 '16 at 13:36

score 2 · Answer 1 · answered Jan 26 '13 at 04:09

Something which might be a good compromise - if you use the indent fold - is to set the foldminlines parameter to a higher number.

:set foldmethod=indent
:set foldminlines=5

If most of your functions are long, it will affect only your list of parameters. The downside obviously is, that it will automatically unfold also small functions which are smaller then 5 lines long.

score 1 · Answer 2 · answered Nov 19 '12 at 23:13

Try this as a starting point (I have it in my vimrc but I found it online):

" Folding {
function! CssFoldText()
    let line = getline(v:foldstart)
    let nnum = nextnonblank(v:foldstart + 1)
    while nnum < v:foldend+1
        let line = line . " " . substitute(getline(nnum), "^ *", "", "g")
        let nnum = nnum + 1 
    endwhile
    return line
endfunction

setlocal foldtext=CssFoldText()
setlocal foldmethod=marker
setlocal foldmarker={,}
setlocal fillchars=fold:/
setlocal foldlevel=-1
"   highlight Folded term=underline cterm=bold gui=bold guifg=Blue guibg=Black
"   highlight FoldColumn term=underline cterm=bold gui=bold guifg=Blue guibg=Black
"}

Jorengarenar · Answer 3 · 2020-12-15T14:34:45.553

It's possible to do it also with syntax folding. You need to add the following to ~/.vim/after/syntax/c.vim:

let s:contains = ''
if exists("c_curly_error")
  let s:contains = ' contains=ALLBUT,cBadBlock,cCurlyError,@cParenGroup,cErrInParen,cErrInBracket,@cStringGroup,@Spell'
endif

let s:pattern = '%('

if &ft ==# "cpp"
  " struct/class inheriting
  let s:pattern .= ''
        \ . '%(<struct|<class)@<='
        \ . '\s\ze\s*\S+[^:]:[^:]\s*\S+.*'
  let s:pattern .= '|'

  " Constructors
  let s:pattern .= ''
        \ . '%('
        \ .    '%([^,:]|\n|^|<%(public|private|protected)>\s*:)'
        \ .    '\n\s*'
        \ . ')@<='
        \ . '%(<%(while|for|if|switch|catch)>)@!'
        \ . '\S\ze\S*%(::\S+)*\s*\(.*\)\s*%(:.*)?'
  let s:pattern .= '|'
endif

let s:pattern .= '%(<%(while|for|if|switch|catch)\(.*)@<=\)\ze\s*' . '|'

let s:pattern .= ''
      \ . '%('
      \ .    '^\s*%(//.*|.*\*/|\{|<%(public|private|protected)>\s*:|.*\>)?'
      \ .    '\s*\n\s*\S+'
      \ . ')@<='
      \ . '\s\ze\s*\S+\s*'
      \ . '%(.*[^:]:[^:].*)@!'
      \ . '%(\s+\S+)*'

let s:pattern .= ')%(;\s*)@<!%(//.*|/\*.*\*/)?\n\s*'

syn clear cBlock
exec 'syn region cBlock_ end="}" fold' . s:contains
      \ . ' start = "\%#=1\C\v' . s:pattern . '\{"'
      \ . ' start = "\%#=1\C\v%(' . s:pattern . ')@<!\{"'

unlet s:contains s:pattern

But beware, if file is big, recalculating folds may be quite heavy.

How can I fold GNU C style functions in Vim correctly?

3 Answers3