This is a function to show what C/C++ function/struct/class the cursor is in. I think this method is fast enough for practical use, but it's not complete.

function! GetProtoLine()
  let ret       = ""
  let line_save = line(".")
  let col_save  = col(".")
  let top       = line_save - winline() + 1
  let so_save = &so
  let &so = 0
  let istypedef = 0
  " find closing brace
  let closing_lnum = search('^}','cW')
  if closing_lnum > 0
    if getline(line(".")) =~ '\w\s*;\s*$'
      let istypedef = 1
      let closingline = getline(".")
    endif
    " go to the opening brace
    normal! %
    " if the start position is between the two braces
    if line(".") <= line_save
      if istypedef
        let ret = matchstr(closingline, '\w\+\s*;')
      else
        " find a line contains function name
        let lnum = search('^\w','bcnW')
        if lnum > 0
          let ret = getline(lnum)
        endif
      endif
    endif
  endif
  " restore position and screen line
  exe "normal! " . top . "Gz\<CR>"
  call cursor(line_save, col_save)
  let &so = so_save
  return ret
endfunction

function! WhatFunction()
  if &ft != "c" && &ft != "cpp"
    return ""
  endif
  let proto = GetProtoLine()
  if proto == ""
    return "?"
  endif
  if stridx(proto, '(') > 0
    let ret = matchstr(proto, '\w\+(\@=')
  elseif proto =~# '\<struct\>'
    let ret = matchstr(proto, 'struct\s\+\w\+')
  elseif proto =~# '\<class\>'
    let ret = matchstr(proto, 'class\s\+\w\+')
  else
    let ret = strpart(proto, 0, 15) . "..."
  endif
  return ret
endfunction

" You may want to call WhatFunction in the statusline
set statusline=%f:%{WhatFunction()}\ %m%=\ %l-%v\ %p%%\ %02B

This function works well in the following testcase:

void draw()
{
    // When cursor is here, WhatFunction() shows "draw"
    glClear(GL_COLOR_BUFFER_BIT {{|}} GL_DEPTH_BUFFER_BIT);
}

typedef struct {
    int ident;  // { <- braces in comments are ignored thanks to %. Great!
    int version;    // here it shows "} HEADER"
} HEADER;

# define EX(a, b, c, d)  a
enum CMD_index
#endif
{
EX(CMD_append, "append", ex_append); // here "enum CMD_index..."
};

class Sys {
public:
    load() {
        // NG: here, it shows "Sys" instead of "load"...
    }
};

class Camera : public Object
{
public:
    void init();
};

void Camera::init()
{
    // here WhatFunction shows "init"
}

Comments

I again had some problems with scrolling. This time, side-to-side scrolling in diff mode (specifically no line wrap). When the text was scrolled left, pressing 'h' or 'l' would act as if I'd pressed 'zh' or 'zl'.

Similar to the previous issue, I solved the problem by storing the value returned from wincol() in a variable, at the beginning of GetProtoLine(). Then at the end of GetProtoLine(), if wincol() is different, I scroll appropriately.

So:

  " restore position and screen line
  exe "normal! " . top . "Gz\<CR>"
  call cursor(line_save, col_save)
  let &so = so_save

Became:

  " restore position and screen line
  exe "normal! " . top . "Gz\<CR>"
  call cursor(line_save, col_save)
  let line_diff = winline() - window_line
  if line_diff > 0
    exe 'normal ' . line_diff . '^E'
  elseif line_diff < 0
    exe 'normal ' . -line_diff . '^Y'
  endif
  let &so = so_save

---

But should be:

  " restore position and screen line
  exe "normal! " . top . "Gz\<CR>"
  call cursor(line_save, col_save)
  let line_diff = winline() - window_line
  " check if we are in diff mode
  if &diff
    if line_diff > 0
      exe 'normal ' . line_diff . '^E'
    elseif line_diff < 0
      exe 'normal ' . -line_diff . '^Y'
    endif
  endif
  let &so = so_save

We need to check if we are in diff mode or it will fail otherwise

---

---

Calling WhatFunction() in the status line breaks multi-line actions like "2yy" for me, just one line is copied instead of two. Any idea how to fix that?

---

To use it, simply enter this (perhaps using a mapping) to show the function name:

:echo WhatFunction()

Or use it in the statusline as already mentioned.

The method of finding opening brace can be replaced by the one of script#1628. That's better?

---

The regexp used to find the function name, assumes that the function name would not have underscores

present code:

let ret = matchstr(proto, '\w\+(\@=')

could be:

let ret = matchstr(proto, '[[:alnum:]_ ]\+(\@=')

---

Don't forget that you'll have tildes in destructor names.

So:

let ret = matchstr(proto, '[[:alnum:]_ ]\+(\@=')

could be:

let ret = matchstr(proto, '\~\?[[:alnum:]_ ]\+(\@=')

---

I set this up to show the function name in my statusline. However, when I was diff-ing two different versions of the same file, and odd scrolling behavior occurred... With the cursor on the bottom line of the window, I pressed 'k', and vi acted as if I pressed 'Ctrl-y'.

I solved the problem by storing the value returned from winline() in a variable, at the beginning of GetProtoLine(). Then at the end of GetProtoLine(), if winline() is different, I scroll appropriately.

---

A shorter (but not perfect) method

type "[[" - jump to the previous '{' in the first column. Of course functions must look like this:

  type function_name( ... )
  {
      ...
  }

not

  type function_name( ... ) {
     ...
  }

jump back with "CTRL-O"

---

Jumplist fix

The script modified the :jumplist, to fix this, change normal! % to keepjumps normal! % and exe "normal! " . top . "Gz\<CR>" to exe "keepjumps normal! " . top . "Gz\<CR>".

(BTW, the original reg ex accepts "_", because it is in \w, why should a change be needed?)

---

I think it could be helpful to add a way to quickly disable it for a buffer:

  " allow to quickly disable it (:let b:noWhatFunction=1)
  if exists("b:noWhatFunction") && b:noWhatFunction
    return ""
  endif

---

All-in-One-Version

To simplify using all the improvements, here an update C&P-ready:

function! GetProtoLine()
  let ret       = ""
  let line_save = line(".")
  let col_save  = col(".")
  let window_line = winline()
  let top       = line_save - winline() + 1
  let so_save = &so
  let &so = 0
  let istypedef = 0
  " find closing brace
  let closing_lnum = search('^}','cW')
  if closing_lnum > 0
    if getline(line(".")) =~ '\w\s*;\s*$'
      let istypedef = 1
      let closingline = getline(".")
    endif
    " go to the opening brace
    keepjumps normal! %
    " if the start position is between the two braces
    if line(".") <= line_save
      if istypedef
        let ret = matchstr(closingline, '\w\+\s*;')
      else
        " find a line contains function name
        let lnum = search('^\w','bcnW')
        if lnum > 0
          let ret = getline(lnum)
        endif
      endif
      let lines = closing_lnum - line(".")
      let line_rel = line_save - line(".")
      let ret = ret . ':' . line_rel . '/' . lines
      "let ret .= ":" . line_save - line(".")
    endif
  endif
  exe "keepjumps normal! " . top . "Gz\<CR>"
  " restore position and screen line
  call cursor(line_save, col_save)
  " needed for diff mode (scroll fixing)
  let line_diff = winline() - window_line
  if line_diff > 0
    exe 'normal ' . line_diff . '^E'
  elseif line_diff < 0
    exe 'normal ' . -line_diff . '^Y'
  endif
  let &so = so_save
  return ret
endfunction

function! WhatFunction()
  " allow to quickly disable it (:let b:noWhatFunction=1)
  if exists("b:noWhatFunction") && b:noWhatFunction
    return ""
  endif
  if &ft != "c" && &ft != "cpp"
    return ""
  endif
  let proto = GetProtoLine()
  if proto == ""
    return "?"
  endif
  let line_info = matchstr(proto, ':\d\+\/\d\+')
  if stridx(proto, '(') > 0
    let ret = matchstr(proto, '\~\?\w\+(\@=')
  elseif proto =~# '\<struct\>'
    let ret = matchstr(proto, 'struct\s\+\w\+')
  elseif proto =~# '\<class\>'
    let ret = matchstr(proto, 'class\s\+\w\+')
  else
    let ret = strpart(proto, 0, 15) . "..."
  endif
  let ret .= line_info
  return ret
endfunction