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Re: Functionality to maintain function prototypes in C

From: Pascal J. Bourguignon
Subject: Re: Functionality to maintain function prototypes in C
Date: Fri, 28 Oct 2016 23:38:04 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)

Nikolai Weibull <> writes:

> Hi!
> C has the issue of being compiled in a single pass.  After many years
> of working around this issue by defining my static functions in
> reverse order, which is good for the compiler, but bad for the user,
> I’m now looking to try writing them in a more natural order.  The main
> issue with this is maintaining the static-function prototypes.  I’ve
> looked around, but I can’t find a minor mode that’ll add, update, and
> remove static-function prototypes automatically, either by command or
> at file save, so I was hoping that someone here could point me in the
> right direction.

Once upon a time, I used macros:

In a file named BcInterface.h:

#define PROCEDURE(nam,prm,res)       extern         res      nam  prm    ;

In a file named BcImplementation.h:

#define PROCEDURE(nam,prm,res)                      res      nam  prm

Then it was a simple matter of:

( cat ${source}_header_prefix
  grep PROCEDURE ${source}.c
  cat ${source}_header_suffix ) > ${source}.h

But that was before I used emacs :-)

;;; Code:

(defun c-collect-defun-signatures ()
  "Return a list of C function signatures found in the buffer."
  (let ((signatures '())
        (last-defun -1))
    (goto-char (point-min))
    (while (/= last-defun (point))
      (setf last-defun (point))
      (when (re-search-forward "\\(.*(.*)\\)[^(){}]*{" nil t)
        (push (match-string 1) signatures))

(defun c-update-forward-defun-signatures ()
  "Update the forward function signatures.
If a section doesn't already exist, creates it at point."
  (let ((signatures (save-excursion (nreverse (c-collect-defun-signatures))))
        (section-begin "\n// BEGIN FORWARD FUNCTION SIGNATURES\n")
        (section-end   "\n// END FORWARD FUNCTION SIGNATURES\n"))
    (goto-char (or (save-excursion
                    (goto-char (point-min))
                    (when (re-search-forward
                           (format "%s.*%s" section-begin section-end)
                           nil t)
                      (delete-region (match-beginning 0) (match-end 0))
                      (match-beginning 0)))
    (insert section-begin)
    (dolist (signature signatures)
      (insert signature ";\n"))
    (insert section-end)))

(provide 'c-defun)
;;; c-defun.el ends here

The first time, move the point where you want the forward signatures to
be inserted and M-x c-update-forward-defun-signatures RET

Then  M-x c-update-forward-defun-signatures RET again will update the
same section, wherever the point is.

Now, you will have to move all the type definition used in the function
signature before this section…

__Pascal Bourguignon__       
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk

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