I'm trying to write c/c++ code with comments in LaTeX.

My .emacs file has the single line

(require 'org)

My source c/c++ file has the single line

\[ \int x \]

If I'm in python mode, fortran mode, org mode (or almost any mode) then doing org-latex-preview renders my LaTeX correctly. However, if I'm in c/c++ mode I get the error "wrong argument type: stringp, nil" and I'm just left with the raw LaTeX.

The debug backtrace is


Note that on my home machine I'm actually doing org-toggle-latex-fragment rather than org-latex-preview because the latter does not exist. I guess that's a different mystery, but the above problem applies to both my home and work setups.

My emacs lisp knowledge is almost non-existent but it seems to be failing to find anything that it classifies as LaTeX.

  • this is the first time I’ve learned that I can preview LaTeX in the code comments. amazing
    – shynur
    Commented Jul 14, 2023 at 11:40
  • I probably misunderstand what you are doing: can you post a complete file (in, say, python mode) and give a complete recipe of what you are doing and what the result is? AFAICT, previews only work if the file is in Org mode. They don't work for me if I have a comment in a python file (but no error) and they give me an error in a C file. My tentative conclusion is that any case where it "works" is accidental.
    – NickD
    Commented Jul 14, 2023 at 14:13
  • @NickD Thanks for looking into it. I've already posted everything though. The .emacs file is empty expect for "(require 'org)". My bob.py file is empty except for "[ \int x ]". To display the LaTeX I run either org-latex-preview or org-toggle-latex-fragment. That's it.Do you have LaTeX installed? Do you have dvipng installed (I think that's important). Commented Jul 14, 2023 at 14:53
  • 1
    When I try this it works for tmp.py, but gives an error in tmp.c, along with the recommendation to report this as a bug to the org mailing list. I'm not sure it's an actual bug though, I think org-latex-preview is meant to work in org-mode files, and it may just be a happy accident that it works in python as well? I'm not sure, but the org mailing list would be the best place to get an authoritative answer.
    – Tyler
    Commented Jul 14, 2023 at 15:06
  • My org-preview-latex-default-process is imagemagick rather than dvipng but I now see that it does work in a python mode buffer - not sure what I did earlier. I still think it's accidental, so I second @Tyler's recommendation.
    – NickD
    Commented Jul 14, 2023 at 15:15

1 Answer 1


You can apply AUCTeX's preview system to source code comments for C++ (or any language) by upgrading to AUCTeX 14.0.5 and adding the following to your config:

(defun my/set-TeX-master ()
  (setq TeX-master
        ;; Replace with the name of some basic tex file containing
        ;; your favorite packages and macros.

(add-hook 'prog-mode-hook #' my/set-TeX-master)

(unless (package-installed-p 'preview-auto)
  (package-vc-install "https://github.com/ultronozm/preview-auto.el"))
(use-package preview-auto
  :after latex
  (setq preview-protect-point t)
  (setq preview-locating-previews-message nil)
  (setq preview-leave-open-previews-visible t)

Then use M-x preview-auto-mode to toggle (automatic) previews and (e.g.) M-x preview-clearout-buffer to get rid of them.

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