I want to see the source code of the function other-buffer. When I use M-x- xref-find-definitions, Emacs shows:visit tags table (default TAGS). Then I press RET, Emacs shows:File /TAGS does not exist.
What should I do if I want to see the source code?
I'm reading an introduction book and I got stuck with the expression:
(other-buffer (current-buffer) t)
This is why I want to see the source code. And this is my second day learning Emacs.

System: macOS

  • Are you on Linux, Mac or Windows?
    – nephewtom
    Jan 14, 2021 at 14:39
  • @nephewtom MacOS
    – Lluvio Liu
    Jan 18, 2021 at 6:13
  • Honestly, if you are an Emacs newcomer, I would not recommend starting with its C source code.
    – nephewtom
    Jan 18, 2021 at 14:02

2 Answers 2


Unless you've compiled your Emacs you have to download the C source code separately. If you're on GNU, some distros allow downloading the source code using the package manager, which makes upgrading a bit easier. For example here's a tutorial for installing the source code on Fedora.

Once you have the source code tree in a directory, say ~/src/emacs-27.1/src, add

(setq find-function-C-source-directory (concat "~/src/emacs-" emacs-version "/src"))

to your init.el. The (concat "~/src/emacs-" emacs-version "/src") bit evaluates to "~/src/emacs-27.1/src" (assuming your Emacs is version 27.1), so you don't need to update this setting when you upgrade Emacs. The variable find-function-C-source-directory stores the directory Emacs looks into for the C source files (see C-hv find-function-C-source-directory).

Since you're on MacOS I can't suggest anything in particular but to try

git clone https://git.savannah.gnu.org/git/emacs.git

That should get you the full source tree. Place it on a directory of your choice and set find-function-C-source-directory, then both xref-find-definitions and links in describe-function/describe-variable (C-h f/C-h v) and should work.


Usually the way to do that is to type M-x describe-function in the minibuffer, then enter other-buffer. That will show you a help window on the function with the documentation on that function. At the top is usually a link to the source code of the function you can click on to get there. other-buffer is implemented in the C source code though so you unless you installed emacs from source you probably can't get to it this way.

  • There's been discussion about always installing the C-sources precisely for this use case. Disk space is cheap after all (but the distributions would probably just strip it out again <sigh>)
    – rpluim
    Jan 14, 2021 at 10:48
  • 2
    See also M-x find-function RET.
    – Basil
    Jan 14, 2021 at 11:26

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