emacs lisp, how to get buffer major mode?

Question

I have tried to search Google and look in the manual, but still cannot find how to get major mode of a buffer object. Can you help me with an example or a reference. Thanks

only solution I could find was to query major-mode after changing the buffer and then changing back to original buffer. Is there a better way to do it?

Cinerator

Answer 1

Is there a problem with that?

(defun buffer-mode (buffer-or-string)
  "Returns the major mode associated with a buffer."
  (with-current-buffer buffer-or-string
     major-mode))

with-current-buffer will restore your buffer when it returns.

Twitter

You could also do this with (with-current-buffer buffer-or-string major-mode) instead of save-excursion. – Alonaalone

@haxney: Using (save-excursion (set-buffer ..) ...) is indeed deprecated in favor of (with-current-buffer ...). The byte-compiler of Emacs-24 warns about such uses. – Paraformaldehyde

@stefan: Where might an emacs noob see such deprecations? – Frowsy

As noted, the byte-compiler warns about it: just byte-compile your files, it will give you useful advice. – Paraformaldehyde

It works, but I'm curious if emacs can handle this straightforward? Why should we change the target buffer shortly to current, apply function, and change it back? Why isn't there a function that takes a buffer and return its major-mode directly? Is it for some historical convention? Or there are deeper facts in emacs that prevent us doing that? – Stranglehold

Answer 2

For current buffer:

(message "%s" major-mode)

Musjid

Answer 3

A simple way to do this is to use the buffer-local-value function since major-mode is a buffer-local variable:

(buffer-local-value 'major-mode (get-buffer "*scratch*"))

Oscan

This actually answers the original asker's question. which is how to do this without switching buffers. – Scrouge

Answer 4

Just extending from previous answers - call with no arguments to get the current buffer's mode:

(defun buffer-mode (&optional buffer-or-name)
  "Returns the major mode associated with a buffer.
If buffer-or-name is nil return current buffer's mode."
  (buffer-local-value 'major-mode
   (if buffer-or-name (get-buffer buffer-or-name) (current-buffer))))

E.g. in *scratch* buffer:

(buffer-mode) => 'lisp-interaction-mode

(buffer-mode "tasks.org") => 'org-mode

Uncork

Thanks for offering a comprehensive solution! – Haftarah

Answer 5

Well, describe-mode takes an optional buffer argument, but that displays the help... and I'm not exactly sure what it returns...

But that's the best I could find in a brief search... sorry...

Cowie

Answer 6

Simply evaluate this:

(print major-mode)

Indicia

Answer 7

Another way, apart from directly readind the major-mode variable would be by directly readind the mode-name variable.

Phalansterian