ediff-split-window-function horizontal==vertical?

Question

Emacs 23.1.1 Ediff 2.81.2 on CentOs 6

Prior to any customization, Ediff would, by default, split the windows horizontally (one on top of the other).

I wante

Answer 1

I used emacs variable customization, invoked with C-h v ediff-split-window-function to change the value. After clicking Save for future sessions the following was written to my .emacs:

(custom-set-variables
...
 '(ediff-split-window-function (quote split-window-horizontally))
...)

And it does exactly what I want: putting the two buffers side-by-side. And yes, emacs uses horizontal/vertical in the opposite of what you had in mind. If you read this question again, you will see the explanation, others were confused, too.

Answer 2

Hitting "|" when you are in ediff mode with the 2 files loaded switches from horizontal to vertical.
"?" gives a little ediff help menu. (I'm on Debian Wheezy with emacs 23.4+1-4)

Answer 3

While it doesn't quite answer your problem, you could also use a function to specify whether to split vertically or horizontally depending on window dimensions:

(setq ediff-split-window-function 'split-window-sensibly)

split-window-sensibly is built-in.