How could "C-x 4 b "which pop-up-window but display to the right?

Question

In emacs -Q, I strike C-x 4 b which invoke (switch-to-buffer-other-window) and display the other window vertically as

I reference it's source code

(defun switch-to-buffer-other-window (buffer-or-name &optional norecord)
  (interactive
   (list (read-buffer-to-switch "Switch to buffer in other window: ")))
  (let ((pop-up-windows t))
    (pop-to-buffer buffer-or-name t norecord)))

It apply the procedure of pop-up-window.

How could use "C-x 4 b" pop up the other window which display horizontally instead of vertically?

Answer 1

Try setting the value of split-width-threshold as it works for me when I have wide frames: switching to a buffer in another window splits to the right.

Answer 2

Try M-x windmove-display-right RET C-x 4 b.

In general, other than binding windmove-display-* functions, you can evaluate (windmove-display-default-keybindings '(control meta shift)), then you can use C-M-S-arrow key to tell Emacs where to open the next buffer. For instance, C-M-S-right C-x 4 b. I think windmove-display-default-keybindings is available only on Emacs 27 or newer, but AFAIK windmove-display-* may be available in older versions.