I write a elisp function to copy the current line if no region has be selected, but it does not work on emacs 24.5. When I hit the "M-w" keystrokes , there comes a message "Mark set" in the minibuffer. Did I miss something?
(defun copy-region-or-current-line (beg end)
"copy current if no region selected, copy the region otherwise"
(interactive "r")
(let ((cur-pos (point)))
(if (region-active-p)
(kill-ring-save beg end)
(progn
(kill-whole-line)
(yank)
(goto-char cur-pos)))))
(global-set-key (kbd "M-w") 'copy-region-or-current-line)
Your function works: You're calling yank and that command sets the mark; hence the message.
That's a side effect you undoubtedly don't want, though, and the kill+yank sequence isn't necessary.
You already know about kill-ring-save, so just use that with (line-beginning-position) and (line-end-position).
FYI, on account of the optional REGION argument to kill-ring-save, you could rewrite this as:
(defun copy-region-or-current-line ()
"Copy the active region or the current line to the kill ring."
(interactive)
(if (region-active-p)
(kill-ring-save nil nil t)
(kill-ring-save (line-beginning-position) (line-end-position))))