Re: How to use c-style to comment a region?

[martin rudalics <rudalics@gmx.at>]

 > I'm not sure I understand the problem (and hence the solution).  Can you
 > show me a recipe to reproduce this problem?

Sorry for being cryptic.  With emacs -Q customize `comment-style' to box
or box-multi.  In *scratch* insert

(foo bar baz)

set the region around bar and do `comment-region'.  Gets you

(foo ;; bar ;; baz)

instead of

(foo ;; bar ;;
      baz)

Responsible is the

     (when block (unless ce (setq ce (comment-string-reverse cs))))

line in `comment-region-internal' which makes the subsequent

       (unless (or ce (eolp)) (insert "\n") (indent-according-to-mode))

fail.  Obviously it fails in the cpp example of the OP as well.