questions about the value of local variables

[Hongxu Chen]

Hi,

  I am using Emacs for some C/C++ coding.

  One of the problem I am facing is that I need to specify some value of
  Emacs variables in the .dir-locals.el file so that I can make the
  programming environment much easier, one of which is
  `ffap-c-path'. Since I also need the default value , I hope I can
  append it rather that `setq'(like the default behavior of
  `.dir-locals.el'). But I just cannot figure how. May be I need to use
  `eval'?

  Another problem is that the file local variables I set cannot take
  effect before I type `M-x normal-mode', and for dir local variables it
  seems that I need to kill all the buffers who is inside the
  directory. So it there any easier way to do this?

  Still another question, is there any good practice to set the
  variables with proper hooks in c family programming language modes?
  There seems quite a lot of hooks there
  (`c-initialization-hook',`cc-mode-hook', `c-mode-hook',
  `c-mode-common-hook', etc) and I just get lost.
  

-- 
Regards,
Hongxu Chen