我的Emacs配置里C语言默认的缩进风格是用4个空格，最近要修改Chromium的代码，而Google的C/C++风格统一为2个空格缩进，所以改代码的时候要把c-basic-offset设置为2。这样在不同项目间切换的时候很不方便。

在stackoverflow上发帖求助后发现了Emacs 23.1一个很好用的新功能，Per-Directory Local Variables，只需要在项目主目录下放一个.dir-locals.el文件，里面设置该项目特有的变量值，就能应用到整个项目了。

以我的Chromium为例，Google已经提供了一份C/C++风格的配置，只需要在~/chromius/src/.dir-locals.el里把google-c-style常量粘贴进去即可。另外我不知道为啥加上c-offsets-alist那段后Emacs缩进会变得很奇怪，所以我把它删了。附修改后的.dir-locals.el

((c++-mode . ((c-recognize-knr-p . nil)
              (c-enable-xemacs-performance-kludge-p . t) ; speed up indentation in XEmacs
              (c-basic-offset . 2)
              (indent-tabs-mode . nil)
              (c-comment-only-line-offset . 0)
              (c-hanging-braces-alist . ((defun-open after)
                                         (defun-close before after)
                                         (class-open after)
                                         (class-close before after)
                                         (namespace-open after)
                                         (inline-open after)
                                         (inline-close before after)
                                         (block-open after)
                                         (block-close . c-snug-do-while)
                                         (extern-lang-open after)
                                         (extern-lang-close after)
                                         (statement-case-open after)
                                         (substatement-open after)))
              (c-hanging-colons-alist . ((case-label)
                                         (label after)
                                         (access-label after)
                                         (member-init-intro before)
                                         (inher-intro)))
              (c-hanging-semi&comma-criteria
                . (c-semi&comma-no-newlines-for-oneline-inliners
                    c-semi&comma-inside-parenlist
                    c-semi&comma-no-newlines-before-nonblanks))
              (c-indent-comments-syntactically-p . nil)
              (comment-column . 40)
              (c-cleanup-list . (brace-else-brace
                                  brace-elseif-brace
                                  brace-catch-brace
                                  empty-defun-braces
                                  defun-close-semi
                                  list-close-comma
                                  scope-operator)))))