Question

I usually use 4 white spaces to indent C programs, but in order to keep in consistent with some open source projects, I have to change to 2-white-space indenting sometimes.

Currently my indenting style is assigned in my .emacs file with

(setq c-basic-offset 4)

And when I want to work on those 2-white-space indenting projects. I have to close my Emacs, modify the value, and start again. Is there any simpler way to do this?

Many thanks.

---

PS.
Setting c-basic-offset variable every time I open a source file is too much work, is it possible to choose different value depending on working directory?

Answer 1

Create a file in the directory you want to customize named .dir-locals.el, and edit it to contain:

((c-mode . ((c-basic-offset . 4))))

Note: This is new functionality in Emacs 23.1.

This takes advantage of the Per-Directory Local Variables. From the documentation in the link:

The .dir-locals.el file should
hold a specially-constructed list.
This list maps Emacs mode names
(symbols) to alists; each alist
specifies values for variables to use
when the respective mode is turned on.
The special mode name `nil’ means that
its alist applies to any mode.
Instead of a mode name, you can
specify a string that is a name of a
subdirectory of the project’s
directory; then the corresponding
alist applies to all the files in that
subdirectory.

Here’s an example of a
.dir-locals.el file:

 ((nil . ((indent-tabs-mode . t)
          (tab-width . 4)
          (fill-column . 80)))
  (c-mode . ((c-file-style . "BSD")))
  (java-mode . ((c-file-style . "BSD")))
  ("src/imported"
   . ((nil . ((change-log-default-name . "ChangeLog.local"))))))