21.12.2 Customizing Indentation in CC Mode

A very brief introduction is included here on customizing CC Mode. CC Mode has many features, including useful minor modes, that are completely documented in its own manual.

CC Mode implements several different “styles” for C code (and the other languages supported by CC Mode). If you need to change the indentation style for CC Mode it is recommended that you first see if an existing style meets your requirements. The style chosen will affect the placement of language elements like braces, function declarations and comments. You can choose a style interactively by typing C-c . and pressing the space bar at the prompt to get a list of supported styles. C-c . runs the function c-set-style which applies to all CC Mode language modes though its name might suggest otherwise. A few of the the supported styles are listed below.

• “gnu” — The recommeded style from the Free Software Foundation for GNU software.
• “k&r” — The classic style from Kernighan and Ritchie.
• “linux” — The style recommended for code in the Linux kernel.
• “bsd” — The style recommended for software developed in BSD.
• “java — The “traditional” Java style.

The default style in SXEmacs is “gnu” except for Java mode where it is the “java” style (this is governed by the variable c-default-style).

The styles included in CC Mode all use a buffer local variable called c-basic-offset as the basic indentation level (this buffer local variable is used in all CC Mode language modes though its name might suggest otherwise). All indentation is, by default, expressed in multiples of c-basic-offset.

Each style defines a default value for c-basic-offset, for the “gnu” style sets it to 2. A very common customization scenario is where a user wants to use an existing style but with a different basic offset value. An easy way to do this is to set c-basic-offset in the language mode hook after selecting the chosen style.

For example, a user might want to follow a local coding convention of using the “k&r” style for C code with indentation in two columns multiples (instead of the five column default provided by the CC Mode “k&r” style). This can be achieved with the following code in the initialization file (see Init File)

(defun my-c-mode-hook ()
  (c-set-style "k&r")
  (setq c-basic-offset 2))
(add-hook 'c-mode-hook 'my-c-mode-hook)

Most customizations for indentation in various CC modes can be accomplished by choosing a style and then choosing value for c-basic-offset that meets the local coding convention. CC Mode has a very customizable indentation engine and a furthur discussion is really beyond the scope of this manual. See Indentation Engine in The CC Mode Manual.