6.2 Style Variables

The variables that CC Mode’s style system control are called style variables. Note that style variables are ordinary Lisp variables, which the style system initializes; you can change their values at any time (e.g., in a hook function). The style system can also set other variables, to some extent. See Styles.

Style variables are handled specially in several ways:

• Style variables are by default buffer-local variables. However, they can instead be made global by setting c-style-variables-are-local-p to nil before CC Mode is initialized.
• The default global binding of any style variable (with two exceptions - see below) is the special symbol set-from-style. When the style system initializes a buffer-local copy of a style variable for a CC Mode buffer, if its global binding is still that symbol then it will be set from the current style. Otherwise it will retain its global default¹⁶. This “otherwise” happens, for example, when you’ve set the variable with setq at the top level of your .emacs (see Config Basics).
• The style variable c-offsets-alist (see c-offsets-alist) is an association list with an element for each syntactic symbol. It’s handled a little differently from the other style variables. It’s default global binding is the empty list nil, rather than set-from-style. Before the style system is initialized, you can add individual elements to c-offsets-alist by calling c-set-offset (see c-offsets-alist) just like you would set other style variables with setq. Those elements will then prevail when the style system later initializes a buffer-local copy of c-offsets-alist.
• The style variable c-special-indent-hook is also handled in a special way. Styles can only add functions to this hook, not remove them, so any global settings you put on it are always preserved¹⁷. The value you give this variable in a style definition can be either a function or a list of functions.
• The global bindings of the style variables get captured in the special user style when the style system is first initialized. See Built-in Styles, for details.

The style variables are:
c-indent-comment-alist, c-indent-comments-syntactically-p (see Indentation Commands);
c-doc-comment-style (see Doc Comments);
c-block-comment-prefix, c-comment-prefix-regexp (see Custom Filling and Breaking);
c-hanging-braces-alist (see Hanging Braces);
c-hanging-colons-alist (see Hanging Colons);
c-hanging-semi&comma-criteria (see Hanging Semicolons and Commas);
c-cleanup-list (see Clean-ups);
c-basic-offset (see Customizing Indentation);
c-offsets-alist (see c-offsets-alist);
c-comment-only-line-offset (see Comment Line-Up);
c-special-indent-hook, c-label-minimum-indentation (see Other Indentation);
c-backslash-column, c-backslash-max-column (see Custom Macros).