Subword Movement (CC Mode Manual)

4.9 Subword Movement and Editing

In spite of the GNU Coding Standards, it is popular to name a symbol by mixing uppercase and lowercase letters, e.g. ‘GtkWidget’, ‘EmacsFrameClass’, or ‘NSGraphicsContext’. Here we call these mixed case symbols nomenclatures. Also, each capitalized (or completely uppercase) part of a nomenclature is called a subword. Here are some examples:

Nomenclature	Subwords
‘`GtkWindow`’	‘`Gtk`’ and ‘`Window`’
‘`EmacsFrameClass`’	‘`Emacs`’, ‘`Frame`’, and ‘`Class`’
‘`NSGraphicsContext`’	‘`NS`’, ‘`Graphics`’, and ‘`Context`’

The subword minor mode replaces the basic word oriented movement and editing commands with variants that recognize subwords in a nomenclature and treat them as separate words:

Key	Word oriented command	Subword oriented command
`M-f`	`forward-word`	`c-forward-subword`
`M-b`	`backward-word`	`c-backward-subword`
`M-@`	`mark-word`	`c-mark-subword`
`M-d`	`kill-word`	`c-kill-subword`
`M-DEL`	`backward-kill-word`	`c-backward-kill-subword`
`M-t`	`transpose-words`	`c-transpose-subwords`
`M-c`	`capitalize-word`	`c-capitalize-subword`
`M-u`	`upcase-word`	`c-upcase-subword`
`M-l`	`downcase-word`	`c-downcase-subword`

Note that if you have changed the key bindings for the word oriented commands in your .emacs or a similar place, the keys you have configured are also used for the corresponding subword oriented commands.

Type C-c C-w to toggle subword mode on and off. To make the mode turn on automatically, put the following code in your .emacs:

(add-hook 'c-mode-common-hook
          (lambda () (c-subword-mode 1)))

As a bonus, you can also use c-subword-mode in non-CC Mode buffers by typing M-x c-subword-mode.