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.