Modifier Keys

Conceptually, there are eight modifier keys. The global modifiers() function returns a value that encodes the current status of all eight of these keys. You can test for the state of a particular modifier key by comparing modifiers() with the constants listed in the table below. For example, here’s how you can see if the user is holding down one of the Shift keys:

if (modifiers() | B_SHIFT_KEY) {
   /* a shift key is down */
}

The modifier mask is also included in the “modifiers” field in BMessages that report keyboard and mouse events.

How your application uses modifier keys is up to you. The list below lists the eight keys and how they’re typically used.

Constant	Description
B_SHIFT_KEY	Maps character keys to their uppercase or alternative versions.
B_COMMAND_KEY	In combination with a character key, performs a keyboard shortcut.
B_CONTROL_KEY	Turns alphabetic keys into control characters.
B_OPTION_KEY	Maps keys to alternative characters, typically characters in an extended set—multibyte UTF-8 characters.
B_MENU_KEY	Pops open a menu.
B_CAPS_LOCK	Reverses the effect of the Shift key on alphabetic characters.
B_NUM_LOCK	Reverses the effect of the Shift key on numeric characters.
B_SCROLL_LOCK	Stops the display from scrolling.

If you’re interested in whether the left or right modifer key of a given type was pressed, you can check against these additional values:

B_LEFT_SHIFT_KEY   B_RIGHT_SHIFT_KEY
B_LEFT_CONTROL_KEY B_RIGHT_CONTROL_KEY
B_LEFT_OPTION_KEY  B_RIGHT_OPTION_KEY
B_LEFT_COMMAND_KEY B_RIGHT_COMMAND_KEY

Most of the modifiers map to single, specific keys: Shift and Caps Lock are examples. But others don’t: the Menu key maps to Shortcut+Escape (where Shortcut is either Alt, Command, or Control, depending on the user’s preferences and keyboard).