xtd - Reference Guide  0.1.0
Modern c++17 framework to create console, gui and unit test applications on Windows, macOS and Linux.

§ check_state

Specifies the state of a control, such as a check box, that can be checked, unchecked, or set to an indeterminate state.

Remarks
Multiple methods in check_box, checked_list_box, and item_check_event_args use this enumeration.
Note
Use an indeterminately checked control when you do not want to set a default value.
Enumerator
unchecked 

The control is unchecked.

checked 

The control is checked.

indeterminate 

The control is indeterminate. An indeterminate control generally has a shaded appearance.