Obtains the selected date from a GtkCalendar.
location to store the year as a decimal number (e.g. 2011), or NULL. out[allow-none]
location to store the month number (between 0 and 11), or NULL. out[allow-none]
location to store the day number (between 1 and 31), or NULL. out[allow-none]
See Implementation
Obtains the selected date from a GtkCalendar.