Bitwise OR of constants
- by ryyst
While reading some documentation here, I came across this:
unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit;
NSDateComponents *comps = [gregorian components:unitFlags fromDate:date];
I have no idea how this works. I read up on the bitwise operators in C, but I do not understand how you can fit three (or more!) constants inside one int and later being able to somehow extract them back from the int? Digging further down the documentation, I also found this, which is probably related:
typedef enum {
kCFCalendarUnitEra = (1 << 1),
kCFCalendarUnitYear = (1 << 2),
kCFCalendarUnitMonth = (1 << 3),
kCFCalendarUnitDay = (1 << 4),
kCFCalendarUnitHour = (1 << 5),
kCFCalendarUnitMinute = (1 << 6),
kCFCalendarUnitSecond = (1 << 7),
kCFCalendarUnitWeek = (1 << 8),
kCFCalendarUnitWeekday = (1 << 9),
kCFCalendarUnitWeekdayOrdinal = (1 << 10),
} CFCalendarUnit;
How do the (1 << 3) statements / variables work? I'm sorry if this is trivial, but could someone please enlighten me by either explaining or maybe posting a link to a good explanation?
Thanks!
-- ry
