A C++ scheduling library using cron formatting.
This library uses std::chrono::system_clock::timepoint
as its time unit. While that is UTC by default, the Cron-class
uses a LocalClock
by default which offsets system_clock::now()
by the current UTC-offset. If you wish to work in
UTC, then construct the Cron instance, passing it a libcron::UTCClock
.
This implementation supports cron format, as specified below.
Each schedule expression conststs of 6 parts, all mandatory. However, if 'day of month' specifies specific days, then 'day of week' is ignored.
┌──────────────seconds (0 - 59)
│ ┌───────────── minute (0 - 59)
│ │ ┌───────────── hour (0 - 23)
│ │ │ ┌───────────── day of month (1 - 31)
│ │ │ │ ┌───────────── month (1 - 12)
│ │ │ │ │ ┌───────────── day of week (0 - 6) (Sunday to Saturday)
│ │ │ │ │ │
│ │ │ │ │ │
│ │ │ │ │ │
* * * * * *
- Allowed formats:
-
Special characters: '*', meaning the entire range.
-
'?' used to ignore day of month/day of week as noted below.
-
Ranges: 1,2,4-6
- Result: 1,2,4,5,6
-
Steps: n/m, where n is the start and m is the step.
1/2
yields 1,3,5,7...5/3
yields 5,8,11,14...*/2
yields Result: 1,3,5,7...
-
Reversed ranges:
0 0 23-2 * * *
, meaning top of each minute and hour, of hours, 23, 0, 1 and 2, every day.- Compare to
0 0 2-23 * * *
which means top of each minute and hour, of hours, 2,3...21,22,23 every day.
- Compare to
-
For month
, these (case insensitive) strings can be used instead of numbers: JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC
.
Example: JAN,MAR,SEP-NOV
For day of week
, these (case insensitive) strings can be used instead of numbers: SUN, MON, TUE, WED, THU, FRI, SAT
.
Example: MON-THU,SAT
Each part is separated by one or more whitespaces. It is thus important to keep whitespaces out of the respective parts.
-
Valid:
- 0,3,40-50 * * * * ?
-
Invalid:
- 0, 3, 40-50 * * * * ?
Day of month
and day of week
are mutually exclusive so one of them must at always be ignored using
the '?'-character unless one field already is something other than '*'.
Expression | Meaning |
---|---|
* * * * * ? | Every second |
0 0 12 * * MON-FRI | Every Weekday at noon |
0 0 12 1/2 * ? | Every 2 days, starting on the 1st at noon |
0 0 */12 ? * * | Every twelve hours |
Howard Hinnant's date libraries