(PHP 4 >= 4.1.0, PHP 5, PHP 7)
Converts from a supported calendar to Julian Day Count
int cal_to_jd ( int $calendar, int $month, int $day, int $year )
cal_to_jd() calculates the Julian day count for a date in the specified calendar. Supported calendars are CAL_GREGORIAN, CAL_JULIAN, CAL_JEWISH and CAL_FRENCH.
Parameters:
calendar
Calendar to convert from, one of CAL_GR