JDDayOfWeek()

(PHP 4, PHP 5, PHP 7)

返回星期的日期

说明

jddayofweek(int $julianday[,int $mode= CAL_DOW_DAYNO]): mixed

返回星期的日期，根据模式不同可能是字符串或是整数。

参数

$julianday

一个julian天数。

$mode

历法星期模式

Mode	Meaning
0(默认)	返回数字形式(0=Sunday, 1=Monday, etc)
1	返回字符串形式(English-Gregorian)
2	返回缩写形式的字符串(English-Gregorian)

返回值

数字或字符串形式的星期数。

You need to check to see how your client wants to represent the day of week. This function returns 0 for Sundays. ISO 8601 uses 7 for Sundays.
BTW, You can also calculate the day of week with modular division:
$dow = (1 + $julianday) % 7; // returns 0 for Sundays.
$dow = ($julianday % 7) + 1; // returns 7 for Sundays.
https://en.wikipedia.org/wiki/Julian_day#Finding_day_of_week_given_Julian_day_number
To make matters confusing. The Julian Date starts at noon UTC. Some programs such as SQLITE3 use real numbers to record date and time. If you pass this function a float; it will return a different day of week for the morning than for the afternoon.
When given a julianday with a decimal part you will need to add a half day and may need further adjustment for your timezone.