VI. Calendar Functions
The calendar extension presents a series of functions to simplify converting between different calendar formats. The intermediary or standard it is based on is the Julian Day Count. The Julian Day Count is a count of days starting from January 1st, 4713 B.C. To convert between calendar systems, you must first convert to Julian Day Count, then to the calendar system of your choice. Julian Day Count is very different from the Julian Calendar! For more information on Julian Day Count, visit http://www.hermetic.ch/cal_stud/jdn.htm. For more information on calendar systems visit http://www.boogle.com/info/cal-overview.html. Excerpts from this page are included in these instructions, and are in quotes.
To get these functions to work, you have to compile PHP with --enable-calendar.
PHP 的 Windows 版本已经内置该扩展模块的支持。您无需加载任何附加的扩展库即可使用这些函数。
由于这些常量是由该扩展模块定义的，因此只有在该扩展模块被编译到 PHP 中，或者在运行时被动态加载后，这些常量才有效。
The following constants are available since PHP 4.3.0 :
The following constants are available since PHP 5.0.0 :