(PHP 5 >= 5.5.0, PHP 7, PHP 8, PECL >= 3.0.0a1)
IntlCalendar::setFirstDayOfWeek — Set the day on which the week is deemed to start
面向对象风格
过程化风格
   Defines the day of week deemed to start the week. This affects the behavior
   of fields that depend on the concept of week start and end such as
   IntlCalendar::FIELD_WEEK_OF_YEAR and
   IntlCalendar::FIELD_YEAR_WOY.
  
calendarIntlCalendar 实例。
dayOfWeek
      One of the constants IntlCalendar::DOW_SUNDAY,
      IntlCalendar::DOW_MONDAY, …,
      IntlCalendar::DOW_SATURDAY.
     
   总是返回 true。
  
示例 #1 IntlCalendar::setFirstDayOfWeek()
<?php
ini_set('date.timezone', 'Europe/Lisbon');
ini_set('intl.default_locale', 'es_ES');
$cal = IntlCalendar::createInstance();
$cal->set(2013, 5 /* June */, 30); // A Sunday
var_dump($cal->getFirstDayOfWeek()); // 2 (Monday)
echo IntlDateFormatter::formatObject($cal, <<<EOD
'local day of week: 'cc'
week of month    : 'W'
week of year     : 'ww
EOD
), "\n";
$cal->setFirstDayOfWeek(IntlCalendar::DOW_SUNDAY);
echo IntlDateFormatter::formatObject($cal, <<<EOD
'local day of week: 'cc'
week of month    : 'W'
week of year     : 'ww
EOD
), "\n";以上示例会输出:
int(2) local day of week: 7 week of month : 4 week of year : 26 local day of week: 1 week of month : 5 week of year : 27
