Example of date_time_period boost::locale::period::first_day

Question

在boost：：locale文档中它说：

date_time_period boost：：locale：:p eriod：：first_day_of_week（int v） [inline]

获取以下方面的date_time_period：一周的第一天，常量，例如美国的星期日 = 1，法国的星期一 = 2

那些返回date_time_period的函数可用于创建自定义boost::locale::date_time对象。

我尝试创建一个std::locale设置为 "en_US.UTF-8" ，因此一周的第一天默认为星期日，然后将其修改为星期一。代码如下：

#include <iostream>
#include <boost/locale.hpp>
int main() {
  using namespace boost::locale;
  date_time_period_set s;
  generator gen;
  std::locale locale = gen("en_US.UTF-8");
  std::locale::global(locale);
  std::cout.imbue(locale);
  s.add(period::year(2000));
  s.add(period::month(6));
  s.add(period::day(5));
  s.add(period::hour(9));
  s.add(period::minute(0));
  s.add(period::second(0));
  s.add(period::first_day_of_week(2));// set the first day of week to Monday
  date_time now(s); // should be 2000-07-05 09:00:00, week starts from Monday
  std::cout << now << std::endl;
}

但是，运行该程序会导致错误：

terminate called after throwing an instance of 'std::invalid_argument'
what():  Invalid date_time period type

错误来自其 ICU 后端适配器：

  static UCalendarDateFields to_icu(period::marks::period_mark f)
  {
      using namespace period::marks;
      switch(f) {
      case era: return UCAL_ERA;
      case year: return UCAL_YEAR;
      case extended_year: return UCAL_EXTENDED_YEAR;
      case month: return UCAL_MONTH;
      case day: return UCAL_DATE;
      case day_of_year: return UCAL_DAY_OF_YEAR;
      case day_of_week: return UCAL_DAY_OF_WEEK;
      case day_of_week_in_month:  return UCAL_DAY_OF_WEEK_IN_MONTH;
      case day_of_week_local: return UCAL_DOW_LOCAL;
      case hour: return UCAL_HOUR_OF_DAY;
      case hour_12: return UCAL_HOUR;
      case am_pm: return UCAL_AM_PM;
      case minute: return UCAL_MINUTE;
      case second: return UCAL_SECOND;
      case week_of_year: return UCAL_WEEK_OF_YEAR;
      case week_of_month: return UCAL_WEEK_OF_MONTH;
      default:
          throw std::invalid_argument("Invalid date_time period type");
      }
  }

first_day_of_week是不可接受的。

所以问题是：

1. 是否可以使用修改后的"一周的第一天"创建boost::locale::date_time对象？如果属实，该怎么做？
2. 如何（或在哪里）使用date_time_period boost::locale::period::first_day_of_week(int v)？

Answer 1

这

似乎确实令人困惑。

预赛：

std::locale english = gen("en_US.UTF-8");
std::locale french  = gen("fr_FR.UTF-8");
std::cout.imbue(english); // this one doesn't matter
std::locale::global(french);

经过一些（广泛的）测试，我发现date_time实例上的first_day_of_week值为：

• 从构造时的全局区域设置设置

  std::locale::global(english);
  assert(1 == period::first_day_of_week(date_time()));
  std::locale::global(french);
  assert(2 == period::first_day_of_week(date_time()));
  

• 或者：从构造期间传递的区域设置中设置

  assert(1 == period::first_day_of_week(date_time(english)));
  assert(2 == period::first_day_of_week(date_time(french)));
  

• 或者：从复制构造期间传递的date_time对象设置（忽略区域设置）

  date_time edt(english), fdt(french);
  assert(1 == period::first_day_of_week(edt));
  edt = date_time(french);
  assert(2 == period::first_day_of_week(edt));
  fdt = date_time(english);
  assert(1 == period::first_day_of_week(fdt));
  

• 最重要的是：不能从区域设置以外的其他来源设置

  {
      date_time_period_set dtps;
      dtps.add(period::friday());
      dtps.add(period::week_of_year(4));
      // no effect
      dtps.add(period::first_day_of_week(1));
      assert(2 == period::first_day_of_week(date_time(dtps)));
  }
  {
      date_time dt;
      // no effect:
      dt.set(period::first_day_of_week(), 1);
      assert(2 == period::first_day_of_week(dt));
  }
  

无论这是否是一个错误，我都留给开发人员。你也许可以在提升邮件列表中询问它。这确实令人惊讶，因为set接口的存在表明可以更改此属性。

事实上，第一个工作日属性似乎首先不是date_time的属性，而是locale的属性，并且似乎"灌输"在date_time实例上的区域设置不能更改，除非在构造/分配时。

完整测试：Live On Coliru

#include <boost/locale.hpp>
#include <iostream>
int main()
{
    using namespace boost::locale;
    generator gen;
    std::locale english = gen("en_US.UTF-8");
    std::locale french  = gen("fr_FR.UTF-8");
    std::cout.imbue(english); // this one doesn't matter
    std::locale::global(french);
    {
        std::locale::global(english);
        assert(1 == period::first_day_of_week(date_time()));
        std::locale::global(french);
        assert(2 == period::first_day_of_week(date_time()));
    }
    {
        assert(1 == period::first_day_of_week(date_time(english)));
        assert(2 == period::first_day_of_week(date_time(french)));
    }
    {
        date_time_period_set dtps;
        dtps.add(period::friday());
        dtps.add(period::week_of_year(4));
        // no effect
        dtps.add(period::first_day_of_week(1));
        assert(2 == period::first_day_of_week(date_time(dtps)));
    }
    {
        date_time dt;
        // no effect:
        dt.set(period::first_day_of_week(), 1);
        assert(2 == period::first_day_of_week(dt));
    }
    {
        // associated locale gets copied:
        date_time edt(english), fdt(french);
        assert(1 == period::first_day_of_week(edt));
        edt = date_time(french);
        assert(2 == period::first_day_of_week(edt));
        fdt = date_time(english);
        assert(1 == period::first_day_of_week(fdt));
    }
    std::cout << "All tests passedn";
}