date_time_period示例boost :: locale :: period :: first_day_of_week（int v） [英] Example of date_time_period boost::locale::period::first_day_of_week(int v)

问题描述

在 boost :: locale文档它说：

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

取得date_time_period：星期几，常数，例如美国= 1的星期日，法国星期一= 2

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

我试图创建一个 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。这里是代码：

  #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））; //将星期的第一天设置为星期一
 date_time now（s）; // should be 2000-07-05 09:00:00，week starts from Monday 
 std :: cout<<现在< std :: endl;但是，运行程序会导致错误：
 $ b <$ p 
 
 
 
 $ b $ $ 
 $ b 
 在抛出'std :: invalid_argument'实例后调用terminate 
 what（）：无效的date_time期型类型
  
错误来自其ICU后端适配器：
  static UCalendarDateFields to_icu（period :: marks :: period_mark f）
 {
使用命名空间period :: marks; 
 
 switch（f）{
 case era：return UCAL_ERA; 
 case年：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小时：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; 
默认值：
 throw std :: invalid_argument（日期时间段类型无效）; 
} 
} 
  
  first_day_of_week 不可接受。
 
 
 
所以问题是：
 
 
创建一个 boost :: locale :: date_time 对象，并修改星期的第一天？ 
 
 
如何使用 date_time_period boost :: locale :: period :: first_day_of_week（int v） 
 
     b 
 
预备：
  std :: locale english = gen（en_US.UTF-8） ; 
 std :: locale french = gen（fr_FR.UTF-8）; 
 std :: cout.imbue（english）; //这一个不重要
 std :: locale :: global（french）; 
 
经过一些（广泛的）测试后，我发现 first_day_of_week  date_time 上的实例是：
 
 
 
 
 
 
 
 
 
 
  std :: locale :: global （英语）; 
 assert（1 == period :: first_day_of_week（date_time（）））; 
 
 std :: locale :: global（french）; 
 assert（2 == period :: first_day_of_week（date_time（）））; 
  
 
 
 
 
  或： 在建造期间传递的语言环境
  assert（1 == period :: first_day_of_week（date_time（english）））; 
 assert（2 == period :: first_day_of_week（date_time（french）））; 
  
 
 
 
 
  或：   （忽略区域设置）
传递的 date_time 对象
  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））; 
  
 
 
 
 
  和 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））; 
 //无效果
 dtps.add（period :: first_day_of_week（1））; 
 
 assert（2 == period :: first_day_of_week（date_time（dtps）））; 
} 
 
 {
 date_time dt; 
 //无效果：
 dt.set（period :: first_day_of_week（），1）; 
 assert（2 == period :: first_day_of_week（dt））; 
} 
  
 
 
 
 
 
 
是一个bug，我离开devs。你可以在boost邮件列表上问一下。肯定是令人惊讶的，因为一个 set 接口的存在表明这个属性可以改变。 
 
 
 
实际上，第一个weekday属性不是 date_time ，而是 locale 的属性，并且在 date_time 上显示为imbued 
 
 
 
完整测试：  Live on Coliru   
  #include< boost / locale.hpp> 
 #include< iostream> 
 
 int main（）
 {
使用命名空间boost :: locale; 
 generator gen; 
 
 std :: locale english = gen（en_US.UTF-8）; 
 std :: locale french = gen（fr_FR.UTF-8）; 
 std :: cout.imbue（english）; //这一个不重要
 std :: locale :: global（french）; 
 
 {
 std :: localale :: 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））; 
 //无效果
 dtps.add（period :: first_day_of_week（1））; 
 
 assert（2 == period :: first_day_of_week（date_time（dtps）））; 
} 
 
 {
 date_time dt; 
 //无效果：
 dt.set（period :: first_day_of_week（），1）; 
 assert（2 == period :: first_day_of_week（dt））; 
} 
 
 {
 //关联的区域设置被复​​制：
 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<< 所有测试通过了\\\
; 
} 
  
 
In boost::locale document it says:

  
date_time_period boost::locale::period::first_day_of_week(int v) [inline]
  
  
Get date_time_period for: First day of week, constant, for example Sunday in US = 1, Monday in France = 2
Those functions which return date_time_period can be used to create custom boost::locale::date_time objects.

I tried to create one with std::locale set to "en_US.UTF-8", so the first day of week is default to Sunday, and then modified it to Monday. Here's the code:
#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;
}
However, running the program results to an error:
terminate called after throwing an instance of 'std::invalid_argument'
what():  Invalid date_time period type
The error comes from its ICU backend adapter:
  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 is not acceptable.

So the questions are:

Can a boost::locale::date_time object be created with modified "the first day of week"? If true, how to do it?
How (or where) to use date_time_period boost::locale::period::first_day_of_week(int v)?

解决方案
This seems confusing indeed.

Preliminaries:
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);
After some (extensive) tests, I figured out that the value for first_day_of_week on a date_time instance is:


set from the global locale at the time of the construction
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()));

or: set from the locale that is passed during construction
assert(1 == period::first_day_of_week(date_time(english)));
assert(2 == period::first_day_of_week(date_time(french)));

or: set from the date_time object that is passed during copy construction (ignoring locale)
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));

and most importantly: cannot be set from another source than the locale
{
    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));
}



Whether or not this is a bug, I leave up to the devs. You can maybe ask it on the boost mailing list. It sure is surprising, as the presence of a set interface suggests that this property can be changed. 

In fact it appears that the first weekday property is not a property of a date_time in the first place, but rather a property of the locale, and it appears that the locale "imbued" on a date_time instance can not be changed except at construction/assignment.

Full tests: 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 passed\n";
}


                        
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