我使用公历，想要实现IS0 8601的周数，但是在计算任何一周的日期时遇到了一些问题。例如，ISO日期2010-W01-1应该返回2010年1月4日，而2009-W01-1应该返回2008年12月29日。
// Get the date for a given year, week and weekday(1-7)
time_t *GetDateFromWeekNumber(int year, int week, int dayOfWeek)
{
// Algorithm here
}
编辑： 我尝试了很多在线算法，但都没有成功，现在有些困难。
GetDayAndMonthFromWeekInYear应该输出month中的1和dayInMonth中的2，表示2017-W01从星期一开始，即2017-01-02，而不是输出公历日期2017-01-01。 这个免费，开源的C++11 / 14库使用以下语法正确地将ISO周转换为公历日期。#include "date/date.h"
#include "date/iso_week.h"
#include <iostream>
int
main()
{
using namespace iso_week::literals;
std::cout << date::year_month_day{2017_y/1_w/mon} << '\n';
}
2017-01-02
2017_y/1_w/mon转换为自1970年01月01日以来的天数的序列计数：CONSTCD14
inline
year_weeknum_weekday::operator sys_days() const NOEXCEPT
{
return sys_days{date::year{int{y_}-1}/date::dec/date::thu[date::last]}
+ (date::mon - date::thu) + weeks{unsigned{wn_}-1} + (wd_ - mon);
}
然后，使用以下算法将连续的天数转换为 年/月/日 字段类型：
CONSTCD14
inline
year_month_day
year_month_day::from_sys_days(const sys_days& dp) NOEXCEPT
{
static_assert(std::numeric_limits<unsigned>::digits >= 18,
"This algorithm has not been ported to a 16 bit unsigned integer");
static_assert(std::numeric_limits<int>::digits >= 20,
"This algorithm has not been ported to a 16 bit signed integer");
auto const z = dp.time_since_epoch().count() + 719468;
auto const era = (z >= 0 ? z : z - 146096) / 146097;
auto const doe = static_cast<unsigned>(z - era * 146097); // [0, 146096]
auto const yoe = (doe - doe/1460 + doe/36524 - doe/146096) / 365; // [0, 399]
auto const y = static_cast<sys_days::rep>(yoe) + era * 400;
auto const doy = doe - (365*yoe + yoe/4 - yoe/100); // [0, 365]
auto const mp = (5*doy + 2)/153; // [0, 11]
auto const d = doy - (153*mp+2)/5 + 1; // [1, 31]
#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable: 4146) // unary minus operator applied to unsigned type, result still unsigned
#endif
auto const m = mp + (mp < 10 ? 3 : -9u); // [1, 12]
#ifdef _MSVC_VER
#pragma warning(pop)
#endif
return year_month_day{date::year{y + (m <= 2)}, date::month(m), date::day(d)};
}
后一种算法在此处已经被详细地记录。
#include <boost/date_time/gregorian/gregorian.hpp>
// Get the date for a given year, week and weekday(0-6)
time_t *GetDateFromWeekNumber(int year, int week, int dayOfWeek)
{
using namespace boost::gregorian;
date d(year, Jan, 1);
int curWeekDay = d.day_of_week();
d += date_duration((week - 1) * 7) + date_duration(dayOfWeek - curWeekDay);
tm tmp = to_tm(d);
time_t * ret = new time_t(mktime(&tmp));
return ret;
}
星期日 = 0，星期一 = 1，...，星期六 = 6。如果这不能满足您的需求，您可以使用这个稍微改变的函数：#include <boost/date_time/gregorian/gregorian.hpp>
// Get the date for a given year, week and weekday(1-7)
time_t *GetDateFromWeekNumber(int year, int week, int dayOfWeek)
{
using namespace boost::gregorian;
date d(year, Jan, 1);
if(dayOfWeek == 7) {
dayOfWeek = 0;
week++;
}
int curWeekDay = d.day_of_week();
d += date_duration((week - 1) * 7) + date_duration(dayOfWeek - curWeekDay);
tm tmp = to_tm(d);
time_t * ret = new time_t(mktime(&tmp));
return ret;
}
编辑：
经过思考，我找到了一种不使用boost也可以实现相同功能的方法。以下是代码：
警告：下面的代码有问题，请勿使用！
// Get the date for a given year, week and weekday(1-7)
time_t *GetDateFromWeekNumber(int year, int week, int dayOfWeek)
{
const time_t SEC_PER_DAY = 60*60*24;
if(week_day == 7) {
week_day = 0;
week++;
}
struct tm timeinfo;
memset(&timeinfo, 0, sizeof(tm));
timeinfo.tm_year = year - 1900;
timeinfo.tm_mon = 0;
timeinfo.tm_mday = 1;
time_t * ret = new time_t(mktime(&timeinfo)); // set all the other fields
int cur_week_day = timeinfo.tm_wday;
*ret += sec_per_day * ((week_day - cur_week_day) + (week - 1) * 7);
return ret;
}
编辑2：
是的，编辑中的代码完全失效，因为我没有花足够的时间了解如何分配周数。
使用 F#
open System
open System.Globalization
//wday: 1-7, 1:Monday
let DateFromWeekOfYear y w wday =
let dt = new DateTime(y, 1, 4) //first week include 1/4
let dow = if dt.DayOfWeek = DayOfWeek.Sunday then 7 else int dt.DayOfWeek //to 1-7
let dtf = dt.AddDays(float(wday - dow))
GregorianCalendar().AddWeeks(dtf, w - 1)