从C / C周数计算公历日期++ [英] Calculate Gregorian date from week number in C/C++

问题描述

我使用的公历，我想实现IS08601周，但我无意中发现了一个问题，计算任何周数的日期。例如，ISO日期 2010-W01-1 应该返回的 2010年1月4日和 2009年W01-1 应该返回的 2008年12月29日的。

I'm using the Gregorian calendar the and I want to implement IS0 8601 weeks, but I've stumbled onto a issue calculating the date of any week number. For example the ISO dates 2010-W01-1 should return January 4, 2010 and 2009-W01-1 should return December 29, 2008.

// 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： 我还没有发现，在线工作的任何算法，尝试了很多，但那种我现在卡住了。

I havent found any algorithm that works online, tried a lot but I'm kind of stuck now.

推荐答案

我花了二看我的C / C ++算法，并终于得到了我的周数，以日期转换公历工作（见 GetDayAndMonthFromWeekInYear（）以下）。因为我还没有发现这种转换在线（除了霍华德Hinnant（欣南特）的code）我已经决定要与你分享。在code传递的是基于维基百科的文章 HTTP发现的例子所有单元测试：// en.wikipedia.org/wiki/ISO_week_date#Examples 。

I took a second look at my C/C++ algorithms and finally got I the week number to date conversion to work with the Gregorian calendar (see GetDayAndMonthFromWeekInYear() below). Since I have not found this kind of conversion online (except for Howard Hinnant's code) I've decided to share it with you. The code passes all unit tests that are based on examples found in the Wikipedia article http://en.wikipedia.org/wiki/ISO_week_date#Examples .

/** ISO number of days in a year */
#define ISO_DAYS_A_YEAR 365

/** ISO number of days in a leap year */
#define ISO_DAYS_A_LEAP_YEAR 366

/** Number of ISO days a week */
#define ISO_DAYS_A_WEEK 7

/** Number of ISO days a week */
#define ISO_MONTHS_A_YEAR 12

/** ISO number of days in February */
#define ISO_DAYS_IN_FEBRUARY 28

/** ISO number of days in February in a leap year */
#define ISO_LEAP_YEAR_DAYS_IN_FEBRUARY 29

/** First month number in a ISO year */
#define ISO_FIRST_MONTH_IN_YEAR 1

/*!
\brief Get the year, month, and day in month from a week in year
\details An ISO week-numbering year has 52 or 53 full weeks (364 or 371 days)
\param year [in, out] Gregorian year
\param weekInYear [in] Gregorian week in a year
\param month [out] Gregorian month
\param dayInMonth [out] Gregorian day in month
\returns \c True if success or \c False if error
*/
bool GetDayAndMonthFromWeekInYear(int *year, int weekInYear, int *month, 
    int *dayInMonth) 
{
    int daysInMonth;
     int weeksInYear;
    *month = ISO_FIRST_MONTH_IN_YEAR;
    bool hasChanged;

    do
    {
        hasChanged = false;

        weeksInYear = GetNumberOfWeeksInYear(*year);
        if (weekInYear > weeksInYear)
        {
            weekInYear -= weeksInYear;
            (*year)++;
            hasChanged = true;
        }

    } while(hasChanged);

    int dayInYear = (weekInYear - 1)  * ISO_DAYS_A_WEEK + 1;

    // Since the first day of week 1 in a year in the Gregorian calendar is not usually January 1st we need to handle the offset
    static int t[] = {0, 0, -1, -2, -3, 3, 2, 1};
    int jan1DayOfWeek = GetDayOfTheWeek(*year, 1, 1); 
    dayInYear += t[jan1DayOfWeek];

    if (dayInYear <= 0)
    {
        // dayInYear is in the previous year
        (*year)--;
        dayInYear += GetDaysInYear(*year);
    }
    else
    {
        int daysInYear = GetDaysInYear(*year);
        if (dayInYear > daysInYear)
        {
            // dayInYear is in the next year
            (*year)++;
            dayInYear -= daysInYear;
        }
    }

    if (!GetDayAndMonthFromDayInYear(*year, dayInYear, month, dayInMonth))
        return false;

    return true;
}

enum EGregorianMonth
{
    EGregorianMonth_January = 1,
    EGregorianMonth_February = 2,
    EGregorianMonth_March = 3,
    EGregorianMonth_April = 4,
    EGregorianMonth_May = 5,
    EGregorianMonth_June = 6,
    EGregorianMonth_July = 7,
    EGregorianMonth_August = 8,
    EGregorianMonth_September = 9,
    EGregorianMonth_October = 10,
    EGregorianMonth_November = 11,
    EGregorianMonth_December = 12
};

/*!
\brief Check if leap year
\par Algorithm
Checks if the year is divisible by 400 or by 4
\code
    if year is divisible by 400 then
       is_leap_year
    else if year is divisible by 100 then
       not_leap_year
    else if year is divisible by 4 then
       is_leap_year
    else
       not_leap_year
\endcode
\returns \c True if a leap year or \c False if not a leap year
\see http://en.wikipedia.org/wiki/Leap_year#Algorithm
*/
bool IsALeapYear(int year) 
{
    return (!(year % 4) && (year % 100)) || !(year % 400);
}

/*!
\brief Get number of days in a year in a Gregorian calendar
*/
int GetDaysInYear(int year) 
{
    return IsALeapYear(year) ? ISO_DAYS_A_LEAP_YEAR : ISO_DAYS_A_YEAR;
}

/*!
\brief Get number of days in a month according to the Gregorian calendar
*/
int GetDaysInMonth(int year, int month) 
{
    int daysInMonth;

    switch (month)
    {
        case EGregorianMonth_February:
            daysInMonth = IsALeapYear(year) ? ISO_LEAP_YEAR_DAYS_IN_FEBRUARY : ISO_DAYS_IN_FEBRUARY;
            break;
        case EGregorianMonth_April:
        case EGregorianMonth_June:
        case EGregorianMonth_September:
        case EGregorianMonth_November:
            daysInMonth = 30;
            break;
        default:
            daysInMonth = 31;
            break;
    }

    return daysInMonth;
}

/*!
\brief Gets the month and day in month from a day in year
\param year [in] Gregorian year
\param dayInYear [in] Gregorian day on year (1-365 or 1-366 i leap year)
\param month [out] Gregorian month
\param dayInMonth [out] Gregorian day in month
\returns \c True if success or \c False if error
*/
bool GetDayAndMonthFromDayInYear(int year, int dayInYear, int *month, 
    int *dayInMonth) 
{
    int daysInMonth;
    *month = ISO_FIRST_MONTH_IN_YEAR;

    for (int i = ISO_FIRST_MONTH_IN_YEAR; i <= ISO_MONTHS_A_YEAR ; i++)
    {
        daysInMonth = GetDaysInMonth(year, i);

        if (dayInYear <= daysInMonth) break;

        (*month)++;
        dayInYear -= daysInMonth;
    }

    *dayInMonth = (int)dayInYear;

    return true;
}

/*!
\brief Get the number of weeks in a year
\par Algorithm
There are 52 weeks in most years however, years that begin on a Thursday and leap years that begin on a Wednesday have 53 weeks.                
*/
int GetNumberOfWeeksInYear(int year) 
{
    int jan1DayOfWeek = GetDayOfTheWeek(year, 1, 1);                    
    return jan1DayOfWeek == 4 || (jan1DayOfWeek == 3 && IsALeapYear(year)) ? 53 : 52;
}

/*!
\brief Get the day of week in a Gregorian calendar
\par Algorithm
Uses the Claus Tøndering algorithm
\see http://en.wikipedia.org/wiki/Calculating_the_day_of_the_week#T.C3.B8ndering.27s_algorithm
*/
int GetDayOfTheWeek(int year, int month, int day) 
{
   static int t[] = {0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4};
   year -= month < 3;
   return (year + year/4 - year/100 + year/400 + t[month-1] + day) % 7;
}

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