NoOfDays = (CurrentDate - YearStartDate)+1
IF NoOfDays MOD 7 = 0 Then
WeekNo = INT(NoOfDays/7)
ELSE
WeekNo = INT(NoOfDays/7)+1
END
我的假设是一年中的第一周可能包含最多7天，就像Olie的回答所示。 该代码无法处理周起始日不是星期日的文化，而这占据了世界上很大一部分。
tm t = ... //the date on which to find week of year
int wy = -1;
struct tm t1;
t1.tm_year = t.tm_year;
t1.tm_mday = t1.tm_mon = 1; //set to 1st of January
time_t tt = mktime(&t1); //compute tm
//remove days for 1st week
int yd = t.tm_yday - (7 - t1.tm_wday);
if(yd <= 0 ) //first week is now negative
wy = 0;
else
wy = (int)std::ceil( (double) ( yd/7) ); //second week will be 1
time_t t = time(NULL);
tm* timePtr = localtime(&t);
double day_of_year=timePtr->tm_yday +1 ; // 1-365
int week_of_year =(int) ceill(day_of_year/7.0);
/**
* @brief WeekNo
* @param yr
* @param mon
* @param day
* @param iso
* @return
*
* Given a date, return the week number
* Note. The first week of the year begins on the Monday
* following the previous Thursday
* Follows ISO 8601
*
* Mutually equivalent definitions for week 01 are:
*
* the week with the year's first Thursday in it (the ISO 8601 definition)
* the week with the Thursday in the period 1 – 7 January
* the week starting with the Monday in the period 29 December – 4 January
* the week starting with the Monday which is nearest in time to 1 January
* the week ending with the Sunday in the period 4 – 10 January
* the week with 4 January in it
* the first week with the majority (four or more) of its days in the starting year
* If 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in week 01.
* If 1 January is on a Friday, Saturday or Sunday, it is part of week 52 or 53 of the previous year.
* the week with the year's first working day in it (if Saturdays, Sundays, and 1 January are not working days).
*** strftime has a conversion of struct tm to weeknumber. strptime fills in tm struct**
* Code uses strptime, strftime functions.
*/
int WeekNo( int yr,int mon, int day, int iso)
{
struct tm tm;
char format[32];
//memset(tm,0,sizeof(tm));
sprintf(format,"%d-%02d-%02d",yr,mon,day);
strptime(format, "%Y-%m-%d", &tm);
// structure tm is now filled in for strftime
strftime(format, sizeof(format), iso? "%V":"%U", &tm);
//puts(format);
return atoi(format);
}
调用 Weekno(2015,12,23,1); //获取 ISO 周数。 Weekno(2015,12,23,0) //获取非 ISO 周数