VB.Net Convert to/from Gregorian Calendar

VB.Net - Converting Calendar Dates

Guide Contents

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Calendars

This section provides a set of functions for converting dates between calendars. E.g. Convert a date in the normal western (Gregorian) calendar to the equivilent date using the Chinese LuniSolar Calendar.

When converting between calendars, it is very important to understand how each of your chosen calenders work. Converting to/from unfamiliar calendars is likely to produce unexpected results for a variety of reasons including the following...

Calendars may have Leap Days (29 February)
Calendars may have Leap Months, the leap month is usually allocated a month number. All months after the leap month will have a month number 1 more than expected.
Calendars sometimes use rules based on lunar sightings. It may not be possible to determine the exact date a sighting will occur and computer functions can only estimate the approimate date conversion. (Usually less than 2 days error margin.) Some functions include a correction factor which will allow a pricise conversion after the sighting date has been confirmed.
Although Gregorian days start at midnight, other calandars start the day at different times. These are some of the common times for switch from one date to the next... 00:00 (Midnight,) 06:00, dawn (daybreak), 12:00 (midday), 18:00 and dusk (nightfall). This means that the time of day can affect the date when converting calendars
The date can be affected by timezone - Alaska Time is sometimes -9 hours away from London Time and parts of Australia can be +10 hours from London Time. This is a 19 hour spread. Although both countries use the Gregorian calendar, there would only be 5 hours per day when their clocks show the same date.
Some countries change their clocks twice (or even 4 times,) a year but others do not. The exact dates/times for changing clocks can also vary between countries. (E.g. Europe and USA both adjust clocks but not on the same date.) Clock adjustments will occassionally affect date calculations.
Some calendars bearing the same name can vary due to cultural or geographic factors. Take particular care when considering religious activities

The VB.Net Date command adjusts itself, according to system settings etc. This can cause confusion when using multiple calendars. When using certain calendars we also need to identify any leap months. For this reason, these examples all use a custom date structure (I have called this YMD) which includes Year, Month, Day and LeapMonth. When LeapMonth is set,it will identify the month number for the leap month in the specified year. LeapMonth = 0 indicates that either the calendar does not use leap months or that there is no leap month in the requested year.

Date structure used with Calendar functions


Private Structure YMD

 Dim Y As Integer 

 ' year number

 Dim m As Integer

 ' month number in year

 Dim d As Integer

 ' day nummer in month

 Dim LeapMonth As Integer

 ' LeapMonth is not used by some calendars - it can be set to 0 when not required

End Structure

Calendar Conversion Functions

This function is required by many of the date converion routines


 Private Shared Function DDif(y As Integer, md1 As Integer, md2 As Integer) As Integer

 Dim dat1, dat2 As Date

 dat1 = New Date(y, CInt(md1 \ 100), md1 Mod 100, 12, 0, 0, 0)

 dat2 = New Date(y, CInt(md2 \ 100), md2 Mod 100, 12, 0, 0, 0)

 Return 1 + CInt(DateDiff(DateInterval.Day, dat1, dat2))

End Function

And Finally, here is an assortment of date conversion functions


 Private Shared Function Chinese_Date_To_Gregorian_Date(ChinDate As YMD) As YMD

 Dim ret As New YMD

 Dim dat As Date

 Try

 Dim chinese As New Globalization.ChineseLunisolarCalendar

 Dim gregorian As New Globalization.GregorianCalendar

 Dim chineseDate As Date = chinese.ToDateTime(ChinDate.Y, ChinDate.m, ChinDate.d, 12, 0, 0, 0)

 dat = New Date(gregorian.GetYear(chineseDate), gregorian.GetMonth(chineseDate), gregorian.GetDayOfMonth(chineseDate), 12, 0, 0, 0)

 ret.Y = dat.Year : ret.m = dat.Month : ret.d = dat.Day

 Catch ex As Exception

 ret.Y = 0 : ret.m = 0 : ret.d = 0 : ret.LeapMonth = 0

 End Try

 Return ret

End Function

'

 Private Shared Function Gregorian_Date_To_Chinese_Date(ymd1 As YMD) As YMD

 Dim ret As YMD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim gChin As New Globalization.ChineseLunisolarCalendar

 Dim CurCulture As String = Threading.Thread.CurrentThread.CurrentCulture.IetfLanguageTag

 Dim newCulture As Globalization.CultureInfo = Globalization.CultureInfo.CreateSpecificCulture("zh-CN")

 Threading.Thread.CurrentThread.CurrentUICulture = newCulture

 Threading.Thread.CurrentThread.CurrentCulture = newCulture

 ' Make current UI culture consistent with current culture.

 ret.Y = gChin.GetYear(dat)

 ret.m = gChin.GetMonth(dat)

 ret.d = gChin.GetDayOfMonth(dat)

 ret.LeapMonth = gChin.GetLeapMonth(dat.Year)

 Threading.Thread.CurrentThread.CurrentUICulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Threading.Thread.CurrentThread.CurrentCulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Return ret

End Function

'

 Private Shared Function Year_and_Day_Number_To_Gregorian_Date(ym1 As YD) As YMD

 Dim dat As New Date(ym1.Y, 1, 1, 12, 0, 0, 0)

 dat = dat.AddDays(ym1.d - 1)

 Dim ret As YMD

 If dat.Year <> ym1.Y Then

 ret.Y = 0 : ret.m = 0 : ret.d = 0 : ret.LeapMonth = 0

 Return ret

 End If

 ret.Y = dat.Year : ret.m = dat.Month : ret.d = dat.Day : ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_Year_and_Day_Number(ymd1 As YMD) As YD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim ret As YD

 If ((dat.Year <> ymd1.Y) Or (dat.Month <> ymd1.m) Or (dat.Day <> ymd1.d)) Then

 ret.Y = 0 : ret.d = 0

 Return ret

 End If

 ret.Y = dat.Year : ret.d = dat.DayOfYear

 Return ret

 End Function

' 

 Private Shared Function Gregorian_Date_To_Epoch_Date(gregDate As YMD, epochDate As YMD) As Integer

 Dim gDate As New Date(gregDate.Y, gregDate.m, gregDate.d, 12, 0, 0, 1, 0)

 Dim eDate As New Date(epochDate.Y, epochDate.m, epochDate.d, 12, 0, 0, 0, 0)

 Dim t As Long = DateDiff(DateInterval.Day, eDate, gDate)

 Return CInt(t)

 ' Epoch calendars are all based on counting days from an epochDate

 ' Leap month is not used and can be set to 0

 ' NT Day (Epoch 1601) = 01/01/1601

 ' Unix Day (Epoch 1970) = 01/01/1970

 ' Day Count (Epoch 1980) = 01/01/1980

 ' Millenium (Epoch 2000) = 01/01/2000

 ' Post Covid (Epoch 2020)= 01/01/2020

 End Function

'

 Private Shared Function Epoch_Date_To_Gregorian_Date(epoch As Integer, epochdate As YMD) As YMD

 Dim ret As YMD

 Dim eDate As New Date(epochdate.Y, epochdate.m, epochdate.d, 12, 0, 0, 0)

 eDate = eDate.AddDays(epoch)

 ret.Y = eDate.Year : ret.m = eDate.Month : ret.d = eDate.Day : ret.LeapMonth = 0

 Return ret

 ' Epoch calendars are all based on counting days from an epochDate

 ' Leap month is not used and can be set to 0

 ' NT Day (Epoch 1601) = 01/01/1601

 ' Unix Day (Epoch 1970) = 01/01/1970

 ' Day Count (Epoch 1980) = 01/01/1980

 ' Millenium (Epoch 2000) = 01/01/2000

 ' Post Covid (Epoch 2020)= 01/01/2020

 End Function

' 

 Private Shared Function Gregorian_Date_To_Hebrew_Date(ymd1 As YMD) As YMD

 Dim ret As YMD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim gHeb As New Globalization.HebrewCalendar

 Dim CurCulture As String = Threading.Thread.CurrentThread.CurrentCulture.IetfLanguageTag

 Dim newCulture As Globalization.CultureInfo = Globalization.CultureInfo.CreateSpecificCulture("he-IL")

 Threading.Thread.CurrentThread.CurrentUICulture = newCulture

 Threading.Thread.CurrentThread.CurrentCulture = newCulture

 ' Make current UI culture consistent with current culture.

 ret.Y = gHeb.GetYear(dat)

 ret.m = gHeb.GetMonth(dat)

 ret.d = gHeb.GetDayOfMonth(dat)

 ret.LeapMonth = gHeb.GetLeapMonth(ret.Y)

 Threading.Thread.CurrentThread.CurrentUICulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Threading.Thread.CurrentThread.CurrentCulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 End Function

' 

 Private Shared Function Hebrew_Date_To_Gregorian_Date(HebDate As YMD) As YMD

 Dim ret As New YMD

 Dim dat As Date

 Try

 Dim hebrew As New Globalization.HebrewCalendar

 Dim gregorian As New Globalization.GregorianCalendar

 Dim hebrewDate As Date = hebrew.ToDateTime(HebDate.Y, HebDate.m, HebDate.d, 12, 0, 0, 0)

 dat = New Date(gregorian.GetYear(hebrewDate), gregorian.GetMonth(hebrewDate), gregorian.GetDayOfMonth(hebrewDate), 12, 0, 0, 0)

 ret.Y = dat.Year : ret.m = dat.Month : ret.d = dat.Day : ret.LeapMonth = 0

 Catch ex As Exception

 ret.Y = 0 : ret.m = 0 : ret.d = 0 : ret.LeapMonth = 0

 End Try

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_Hijri_Date(ymd1 As YMD, Optional adjustment As Integer = 0) As YMD

 Dim ret As YMD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim gHij As New Globalization.HijriCalendar

 If ((adjustment < -2) Or (adjustment > 2)) Then adjustment = 0

 gHij.HijriAdjustment = adjustment

 Dim CurCulture As String = Threading.Thread.CurrentThread.CurrentCulture.IetfLanguageTag

 Dim newCulture As Globalization.CultureInfo = Globalization.CultureInfo.CreateSpecificCulture("ar-JO")

 Threading.Thread.CurrentThread.CurrentUICulture = newCulture

 Threading.Thread.CurrentThread.CurrentCulture = newCulture

 ret.Y = gHij.GetYear(dat)

 ret.m = gHij.GetMonth(dat)

 ret.d = gHij.GetDayOfMonth(dat)

 ret.LeapMonth = gHij.GetLeapMonth(dat.Year)

 Threading.Thread.CurrentThread.CurrentUICulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Threading.Thread.CurrentThread.CurrentCulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Return ret

 End Function

'

 Private Shared Function Hijri_Date_To_Gregorian_Date(ymd1 As YMD, Optional adjustment As Integer = 0) As YMD

 Dim gIn As New Globalization.HijriCalendar

 If ((adjustment < -2) Or (adjustment > 2)) Then adjustment = 0

 gIn.HijriAdjustment = adjustment

 Dim gout As New Globalization.GregorianCalendar

 Dim date1 As New DateTime(ymd1.Y, ymd1.m, ymd1.d, gIn)

 Dim ret As YMD

 ret.Y = gout.GetYear(date1) : ret.m = gout.GetMonth(date1) : ret.d = gout.GetDayOfMonth(date1) : ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Indian_Civil_dsate_To_Gregorian_Date(ymd1 As YMD) As YMD

 Dim leaptest As Integer = ymd1.Y + 78

 Dim isleap As Boolean = False

 If leaptest Mod 4 = 0 Then isleap = True

 If leaptest Mod 100 = 0 Then isleap = False

 If leaptest Mod 400 = 0 Then isleap = True

 Dim dat As New Date(2000, 1, 1, 12, 0, 0, 0, 0)

 ' Get date on first of the Indian Month

 Select Case ymd1.m

 Case 1

 If isleap Then

  dat = New Date(ymd1.Y + 78, 3, 21, 12, 0, 0, 0, 0)

 Else

  dat = New Date(ymd1.Y + 78, 3, 22, 12, 0, 0, 0, 0)

 End If

 Case 2 : dat = New Date(ymd1.Y + 78, 4, 21, 12, 0, 0, 0, 0)

 Case 3 : dat = New Date(ymd1.Y + 78, 5, 22, 12, 0, 0, 0, 0)

 Case 4 : dat = New Date(ymd1.Y + 78, 6, 22, 12, 0, 0, 0, 0)

 Case 5 : dat = New Date(ymd1.Y + 78, 7, 23, 12, 0, 0, 0, 0)

 Case 6 : dat = New Date(ymd1.Y + 78, 8, 23, 12, 0, 0, 0, 0)

 Case 7 : dat = New Date(ymd1.Y + 78, 9, 23, 12, 0, 0, 0, 0)

 Case 8 : dat = New Date(ymd1.Y + 78, 10, 23, 12, 0, 0, 0, 0)

 Case 9 : dat = New Date(ymd1.Y + 78, 11, 22, 12, 0, 0, 0, 0)

 Case 10 : dat = New Date(ymd1.Y + 78, 12, 22, 12, 0, 0, 0, 0)

 Case 11 : dat = New Date(ymd1.Y + 77, 1, 21, 12, 0, 0, 0, 0)

 Case 12 : dat = New Date(ymd1.Y + 78, 2, 20, 12, 0, 0, 0, 0)

 End Select

 dat = DateAdd(DateInterval.Day, ymd1.d - 1, dat)

 If ymd1.m = 10 And ymd1.d >= 10 Then dat = DateAdd(DateInterval.Year, 1, dat)

 Dim ret As YMD

 ret.Y = dat.Year

 ret.m = dat.Month

 ret.d = dat.Day

 ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_Indian_Civil_Date(ymd1 As YMD) As YMD

 Dim Leap As Boolean = False

 If ymd1.Y Mod 4 = 0 Then Leap = True

 If ymd1.Y Mod 100 = 0 Then Leap = False

 If ymd1.Y Mod 400 = 0 Then Leap = True

 Dim gMD As Integer = ymd1.m * 100 + ymd1.d

 Dim iY As Integer = 0

 Dim iM As Integer = 0

 Dim iD As Integer = 0

 Dim iMD(12) As Integer

 If gMD >= 101 And gMD < 121 Then iY = ymd1.Y - 77 : iM = 10 : iD = DDif(ymd1.Y, 101, gMD) + 10

 If gMD >= 121 And gMD < 220 Then iY = ymd1.Y - 77 : iM = 11 : iD = DDif(ymd1.Y, 121, gMD)

 If Leap Then

  If gMD >= 220 And gMD < 321 Then iY = ymd1.Y - 77 : iM = 12 : iD = DDif(ymd1.Y, 220, gMD)

  If gMD >= 321 And gMD < 421 Then iY = ymd1.Y - 78 : iM = 1 : iD = DDif(ymd1.Y, 321, gMD)

 Else

  If gMD >= 220 And gMD < 322 Then iY = ymd1.Y - 77 : iM = 12 : iD = DDif(ymd1.Y, 220, gMD)

  If gMD >= 322 And gMD < 421 Then iY = ymd1.Y - 78 : iM = 1 : iD = DDif(ymd1.Y, 322, gMD)

 End If

 If gMD >= 421 And gMD < 522 Then iY = ymd1.Y - 78 : iM = 2 : iD = DDif(ymd1.Y, 421, gMD)

 If gMD >= 522 And gMD < 623 Then iY = ymd1.Y - 78 : iM = 3 : iD = DDif(ymd1.Y, 522, gMD)

 If gMD >= 623 And gMD < 723 Then iY = ymd1.Y - 78 : iM = 4 : iD = DDif(ymd1.Y, 623, gMD)

 If gMD >= 723 And gMD < 823 Then iY = ymd1.Y - 78 : iM = 5 : iD = DDif(ymd1.Y, 723, gMD)

 If gMD >= 823 And gMD < 923 Then iY = ymd1.Y - 78 : iM = 6 : iD = DDif(ymd1.Y, 823, gMD)

 If gMD >= 923 And gMD < 1023 Then iY = ymd1.Y - 78 : iM = 7 : iD = DDif(ymd1.Y, 923, gMD)

 If gMD >= 1023 And gMD < 1122 Then iY = ymd1.Y - 78 : iM = 8 : iD = DDif(ymd1.Y, 1023, gMD)

 If gMD >= 1122 And gMD < 1222 Then iY = ymd1.Y - 78 : iM = 9 : iD = DDif(ymd1.Y, 1122, gMD)

 If gMD >= 1222 And gMD < 9999 Then iY = ymd1.Y - 78 : iM = 10 : iD = DDif(ymd1.Y, 1222, gMD)

 Dim ret As YMD

 ret.Y = iY : ret.m = iM : ret.d = iD : ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_Iso_Date(dat As Date) As ISO

 ' note some software uses non standard Week/day numbering systems

 ' this function is based on the offcial ISO standard

 Dim ret As ISO

 Dim FirstDay As Date = ISOFirstMonday(dat)

 Dim days As Integer

 If dat >= FirstDay Then

  ret.y = dat.Year

  ret.d = (dat.DayOfWeek + 6) Mod 7 + 1

  days = CInt(DateDiff(DateInterval.Day, FirstDay, dat))

  ret.w = (days \ 7) + 1

  Return ret

 End If

 ' if we get here, the ISO week is based on previous ISO year (first few days of Jan)

 Dim dat2 As Date = dat.AddYears(-1)

 FirstDay = ISOFirstMonday(dat2)

 ret.y = dat.Year - 1

 ret.d = (dat.DayOfWeek + 6) Mod 7 + 1

 days = CInt(DateDiff(DateInterval.Day, FirstDay, dat))

 ret.w = (days \ 7) + 1

 Return ret

 End Function

 Private Shared Function ISOFirstMonday(dat1 As Date) As Date

 Dim MondayWeekOne As New Date(dat1.Year, 1, 4, 12, 0, 0, 0)

 While MondayWeekOne.DayOfWeek <> DayOfWeek.Monday

  MondayWeekOne = MondayWeekOne.AddDays(-1)

 End While

 Return MondayWeekOne

 End Function

'

 Private Shared Function Iso_Date_To_Gregorian_Date(iso1 As ISO) As YMD

 Dim daycount As Integer = ((iso1.w - 1) * 7) + (iso1.d - 1)

 ' initially assume Greg year matches Iso Year (we will fix year-bounces later)

 Dim year As Integer = iso1.y

 'get date of first monday (30 June chosen because it is well away from any Iso/Greg year mismatches)

 Dim FMdat As Date = ISOFirstMonday(New Date(year, 6, 30, 12, 0, 0, 0))

 ' get "posible" date - if we have correct GregYear

 Dim testDat As Date = FMdat.AddDays(163)

 While testDat.Year < iso1.y

  year -= 1

  FMdat = ISOFirstMonday(New Date(year, 6, 30, 12, 0, 0, 0))

  testDat = FMdat.AddDays(163)

 End While

 While testDat.Year > iso1.y

  year += 1

  FMdat = ISOFirstMonday(New Date(year, 6, 30, 12, 0, 0, 0))

  testDat = FMdat.AddDays(163)

 End While

 ' return the result

 Dim gDat As Date = FMdat.AddDays(daycount)

 Dim ret As YMD

 ret.Y = gDat.Year : ret.m = gDat.Month : ret.d = gDat.Day : ret.LeapMonth = 0

 Return ret

 End Function

 Private Shared Function ISOFirstMonday(dat1 As Date) As Date

 Dim MondayWeekOne As New Date(dat1.Year, 1, 4, 12, 0, 0, 0)

 While MondayWeekOne.DayOfWeek <> DayOfWeek.Monday

  MondayWeekOne = MondayWeekOne.AddDays(-1)

 End While

 Return MondayWeekOne

 End Function

'

 Private Shared Function Gregorian_Date_To_Julian_Date(ymd1 As YMD) As YMD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim TryDat As Date

 Dim tryYMD As YMD

 Dim newGreg As YMD

 tryYMD.LeapMonth = 0

 ' try -13 days first - that will work for all of 1901 to 2099

 TryDat = dat.AddDays(-13)

 tryYMD.Y = TryDat.Year : tryYMD.m = TryDat.Month : tryYMD.d = TryDat.Day : tryYMD.LeapMonth = 0

 newGreg = Julian_Date_To_Gregorian_Date(tryYMD)

 If ((newGreg.d = ymd1.d) AndAlso (newGreg.m = ymd1.m) AndAlso (newGreg.Y = ymd1.Y)) Then

  Return tryYMD

 End If

 ' ok lets try values for +/- a few centuaries

 For i As Integer = -17 To -10

  TryDat = dat.AddDays(i)

  tryYMD.Y = TryDat.Year : tryYMD.m = TryDat.Month : tryYMD.d = TryDat.Day : tryYMD.LeapMonth = 0

  newGreg = Julian_Date_To_Gregorian_Date(tryYMD)

  If ((newGreg.d = ymd1.d) AndAlso (newGreg.m = ymd1.m) AndAlso (newGreg.Y = ymd1.Y)) Then

  Exit For

  End If

 Next

 Return tryYMD

 End Function

'

 Private Shared Function Julian_Date_To_Gregorian_Date(ymd1 As YMD) As YMD

 Dim gIn As New Globalization.JulianCalendar

 Dim gout As New Globalization.GregorianCalendar

 Dim date1 As New DateTime(ymd1.Y, ymd1.m, ymd1.d, gIn)

 Dim ret As YMD

 ret.Y = gout.GetYear(date1) : ret.m = gout.GetMonth(date1) : ret.d = gout.GetDayOfMonth(date1) : ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_Modified_Julian_Day(ymd1 As YMD) As Integer

 Dim dat As New Date(1858, 11, 17, 12, 0, 0, 0)

 Dim ret As Integer

 ret = CInt(DateDiff(DateInterval.Day, dat, New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 1, 0)))

 Return ret

 End Function

'

 Private Shared Function Modified_Julian_Day_To_Gregorian_Date(mjd As Integer) As YMD

 Dim ret As YMD

 Dim dat As New Date(1858, 11, 17, 12, 0, 0, 0)

 dat = dat.AddDays(mjd)

 ret.Y = dat.Year : ret.m = dat.Month : ret.d = dat.Day : ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_Korean_Date(ymd1 As YMD) As YMD

 Dim ret As YMD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim gKor As New Globalization.KoreanCalendar

 Dim CurCulture As String = Threading.Thread.CurrentThread.CurrentCulture.IetfLanguageTag

 Dim newCulture As Globalization.CultureInfo = Globalization.CultureInfo.CreateSpecificCulture("ko-KR")

 Threading.Thread.CurrentThread.CurrentUICulture = newCulture

 Threading.Thread.CurrentThread.CurrentCulture = newCulture

 ret.Y = gKor.GetYear(dat)

 ret.m = gKor.GetMonth(dat)

 ret.d = gKor.GetDayOfMonth(dat)

 ret.LeapMonth = gKor.GetLeapMonth(ret.Y)

 Threading.Thread.CurrentThread.CurrentUICulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Threading.Thread.CurrentThread.CurrentCulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Return ret

 End Function

'

 Private Shared Function Korean_Date_To_Gregorian_Date(ymd1 As YMD) As YMD

 Dim gIn As New Globalization.KoreanCalendar

 Dim gout As New Globalization.GregorianCalendar

 Dim date1 As New DateTime(ymd1.Y, ymd1.m, ymd1.d, gIn)

 Dim ret As YMD

 ret.Y = gout.GetYear(date1) : ret.m = gout.GetMonth(date1) : ret.d = gout.GetDayOfMonth(date1) : ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_Korean_Lunisolar_Date(ymd1 As YMD) As YMD

 Dim ret As YMD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim gKor As New Globalization.KoreanLunisolarCalendar

 Dim CurCulture As String = Threading.Thread.CurrentThread.CurrentCulture.IetfLanguageTag

 Dim newCulture As Globalization.CultureInfo = Globalization.CultureInfo.CreateSpecificCulture("ko-KR")

 Threading.Thread.CurrentThread.CurrentUICulture = newCulture

 Threading.Thread.CurrentThread.CurrentCulture = newCulture

 ret.Y = gKor.GetYear(dat)

 ret.m = gKor.GetMonth(dat)

 ret.d = gKor.GetDayOfMonth(dat)

 ret.LeapMonth = gKor.GetLeapMonth(ret.Y)

 Threading.Thread.CurrentThread.CurrentUICulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Threading.Thread.CurrentThread.CurrentCulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Return ret

 End Function

'

 Private Shared Function Korean_Lunisolar_Date_To_Gregorian_Date(ymd1 As YMD) As YMD

 Dim gIn As New Globalization.KoreanLunisolarCalendar

 Dim gout As New Globalization.GregorianCalendar

 Dim date1 As New DateTime(ymd1.Y, ymd1.m, ymd1.d, gIn)

 Dim ret As YMD

 ret.Y = gout.GetYear(date1) : ret.m = gout.GetMonth(date1) : ret.d = gout.GetDayOfMonth(date1) : ret.LeapMonth = 0

 Return ret

 End Function

'

 Private Shared Function Gregorian_Date_To_UmAlQura_Date(ymd1 As YMD) As YMD

 Dim ret As YMD

 Dim dat As New Date(ymd1.Y, ymd1.m, ymd1.d, 12, 0, 0, 0)

 Dim gUm As New Globalization.UmAlQuraCalendar

 Dim CurCulture As String = Threading.Thread.CurrentThread.CurrentCulture.IetfLanguageTag

 Dim newCulture As Globalization.CultureInfo = Globalization.CultureInfo.CreateSpecificCulture("ar-SA")

 Threading.Thread.CurrentThread.CurrentUICulture = newCulture

 Threading.Thread.CurrentThread.CurrentCulture = newCulture

 ret.Y = gUm.GetYear(dat)

 ret.m = gUm.GetMonth(dat)

 ret.d = gUm.GetDayOfMonth(dat)

 ret.LeapMonth = gUm.GetLeapMonth(ret.Y)

 Threading.Thread.CurrentThread.CurrentUICulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Threading.Thread.CurrentThread.CurrentCulture = Globalization.CultureInfo.CreateSpecificCulture(CurCulture)

 Return ret

 End Function

'

 Private Shared Function UmAlQura_Date_To_Gregorian_Date(ymd1 As YMD) As YMD

 Dim gIn As New Globalization.UmAlQuraCalendar

 Dim gout As New Globalization.GregorianCalendar

 Dim date1 As New DateTime(ymd1.Y, ymd1.m, ymd1.d, gIn)

 Dim ret As YMD

 ret.Y = gout.GetYear(date1) : ret.m = gout.GetMonth(date1) : ret.d = gout.GetDayOfMonth(date1) : ret.LeapMonth = 0

 Return ret

 End Function

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