BUG: Format atau DatePart fungsi dapat kembali salah angka minggu untuk Senin lalu tahun

  ISO 8601 "Data elements and interchange formats - Information interchange   - Representation of dates and times"
  ISO 8601 : 1988 (E) paragraph 3.17:
  "week, calendar: A seven day period within a calendar year, starting
  on a Monday and identified by its ordinal number within the year;
  the first calendar week of the year is the one that includes the
  first Thursday of that year. In the Gregorian calendar, this is
  equivalent to the week which includes 4 January."
				

• Satu tahun dibagi menjadi 52 atau 53 minggu kalender.
• Minggu kalender memiliki 7 hari. Senin adalah hari 1, Minggu adalah hari 7.
• Kalender minggu pertama tahun adalah salah satu yang berisi sekurang-kurangnya 4 hari.
• Jika satu tahun tidak menyimpulkan pada hari Minggu, 1-3 hari-hari terakhir milik minggu kalender pertama tahun depan atau 1-3 hari pertama tahun depan milik tahun sekarang kalender minggu lalu.
• Hanya setahun memulai atau menyimpulkan pada hari Kamis telah 53 kalender minggu.

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Langkah-langkah untuk mereproduksi perilaku

1. Mulai projek Standard EXE dalam Visual Basic. Form1 dibuat secara default.
2. Menambahkan dua CommandButtons Form1.
3. Paste kode berikut ke dalam jendela kode Form1:

   Option Explicit
   
   Private Sub Command1_Click()
   ' This code tests a "problem" date and the days around it
   Dim DateValue As Date
   Dim i As Integer
   
   Debug.Print "   Format function:"
   DateValue = #12/27/2003#
   For i = 1 To 4   ' examine the last 4 days of the year
       DateValue = DateAdd("d", 1, DateValue)
       Debug.Print "Date: " & DateValue & "   Day: " & _
         Format(DateValue, "ddd") & "   Week: " & _
         Format(DateValue, "ww", vbMonday, vbFirstFourDays)
   Next i
   End Sub
   
   Private Sub Command2_Click()
   ' This code lists all "Problem" dates within a specified range
     Dim MyDate As Date
     Dim Years As Long
     Dim days As Long
     Dim woy1 As Long
     Dim woy2 As Long
     Dim ToPrint As String
   
     For Years = 1850 To 2050
       For days = 0 To 3
         MyDate = DateSerial(Years, 12, 28 + days)
         woy1 = Format(MyDate, "ww", vbMonday, vbFirstFourDays)
         woy2 = Format(MyDate, "ww", vbMonday, vbFirstFourDays)
         If woy2 > 52 Then
           If Format(MyDate + 7, "ww", vbMonday, vbFirstFourDays) = 2 Then _
             woy2 = 1
         End If
         If woy1 <> woy2 Then
           ToPrint = MyDate & String(13 - Len(CStr(MyDate)), " ")
           ToPrint = ToPrint & Format(MyDate, "dddd") & _
             String(10 - Len(Format(MyDate, "dddd")), " ")
           ToPrint = ToPrint & woy1 & String(5 - Len(CStr(woy1)), " ")
           ToPrint = ToPrint & woy2
           Debug.Print ToPrint
         End If
       Next days
     Next Years
   End Sub
   					

4. Tahan tombol CTRL dan tekan tombol g untuk membuka jendela segera.
5. Menjalankan proyek, klik Command1, dan mencatat hasil berikut di jendela segera:

      Format function:
   Date: 12/28/03   Day: Sun   Week: 52
   Date: 12/29/03   Day: Mon   Week: 53
   Date: 12/30/03   Day: Tue   Week: 1
   Date: 12/31/03   Day: Wed   Week: 1
   						

   Perhatikan bahwa dengan format ini, semua minggu dimulai dengan Senin, sehingga 12/29/2003 harus dianggap sebagai awal minggu 1 dan bukan bagian dari 53 minggu.
6. Klik pada Command2 untuk melihat daftar tanggal dalam kisaran tertentu yang mengalami masalah ini. Daftar ini mencakup tanggal, minggu hari (selalu Senin), minggu # dikembalikan oleh Format (53), dan nomor minggu itu harus kembali (1.) Misalnya:

   12/29/1851   Monday    53   1
   12/31/1855   Monday    53   1
   12/30/1867   Monday    53   1
   12/29/1879   Monday    53   1
   12/31/1883   Monday    53   1
   12/30/1895   Monday    53   1
   ...
   					

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Penyelesaian masalah

Function WOY (MyDate As Date) As Integer   ' Week Of Year
  WOY = Format(MyDate, "ww", vbMonday, vbFirstFourDays)
  If WOY > 52 Then
    If Format(MyDate + 7, "ww", vbMonday, vbFirstFourDays) = 2 Then WOY = 1
  End If
End Function
				

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Langkah demi langkah contoh

1. Mulai projek Standard EXE dalam Visual Basic. Form1 dibuat secara default.
2. Dari Project menu, menambahkan modul baru, dan kemudian paste kode berikut:

   Option Explicit
   
   Function WeekNumber(InDate As Date) As Integer
     Dim DayNo As Integer
     Dim StartDays As Integer
     Dim StopDays As Integer
     Dim StartDay As Integer
     Dim StopDay As Integer
     Dim VNumber As Integer
     Dim ThurFlag As Boolean
   
     DayNo = Days(InDate)
     StartDay = Weekday(DateSerial(Year(InDate), 1, 1)) - 1
     StopDay = Weekday(DateSerial(Year(InDate), 12, 31)) - 1
     ' Number of days belonging to first calendar week
     StartDays = 7 - (StartDay - 1)
     ' Number of days belonging to last calendar week
     StopDays = 7 - (StopDay - 1)
     ' Test to see if the year will have 53 weeks or not
     If StartDay = 4 Or StopDay = 4 Then ThurFlag = True Else ThurFlag = False
     VNumber = (DayNo - StartDays - 4) / 7
     ' If first week has 4 or more days, it will be calendar week 1
     ' If first week has less than 4 days, it will belong to last year's
     ' last calendar week
     If StartDays >= 4 Then 
        WeekNumber = Fix(VNumber) + 2 
     Else 
        WeekNumber = Fix(VNumber) + 1
     End If
     ' Handle years whose last days will belong to coming year's first 
     ' calendar week
     If WeekNumber > 52 And ThurFlag = False Then WeekNumber = 1
     ' Handle years whose first days will belong to the last year's 
     ' last calendar week
     If WeekNumber = 0 Then
        WeekNumber = WeekNumber(DateSerial(Year(InDate) - 1, 12, 31))
     End If
   End Function
   
   Function Days(DayNo As Date) As Integer
     Days = DayNo - DateSerial(Year(DayNo), 1, 0)
   End Function
   					

3. Tambahkan CommandButton Form1.
4. Paste kode berikut ke dalam jendela kode Form1:

   Private Sub Command1_Click()
      Dim DateValue As Date, i As Integer
      
      Debug.Print "   WeekNumber function:"
      DateValue = #12/27/2003#
      For i = 1 To 4   ' examine the last 4 days of the year
          DateValue = DateAdd("d", 1, DateValue)
          Debug.Print "Date: " & DateValue & "   Day: " & _
             Format(DateValue, "ddd") & "   Week: " & WeekNumber(DateValue)
      Next i
   End Sub
   					

5. Tahan tombol CTRL dan tekan tombol g untuk membuka jendela segera.
6. Menjalankan proyek dan klik pada Command1 untuk melihat hasil berikut di jendela segera:

      WeekNumber function:
   Date: 12/28/03   Day: Sun   Week: 52
   Date: 12/29/03   Day: Mon   Week: 1
   Date: 12/30/03   Day: Tue   Week: 1
   Date: 12/31/03   Day: Wed   Week: 1
   					

   Perhatikan bahwa Senin dianggap Minggu 1 sebagaimana mestinya.

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