Date Comparison

Which code should I use to compare two different date in VB6. That is to know if the dates

are equal or less than or greater than the other one

hi

Code:

---

dim var_d1 date, var_d2 date
.
.
.
.
if var_d1>var_d2 then
..
..
else
..
..
end if

---

Better make it
Dim var_d1 AS Date, var_d2 AS Date

Without "As" it is not a valid Dim statement. The comparison is correct, though.

I use the following in my sort class when comparing date/time values.
This is the general idea. Maybe this will help.

ReDim astrData(lngLow To lngHigh - 1) ' Resize temp data array
strFmt = String$(28, 48) ' Twenty-eight zeroes

' Convert date and/or time
' CStr(CDec(CDbl(CDate("3/18/2006 6:18:46 AM")))) -> "38794.2630324074" (Date and time)
' CStr(CDec(CDbl(CDate("3/18/2006")))) -> "38794" (Date only)
' CStr(CDec(CDbl(CDate("6:18:46 AM")))) -> "0.263032407407407" (Time only)
For lngIndex = lngLow To (lngHigh - 1)
strTemp = CStr(CDec(CDbl(CDate(avntData(lngIndex))))) ' Create big number
astrData(lngIndex) = Left$(strTemp & strFmt, 28) ' Format fixed length big number
Next lngIndex ' ex: "38794.2630324074000000000000"

Select Case mlngSortDirection

Case eSort_Ascending
If StrComp(astrData(lngLow), astrData(lngHigh - 1), vbBinaryCompare) = 1 Then
SwapData avntData(lngLow), avntData(lngHigh - 1)
End If

Case eSort_Descending
If StrComp(astrData(lngLow), astrData(lngHigh - 1), vbBinaryCompare) = -1 Then
SwapData avntData(lngLow), avntData(lngHigh - 1)
End If

End Select

Quote:

---

Originally Posted by Kenaso

I use the following in my sort class when comparing date/time values.
This is the general idea. Maybe this will help.

---

That is a great way to do it when the following conditions apply:

• Efficiency isn't a concern
• Getting the correct answer isn't, either :rolleyes:

Your method compares dates in lexical order (as number of days from 1st Jan 1900), not chronological order.

So "4000" (someday in 1910) compares higher than both "38794" (18th March 2006) and "300" (somewhere in 1900). I think you see the problem.

Yes, if efficience isn't a concern, you could use
strTemp = Format(CDec(CDbl(CDate(avntData(lngIndex)))), "00000000.#")
to avoid lexical disorder as described by Peter.

But why don't you simply do a If date1 > date2 then...
Have anything against speed and simplicity?

Gentlemen,
I am working within a twenty year range therefore such extreme dates never entered the equation. Sorry. Anymore ideas?

Quote:

---

Originally Posted by Kenaso

Gentlemen,
I am working within a twenty year range therefore such extreme dates never entered the equation. Sorry. Anymore ideas?

---

Yes, use date1 > date2. This will work for any two dates.
Why don't you use this? :confused:

I found this piece of code by Karl Peterson. Works great. I have tested with random dates and/or times between 1800 to present. This should work for you.


ReDim adblData(lngLow To lngHigh - 1) ' Resize temp data array

For lngIndex = lngLow To (lngHigh - 1)
' Convert date and/or time to
' seconds prior to loading array
' ex: 12-May-1866 3:27:36 AM -> -3270573144 (date and time)
' 5/12/1866 -> -3270585600 (date only)
' 3:27:36 AM -> -2209149144 (time only)
adblData(lngIndex) = DateToSeconds(CDate(avntData(lngIndex)))
Next lngIndex

Do my sort comparison "if x > y", etc.

Private Function DateToSeconds(ByVal datDate As Date) As Double

' 16-Feb-2010 Karl E. Peterson http://vb.mvps.org/

Dim dblSeconds As Double

Const BASE_DATE As Date = #1/1/1970#
Const BIT_31 As Double = 2147483648#
Const BIT_32 As Double = 4294967296#

' Calculate difference in seconds between
' base date and date passed here
dblSeconds = CDbl(DateDiff("s", BASE_DATE, datDate))

Select Case dblSeconds
Case Is >= BIT_32: dblSeconds = 0
Case Is >= BIT_31: dblSeconds = dblSeconds - BIT_32
End Select

DateToSeconds = dblSeconds

End Function

I found this piece of code by hensa22 in the original reply to this thread. Works great. I have not tested it because there is not need to - the documentation says it works for any date which can be represented by a Date object. This will work for you, so why don't you use it? :confused:

Code:

---

var_d1 > var_d2

---

Now, your code still does not work properly. It may work for the dates you tested it with but it is not hard to find some dates it doesn't work for.

Suppose we had a list of events associated with the Star Trek universe. We want to sort these by date:

1947 - Quark, Rom and Nog crash land at Roswell and spark of all those alien rumours
2063 - Zephram Cochrane makes the first human warp flight in the Phoenix
2165 - Sarek, father of Spock, is born on Vulcan
(NB: I took these off Wikipedia - I'm not enough of a geek to know these! I just wanted some events in the near future...)

Approx seconds since 1st Jan 1970 (i.e. dblSeconds in your code):
1947 = -725824800
2063 = 2934856800
2165 = 6153732000
(all calculated by (year-1970)*365.25*86400)

Then after the Select statement they become:
1947 - this is negative so neither case fits, so result stays as -725824800
2063 - initial value is >= 2147483648 (BIT_31) so we subtract BIT_32 giving us -1360110496
2165 - initial value is >= 4294967296 (BIT_32) so we set it to 0

The final order (from low to high) will be 2063, 1947, 2165. I don't know how time works where you live but this doesn't seem correct to me somehow. :rolleyes:

Why do you persist in giving an incorrect answer to a thread which was answered correctly in the very first reply?

VB6 uses the old DATE range. 200 years ago didn't exist 30 years ago (in DOS)

Thanks for that correction dglienna. According to this link (http://msdn.microsoft.com/en-us/libr...(v=vs.60).aspx) the valid range is January 1, 1980 through December 31, 2099 (for Win95) or January 1, 1980 through December 31, 2079 (for WinNT). This doesn't affect my conclusions about Kenaso's code, though.

Anything which is more than 2147483648 seconds later than 1st Jan 1970, which is any date later than about 2038, will wrap around to negative values. So 2063 will still be considered earlier than 1980.

I got the code from here:

The Next Y2K
http://visualstudiomagazine.com/arti...-next-y2k.aspx

Karl has been coding for quite some time and is very respected in the Visual Basic world. Please take the time to read his article as it is very short and informative. Thank you.

Star Trek??

Quote:

---

Originally Posted by Kenaso

I got the code from here:

The Next Y2K
http://visualstudiomagazine.com/arti...-next-y2k.aspx

Karl has been coding for quite some time and is very respected in the Visual Basic world. Please take the time to read his article as it is very short and informative. Thank you.

---

Karl's reputation is completely irrelevant here. Once you have a piece of code, whether it is correct or not does not depend upon the author's reputation. It depends solely upon whether, when you run it, it gives the correct answer.

But Karl is not actually at fault here. His code is a bit weird but serves the purpose he designed it for - which is to encode a VB Date as UNIX time in a Long variable, with dates from 1970 to 2038 being encoded as positive values and dates from 2038 to 2106 being encoded as negative values.

He provides two functions which convert back and forth between these, called NetTimeToVbTime() and VbTimeToNetTime().

His code works when used for the purpose for which it was written. But nowhere in that article does it say that you can determine which of two dates is earliest by encoding them using his function and then comparing the results using the < operator. This is what you are doing, though, so this is why the method you presented doesn't work.

Have you actually read and understood my walkthroughs of the DateToSeconds() function you posted? If you had then you would see exactly why it doesn't work for comparing dates.

To make it easy for you I have knocked up a little app. A screenshot of this is shown below. All you have to do is put a date in each text box and click the 'Compare!' button. It will then tell you whether the first date is considered to be earlier than the second date, using both the correct way to compare dates (the < operator) or the wrong way (comparing the values of DateToSeconds() for the two dates). Give it a go. If you still insist that your way of comparing dates is valid please tell me exactly what is wrong with this application.

Quote:

---

Originally Posted by Kenaso

Star Trek??

---

I just needed a concrete example of why you might want to compare dates in the range ~1900 up to ~2100. A list of things in the Star Trek timeline was the first thing that came to mind for dates like these. :)

I'll just post the code here as well so people don't have to download the zip file if they just want to see it. The comparisons are highlighted in red:

Code:

---

Private firstDate As Date
Private secondDate As Date

Private Sub cmdCompare_Click()

    ' Set the dates from text boxes
    firstDate = CDate(txtFirstDate.Text)
    secondDate = CDate(txtSecondDate.Text)
   
    CompareUsingLessThan (void)
    CompareUsingDateToSeconds (void)
       
End Sub

Private Function CompareUsingLessThan(void)
    If firstDate < secondDate Then
        lblLessThanResult.Caption = "< operator says: Yes"
    Else
        lblLessThanResult.Caption = "< operator says: No"
    End If

End Function

Private Function CompareUsingDateToSeconds(void)
    If DateToSeconds(firstDate) < DateToSeconds(secondDate) Then
        lblDateToSecondsResult.Caption = "DateToSeconds() says: Yes"
    Else
        lblDateToSecondsResult.Caption = "DateToSeconds() says: No"
    End If

End Function

Private Function DateToSeconds(ByVal datDate As Date) As Double

    ' 16-Feb-2010 Karl E. Peterson http://vb.mvps.org/

    Dim dblSeconds As Double

    Const BASE_DATE As Date = #1/1/1970#
    Const BIT_31 As Double = 2147483648#
    Const BIT_32 As Double = 4294967296#

    ' Calculate difference in seconds between
    ' base date and date passed here
    dblSeconds = CDbl(DateDiff("s", BASE_DATE, datDate))

    Select Case dblSeconds
    Case Is >= BIT_32: dblSeconds = 0
    Case Is >= BIT_31: dblSeconds = dblSeconds - BIT_32
    End Select

    DateToSeconds = dblSeconds
End Function

---

No idea why anyone would want to make it that complicated, as pointed out before by others a simple Date1< Date2 will do or if you want to know ho wmuch difference then a simple call to datediff() will do.

There is no need for all the conversions, all it does is complicates the code and slows it down while also providing the possibilty of false results.

@DataMiser: I know, it really infuriates me when people spread complicated, slow, buggy ways of doing something which can be done easily, quickly and correctly. The reason I went into so much detail was because I was trying to convince Kenaso where he/she was going wrong - and, more importantly, to make sure that any inexperienced programmers reading this thread would not go away with the wrong idea.

But Kenaso hasn't been online since his last reply, so won't even have read my reply to his last post. No doubt he has gone away still believing his way is better as it came from someone who "has been coding for quite some time and is very respected in the Visual Basic world" :(

Hi,
This may be helpful for you.

The following code's form is also attached with the reply.

To get date difference between two dates in months, days and years and etc you can use the following code.
Add two DTPickers and set values as per your requirement, you can use two date variables too to instead of these controls.
Then compare these dates with the following lines of code


Private Sub cmdCalculate_Click()
lblYears.Caption = ""
lblMonths.Caption = ""
lblDays.Caption = ""
lblQuarter.Caption = ""
lblCalenderWeeks.Caption = ""
lblWeeks.Caption = ""
lblHours.Caption = ""
lblMinutes.Caption = ""
lblSeconds.Caption = ""

lblYears.Caption = DateDiff("YYYY", dtpStartDate.Value, dtpEndDate.Value)
lblMonths.Caption = DateDiff("M", dtpStartDate.Value, dtpEndDate.Value)
lblDays.Caption = DateDiff("D", dtpStartDate.Value, dtpEndDate.Value)
lblQuarter.Caption = DateDiff("Q", dtpStartDate.Value, dtpEndDate.Value)
lblCalenderWeeks.Caption = DateDiff("WW", dtpStartDate.Value, dtpEndDate.Value)
lblWeeks.Caption = DateDiff("W", dtpStartDate.Value, dtpEndDate.Value)
lblHours.Caption = DateDiff("H", dtpStartDate.Value, dtpEndDate.Value)
lblMinutes.Caption = DateDiff("N", dtpStartDate.Value, dtpEndDate.Value)
lblSeconds.Caption = DateDiff("S", dtpStartDate.Value, dtpEndDate.Value)
End Sub

Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
If KeyCode = 27 Then
End
End If
End Sub

Private Sub Form_Load()
dtpStartDate.Value = Date
dtpEndDate.Value = Date
End Sub

In case of any issue please do revert back. :wave:

Private Sub cmdCalculate_Click()
lblYears.Caption = ""
lblMonths.Caption = ""
lblDays.Caption = ""
lblQuarter.Caption = ""
lblCalenderWeeks.Caption = ""
lblWeeks.Caption = ""
lblHours.Caption = ""
lblMinutes.Caption = ""
lblSeconds.Caption = ""

lblYears.Caption = DateDiff("YYYY", dtpStartDate.Value, dtpEndDate.Value)
lblMonths.Caption = DateDiff("M", dtpStartDate.Value, dtpEndDate.Value)
lblDays.Caption = DateDiff("D", dtpStartDate.Value, dtpEndDate.Value)
lblQuarter.Caption = DateDiff("Q", dtpStartDate.Value, dtpEndDate.Value)
lblCalenderWeeks.Caption = DateDiff("WW", dtpStartDate.Value, dtpEndDate.Value)
lblWeeks.Caption = DateDiff("W", dtpStartDate.Value, dtpEndDate.Value)
lblHours.Caption = DateDiff("H", dtpStartDate.Value, dtpEndDate.Value)
lblMinutes.Caption = DateDiff("N", dtpStartDate.Value, dtpEndDate.Value)
lblSeconds.Caption = DateDiff("S", dtpStartDate.Value, dtpEndDate.Value)
End Sub

Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
If KeyCode = 27 Then
End
End If
End Sub

Private Sub Form_Load()
dtpStartDate.Value = Date
dtpEndDate.Value = Date
End Sub

Hello. I have been working the late shift and spending my off hours searching for pin holes in my eye lids. I am trying to get caught up on the discussion. How goes the sorting?

Sorry. That was me looking for date comparisons for sorting.