Date Comparison
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Thread: Date Comparison

  1. #1
    Join Date
    Apr 2012
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    4

    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

  2. #2
    Join Date
    Sep 2006
    Posts
    635

    Re: Date Comparison

    hi

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

  3. #3
    Join Date
    Jul 2006
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    Re: Date Comparison

    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.

  4. #4
    Join Date
    Mar 2006
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    16

    Re: Date Comparison

    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

  5. #5
    Join Date
    Jan 2009
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    596

    Re: Date Comparison

    Quote Originally Posted by Kenaso View Post
    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

    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.

  6. #6
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    Germany
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    Re: Date Comparison

    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?

  7. #7
    Join Date
    Mar 2006
    Posts
    16

    Re: Date Comparison

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

  8. #8
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    Jan 2009
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    596

    Re: Date Comparison

    Quote Originally Posted by Kenaso View Post
    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?

  9. #9
    Join Date
    Mar 2006
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    16

    Re: Date Comparison

    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

  10. #10
    Join Date
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    596

    Re: Date Comparison

    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?
    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.

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

  11. #11
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    Re: Date Comparison

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

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  12. #12
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    Jan 2009
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    596

    Re: Date Comparison

    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.

  13. #13
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    Mar 2006
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    Re: Date Comparison

    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??

  14. #14
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    Re: Date Comparison

    Quote Originally Posted by Kenaso View Post
    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 View Post
    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.
    Attached Images Attached Images  
    Attached Files Attached Files

  15. #15
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    Jan 2009
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    596

    Re: Date Comparison

    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

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