strange result of Date value comparsion

[c676228]

Hi all,

I hope I am not out of my mind.

I have the following code:
The iMonthlenght here is 1, EffectiveDate is 12/16/2008,
expiration date is 1/12/2009. I displayed in the web already.

'*****************************
Response.Write "Effective Date Value again: " & DateAdd("m", iMonthLength,
EffectiveDate) & "<br>"
Response.Write "Expiration Date again before comparision: " &
ExpirationDate & "<br>"
'********************
'after checking, the debugging message still shows that EffectiveDate is
12/16/2008,
expiration date is 1/12/2009, while DateAdd("m", iMonthLength,
EffectiveDate) is
1/16/2009. but somehow
DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate
evaluates to be true. I don't get it. How come 1/16/2009 is earlier than
1/12/2009.

if DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate then
'my program gets to here for the data I gave
above????
Response.Write "strange value again?: " & "<br>"
Response.Write DateAdd("m", iMonthLength, EffectiveDate)
Response.Write "<br>"
Response.Write ExpirationDate & "<br>"
' it tells me in black and while that my
effectiveDate and expiration don't change at all, that's what I expected but
how come this statement -DateAdd("m", iMonthLength, EffectiveDate) <=
ExpirationDate
would be true?

end if

 

[Allen Chen [MSFT]]

Hi Betty,

My name is Allen Chen. It's my pleasure to work with you on this issue.

From your description the problem is that the following expression returns
true:

DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate

when DateAdd("m", iMonthLength, EffectiveDate) is 1/16/2009 and
ExpirationDate is 1/12/2009. Is my understanding correct?

If so I think I need to know the type of the EffectiveDate and
ExpirationDate. In addition, I think the code of DateAdd method is also
important for us to diagnose this issue. So could you send me a demo
project that can reproduce this problem? My email is
(e-mail address removed). Please update here after sending the project in
case I missed that email.

Regards,
Allen Chen
Microsoft Online Community Support

Delighting our customers is our #1 priority. We welcome your comments and
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[Anthony Jones]

Hi Betty,

My name is Allen Chen. It's my pleasure to work with you on this issue.

From your description the problem is that the following expression returns
true:

DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate

when DateAdd("m", iMonthLength, EffectiveDate) is 1/16/2009 and
ExpirationDate is 1/12/2009. Is my understanding correct?

If so I think I need to know the type of the EffectiveDate and
ExpirationDate. In addition, I think the code of DateAdd method is also
important for us to diagnose this issue.

In that case you best go dust off some old source code for VBScript, DateAdd
is function intrinsic to VBScript.

 

[Anthony Jones]

Hi all,

I hope I am not out of my mind.

I have the following code:
The iMonthlenght here is 1, EffectiveDate is 12/16/2008,
expiration date is 1/12/2009. I displayed in the web already.

'*****************************
Response.Write "Effective Date Value again: " & DateAdd("m", iMonthLength,
EffectiveDate) & "<br>"
Response.Write "Expiration Date again before comparision: " &
ExpirationDate & "<br>"
'********************
'after checking, the debugging message still shows that EffectiveDate is
12/16/2008,
expiration date is 1/12/2009, while DateAdd("m", iMonthLength,
EffectiveDate) is
1/16/2009. but somehow
DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate
evaluates to be true. I don't get it. How come 1/16/2009 is earlier than
1/12/2009.

if DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate then
'my program gets to here for the data I gave
above????
Response.Write "strange value again?: " & "<br>"
Response.Write DateAdd("m", iMonthLength, EffectiveDate)
Response.Write "<br>"
Response.Write ExpirationDate & "<br>"
' it tells me in black and while that my
effectiveDate and expiration don't change at all, that's what I expected
but
how come this statement -DateAdd("m", iMonthLength, EffectiveDate) <=
ExpirationDate
would be true?

I don't think you are going out of your mind. Here is a one line VBS file
which works fine:-

MsgBox DateAdd("m" , 1, "12/16/2008") <= CDate("1/12/2009")

However in this specific case this would also work:-

MsgBox DateAdd("m" , 1, "12/16/2008") <= "1/12/2009"

This would compare strings, however if infact ExpirationDate contains say
some control characters like tab or CR at the start it wouldn't work. If
you haven't done so already make sure the variables are actually dates using
CDate. Also use Response.Write GetLocale() to discover what locale VBScript
thinks its using. The tests above are done with "en-us" locale.

 

[Daniel Crichton]

c676228 wrote on Mon, 8 Dec 2008 17:16:04 -0800:

Hi all,

I hope I am not out of my mind.

I have the following code:
The iMonthlenght here is 1, EffectiveDate is 12/16/2008, expiration
date is 1/12/2009. I displayed in the web already.

'*****************************
Response.Write "Effective Date Value again: " & DateAdd("m",
iMonthLength,
EffectiveDate) & "<br>"
Response.Write "Expiration Date again before comparision: " &
ExpirationDate & "<br>"
'********************
'after checking, the debugging message still shows that EffectiveDate
is 12/16/2008, expiration date is 1/12/2009, while DateAdd("m",
iMonthLength,
EffectiveDate) is 1/16/2009. but somehow
DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate evaluates
to be true. I don't get it. How come 1/16/2009 is earlier than
1/12/2009.

if DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate then
'my program gets to here for the data I gave above????
Response.Write "strange value again?: " & "<br>"
Response.Write DateAdd("m", iMonthLength, EffectiveDate)
Response.Write "<br>"
Response.Write ExpirationDate & "<br>"
' it tells me in black and while that
my effectiveDate and expiration don't change at all, that's what I
expected but how come this statement -DateAdd("m", iMonthLength,
EffectiveDate) <=
ExpirationDate would be true?

end if

As well as Anthony's suggestion that you might be doing a string comparison
(so just put CDate around the ExpirationDate in the If statement), have you
checked the regional settings to make sure the date formats are US? It might
be that 12/16/2008 is 16th Dec 2008 (because there is no month 16, so the
script engine knows that it must be Dec 16th), but 1/12/2009 might be
treated as 1st Dec 2009 (in UK time format) and so when you compare to your
1 month added date 1/16/2009 which would be 16th Jan 2009 (again, no month
16 so the script engine swaps the day and month around) then the comparison
will be the opposite to what you expect.

Can you add the following to your code before the comparison?

Response.Write "EffectiveDate: " & FormatDateTime(EffectiveDate,vbLongDate)
& "<br>"
Response.Write "ExpirationDate: " &
FormatDateTime(ExpirationDate,vbLongDate) & "<br>"

and, assuming that the regional settings for long date format use the month
name rather than number, it should help to determine if you're hitting a
regional date handling issue as this will show the month names, eg. 12
January 2009.

 

[c676228]

Hi all,

Thanks to you all for your guys input. As some of you imagined it does have
something to do with date format.

I figured out last night somehow. It is the format issue. I have to
acknowledge that my husband(he is not a programmer) helped. He said it
probably has something to do with date format.

Initially I didn't take it seriously since I can DateDiff and DateAdd to both
effectiveDate and expirationDate without any problem. But I checked my code
both my effectiveDate and expirationDate are in string format before doing
any calculation.
I think it's probably like this: DateAdd and AddDiff etc. functions will
return a Date formula even with string data type EffectiveDate, so in the
following statement,
the left side returns a Date format, while the right side is still in string
format since it doesn't employ any date functions. When these two compare,
the data is messed up.
DateAdd("m", iMonthLength, EffectiveDate) <= ExpirationDate

I fixed with EffectiveDate=CDate(EffectiveDAte)
ExpirationDate=CDate(ExpirationDate)

Then I can do comparisons and date calculations without any problems. The
bug is really nasty since the behavior is not consistent, sometimes is Ok and
sometimes is not OK. That's why it took me so long.

Thanks for your contributions.

Thank

 

[Adrienne Boswell]

Gazing into my crystal ball I observed (e-mail address removed)
(Allen Chen [MSFT]) writing in

Regards,
Allen Chen
Microsoft Online Community Support

<snip 23 remaining line of signature>

Allen, please, please, for the sake God and all humanity, reduce your
signature to the Usenet conventional 4 lines,
eg:

-- (that is two dashes, a space and a carriage return)
Allen Chen
Microsoft Online Community Support
Your URL (if you want to)

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