Monthly generation with a given dates - vbscript

Question

Trying to Achieve
I fixed a date on my code say 31-01-2019. Then everyday I will execute my code but only on 28-02-2019/29-02-2020, 31-03-2019, 30-04-2019... I wish to execute the code. It is something like monthly generation. In addition, if the fixed date is 30-01-2019, I wish to execute the code on 28-02-2019/29-02-2020, 30-03-2019, 30-04-2019...
For example
What I have done
I have followed the question VBScript DateDiff month, and have tried out the following code but it is not working.
If I were to have a date say 31-Jan-2010 by DateAdd
endFeb = DateAdd("m",1,"31-Jan-10")
endMar = DateAdd("m",1,endFeb)
endApr = DateAdd("m",1,endMar)
The result
endFeb: 28/02/2010
endMar: 28/03/2010
endApr: 28/04/2010
What I want is
endFeb: 28/02/2010
endMar: 31/03/2010
endApr: 30/04/2010
Code
sFixedDate = "2019-01-31" '==== Fixed
sProcessDate = "2019-02-28" '==== Changes daily
d1 = CDate(sFixedDate)
d2 = CDate(sProcessDate)
diff = DateDiff("m", d1, d2)
If request("btnProcess") <> "" Then
If diff Mod 1 = 0 Then '=== Not as simple as I thought
'=== Trying to do monthly GENERATION.
'===Excecute the CODE
End If
End If

Answer 1

Basically, you want to run something on the last day of each month. Meaning that the day after would be a different month, so you could do something like this for calculating the last day of the next month:
today = Date
tomorrow = today + 1
If request("btnProcess") <> "" Then
If Month(today) <> Month(tomorrow) Then
endNextMonth = DateAdd("m", 1, tomorrow) - 1
End If
End If
To get the last day for any given month adjust the number of months to add to tomorrow's date.
The above assumes that you're doing the calculation on the last day of a month. If you want to calculate the last day of any given month on any day of a month please see Ekkehard Horner's answer.

Answer 2

Use DateSerial:
For m = 1 To 13
d1 = DateSerial(2019, m, 1) ' First day of month is easy
d2 = DateAdd("d", d1, -1) ' Last day of previous month is just 1 day before
WScript.Echo m, d1, d2
Next
cscript lom.vbs
1 01.01.2019 31.12.2018
2 01.02.2019 31.01.2019
3 01.03.2019 28.02.2019
4 01.04.2019 31.03.2019
5 01.05.2019 30.04.2019
6 01.06.2019 31.05.2019
7 01.07.2019 30.06.2019
8 01.08.2019 31.07.2019
9 01.09.2019 31.08.2019
10 01.10.2019 30.09.2019
11 01.11.2019 31.10.2019
12 01.12.2019 30.11.2019
13 01.01.2020 31.12.2019

Answer 3

It seems like for a given start date, you want to calculate x months into the future what that new date is, and if the start date as a day that is greater than the future month, to give the last day of the month instead.
Function CalculateFutureDate(startDate, monthsInFuture)
' Assumes startDate is in the past
Dim dtRepeatDate
Dim dtNewDate
If (IsDate(startDate)) Then
dtRepeatDate = CDate(startDate)
' months between now and Start Date
Dim intMonthsToAdd
Dim dtCurrentDate
dtCurrentDate = Now()
intMonthsToAdd = DateDiff("m", startDate, dtCurrentDate)
If intMonthsToAdd > 0 And Day(startDate) < Day(dtCurrentDate) Then
intMonthsToAdd = intMonthsToAdd - 1
End If
' Add the future months to the month offset
intMonthsToAdd = intMonthsToAdd + monthsInFuture
' Now calculate future date
dtNewDate = DateAdd("m", intMonthsToAdd, dtRepeatDate)
CalculateFutureDate = dtNewDate
End If
End Function
And then you can do something like:
CalculateFutureDate(CDate("2019-01-31"), intFutureMonths)
This will output:
?CalculateFutureDate(CDate("2019-01-31"), 1)
2/28/2019
?CalculateFutureDate(CDate("2019-01-31"), 2)
3/31/2019
?CalculateFutureDate(CDate("2019-01-31"), 3)
4/30/2019

Answer 4

dtLoan = CDate("2019-01-30")
dtProcess = CDate ("2020-02-28")
'dtLoan = CDate("2019-01-31")
'dtProcess = CDate ("2020-02-29")
'dtLoan = CDate("2019-02-28")
'dtProcess = CDate ("2020-02-29")
if LastDateOfMonth(dtLoan) = dtLoan AND dtProcess = LastDateOfMonth(dtProcess) then
response.write " this mean that the Loan date is end of the month, say 31 Jan, 28, 29 of Feb, 31 Feb "
response.write " and Process Date is also end of the month " & "<br>"
response.write " **** End of the month Loan Date : " & dtLoan & "<br>"
response.write " **** End of the month Process Date : " & dtProcess & "<br>"
elseif LastDateOfMonth(dtLoan) <> dtLoan AND dtProcess <> LastDateOfMonth(dtProcess) then
daysFromEndOfLoanMth = DateDiff("d",LastDateOfMonth(dtLoan),dtLoan)
response.write " How many days from end of Loan month: " & daysFromEndOfLoanMth & "<br>"
daysFromEndOfProcessMth = DateAdd("d",daysFromEndOfLoanMth,LastDateOfMonth(dtProcess))
response.write " From end of the month Add " & daysFromEndOfLoanMth & " Days = " & daysFromEndOfProcessMth & "<br>"
response.write " The date of process : " & dtProcess & "<br>"
dtShouldProcess = day(dtLoan) & "/" & Month(dtProcess) & "/" & Year(dtProcess)
if isDate(dtShouldProcess) then
dtShouldProcess=CDate(dtShouldProcess)
else
dtShouldProcess=daysFromEndOfProcessMth
end if
response.write " ** The date of should Process : ** " & dtShouldProcess & "<br>"
if dtProcess = dtShouldProcess then
'if dtProcess = daysFromEndOfProcessMth then
response.write " **** Loan Date : " & dtLoan & "<br>"
response.write " **** Process Date : " & dtProcess & "<br>"
end if
'daysFromEndOfProcessMth = DateDiff("d",LastDateOfMonth(dtProcess1),dtProcess1)
'response.write " How many days from Process Date end of the month: " & daysFromEndOfProcessMth & "<br>"
end if