March 17 2023 - Compare two dates in VBA

Compare two dates in VBA.md

Compare two dates in VBA

Simple example showing how to compare two dates by first converting them to epoch Unix timestamps.

compare_two_dates.vba

Option Explicit

'Compares `leftDate` (first param) to `rightDate` (second param).
'Returns true if leftDate is LESS than (earlier in time) than
'rightDate, otherwise false. HANDLES ONLY DATES IN "AD" (no dates
'in "BC" format are valid. :(
'
'@param String leftDate
'@param String rightDate
'@returns Bool
'    True if first date is earlier than second date, otherwise false.
Public Function dateDifference(leftDate As Date, rightDate As Date) As Boolean
    Dim lDateUnix As LongLong
    Dim rDateUnix As LongLong
    lDateUnix = DateDiff("s", "1/1/0001 00:00:00", leftDate)
    rDateUnix = DateDiff("s", "1/1/0001 00:00:00", rightDate)
    
    If lDateUnix < rDateUnix Then
        dateDifference = True
        Exit Function
    End If
    
    dateDifference = False
End Function

Sub dateExamples()
    Debug.Print dateDifference("10/10/2010", "11/11/2010") ' True
    Debug.Print dateDifference("10/10/2010", "10/10/2010") ' False
    Debug.Print dateDifference("13/01/2021", "01/13/2021") ' <--- unexpected results mixing TWO date formats!! Are these the same day? Who knows!? Booo...
    Debug.Print dateDifference("5/2/1751", "5/3/1751") ' True
    Debug.Print dateDifference("1999-11-01", "01/13/2001") ' Mixing formats (again). When it comes to dates, VBA is too permissive with these kinds of things!
End Sub