I have a VBA function that is basically along these lines:
Public Function JoinDateTime(DateTime As String, Time As String) As Date
Dim dtDate As Date
dtDate = CDate(Format(DateTime, "dd/mm/yyyy"))
dtDate = dtDate & " " & Format(Time, "hh:mm")
JoinDateTime = dtDate
End Function
It glues a date and a time together into a datetime value. (The real function has some more logic behind it.)
The problem is, I'd like to add handling for annoying values being passed to it. This is mostly for empty/null values - if DateTime is empty, return empty. If it's a text string returning #Error so it doesn't just fail silently seems like a good idea.
Problem is, I'm not sure how to do so. I'd thought about doing an early return, maybe something like shoving this at the start of the function:
If DateTime = Null or DateTime = "" Then
JoinDateTime = Null
End If
but it doesn't seem to consider that as a return and still executes the rest of the function.
Is there a way to do this? A better way, ideally?
To prematurely return from a function in VBA, you need to use the Exit Function
statement, similar to Exit Sub
, Exit For
, etc. So, this
If DateTime = Null or DateTime = "" Then
JoinDateTime = Null
Exit Function 'Au revoir
End If
will prevent the rest of the code below from executing.
First off, you need to change your function declaration to use Variant
instead of String
. This is because in VBA, the String
data type cannot hold the value Null
. If you want your function to return Null
for invalid dates, then you will need to change the return type to Variant
as well. I would also take Mitch Wheat's advice and rename your arguments to something that doesn't conflict with built-in functions (such as dateSection
and timeSection
).
Second, the comparison DateTime = Null
will never evaluate to true. Any comparison to a Null
value will result in a Null
value. Instead, you should use the IsNull() function (see Error 5).
Third, you might consider using the IsDate() function. This function will ensure that the argument is a valid date, which includes checking for nulls. It depends on whether you want poorly formatted dates to fail silently, too.
Putting it all together:
Public Function JoinDateTime(dateSection As Variant, timeSection As Variant) As Variant
Dim dtDate As Date
If IsNull(dateSection) Then
JoinDateTime = Null
Else
dtDate = CDate(Format(dateSection, "dd/mm/yyyy"))
dtDate = dtDate & " " & Format(timeSection, "hh:mm")
JoinDateTime = dtDate
End If
End Function
The cleanest and most error-proof way to do this is by raising an error.
Public Function JoinDateTime(DateTime As String, Time As String) As Date
If DateTime = "" Then
Err.Raise _
Number:=12345, _
Source:="JoinDateTime", _
Description:="Invalid input. DateTime cannot be empty string."
End If
'NB: could also check for IsNull(DateTime) if DateTime were type Variant.
' etc.
This will display an error with the following message: "Run-time error '12345': Invalid input. DateTime cannot be empty string." and execution will stop.
If you don't want execution to stop, you can handle the error in the procedure that calls JoinDateTime
. For example:
Sub tester()
On Error GoTo ErrorHandler ' Telling VBA where to go when an error is raised
Dim d As String
Dim j As Date
d = InputBox("Date please:")
j = JoinDateTime(d) ' Raises an error upon invalid input
MsgBox Prompt:=j
ErrorHandler:
Select Case Err.Number
Case 12345 ' "Invalid input" error was raised, therefore do the following...
' Whatever you want to happen when this error occurs, e.g.
' MsgBox Prompt:=Err.Description
' or
' j = 0
' Resume Next
End Select
Resume ExitProcedure
ExitProcedure:
'Cleanup code goes here
End Sub
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