How do I test if optional arguments are supplied or not?

Question

How do I test if optional arguments are supplied or not? -- in VB6 / VBA

Function func (Optional ByRef arg As Variant = Nothing)

    If arg Is Nothing Then   <----- run-time error 424 "object required"
        MsgBox "NOT SENT"
    End If

End Function 

Answer 1

Use IsMissing:

If IsMissing(arg) Then
    MsgBox "Parameter arg not passed"
End If

However, if I remember correctly, this doesn’t work when giving a default for the argument, and in any case it makes using the default argument rather redundant.

Answer 2

If IsMissing(arg) Then ...

Answer 3

You can use the IsMissing() Function. But this one only works with the Variant datatype.

Sub func(Optional s As Variant)
   If IsMissing(s) Then
      ' ...
   End If
End Sub

Answer 4

"IsMissing"...Figured there would have to be a way. Thanks all!

SQL has a function, In(), where you can pass multiple arguments to see if the target value is in the list. I've always liked that as a solution, so here's my take on that, hope it helps:

Public Function IsIn(ByVal TestVal, ByVal VersusVal1, _
            Optional ByVal VersusVal2, Optional ByVal VersusVal3, _
            Optional ByVal VersusVal4, Optional ByVal VersusVal5, _
            Optional ByVal VersusVal6, Optional ByVal VersusVal7, _
            Optional ByVal VersusVal8, Optional ByVal VersusVal9, _
            Optional ByVal VersusVal10, Optional ByVal VersusVal11, _
            Optional ByVal VersusVal12, Optional ByVal VersusVal13, _
            Optional ByVal VersusVal14, Optional ByVal VersusVal15, _
            Optional ByVal VersusVal16, Optional ByVal VersusVal17, _
            Optional ByVal VersusVal18, Optional ByVal VersusVal19, _
            Optional ByVal VersusVal20) As Boolean

Dim CheckVals(1 To 20) as Variant
VersusVals(1) = VersusVal1
VersusVals(2) = VersusVal2
VersusVals(3) = VersusVal3
VersusVals(4) = VersusVal4
VersusVals(5) = VersusVal5
VersusVals(6) = VersusVal6
VersusVals(7) = VersusVal7
VersusVals(8) = VersusVal8
VersusVals(9) = VersusVal9
VersusVals(10) = VersusVal10
VersusVals(11) = VersusVal11
VersusVals(12) = VersusVal12
VersusVals(13) = VersusVal13
VersusVals(14) = VersusVal14
VersusVals(15) = VersusVal15
VersusVals(16) = VersusVal16
VersusVals(17) = VersusVal17
VersusVals(18) = VersusVal18
VersusVals(19) = VersusVal19
VersusVals(20) = VersusVal20

On Error Goto 0

IsIn = False

For x = 1 To 20
   If Not IsMissing(VersusVals(x)) Then
      If TestVal = VersusVals(x) Then
         IsIn = True
         Exit For
      End If
   End If
Next x

End Function

So, that's obviously why I needed "IsMissing"; doesn't work without it.

Answer 5

Most of these refer to the variant type, or test if a value is blank.

However, sometimes you want to check if a range, workbook, worksheet, or other type of object is not passed, without checking things like sheetnames.

In that case:

DesiredRange is Nothing

Returns a boolean. For example:

    If DestinationRange Is Nothing Then
        MsgBox "Need a destination range when importing data"
    Else
        'We're happy
    End If

Answer 6

"IsMissing(var)" for variants
"StrPtr(var) = 0" for strings

For other data types there's no perfect solution, you can only test for their default values, therefore not distinguishing between a not passed argument and a passed argument valued as default.

Answer 7

You can use something like:

function func(optional vNum as integer:=&HFFFF) '&HFFFF value that is NEVER set on vNum

If vNum = &HFFFF Then
    MsgBox "NOT SENT"
End If

End Function

Answer 8

If you are using a string or number variable you can check the value of the variable. For example:

Function func (Optional Str as String, Optional Num as Integer)

If Str = "" Then
    MsgBox "NOT SENT"
End If

If Num = 0 Then
    MsgBox "NOT SENT"
End If

End Function

This allows you to use non-variant variables.

Answer 9

With a variant I would use the NZ function:

Function func (Optional ByRef arg As Variant = Nothing)
    If nz ( arg, 0 ) = 0 Then
        MsgBox "NOT SENT"
    End If
End Function 

It can be used with other data types too, just keep in mind that Zero counts as neither Null nor Zero-Length, so nz(0,"") still returns 0.