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          


        

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 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.