IsMissing without using Variant data type

[Jaafar Tribak]

Hi all,

A recent question posted today https://www.mrexcel.com/forum/excel-questions/1020927-checking-input-function.html has intrigued me .

My question is : Is it possible to check if an optional argument has been passed to a function or not where the argument is not of variant data type ?

Thanks.

 

[RoryA]

No, I don't believe so. According to the language spec, if the default value for an optional argument that is not a Variant is not specified, it is treated as being the default value for the relevant data type. So a value is always provided, it's just that Variant allows the use of the Missing type.

 

[shg]

Seems doubtful.

I think a missing (optional, per force) variable is passed on the stack with the default value (e.g., 0 for a number, Empty with the IsMissing flag for a Variant) just like any value passed ByVal (versus the address of a variable being on the stack if passed ByRef).

 

[Jaafar Tribak]

Thanks .. I was thinking maybe the function stack size would differ if no arg was supplied but like you said, vb coerces the missing arg to the default value for the relevant data type so the size would always be the same.

One tacky workaround I can think of is to set the default value as unlikely value .. Something like this :

Function Test(Optional arg As Double = -0.1152254411411) As String

If arg = -0.1152254411411 Then MsgBox "Arg missing" Else MsgBox "You passed : " & arg

 

[shg]

If I were going to use a particular number, it would be the biggest a Double can contain:

Const dBig = 9E+307 + 8.97693134862315E+307 + 6E+292

Function test1(Optional d As Double = dBig) As Double
  test1 = d
End Function

... because it can't be entered from the UI, and it's hard to arrive at as a result of a calculation.

 

[Jaafar Tribak]

If I were going to use a particular number, it would be the biggest a Double can contain:

Const dBig = 9E+307 + 8.97693134862315E+307 + 6E+292

Function test1(Optional d As Double = dBig) As Double
  test1 = d
End Function

... because it can't be entered from the UI, and it's hard to arrive at as a result of a calculation.

Yes I agree