C ++ Map as function output in VBA

I have a C ++ code that returns a map to me. I have created a dll and I call it from an Excel macro.

Then, in that macro, I need a dictionary (Scripting.Dictionary) .

I tried to do the following:

Declare Function ExlFunct Lib "direccion" (InputDict As Variant, ByVal a As Integer) As Scripting.Dictionary
Dim a As Integer
Dim InputDict As New Scripting.Dictionary
Dim Out As New Scripting.Dictionary
//creo el dicionario de entrada y le asigno un valor a "a"
Out = ExlFunct (InputDict, a )

It returns the following error:

Error de compilacion: El argumento no es opcional

Can the error be caused by problems between the c ++ map and the vba dictionary? How could I solve it?