devxlogo

Manufacture a Missing value

Manufacture a Missing value

Visual Basic doesn’t provide you with a means for creating a Missing value, a feature that in some cases would prove useful in order to simplify the syntax of calls to procedures that expects a variable number of arguments. It isn’t difficult, however, to create such a value programmatically, as follows:

' never pass an argument to this functionFunction MissingValue(Optional DontPassMe As Variant) As Variant    ' If an argument is passed, raise the "Invalid Procedure Call" error    If Not IsMissing(DontPassMe) Then Err.Raise 5           MissingValue = DontPassMeEnd Function

There is an alternative way, however, that doesn’t require that you intentially avoid to pass an Optional argument to a procedure. This latter method actually manufactures the internal representation of a Variant:

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (dest As _    Any, source As Any, ByVal bytes As Long)Function MissingValue() As Variant    ' A "missing" value is actually an error code equal to hex 80020004    ' so here we store the integer part of this value    MissingValue = &H80020004    ' and then we modify the VarType to vbError (= 10)    CopyMemory MissingValue, 10, 2End Function

devxblackblue

About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

About Our Journalist