ACC97: IsMissing() Returns False for Non-Variant Data Types

Public Function Test(Optional str1 As String = "Empty String", _
   Optional var2 As Variant)
				

MORE INFORMATION

Optional arguments are used in procedures to indicate that an argument is not required. Although the IsMissing() function always returns False for non-variant data types, it is important to learn what values are returned if the optional argument is not specified when calling the procedure. The following list summarizes what values are returned if an optional argument is not specified or an optional argument is not initialized with a default value:

   Data Type           Value returned by Default
   ---------           ---------------------------------
   String              "" (returns a zero length string)
   Variant             Error 448
   Integer             0
   Single              0
   Long                0
   Double              0
   Currency            0
   Date                12:00:00 AM
   Byte                0
   Boolean             False
   Object              (Run-time error 91: "Object variable or With block
                       variable not set")
				

Steps to Reproduce Behavior

The following example demonstrates what the IsMissing() function will return, given an optional String and optional Variant arguments. In order to assure the optional String argument won't return a zero-length string, you will want to replace the function definition with the one noted in the "Resolution" section of this article:

1. Create a module and type the following line in the Declarations section if it is not already there:

   Option Explicit
   						

2. Type the following procedure:

   Public Function Test1(Optional str1 as String, _
                       Optional var2 as Variant)
      Debug.Print "IsMissing(str1) = " & IsMissing(str1)
      Debug.Print "IsMissing(var2) = " & IsMissing(var2)
      Debug.Print str1
      Debug.Print var2
   
   End Function
   					

3. To test this function, type the following line in the Debug window, and then press ENTER.

   ?Test1()

   Note that the following information is returned:
   IsMissing(str1) = False
   IsMissing(var2) = True
   
   Error 448