ACC97: IsMissing() Returns False for Non-Variant Data Types
ID: Q162534
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The information in this article applies to:
SYMPTOMS
Advanced: Requires expert coding, interoperability, and multiuser skills.
When you pass optional arguments that are of a data type other than
Variant to a Visual Basic for Applications function, the IsMissing()
function returns a value of False for those Optional arguments.
This is perceived as a problem because IsMissing() will return False for
any non-Variant data type, regardless of whether an optional argument is
passed or not.
CAUSE
The IsMissing() function is used to detect whether or not optional Variant
arguments have been provided in calling a procedure. It will always return
False for non-Variant data types.
RESOLUTION
This article assumes that you are familiar with Visual Basic for
Applications and with creating Microsoft Access applications using the
programming tools provided with Microsoft Access. For more information
about Visual Basic for Applications, please refer to the "Building
Applications with Microsoft Access 97" manual.
Initialize your optional non-Variant variables with a default value when
defining the function. The following is an example declaration of a
function, including the initialization of an Optional string argument with
a default value of "Empty String":
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:
- Create a module and type the following line in the Declarations section if it is not already there:
Option Explicit
- 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
- 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
REFERENCES
For more information about using optional arguments in procedures, search
the Help Index for "Optional Keyword."
For more information about understanding optional arguments, search the
Help Index for "Optional arguments, Understanding Named Arguments and
Optional Arguments."
For more information about using the IsMissing() function, search the Help
Index for "IsMissing Function."
Additional query words:
type cast form report object ParamArray null
Keywords : kbenv kbprg AccCon
Version : WINDOWS:97
Platform : WINDOWS
Issue type : kbprb