ACC: How to Use Optional Arguments

ID: Q141605

The information in this article applies to:

Microsoft Access versions 7.0, 97

SUMMARY

Advanced: Requires expert coding, interoperability, and multiuser skills.

When you use the Optional keyword in Microsoft Access 7.0 and 97, you can create procedures that accept optional (not required) arguments. This article shows you two examples of how to create and use procedures with optional arguments.

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 your version of the "Building Applications with Microsoft Access" manual.

MORE INFORMATION

NOTE: In Microsoft Access 7.0, it was required that the variables declared as optional were placed at the end of the calling procedure and that the data type was explicitly a Variant. For example:

   Sub MyTest(strTest1 As String, _
       Optional Test2 As Variant, _
       Optional Test3 As Variant)

This was a requirement because optional arguments were passed at the end of the function call. In Microsoft Access 97 improvements have been made to the use of the Optional keyword by allowing the data type casting of the optional variable to be pre-assigned. For example:

    Sub MyTest(strTest1 As String, _
       Optional Test2 As String = "Test2", _
       Optional Test3 As String = "Test3")

This allows for the placement of the optional variable anywhere in the calling order of the function and allows you to test the contents of the variable.

Example 1

1. Create a module and type the following line in the Declarations section

   if it isn't already there:

      Option Explicit

2. Type the following procedure:

      Function CallEmployeeInfo()
         If Forms!employees!Title <> "Sales Representative" Then
           EmployeeInfo Forms!employees!FirstName, Forms!employees!LastName
         Else
           EmployeeInfo Forms!employees!FirstName, _
           Forms!employees!LastName, Forms!employees!Title
         End If
      End Function

      Sub EmployeeInfo(fname, lname, Optional Title)
         If IsMissing(Title) Then
            MsgBox lname & ", " & fname
         Else
            MsgBox lname & ", " & fname & "   " & Title
         End If

      End Sub

3. Open the Employees form in Form view.

4. To test this function, type the following line in the Debug window,

   and then press ENTER:

       ? CallEmployeeInfo()

   Note that the message box opens. If the title is not Sales
   Representative, then the option title argument is not sent to the Sub
   routine but the Sub routine will still process. It just displays the two
   arguments that were provided. If the title is Sales Representative, the
   argument title is sent and displayed in the message box.

Example 2

1. Create a module and type the following line in the Declarations section

   if it isn't already there:

     Option Explicit

2. Type the following procedure:

      Sub OptionalTest(Optional Country)
         Dim dbs As DATABASE, rst As Recordset
         Dim strSQL As String

         ' Return Database variable pointing to current database.
         Set dbs = CurrentDb
         If IsMissing(Country) Then
            strSQL = "SELECT * FROM Orders"
            'This will return all the records
         Else
            strSQL = "SELECT * FROM Orders WHERE [ShipCountry] = '" &_
            Country & "';"
         'This will return only values matching the argument you entered.
         End If
         Set rst = dbs.OpenRecordset(strSQL)
         rst.MoveLast
         Debug.Print rst.RecordCount

      End Sub

3. Type the following line in the Debug window, and then press ENTER:

      OptionalTest "UK"

   Note that the record count will return the number of records where the
   ShipCountry is equal to UK.

4. Type the following line in the Debug window, and then press ENTER:

      OptionalTest

   Note that you receive a record count for the whole table. This is
   because the optional argument was not supplied when the Sub procedure
   was called. This feature can be very useful for setting up criteria for
   queries.

REFERENCES

For more information about the Optional keyword, search the Help Index for "optional argument," or ask the Microsoft Access 97 Office Assistant.

Additional Query Words:

Keywords          : kbprg
Version           : 7.0 97
Platform          : WINDOWS
Hardware          : x86
Issue type        : kbhowto

Last Reviewed: November 20, 1998