ACC: How to Call Functions by Using a String Variable

• Microsoft Access versions 1.0, 1.1, 2.0, 7.0, 97

SUMMARY

Moderate: Requires basic macro, coding, and interoperability skills.

This article describes how Visual Basic for Application or user-defined functions can be called when the function name is stored in a string variable. This method provides a functionality similar to that of pointers to functions in other programming languages.

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.

NOTE: Visual Basic for Applications is called Access Basic in Microsoft Access versions 1.x and 2.0. For more information about Access Basic, please refer to the "Introduction to Programming" manual in Microsoft Access version 1.x or the "Building Applications" manual in Microsoft Access version 2.0

MORE INFORMATION

To allow significant programming flexibility, you can call a function in Visual Basic for Applications when the function name is stored in a variable. This technique is demonstrated in the following example:

1. Create a new, blank database.



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

   Option Explicit




3. Type the following procedures:
   
   NOTE: In the following sample code, an underscore (_) at the end of a line is used as a line-continuation character. Remove the underscore from the end of the line when re-creating this code in Access Basic.

   
         '------------------------------------------------------------------
         'GLOBAL DECLARATIONS SECTION
         '------------------------------------------------------------------
         Option Explicit
   
         '------------------------------------------------------------------
         ' The CallMyArray() function creates an array of strings, then
         ' loops, using the Eval() function, to call each element of the
         ' array.
         '------------------------------------------------------------------
         Function CallMyArray ()
            Dim MyArray$(), i as Integer, x as Integer
   
             For i = 0 To 2
                ReDim Preserve MyArray$(i)
                MyArray$(i) = "MyFunc" & i & "(" & i & ")"
             Next i
   
             For i = 0 To 2
                 x = Eval(MyArray(i))
             Next i
         End Function
   
         '------------------------------------------------------------------
         '    The first function called by CallMyArray().
         '------------------------------------------------------------------
         Function MyFunc0 (nParam)
            MsgBox "This is function: " & nParam
         End Function
   
         '------------------------------------------------------------------
         '    The second function called by CallMyArray().
         '------------------------------------------------------------------
         Function MyFunc1 (nParam)
            MsgBox "This is function: " & nParam
         End Function
   
         '------------------------------------------------------------------
         '    The third function called by CallMyArray().
         '------------------------------------------------------------------
         Function MyFunc2 (nParam)
            MsgBox "This is function: " & nParam
         End Function 




4. Type the following line in the Debug Window (or Immediate Window in versions 1.x and 2.0):

   
          ? CallMyArray() 

REFERENCES

For more information about the Eval() function, search for eval, and then Eval function using the Microsoft Access 97 Help Index.

Additional query words: string eval

Keywords : kbprg
Version : WINDOWS:1.0,1.1,2.0,7.0,97
Platform : WINDOWS
Issue type : kbhowto