XL97: ParamArrays are Always Zero-Based

• Microsoft Excel 97 for Windows

SYMPTOMS

When you call a custom function created in Visual Basic for Applications from a formula in a worksheet cell, the function returns an incorrect result.

CAUSE

This will occur if the custom function being called accepts a ParamArray argument and assumes that the ParamArray is a one-based array (where the first element in the array is element 1), rather than a zero-based array (where the first element in the array is element 0).

WORKAROUND

In many cases, you should be able to work around this problem by decreasing the index within your custom function by one. For example, if your function looks like this:

   Function MyFunc(ParamArray X())
       MyFunc = X(5)
   End Function

STATUS

This behavior is by design of Microsoft Excel 97. The behavior of earlier versions of Microsoft Excel is incorrect.

MORE INFORMATION

When you write a custom Visual Basic function in Microsoft Excel, the last argument accepted by the function can be declared as a ParamArray. When you do this, the function will accept one or more values and place them in the specified variable as an array. The value(s) can then be used within the function. For example, if you have the following function:

   Function Test(X As Integer, ParamArray Y())
       Test = "Hello"
   End Function

   =Test(6,7,8,9,10)

In earlier versions of Microsoft Excel, if you call a custom function from a formula in a worksheet cell, and if the function contains a ParamArray, the ParamArray is a one-based array. That is, the first element in the array is element 1. In Microsoft Excel 97, the first element in such an array is element 0. You can demonstrate the difference by entering the following function in a Visual Basic module in Microsoft Excel:

   Function TestIndex(ParamArray T())
       TestIndex = T(3)
   End Function

   =TestIndex(1,3,5,7,9)

     T() Element Numbers     Array
   Zero-Based    One-Based   Value
   -------------------------------
       0             1         1
       1             2         3
       2             3         5
       3             4         7
       4             5         9

Note that arrays declared by ParamArray are ALWAYS zero-based if called from another Visual Basic macro. The change in behavior between earlier versions of Microsoft Excel and Microsoft Excel 97 only applies when you call the function in question from a formula in a worksheet cell.