Is it possible to allow Integer Overflow in Excel VBA? - vba

Question

Pretty simple, but I couldn't find anything by Googling. An example of what I want to happen:
Function myFunc()
Dim a As Integer
Dim b As Integer
Dim c As Integer
a = 20000
b = 15000
c = a + b
myFunc = c
End Function
I want myFunc() to return -30536 instead of throwing an overflow exception. I know I could write a function that does that, but I've written a bunch of code for a project with the assumption that overflow was allowed, so I'm hoping there's a quick fix.
EDIT: I don't need help coming up with a function that solves the overflow issue with type conversions. I have one already; I just want to avoid changing hundreds of addition and subtraction operations. I'm also bit frustrated that VBA seems to go out of its way to disable overflow functionality--it should let the user decide if they want to use it or not.

Answer 1

I would suggest writing MyFunc to do the math as Long, and test for integer "overflow" and adjust
Function MyFunc(a As Integer, b As Integer) As Integer
Dim sum As Long
Const Mask As Integer = -1
sum = CLng(a) + CLng(b)
If sum > 32767 Then
sum = sum - 65536
ElseIf sum < -32768 Then
sum = sum + 65536
End If
MyFunc = sum
End Function
Test with
Sub zx()
Debug.Print MyFunc(20000, 15000)
End Sub

Answer 2

In order to prevent Integer overflow in your Excel VBA code, you may use the custom Function to perform the Integer to Long type casting like shown below:
Sub TestIntegerConversion()
Debug.Print myFuncLong(20000, 15000)
End Sub
Function myFuncLong(a As Integer, b As Integer) As Long
myFuncLong = CLng(a) + CLng(b)
End Function
or without using custom Function in a simple form like this:
Sub PreventOverflow()
Dim a As Integer
Dim b As Integer
a = 20000
b = 15000
Debug.Print CLng(a) + CLng(b)
End Sub
Alternatively, you may write your own custom function, which should implement that "overflow math" (you have somehow to specify using plain math notation how to get the number -30536 from 35000) and return the result either as Long, or String. Possible implementation is shown below (note: Overflow exception number is 6)
Sub OverflowCustomMath()
Dim a As Integer
Dim b As Integer
Dim c As Long
a = 20000
b = 15000
On Error GoTo Err:
Debug.Print a + b
Err:
If (Err.Number = 6) Then
'apply your custom overflow math, as for e.g.
Debug.Print CLng(a) + CLng(b)
End If
End Sub
Hope this may help.

Answer 3

Use typical VBA error handler but tests for your case.
Option Explicit
Sub test()
MsgBox myFunc
End Sub
Function myFunc()
On Error GoTo Local_err
Dim a As Integer
Dim b As Integer
Dim c As Integer
a = 20000
b = 15000
c = a + b
myFunc = c
Local_exit:
Exit Function
Local_err:
If Err = 6 Then
myFunc = -30536
Else
MsgBox Err & " " & Err.Description
' myFunc = whatever error value to return
End If
Resume Local_exit
End Function