I'm trying to call a function from a DLL from VBA in Excel.
My Excel VBA macro looks like this:
Declare PtrSafe Function TestFunction1 Lib "mylib.dll" (ByVal k As Double) As Double
Public Function TestDll(k As Double) As Double
Debug.Print ("Start")
Dim r As Double
r = TestFunction1(k)
Debug.Print ("Got result of " + r)
Debug.Print ("Done")
TestDll = r
End Function
Now when I call it from an Excel cell with something like "=TestDll(3.0)", it doesn't work. I see the "Start" string in the immediate window, but nothing else. It's like an error is happening exactly when "TestFunction1" is being called. Excel displays "#VALUE!" in the cell.
I can also set a breakpoint in the debugger, but when I get to the TestFunction1 call, it just ends. There is no sort of error message I can find.
My question is, how do I debug this? I'm not getting any error message. It simply doesn't work. How can I figure out what is going wrong?
The variable which you are using in debug statement,has an error and hence the UDF fails. Rest is fine. Actually you need to convert r to string or use & for concatenation in your debug statement.
Edit: to include error handler.
Public Function TestDll(k As Double) As Double
Debug.Print ("Start")
Dim r As Double
'/ Add a error handler
On Error GoTo errHandler
'/ Assuming that your testfunction will return 10*parameter
r = k * 10
'/ The variable which you are returning,has a error and hence the UDF fails.
'/ Rest is fine. Here you will get type mismatch error.
Debug.Print ("Got result of " + r)
'/ Actually you need to convert it to string or use `&` for concatenation
Debug.Print ("Got result of " + CStr(r))
'/ or
Debug.Print ("Got result of " & r)
Debug.Print ("Done")
TestDll = r
errHandler:
If Err.Number <> 0 Then
'/ Error trapped and you get actual error desc and number.
MsgBox Err.Description, vbCritical, Err.Number
End If
End Function
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