VB6 - ByRef argument type mismatch error - where is it?

Question

For the 10+ years I've been using VB6, every now and then I get a "ByRef argument type mismatch" error where I simply can't find the mismatch. After struggling for a while I've always punted by forcing the type one way or another, but this time I thought I'd ask. I'm including all the code I think could have anything to do with this; but you can skip it now and refer to it after I demonstrate the problem:

Public Type PBufferType
  Location(9) As Integer ' code location
  ValueHi(9) As Integer  ' Vhi code
  ValueLo(9) As Integer  ' Vlo code
  Locked(9) As Integer   ' State of pair
  Gamma(9) As Single     ' Gamma between this segment and next
End Type

Public GammaBuffer(1) As PBufferType ' The main data type

Public SelectedBank as Integer

Function MeasureLuxAtCode(code As Integer) As Single
  Call TestPatternForm.DrawTestWindow(3, code) 
  MeasureLuxAtCode = MeasureLux(1)
End Function

The problem occurs below. The "LuxMinTarget = MeasureLuxAtCode(FirstLevel)" line generates a "ByRef argument type mismatch" error, indicating that FirstLevel is not an integer.

Sub DetermineIdealLuxCurve()
  Dim FirstLevel, FirstDACtoMeasure As Integer
  FirstDACtoMeasure = 0
  FirstLevel = GammaBuffer(SelectedBank).Location(FirstDACtoMeasure)
  LuxMinTarget = MeasureLuxAtCode(FirstLevel)
End Sub

But dang it, FirstLevel is an integer, isn't it? It's dim'ed an int, its value is set by a UDT that returns an int, so where did I go wrong? If I force it to an int like this:

  LuxMinTarget = MeasureLuxAtCode(Int(FirstLevel))

the compiler/interpreter's happy. But I'm not.

So is this a bug in the compiler or just me being dense?

Answer 1

The problem is here:

Dim FirstLevel, FirstDACtoMeasure As Integer

This actually declares FirstLevel as a Variant and not as an Integer as you might expect.

This is a classic VB6 gotcha! (and you are not the first to be bitten by it).

Answer 2

As Mitch pointed out, VB6 only declares the last variable in a comma delimited list as explicitly of the type defined. The previous entries are declared, but as variants.

To have the variables correctly declared, you need to handle them individually.

Dim FirstLevel As Integer
Dim FirstDACtoMeasure As Integer

This was also the case in previous versions of VB, IIRC, not new for for VB6.

Answer 3

John T, You actualy can explicitly declare variables in a list.

Dim FirstLevel as Integer, FirstDACtoMeasure As Integer