Question

Please have a look at the following code, which I have run in VB6 and .NET:

Private Sub Form_Load()
Dim TestArray3() As String
TestArray3 = TestArrayFunction

End Sub

Private Function TestArrayFunction() As String()
    Dim TestArray1(0 To 1) As String
    Dim TestArray2() As String
    TestArray1(0) = "Monday"
    TestArray1(1) = "Tuesday"
    TestArray2 = TestArray1
    TestArray1(0) = "Wednesday"
End Function

When the program gets to the end of TestArrayFunction in VB6, the value of TestArray2(0) is “Monday”, however when run in .NET, it is “Wednesday”. I understand in .NET that an Array is an object and has two references pointing to it in TestArrayFunction. Why is this not the case in VB6?

Answer 1

I am struggling with this nearly daily. While it is perfectly possible to pass an array ByRef to a Function call, the ‘=’ sign will make a shallow copy.

But there is more strange behaviour of arrays in VB6, Suppose you have the following DateTimeClass classmodule in VB6:

Option Explicit

Private m_strDaysOfWeek() As String

Public Property Get DaysOfWeek() As String()

    DaysOfWeek = m_strDaysOfWeek()

End Property

Public Property Let DaysOfWeek(strDaysOfWeek() As String)

    m_strDaysOfWeek() = strDaysOfWeek

End Property

Private Sub Class_Initialize()
    ReDim m_strDaysOfWeek(7)
    m_strDaysOfWeek(1) = "Monday"
End Sub

You would expect to be able to write code like:

Dim clsDateTime As New DateTimeClass
Dim strDay As String

strDay = clsDateTime.DaysOfWeek(1)

Or:

clsDateTime.DaysOfWeek(2)="Tuesday"

But you can’t. You have to do it like this:

Dim clsDateTime As New DateTimeClass
Dim strDay As String
Dim strDays() As String

strDays = clsDateTime.DaysOfWeek
strDay = strDays(1)
strDays(2) = "Tuesday"
clsDateTime.DaysOfWeek = strDays

What the reasons of the VB6 team were at the time to implement it thus? I don’t know…
I have abandoned the VB6 arrays and use Collections and Dictionaries nearly exclusively.