Here’s another handy bit from my VB6 code shed out back.

If you’ve worked much with databases in VB6, you know that you almost always end up having to deal with database NULLs at some point.

And, in VB6, the only variable type that can actually deal with nulls is the Variant.

For the most part, my code avoids nulls by coercing them to the most appropriate “null value”, either a 0, or a 0 length string, etc, depending on the underlying data type.

However, there are instances where I’ve needed to compare two values directly from the database, and didn’t want to coerce them up front.

That’s where this handy routine comes in.

Public Function CompareVariant(Var1 As Variant, Var2 As Variant, Optional CompareMethod As VbCompareMethod = vbBinaryCompare) As Long
   '---- Compare 2 variants that might contain NULL or empty values

   Dim bVal1Null As Boolean
   Dim bVal2Null As Boolean
   Dim bVal1Empty As Boolean
   Dim bVal2Empty As Boolean
   Dim bSameValues As Boolean

   bVal1Null = IsNull(Var1)
   bVal1Empty = IsEmpty(Var1)
   bVal2Null = IsNull(Var2)
   bVal2Empty = IsEmpty(Var2)

   '---- variants are the same if
   '     1) both are null
   '     2) both are empty
   '     3) they are otherwise equal
   If (bVal1Null And bVal2Null) _
      Or (bVal1Empty And bVal2Empty) Then
      CompareVariant = 0
   Else
      '---- you can only check for equal values is if neither of the values is Null or Empty
      If Not (bVal1Null Or bVal1Empty Or bVal2Null Or bVal2Empty) Then
         If CompareMethod = vbTextCompare Then
            CompareVariant = StrComp(CStr(Var1), CStr(Var2), vbTextCompare)
         Else
            If Var1 > Var2 Then
               CompareVariant = 1
            Else
               CompareVariant = (Var1 < Var2)
            End If
         End If
      ElseIf bVal1Null Then
         '---- This is arbitrary, I'm determining that NULL is < empty
         '     this might not be universally appropriate, though
         CompareVariant = -1
      Else
         CompareVariant = 1
      End If
   End If
End Function

Basically, the idea is similar to the built-in VB function StrComp, but it intelligently deals with potentially NULL or empty variants as well.

Are there faster ways to do this? Probably. But I find I need the functionality so infrequently, it hasn’t been a priority to optimize.

Still, if you need it, coding this up each time would be a complete pain in the ass (and unfortunately, I’ve seen that tack taken more than a few times).

If anyone can improve on this, please let me know!

I’m thinking of starting an ongoing series of posts highlighting some of the more “interesting” things you can do with VB6 that are not, at least to my knowledge, particularly well known. I figure, VB6 has started on that long slow road into SNOBOL-dom, the land where old languages go, not necessarily to die, but to continue living, just with very few people paying any attention. We can only hope C and C++ will head there eventually.

Anyway, might as well collect a few of my favorite hacks, tweaks, and WTF?! bits before they all end up only in the depths of the WayBack machine. 

Here’s one that you don’t see often. If I remember correctly, there is a bit of a performance hit with it, but it’s pretty minor.

Did you know a VB module can actually contain properties?

Huh, you say. Interesting, but so what?

Well, since public elements of modules are public project-wide, you can create some pretty handy functions this way.

For instance, say you have a function to read an entire text file in at one shot, and one to write a whole text file. You could have two subs to do the dirty work. Or you could do something like this (put this code in a BAS module, not a class):

Public Property Let FileTextContent(ByVal FileName$, ByRef NewValue$)
   '---- Block write the entire file's content in one shot
   Dim fh
   
   On Error Resume Next
   fh = FreeFile
   Open FileName$ For Output As fh Len = 2048
   Print #fh, NewValue$;
   Close #fh
End Property


Public Property Get FileTextContent(ByVal FileName$) As String
   '---- Block read the entire file's content in one shot
   Dim buf$
   Dim fh
   
   On Error Resume Next
   fh = FreeFile
   Open FileName$ For Binary Access Read As fh Len = 2048
   buf$ = Space$(LOF(fh))
   Get #fh, , buf$
   Close #fh
   FileTextContent = buf$
End Property

With a property like this in place, you can then read a file’s content with Just:

x$ = FileTextContent(MyFile$)

Which looks exactly like a function call, granted. But you can write a file’s content with:

FileTextContent(MyFile$) = x$

It’s a minor syntactic difference from just using two subs, or maybe a sub and a function. But personally, I think it reads a little nicer.

Of course, you can also use this technique to provide for global scope properties, ie properties that don’t belong to any particular class. This is sometimes handy when you need to expose a value globally, nut you also want to perform some processing on it during an assignment or a retrieval.

You could define the global property via a GLOBAL variable definition, but that gives you no “hook” to do your processing on the value when code retrieves it or sets it. Instead, use something like this in a BAS module:

Private rMyProp as long
Public Property Let MyProp(Byval NewValue as long)
   '---- Block write the entire file's content in one shot
   
   'DO YOUR CODE HERE
   rMyProp = NewValue
End Property

Public Property Get MyProp() As Long
   
   'DO YOUR CODE HERE   
   MyProp = rMyProp
End Property

Now, you have a convenient way to get and set the value from everywhere in your project, AND you have point at which you can hook in to preprocess or post-process the value as necessary.

And, if you name the module something short and sweet, say, like UTILITY, then you’ll get handy intellisense as well (just type “UTILITY.” to get the props and functions available on it).