Hidden features of VBA - vba

Question

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Which features of the VBA language are either poorly documented, or simply not often used?

Answer 1

This trick only works in Access VBA, Excel and others won't allow it. But you can make a Standard Module hidden from the object browser by prefixing the Module name with an underscore. The module will then only be visible if you change the object browser to show hidden objects.
This trick works with Enums in all vb6 based version of VBA. You can create a hidden member of an Enum by encasing it's name in brackets, then prefixing it with an underscore. Example:
Public Enum MyEnum
meDefault = 0
meThing1 = 1
meThing2 = 2
meThing3 = 3
[_Min] = meDefault
[_Max] = meThing3
End Enum
Public Function IsValidOption(ByVal myOption As MyEnum) As Boolean
If myOption >= MyEnum.[_Min] Then IsValidOption myOption <= MyEnum.[_Max]
End Function
In Excel-VBA you can reference cells by enclosing them in brackets, the brackets also function as an evaluate command allowing you to evaluate formula syntax:
Public Sub Example()
[A1] = "Foo"
MsgBox [VLOOKUP(A1,A1,1,0)]
End Sub
Also you can pass around raw data without using MemCopy (RtlMoveMemory) by combining LSet with User Defined Types of the same size:
Public Sub Example()
Dim b() As Byte
b = LongToByteArray(8675309)
MsgBox b(1)
End Sub
Private Function LongToByteArray(ByVal value As Long) As Byte()
Dim tl As TypedLong
Dim bl As ByteLong
tl.value = value
LSet bl = tl
LongToByteArray = bl.value
End Function
Octal & Hex Literals are actually unsigned types, these will both output -32768:
Public Sub Example()
Debug.Print &H8000
Debug.Print &O100000
End Sub
As mentioned, passing a variable inside parenthesis causes it to be passed ByVal:
Sub PredictTheOutput()
Dim i&, j&, k&
i = 10: j = i: k = i
MySub (i)
MySub j
MySub k + 20
MsgBox Join(Array(i, j, k), vbNewLine), vbQuestion, "Did You Get It Right?"
End Sub
Public Sub MySub(ByRef foo As Long)
foo = 5
End Sub
You can assign a string directly into a byte array and vice-versa:
Public Sub Example()
Dim myString As String
Dim myBytArr() As Byte
myBytArr = "I am a string."
myString = myBytArr
MsgBox myString
End Sub
"Mid" is also an operator. Using it you overwrite specific portions of strings without VBA's notoriously slow string concatenation:
Public Sub Example1()
''// This takes about 47% of time Example2 does:
Dim myString As String
myString = "I liek pie."
Mid(myString, 5, 2) = "ke"
Mid(myString, 11, 1) = "!"
MsgBox myString
End Sub
Public Sub Example2()
Dim myString As String
myString = "I liek pie."
myString = "I li" & "ke" & " pie" & "!"
MsgBox myString
End Sub

Answer 2

There is an important but almost always missed feature of the Mid() statement. That is where Mid() appears on the left hand side of an assignment as opposed to the Mid() function that appears in the right hand side or in an expression.
The rule is that if the if the target string is not a string literal, and this is the only reference to the target string, and the length of segment being inserted matches the length of the segment being replaced, then the string will be treated as mutable for the operation.
What does that mean? It means that if your building up a large report or a huge list of strings into a single string value, then exploiting this will make your string processing much faster.
Here is a simple class that benefits from this. It gives your VBA the same StringBuilder capability that .Net has.
' Class: StringBuilder
Option Explicit
Private Const initialLength As Long = 32
Private totalLength As Long ' Length of the buffer
Private curLength As Long ' Length of the string value within the buffer
Private buffer As String ' The buffer
Private Sub Class_Initialize()
' We set the buffer up to it's initial size and the string value ""
totalLength = initialLength
buffer = Space(totalLength)
curLength = 0
End Sub
Public Sub Append(Text As String)
Dim incLen As Long ' The length that the value will be increased by
Dim newLen As Long ' The length of the value after being appended
incLen = Len(Text)
newLen = curLength + incLen
' Will the new value fit in the remaining free space within the current buffer
If newLen <= totalLength Then
' Buffer has room so just insert the new value
Mid(buffer, curLength + 1, incLen) = Text
Else
' Buffer does not have enough room so
' first calculate the new buffer size by doubling until its big enough
' then build the new buffer
While totalLength < newLen
totalLength = totalLength + totalLength
Wend
buffer = Left(buffer, curLength) & Text & Space(totalLength - newLen)
End If
curLength = newLen
End Sub
Public Property Get Length() As Integer
Length = curLength
End Property
Public Property Get Text() As String
Text = Left(buffer, curLength)
End Property
Public Sub Clear()
totalLength = initialLength
buffer = Space(totalLength)
curLength = 0
End Sub
And here is an example on how to use it:
Dim i As Long
Dim sb As StringBuilder
Dim result As String
Set sb = New StringBuilder
For i = 1 to 100000
sb.Append CStr( i)
Next i
result = sb.Text

Answer 3

VBA itself seems to be a hidden feature. Folks I know who've used Office products for years have no idea it's even a part of the suite.
I've posted this on multiple questions here, but the Object Browser is my secret weapon. If I need to ninja code something real quick, but am not familiar with the dll's, Object Browser saves my life. It makes it much easier to learn the class structures than MSDN.
The Locals Window is great for debugging as well. Put a pause in your code and it will show you all the variables, their names, and their current values and types within the current namespace.
And who could forget our good friend Immediate Window? Not only is it great for Debug.Print standard output, but you can enter in commands into it as well. Need to know what VariableX is?
?VariableX
Need to know what color that cell is?
?Application.ActiveCell.Interior.Color
In fact all those windows are great tools to be productive with VBA.

Answer 4

It's not a feature, but a thing I have seen wrong so many times in VBA (and VB6): Parenthesis added on method calls where it will change semantics:
Sub Foo()
Dim str As String
str = "Hello"
Bar (str)
Debug.Print str 'prints "Hello" because str is evaluated and a copy is passed
Bar str 'or Call Bar(str)
Debug.Print str 'prints "Hello World"
End Sub
Sub Bar(ByRef param As String)
param = param + " World"
End Sub

Answer 5

Hidden Features
Although it is "Basic", you can use OOP - classes and objects
You can make API calls

Answer 6

Possibly the least documented features in VBA are those you can only expose by selecting "Show Hidden Members" on the VBA Object Browser. Hidden members are those functions that are in VBA, but are unsupported. You can use them, but microsoft might eliminate them at any time. None of them has any documentation provided, but you can find some on the web. Possibly the most talked about of these hidden features provides access to pointers in VBA. For a decent writeup, check out; Not So Lightweight - Shlwapi.dll
Documented, but perhaps more obscure (in excel anyways) is using ExecuteExcel4Macro to access a hidden global namespace that belongs to the entire Excel application instance as opposed to a specific workbook.

Answer 7

You can implement interfaces with the Implements keyword.

Answer 8

Dictionaries. VBA is practically worthless without them!
Reference the Microsoft Scripting Runtime, use Scripting.Dictionary for any sufficiently complicated task, and live happily ever after.
The Scripting Runtime also gives you the FileSystemObject, which also comes highly recommended.
Start here, then dig around a bit...
http://msdn.microsoft.com/en-us/library/aa164509%28office.10%29.aspx

Answer 9

Typing VBA. will bring up an intellisense listing of all the built-in functions and constants.

Answer 10

With a little work, you can iterate over custom collections like this:
' Write some text in Word first.'
Sub test()
Dim c As New clsMyCollection
c.AddItems ActiveDocument.Characters(1), _
ActiveDocument.Characters(2), _
ActiveDocument.Characters(3), _
ActiveDocument.Characters(4)
Dim el As Range
For Each el In c
Debug.Print el.Text
Next
Set c = Nothing
End Sub
Your custom collection code (in a class called clsMyCollection):
Option Explicit
Dim m_myCollection As Collection
Public Property Get NewEnum() As IUnknown
' This property allows you to enumerate
' this collection with the For...Each syntax
' Put the following line in the exported module
' file (.cls)!'
'Attribute NewEnum.VB_UserMemId = -4
Set NewEnum = m_myCollection.[_NewEnum]
End Property
Public Sub AddItems(ParamArray items() As Variant)
Dim i As Variant
On Error Resume Next
For Each i In items
m_myCollection.Add i
Next
On Error GoTo 0
End Sub
Private Sub Class_Initialize()
Set m_myCollection = New Collection
End Sub

Answer 11

Save 4 whole keystrokes by typing debug.? xxx instead of debug.print xxx.
Crash it by adding: enum foo: me=0: end enum to the top of a module containing any other code.

Answer 12

Support for localized versions, which (at least in the previous century) supported expressions using localized values. Like Pravda for True and Fałszywy (not too sure, but at least it did have the funny L) for False in Polish... Actually the English version would be able to read macros in any language, and convert on the fly. Other localized versions would not handle that though.
FAIL.

Answer 13

The VBE (Visual Basic Extensibility) object model is a lesser known and/or under-utilized feature. It lets you write VBA code to manipulate VBA code, modules and projects. I once wrote an Excel project that would assemble other Excel projects from a group of module files.
The object model also works from VBScript and HTAs. I wrote an HTA at one time to help me keep track of a large number of Word, Excel and Access projects. Many of the projects would use common code modules, and it was easy for modules to "grow" in one system and then need to be migrated to other systems. My HTA would allow me to export all modules in a project, compare them to versions in a common folder and merge updated routines (using BeyondCompare), then reimport the updated modules.
The VBE object model works slightly differently between Word, Excel and Access, and unfortunately doesn't work with Outlook at all, but still provides a great capability for managing code.

Answer 14

IsDate("13.50") returns True but IsDate("12.25.2010") returns False
This is because IsDate could be more precisely named IsDateTime. And because the period (.) is treated as a time separator and not a date separator. See here for a full explanation.

Answer 15

VBA supports bitwise operators for comparing the binary digits (bits) of two values. For example, the expression 4 And 7 evaluates the bit values of 4 (0100) and 7 (0111) and returns 4 (the bit that is on in both numbers.) Similarly the expression 4 Or 8 evaluates the bit values in 4 (0100) and 8 (1000) and returns 12 (1100), i.e. the bits where either one is true.
Unfortunately, the bitwise operators have the same names at the logical comparison operators: And, Eqv, Imp, Not, Or, and Xor. This can lead to ambiguities, and even contradictory results.
As an example, open the Immediate Window (Ctrl+G) and enter:
? (2 And 4)
This returns zero, since there are no bits in common between 2 (0010) and 4 (0100).

Answer 16

Deftype Statements
This feature exists presumably for backwards-compatibility. Or to write hopelessly obfuscated spaghetti code. Your pick.