I often have to test String, Variant or Object variables that have no content and could be considered ‘blank’.
The problem is that testing for “blankness” [can mean many different things to different types]:
* For an `Object` type, the variable can be `Nothing`.
* For a `String` type, the string can have no content at all: `””`, `vbNullString`.
* For a `Variant` type, the string can have any of the following attributes or values:
* it can be `Missing` if the variable is an unused optional parameter,
* it can be `Empty` if it was never assigned,
* it can be `Null` if, for instance it’s bound to a nullable field or unbound with no value,
* it can be an empty string `””`, `vbNullString`.
When having to check these variables in code, it can be tiresome to have to go through testing some of these possibilities just to find out that your variable does or not not contains something useful, regardless of the type of variable you are using.
To avoid having to do all these tests, make the code a bit more tidy and allow me to move on to more important things, I use this small utility function quite often:
‘ True if the argument is Nothing, Null, Empty, Missing or an empty string .
Public Function IsBlank(arg As Variant) As Boolean
Select Case VarType(arg)
IsBlank = True
IsBlank = True
IsBlank = (LenB(arg) = 0)
IsBlank = (arg Is Nothing)
IsBlank = IsMissing(arg)
So now I don’t have to worry so much about the type of the variable I’m testing when I want to know if it contains useful data:
‘ Here assume that CustomerReference is a control on a form.
‘ By using IsBlank() we avoid having to test both for Null and empty string.
If IsBlank(CustomerReference) Then
MsgBox “Customer Reference cannot be left blank.”
Obviously, `IsBlank()` doesn’t replace the other tests but I found it to be more straightforward to use in most cases.
For strings, it is apparently faster to test if LEN(strTest) > 0, since VBA stores strings starting with bytes containing the length of the string.
I have always wanted to know this
Just wondering in what case IsMissing could be used? Is is applicable only to optional arguments.
@Pavlo: yes, IsMissing is only used for optional variant parameters in a function or sub that were not supplied to the caller. It’s only used in that case.
My point was that you do not have Optional arguments in IsBlank function. Thus line: IsBlank = IsMissing(arg) will never be executed?
@Pavlo: it will be executer. the information whether a particular variant is in the Missing state is part of the variant structure itself and so it’s passed on as you pass on the variant to other subs and functions. A variant is only initialised in the Missing state when it’s created to replace an optional argument that was not passed by the caller. To illustrate this: Public Sub Test(Optional optArg As Variant) CheckMissing optArg End Sub Public Sub CheckMissing(arg As Variant) Debug.Print IsMissing(arg) End Sub This will print True, even though the arg argument is not missing.
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