Technical Reference Manual - InduSoft

Overview of VBScript
Scope and Lifetime of Variables
A variable's scope is determined by where you declare it. When you declare a variable within a procedure,
only code within that procedure can access or change the value of that variable. It has local scope and is a
procedure-level variable. If you declare a variable outside a procedure, you make it recognizable to all the
procedures in your script. This is a script-level variable, and it has script-level scope.
The lifetime of a variable depends on how long it exists. The lifetime of a script-level variable extends from
the time it is declared until the time the script is finished running. At procedure level, a variable exists only
as the procedure runs. When the procedure exits, the variable is destroyed. Local variables are ideal as
temporary storage space when a procedure is executing. You can have local variables of the same name in
several different procedures because each is recognized only by the procedure in which it is declared.
Boolean Tags and Boolean Variables
By default, Boolean variables in VBScript are handled differently than Boolean tags are handled in IWS. The
Boolean states of FALSE and TRUE have the same meaning, but the numeric values of TRUE are different, as
shown in the table below.
Boolean State
Numeric Value in…
Project Tag
VBScript Variable
FALSE 0 0
TRUE 1 −1
Note: In VBScript, False and True are also reserved as keywords.
This difference in how Booleans are handled can seriously affect runtime behavior if you use VBScript in
your project. Logical and arithmetic operations — especially the NOT operator — could change tag values in
unexpected ways.
You can change this behavior, if necessary, by changing your project's runtime settings.
Changing How VBScript Handles Boolean Tags
You can change the way VBScript handles Boolean tags by activating "VB Boolean" mode. To do this, edit
your project file (project_name.app) to change the following setting:
[Script]
VBBoolean=value
If VBBoolean is set to 0, then the project will behave as described above: all VBScript functions and
operations will read/write a value of −1 for TRUE to Boolean tags. This is the default setting for projects
created with InduSoft Web Studio v6.1+SP3 or earlier and then updated to v6.1+SP4, in order to maintain
backward compatibility.
If VBBoolean is set to 1, then VBScript — as it is implemented within IWS — will read/write a value of 1
for TRUE to Boolean tags. (This does not affect Integer or Real tags.) This is the default setting for projects
created with InduSoft Web Studio v6.1+SP4 or later.
Note: Be careful when defining a custom property on a Linked Symbol using the #Label:@Pointer
syntax. For example:
'The following statements are valid
If $MyBoolean = 1 Then
End If
If $MyBoolean = True Then
End If
If #Mne:@MyPointer = True Then
End If
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InduSoft Web Studio