VBScript Reference Manual for InduSoft Web Studio

VBScript Reference Manual InduSoft Web Studio
Variable Scope
All VBScript variables have “scope”. Scope defines a variable’s visibility or accessibility from one
procedure (or VBScript Interface) to another, which in IWS is principally determined by where you
declare the variable. As a general rule, when you declare a variable within a procedure, only code
within that procedure can access or change the value of that variable. This is called local scope and is
for 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. However, as previously noted,
InduSoft enforces certain restrictions on the scope of Variables and Procedures.
A variable’s lifetime depends on how long it exists (i.e. for how long memory is allocated for the
variable). The lifetime of a script-level variable extends from the time it is declared until the time the
script is finished running, or until the memory is released (e.g. SET obj = Nothing statement).
At procedure level, a variable exists only for as long as you are in the procedure. When the procedure
exits, the variable is destroyed, and the memory previously allocated to the variable is released. Local
variables are ideal as temporary storage space when a procedure is executing. Local variables with the
same name can exist in several different procedures since the local variable is recognized only by the
procedure in which it is declared.
VBScript allows for explicit declaration of the scope of a variable through the Public or Private
declarations. These declarations can also define the size of an array. The Public or Private
declarations must be made at the beginning of a script, while the Dim declaration can be made at any
point in the script. When using the Public or Private declarations with IWS, be sure to use them in the
variable declaration section. You cannot use Public or Private declarations in IWS with Global
Procedures, Command Dynamic or ActiveX events (these are sections in IWS where VBScript can be
placed). Note that the use of the Public declaration of a variable may be limited by IWS, as Public
variables defined in one section in an IWS application are not necessarily accessible in another section.
See the VBScript Configuration and Operation in IWS section for more details on this topic.
Example:
Sub MySub(a,b)
Dim c
c =a + b
End Sub
Call MySub (1,2) ‘ Call the subroutine MySub
MsgBox c ‘ c will be uninitialized, not the same variable as in
Example:
Sub Calc
Dim a
a = 6
End Sub
Dim a
a = 2
GoSub Calc
MsgBox “a = ” & a ‘ a would equal 2, not 6
Example:
Private MyArray(5) ‘ Private variables
Public MyVal, MyList(5) ‘ Public variables
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