VBScript Reference Manual for InduSoft Web Studio

VBScript Reference Manual InduSoft Web Studio
Empty Variables
Empty is a single VBScript variable that has been declared, but has no explicitly assigned value. This is
also known as an uninitialized variable. There are two ways a variable can be uninitialized. The first is
when it is explicitly declared but has not yet been assigned a value. For example:
Dim a, b
a = 2 ‘ a is initialized, b is still uninitialized
The second way a variable can be uninitialized is by assigning it a value of Empty. Empty is VBScript
keyword. For example:
a = 2 ‘ a is a integer variable
b = “Hello” ‘ b is a string variable
a = Empty ‘ makes variable a uninitialized
b = Empty ‘ makes variable b uninitialized
If the variable was a numeric data subtype and set to a value of Empty (making it a Empty subtype), its
value will be 0. If the variable was a string data subtype and set to a value of Empty, its value will be “”.
The numeric and string subtypes can still be used in statements without generating a VBScript error
although their values were set to Null
Note that a variable being Empty is different that variable having a Null value. An Empty variable is
uninitialized, while a Null variable contains no valid data.
Error Variables
A variable with an Error data subtype contains an error number generated by the VBScript Parser or
Runtime Engine (signifying the VBScript Syntax error or Runtime error). An Error variant data subtype
can only be created by the VBScript Parser or Runtime Engine, or by calls to VBScript Object Methods.
The programmer cannot directly create or manipulate Error data subtypes.
See the Err Object for examples of how to use errors.
Null Variables
A Null variable is a single variable that indicates the variable contains no valid data. A null value is
typically used to represent missing data. A variable becomes a Null variable when it is assigned a null
value by using the Null keyword. For example:
Dim a, b
a = 2 ‘ a is initialized, b is uninitialized
a = Null ‘ a is Null, b is uninitialized (Empty)
One of the main differences between Empty and Null is that a variable can be of type Empty
(uninitialized) when it is declared but not assigned a value, or when it is assigned a value of Empty. A
Null variable, on the other hand, must be assigned a Null value.
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