VBScript Reference Manual for InduSoft Web Studio

InduSoft Web Studio VBScript Reference Manual
IsEmpty
Description Returns a Boolean value indicating whether a variable has been initialized.
Usage boolVal = IsEmpty(expression)
Arguments expression
The expression argument can be any valid expression. However, because IsEmpty is used
to determine if individual variables are initialized, the expression argument is most often a
single variable name.
Return A Boolean value
Remarks IsEmpty returns True if the variable is uninitialized, or is explicitly set to Empty; otherwise, it
returns False. False is always returned if expression contains more than one variable. If two or
more variables are concatenated in expression and one of them is set to Empty, the IsEmpty
function will return False since the expression is not empty.
See Also IsArray, IsDate, IsNull, IsNumeric, IsObject, VarType
Example The following examples uses the IsEmpty function to determine whether a variable has been
initialized:
Dim MyVar, MyCheck
MyCheck = IsEmpty(MyVar) ' Returns True.
MyVar = Null ' Assign Null.
MyCheck = IsEmpty(MyVar) ' Returns False.
MyVar = Empty ' Assign Empty.
MyCheck = IsEmpty(MyVar) ' Returns True.
IsNull
Description Returns a Boolean value that indicates whether an expression contains no valid data (Null).
Usage boolVal = IsNull(expression)
Arguments expression
The expression argument can be any valid expression.
Return A Boolean value
Remarks IsNull returns True if expression evaluates to Null, that is, it contains no valid data; otherwise,
IsNull returns False. The Null value indicates that the variable contains no valid data. Null is not
the same as Empty, which indicates that a variable has not yet been initialized. It is also not the
same as a zero-length string (""), which is sometimes referred to as a null string.
You should always use the IsNull function when checking for Null values since using the normal
operators will return False even if one variable is Null. For example, expressions that you might
expect to evaluate to True under some circumstances, such as If Var = Null and If Var Null,
are always False. This is because any expression containing a Null is itself Null, and therefore,
False.
See Also IsArray, IsDate, IsEmpty, IsNumeric, IsObject, VarType
Example The following example uses the IsNull function to determine whether a variable contains a Null:
Dim MyVar, MyCheck
MyCheck = IsNull(MyVar) ' Returns False.
MyVar = Null ' Assign Null.
MyCheck = IsNull(MyVar) ' Returns True.
MyVar = Empty ' Assign Empty.
MyCheck = IsNull(MyVar) ' Returns False.
InduSoft, Ltd. 143