VBScript Reference Manual for InduSoft Web Studio

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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. 72 InduSoft, Ltd.
InduSoft Web Studio VBScript Reference Manual Object Variables The Object data subtype references an object. Although the topic of objects will be covered in detail later, at this point it is worth noting that there are two types of Objects; Intrinsic (i.e. VBScript-based) and Extrinsic Objects. Intrinsic Objects are pre-defined by VBScript. VBScript includes the intrinsic Err object for error handling. The programmer can only use the Err object name for this object. Extrinsic objects need to be declared, or instantiated (i.e. create an instance of the Object). With extrinsic objects, the programmer defines an object name in the declaration statement. The object name can be any valid variable name allowed by VBScript, although following variable naming conventions is strongly suggested. Depending on the type of extrinsic object, different statements are used to instantiate the object. For example, with user-defined Classes, you would use the following format to instantiate the object. Set cObj = New classname where cObj is the name of the new object being instantiated, New is a VBScript Keyword, and classname is the name of the user-defined class, which is merely a template for the object. Other extrinsic objects include ActiveX Objects, ADO.NET, and OLE Automation Objects such as Microsoft Office applications and components. These objects use a different statement format for instantiation. They use either the CreateObject or GetObject functions. For example: Set cObj = CreateObject(“ADODB.Connection”) Set xlObj = CreateObject(“Excel.Application”) Set xlBook = GetObject(“C:\Test.XLS”) The difference between CreateObject and GetObject is that CreateObject is used to create an interface to a new instance of an application (or object) while the GetObject is used with an application that is already loaded. Real (Single, Double) Variables Real data types in VBScript are floating point numbers that can be either single precision (Single) or double precision (Double). Their ranges are: Single -3.402823E+38 to -1.401298E-45 for negative values 1.401298E-45 to 3.402823E+38 for positive values Double -1.79769313486232E+308 to -4.94065645841247E-324 for negative values 4.94065645841247E-324 to 1.79769313486232E+308 for positive values There are several types of operations that can be performed on the Real data subtype, such as arithmetic, comparison and logical operators. Also, many math functions can be used with this data subtypes. Some examples are: Dim R1, R2, R3, Radius R1 = 3.14159 Radius = 2 R2 = R1 * radius * radius R3 = FormatNumber (R2, 2) ‘ R3 equals 12.57 (R2 = 12.56636) InduSoft, Ltd. 73
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VBScript Reference Manual for InduSoft Web Studio

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