Windows Scripting: VBScript Data Types

How to Work with the VBScript Variant Data Type

Dec 6, 2008

Initially all VBscript variables are of the same type - the variant; however as soon as a value is assigned then they can become any one of 16 data types.

VBScript is different from many other programming languages in that it doesn't need to have variables defined as specific types - instead it used a variable type called a variant. A variant can contain any data type. That's not to say that the data type doesn't change - what actually happens is that VBScript changes the data type for the programmer automatically. So that raises the question - how does a programmer work with Variables in VBScipt?

Defining a Variable in VBScript

Variables can be created with VBScript just by assigning a value to the variable, for example:

However, this is not considered good practice because errors can easily creep in without the programmer being aware of them:

v1 = 20

v1 = vl * v1

msgbox v1 'Result is 0 not 400

A much better solution is to force variable declaration by using the option explicit statement:

Notice that the variable is defined without a data type, but the important point is that the following will now cause an error:

Identifying the VBScript Variable Types

Having said that the variables are all the same data type (variant), the data type does change as soon as a value is assigned to the variable, and the data type of a variable can be examined by using either of two VBScript methods:

Dim x

x = 1

msgbox TypeName(x) 'Returns Integer

msgbox VarType(x) 'Returns 2

In fact, the data type can change continually through the running of the script:

Dim v

msgbox TypeName(v) 'Returns Empty

v=1

msgbox TypeName(v) 'Returns Integer

v=1000000

msgbox TypeName(v) 'Returns Long

v=2.1

msgbox TypeName(v) 'Returns Double

v = "All Done"

msgbox TypeName(v) 'Returns String

Having seen that the data types do change it's worth looking at what those data types are.

The VBScript Variable Types

It should be noted that the numbering for the VBScript constants is not consecutive:

0 Empty

1 Null

2 Integer

3 Long

4 Single

5 Double

6 Currency

7 Date

8 String

9 Object

10 Error

11 Boolean

12 Variant

13 DataObject

17 Byte

8192 Array

Each of the constant values can be used by prefixing the data type name with vb, for example:

if VarType(v) = vbInteger then

msgbox "This is an integer"

end if

However, even though VBScript assigns all of the data type, it is still possible for the programmer to change them.

Manually Changing the Data Types

VBScript will change the data type automatically as the script progresses; however, the programmer can manually change the data type if required. The conversion methods, and the data type that they convert to, are:

cInt - Integer

cLng - Long

cSng - Single

cDbl - Double

cCur - Currency

cDate - Date

cStr - String

cBool - Boolean

cByte - Byte

And so the programmer has the choice to control the variable data types or to let VBScript do all of the hard work.

Summary

Variables in VBScript are very liberal - they allow programmers to create variables with the data type variant and will the automatically assign the correct data type when a value is assigned to the variable; this data type can be queried by using either of two methods:

Of course once the data type has been assigned the programmer can manually change it if the script required it.

The copyright of the article Windows Scripting: VBScript Data Types in Windows Programming is owned by Mark Alexander Bain. Permission to republish Windows Scripting: VBScript Data Types in print or online must be granted by the author in writing.