How to Use the VBScript Scripting Dictionary
Implementing Associative Arrays with VBScript Programming
Jul 22, 2009
Associative arrays (commonly called hashes) are very useful data structures. They allow the contents of an array to be indexed by a string rather than a number, providing the programmer with an easy method of creating look up tables in their applications.
Some programming languages such as perl have associative arrays built into them (for more on this read Using Associative Arrays in Perl Programming) while others, such as VBScript, do not. However, the VBScript programmer need not be concerned. Instead of associative arrays they have the scripting dictionary. With a scripting dictionary the VBScript programmer has no need of an associative array.
Creating and Populating a VBScript Scripting Dictionary
The VBScript programmer creates a new dictionary by using the CreateObject method:
The programmer can then use the dictionary object's add method to populate it. This accepts a key word and value as inputs:
The dictionary's "item" method can be used to do the same job:
Once the programmer has populated the dictionary then they can access and update its contents very easily.
Accessing the Contents of a VBScript Dictionary
A programmer uses the key words to access the contents of a VBScript dictionary by using its "item" method, for example:
They can also use this method to update the dictionary's contents:
In this example the script's user would see the value of "nautical mile" change from "TBA" to 6080 (as shown in figure 1 at the bottom of this article).
Checking for the Existence of a VBScript Dictionary Entry
If the programmer happens to access a non existent key then the dictionary will return an empty string. Therefore the programmer may wish to check if a key actually exists. This (unsurprisingly) is done by using the "Exists" method, for example:
By doing this the programmer can ensure that they only use values from existing dictionary entries. Of course, there is one more issue. When is a nautical mile not a nautical mile?
The Case Sensitive Dictionary
It's important to know that the following will result in two entries being created, not one:
And so:
would return "TBA" and not 6080. That's because the dictionary is case sensitive and sees "nautical mile" as a separate key to "Nautical mile". The answer is to set the dictionary's "CompareMode":
This must be places immediately after the CreateObject statement and before any items are added. If that's done then the keys will no longer be case sensitive.
Calculating the Number of Key-Value Pairs in a VBScript Dictionary
The actual number of key-value pairs in a dictionary can be calculated by using the "count" method":
This can be used to iterate through the whole dictionary when used with two more of the dictionary's methods:
- Keys - returns an array containing the key words
- Items - returns an array containing the values
So these can be used in a number of ways, for example:
or:
Both of which will print out all of the key words and their associated values.
Removing Items
As well as adding and updating elements, the programmer can delete them. They do this by using either the "Remove" or the "RemoveAll" methods. The "Remove" methods deletes a single entry:
or all of the items can be deleted:
And so even though the VBScript programmer does not have an actual associative array structure, they have the scripting dictionary, and this gives them complete control over how named variables are stored and modified with their application.
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