Verifying the Existence of a Specific Key

Microsoft® Windows® 2000 Scripting Guide

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One of the major advantages the Dictionary object has over an array or a standard collection is that you can quickly verify the existence of a particular key. For example, suppose you have a list of files installed on a computer and want to search that list to ensure that a particular set of DLLs has been installed. With either a collection or an array, there is no way to verify the existence of any one file without methodically looping through the entire set and checking each item individually.

With a Dictionary, however, you can use the Exists method to verify the existence of any given key. The Exists method takes a single parameter (the name of the key) and then returns a Boolean value: True if the key is in the Dictionary, False if it is not.

For example, the script in Listing 4.48 creates a Dictionary object and adds three elements: Printer 1, Printer 2, and Printer 3. The script then checks for the existence of a key named Printer 4 and echoes back the results of that check.

Listing 4.48   Verifying the Existence of a Dictionary Key

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Set objDictionary = CreateObject("Scripting.Dictionary") objDictionary.Add "Printer 1", "Printing" objDictionary.Add "Printer 2", "Offline" objDictionary.Add "Printer 3", "Printing" If objDictionary.Exists("Printer 4") Then     Wscript.Echo "Printer 4 is in the Dictionary." Else     Wscript.Echo "Printer 4 is not in the Dictionary." End If

When this script runs, the message "Printer 4 is not in the Dictionary" is echoed to the screen.

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