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VBScript Classes: Part 1 of N
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VBScript Classes: Part 1 of N
By Jon M. Gohr

In the all too brief moments of down time between projects I like to explore. Lately I've been exploring VBScript classes and have decided to prepare a series of articles which will be presented here on ASP 101 to see if I can help shed a little light on the topic. Don't expect a dissertation on Object Oriented Programming and Design, I'm no expert in the field. If you're interested in that topic, you will find quite a few books available at your favorite online book seller's site, or heaven forbid, out amongst the people at a "real" bookstore. They still exist don't they?

The concept of classes/objects can seem very confusing until that light goes off and you "get it". My advice: Don't sweat the details. Use and study them, when they start to make even a little sense go ahead and try to write some. You WILL make mistakes along the way, as long as you learn from the mistakes you have lost nothing!

Required tools: A windows machine running either PWS or IIS. The latest scripting libraries, which are automatically installed on your machine if you installed IE5 or you can download them from the Microsoft Scripting Site . An html/vbscript editor of some type ... use NotePad if it makes you feel tough/cool/macho/whatever or it's all you have, I prefer to use Visual Interdev 6 myself.

Are you ready? Cool! Let's dig in and start looking at some code.

The class that we will be developing in this first article is called cRandom. It's usefulness may be somewhat limited, but the class itself is of sufficient size to be a good practical example of developing a basic class.

cRandom is a wrapper class that seeds the random number generator and has member functions for returning a ranged random integer as well as returning an array of user defined size, populated with ranged random integers, with or without duplicate values. Not very thrilling, but I've used the class in various prototype stages of some development projects.

The first step in the process is to create a new asp page. Call it random.asp or a name of your choice, it really doesn't matter. The cRandom class and some test code are all going to be embedded in the same .asp file for this example. In "The Real World" you'll want to store all of your reusable classes in seperate server side include files. Some people like to use the .inc extension for includes, I typically leave them as .asp files and just delete everything from the page except the code. Leaving the .asp extension on the file helps Visual Interdev know what to do as far as syntax highlighting is concerned. Syntax highlighting and Intellisense are good things.

Have you created your ASP file? Excellent! Now go up to the very first line of the page and define the default scripting language as VBScript (Interdev does this for you automatically based on your language settings) and right after that you had BETTER put in an option explicit tag. If you won't declare option explicit, I ask that you please leave now and never set eyes on my articles again. ALL GOOD BOYS AND GIRLS USE OPTION EXPLICIT. Say that a few times so it sinks in! The first two lines of your page should look like the following:

<%@ Language=VBScript %>
<% option explicit %>

Why use option explicit? It forces you to declare your variables before you use them. Think about VBScript for a second, it is untyped, not case sensitive and you can just start using a variable wherever you want if you don't declare option explicit. When you start developing REALLY advanced scripted pages you'll need all the help you can get in keeping your code organized. There is nothing worse than some undeclared variable floating around in global scope. Imagine a team of programmers working together on an asp page that has 12 different server side includes. Now, imagine everyone with a variable named 'i' or 'counter' in global scope. Things can quickly get out of hand on large projects. Enforce good coding standards on yourself and others within your team.

Next we need to name our class. This is another time when good standards will pay dividends in the long run. All of VBScript's class, variable, function and subroutine names, as well as those that you define, exist in a single name space. You'll want to make sure that the names you choose aren't going to "step" on any others. Communication and good standards are once again essential elements in YOUR success!

Classes have the added side effect of hiding or encapsulating all of their member variables, methods and properties. What this means is that you can have two seperate classes, both containing functions, subroutines and variables with the same names. This simple fact alone can alleviate almost all global name space issues!

My class is named cRandom, the small leading 'c' is obviously meant to differentiate it as a class, follow whatever naming convention you are most comfortable with. Make a choice and stick with it. We will begin the class definition like this:

<%
' Begin the definition with the class keyword, followed by the class name.
class cRandom
 
' Class_Initialize() is one of the two possible events that you can handle in
' the lifetime of a VBScript class, Class_Terminate() being the other. We need to
' seed the random number generator by calling Randomize, the Initialize() event
' seems like a logical place to handle this task.
private sub Class_Initialize()
    Randomize
end sub
 
' The Class_Terminate() event is where we would handle any clean up tasks
' required of the class. Nothing needs to be done in regards to clean up for this
' class so we will leave the Class_Terminate() event handler empty.
private sub Class_Terminate()
end sub
 
end class
%>

Public and Private are essential keywords in the development of a class. They allow you to show or hide methods (functions and subroutines) and properties (typically variables that are accessed via properties or declared as public) within a class structure. This is often called data hiding or encapsulation; it helps ensure that consumers of the class can't get access to sensitive internal methods or properties. We will delve much more deeply into this topic in future articles. The Class_Initialize() and Class_Terminate() subroutines are actually event handlers that are automatically excuted when the class is created and destroyed, respectively. They should never be executed by a consumer of the class, always make them private. Public visibility of methods and properties is the default, for clarity I recommend that you DO NOT exploit that fact and always declare everything with either public or private visibility.

Two public functions and we're through for the day! Make sure you check the source file for more detailed comments. Here's the code (add it right after the Class_Terminate() subroutine and before the end class statement).

public function RangedRandom( lowerBound, upperBound )
    RangedRandom = CInt((upperBound - lowerBound) * Rnd + 1)
end function
public function RangedRandomArray( lowerBound, upperBound, arraySize, duplicates )
    dim tempArray() ' storage for a working array
    dim filledElements, tempValue, badValue, i ' working variables
    
    redim tempArray(arraySize) ' resize the tempArray to arraySize
    
    filledElements = 0 ' Initialize this loop counter to zero
    
    ' We'll loop until filledElements is equal to arraySize + 1
    do until filledElements = arraySize + 1
        ' call the RangedRandom function with the lowerBound and upperBound parameter's
        tempValue = RangedRandom( lowerBound, upperBound )
        
        if duplicates = false then
            ' set the badValue flag to an initial value of false
            badValue = false
            ' loop through the array and check for the existence of the value
            for i = 0 to UBound(tempArray)
                if tempValue = tempArray(i) then
                    badValue = true
                    exit for
                end if
            next
            ' check the value of the flag, if it's false add the value to the array and increment
            ' the value of filledElements counter by 1
            if badValue = false then
                tempArray(filledElements) = tempValue
                filledElements = filledElements + 1
            end if
        else
            ' This is the case where the user doesn't care about duplicate values in the array
            ' so we add the value to the array and increment our counter
            tempArray(filledElements) = tempValue
            filledElements = filledElements + 1
        end if
    loop
    ' Return the array, populated with random integers to the caller of the function
    RangedRandomArray = tempArray
end function
    

 

That's it! Click here to see the test output for the cRandom class and download the code.

What articles are planned next?

In the next installment we will delve into properties and the use of let, set and get. Along the way we will be developing a sortable array class that utilizes the Quicksort algorithm, a LIFO stack class, a FIFO Queue class, some database connectivity and convenience classes and whatever else you can suggest or I can dream up. It should be fun and I'm looking forward to it! When is probably the next logical question to answer, my best answer is ... "I have no idea". I have most of the classes written I just need to wrap them up into nice little articles. Oh ... and we'll probably get into writing some cool classes in Visual Basic 6 that will be wrapped up in ActiveX dll's. Visual Basic offers substantially more power than is available in VBScript.

Questions, Comments, Suggestions and Making Contact with the Author

First off ... I'm a VERY busy, independent contract programmer. Independent means that if I don't work, I don't get paid! I need to keep my priorities pretty straight. Keeping that in mind, if you have long or involved questions that would take significant time (more than about a minute) for me to answer, you likely won't get an answer unless you feel like paying my normal consulting rates at a one hour minimum! ;-) My best advice on most programming related questions is to "try it" and see what happens. The worst that could happen is you'll crash your machine. You will learn so much more from personal exploration than you will from someone just handing you the answer. Learning is a quest that each of us should spend as much time on as possible.

Other options for assistance include the forums on ASP 101, the VBScript documentation that is available online from Microsoft, various books available for purchase and many of the other fine ASP related websites out on the net. Seek and ye shall find.

Got an idea for an article on classes that you'd like to see? Kind words or raging flames? Send me your thoughts. If you intend to email and flame me for being too verbose, don't bother ... I'm well aware of the fact that I ramble on a bit excessively.

Thanks for reading and I hope you enjoyed the article. Now get out there and write some reusable classes! Peace.

Jon M. Gohr

Read Part 2 of this series!
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