Microsoft WSH and VBScript Programming for the Absolute Beginner Part 32 pot

This method is easy to use, as demonstrated by the following: Err.Raise500 For example, if you save the previous statement as a script and run it, you will see the error message shown in

The Errobject also provides two very useful methods One of these methods is the Clear() method This method clears out or removes the previous error, ensuring that the next time

a script checks for an error, it will not get a false status (that is, it won’t see an already han-dled error)

To use the Clear()method, place it at the end of your error-handling routine, as demonstrated

in the previous example VBScript automatically executes the Clear()method on several occa-sions, including

• Whenever the On Error Resume Nextstatement executes

• Whenever an Exit Substatement executes

• Whenever an Exit Functionstatement executes

The second Err object method is the Raise()method This method allows you to generate error messages to test your error-handling routines Without this method, the only way that you could test your error-handling routines would be to deliberately introduce an error sit-uation into your code This method is easy to use, as demonstrated by the following: Err.Raise(500)

For example, if you save the previous statement as a script and run it, you will see the error message shown in Figure 9.8

To use the Raise() method, add it, along with the error number indicating the error that you want to generate, just before the error-handling procedure that you want to test in your script After you have validated that the error handler is working as expected, remove the Raise()statement from your VBScript

Figure 9.7

A custom error

message

generated by a

VBScript error

handler.

Figure 9.8

Using the Err

object’s Raise()

method to

generate a

test error.

Reporting Errors

The best solution for errors is to prevent them from occurring in the first place; however, that’s not always possible The next best solution is to devise a way of dealing with errors, whether it be handling them or simply ignoring them Another option is to report errors by recording them to a log file for later review This allows you to come back and check to see whether any errors have occurred This is important because many time users do not report errors when they occur, allowing errors to go on forever By logging error messages, you create

an audit log that you can come back to and review from time to time to identify and fix any errors that may have occurred

When logging error messages, you have two options The first option is to create your own custom log file The second option is to record error messages in the Windows application event log The second option, however, is only available if the script is running on a com-puter running Windows NT, 2000, or XP

Creating a Custom Log File

To create a custom log file, you must instantiate the FileSystemObjectin your VBScript and then use it’s OpenTextFile()method to open the log file so that your script can write to it as demonstrated in the following example

On Error Resume Next

Err.Raise(7)

Set objFsoObject = WScript.CreateObject(“Scripting.FileSystemObject”)

If (objFsoObject.FileExists(“C:\ScriptLog.txt”)) Then

Set objLogFile = objFsoObject.OpenTextFile(“C:\ScriptLog.txt”, 8)

Else

Set objLogFile = objFsoObject.OpenTextFile(“C:\ScriptLog.txt”, 2, “True”)

End If

objLogFile.WriteLine “Test.vbs Error: “ & Err.Number & “, Description = “ & _

Err.Description & “ , Source = “ & Err.Source

objLogFile.Close()

In this example, the On Error Resume Nextstatement is used to allow the script to recover from errors and the Err.Raise(7)statement is used to simulate an “Out of memory” error

The rest of the script logs the error in a file called ScriptLog.txt, located on the computer’s C:drive If the file does not exist, it is created Error messages are appended to the bottom

of the file each time they are written, allowing a running history of information to accu-mulate For more information about how to work with the FileSystemObjectand its methods and properties, refer to Chapter 8, “Storing and Retrieving Data.”

You can adapt the previous example as the basis for developing an error-logging routine in your VBScripts Just copy and paste all but the first two lines into a function and call it when-ever errors occur Just make sure that you call the function before clearing the error Alter-natively, you can modify the example to use variable substitution and pass the function the error number and description as arguments

Be sure you always close any file that you open before allowing your script to terminate If you don’t, you may have problems with the file the next time you want to open it because its end-of-file marker may be missing

Recording an Error Message in the Application Event Log

An alternative to creating custom log files for your scripts is to record error messages in the Windows application event log This is achieved using the WshShell object’s LogEvent() method:

On Error Resume Next

Err.Raise(7)

Set objWshShl = WScript.CreateObject(“WScript.Shell”)

objWshShl.LogEvent 1, “Test.vbs Error: “ & Err.Number & “, Description = “ & _ Err.Description & “ , Source = “ & Err.Source

In this example, an “Out of memory” error has again been simulated, only this time, the error has been written to the Windows application event log using the WshShell object’s LogEvent()method Only two arguments were processed The first is a number indicating the type of event being logged Table 9.5 lists the different types of events that are supported

by Windows The second argument was the message to be recorded Figure 9.9 shows how the message will appear when viewed from the Event Viewer

T R A P

Back to the Hangman Game

Now that you’ve reviewed the basic steps involved in overcoming VBScript errors, let’s return

to the Hangman game and begin its development I’m going to cover the development of this game from a different angle than in previous chapters By now, you should have a pretty good idea of how things work, and you should be able to read and understand the scripts that you’ll see throughout the remainder of this book (just in case, I’ll leave plenty of comments in the

Figure 9.9

Writing error

messages to the

Windows

application event

log using the

WshShell

object’s

LogEvent()

method.

Value Description

0 Indicates a successful event

1 Indicates an error event

2 Indicates a warning event

4 Indicates an informational event

8 Indicates a successful audit event

16 Indicates a failed audit event

TA B L E 9 5 EV E N T LO G ER R O R IN D I C A T O R S

code to help you along) This time, I’ll provide a much higher explanation of what is going on and offer suggestions for ways to test and develop this script one step at a time I’ll also point out techniques that you can use to test and track the results of functions within the script, so that you can validate their operation without having to first complete the entire script

Designing the Game

The overall design of the Hangman game is fairly complex To simplify things, I’ll begin the game-development process by designing a flowchart, shown in Figure 9.10, which breaks the game down into distinct units, each of which is responsible for performing a unique task

Figure 9.10

A flowchart

providing a

high-level design

for the Hangman

game.

In addition to the Initialization Section and Main Processing Section, this script is made up

of 13 separate procedures Therefore, you will develop this game in 15 steps, as follows:

1 Create a new script, adding your VBScript template and defining the variables, constants, and arrays that are used by this script

2 Develop the controlling logic for the Main Processing Section

3 Using the DoYouWantToPlay()function, create an introductory game splash screen and determine whether the user wants to play

4 Assign a list of game words to an array using the FillArray()function

5 Create a loop in the PlayTheGame()function that controls the actual flow of the game, collecting player guesses and calling other functions as required

6 Retrieve a randomly selected game word using the RetrieveWord()function

7 Display space-separated underscore characters representing each letter in the game word using the InitialDisplayString()function

8 Using the FirstLevelValidation()function, validate the player’s input to make sure the player is providing valid guesses

9 Using the SecondLevelValidation()function, test to determine whether the player has already tried guessing a letter before accepting it as input

10 Using the TestLetterGuess()function, check to see whether the player made an incorrect guess

11 Using the NonGuessedString()function, create a temporary string blanking out the letters correctly guessed by the player

12 Using the CheckIfGameWon()function, check to see whether the player has guessed all the letters that make up the mystery word

13 Using the FlipString()function, spin through the script created in step 11, and reverse the display of each character of the string (that is, now only show the correctly guessed letters)

14 Tell the player whether he or she won or lost using the DisplayGameResults() function

15 Display information about the game as it finishes using the SplashScreen()function

Setting Up the Script Template and Initialization Section

This portion of the script, shown here, should look pretty familiar to you by now, and does not require much explanation As you can see from the code, this section consists of the script template and the definition of the script’s constant, variables, and array

‘Script Name: Hangman.vbs

‘Author: Jerry Ford

‘Created: 02/30/02

‘Description: This script demonstrates how to create a game of Hangman

‘ using VBScript and the WSH.

‘*************************************************************************

‘Initialization Section

Option Explicit

Const cTitlebarMsg = “VBScript HANGMAN”

Dim strChoice, strGameWord, intNoMisses, intNoRight, strSplashImage

Dim intPlayOrNot, strMsgText, intPlayAgain, strWrongGuesses

Dim strRightGuesses, blnWordGuessed, intLetterCounter

Dim strTempStringOne, strTempStringTwo, strWordLetter, strDisplayString

Dim intFlipCounter, intRandomNo, strProcessGuess, blnGameStatus

Dim strCheckAnswer

Dim astrWordList(9) ‘Define an array that can hold 10 game words

Putting Together the Logic for the Main Processing Section

Like the other scripts that you have seen in this book, the logic located in the script’s Main Processing Section is very straightforward It calls upon procedures that determine whether the user wants to play, loads the game words into an array, starts the game, and ultimately ends the game by displaying a splash screen and executing the WScript.Quit()statement

‘Main Processing Section

intPlayOrNot = DoYouWantToPlay()

If intPlayOrNot = 6 Then ‘User elected to play the game

FillArray()

PlayTheGame()

End If

SplashScreen()

WScript.Quit()

At this point in the script, you have enough code in place to run your first test and see whether there are any syntax errors For now, I recommend that you go ahead and define a procedure for each of the preceding functions, placing a MsgBox()function that simply displays the name of the function inside each one Save and execute the script and make sure that the pop-up dialogs all appear when they should You can leave the functions as they are until you are ready to complete them

Using the WScript.Quit()method, as I did in this section, is not required Script execution would have ceased after the display of the splash screen anyway I added this statement for the sake of clarity, and to prevent any statements that

I might have inadvertently left outside of a function in the Procedure Section from accidentally being executed

Building the DoYouWantToPlay() Function

You’ve seen functions very similar to this one in previous chapters All the DoYouWantToPlay() function does is display a clever graphic and ask the user if he or she wants to play a game

of Hangman

Function DoYouWantToPlay()

‘Display the splash screen and ask the user if he or she wants to play

‘Display the splash screen and ask the user if he or she wants to play

strSplashImage = Space(100) & “***********” & vbCrLf & _

“W E L C O M E T O “ & Space(68) & “*” & Space(18) & “*” & _

vbCrLf & Space(100) & “0” & Space(18) & “*” & vbCrLf & _

“V B S c r i p t H A N G M A N !” & Space(50) & “—||—” & _

Space(15) & “*” & vbCrLf & Space(99) & “/” & Space(1) & “\” & _

Space(17) & “*” & vbCrLf & Space(120) & “*” & vbCrLf & Space(120) & _

“*” & vbCrLf & space(113) & “ ******* “ & vbCrLf & _

“Would you like to play a game?” & vbCrLf & “ “

DoYouWantToPlay = MsgBox(strSplashImage, 36, cTitlebarMsg)

End Function

This is a good place to pause and perform another test of your script to ensure that this func-tion looks and works like it should This test allows you to evaluate the operafunc-tion of all the controlling logic in the Main Processing Section

T R I C K

T R I C K

Building the FillArray() Function

The FillArray() function, shown next, simply loads a list of words into an array Later, another procedure will randomly select a game word from the array

Function FillArray()

‘Add the words to the array

astrWordList(0) = “AUTOMOBILE”

astrWordList(1) = “NETWORKING”

astrWordList(2) = “PRACTICAL”

astrWordList(3) = “CONGRESS”

astrWordList(4) = “COMMANDER”

astrWordList(5) = “STAPLER”

astrWordList(6) = “ENTERPRISE”

astrWordList(7) = “ESCALATION”

astrWordList(8) = “HAPPINESS”

astrWordList(9) = “WEDNESDAY”

End Function

You can’t perform much of a test on this function at this point, but you can always save and run the script again to see whether you have any syntax problems You should create a tem-porary script, copy this function into it, and then create a For Next loop that processes and displays the contents of the array to ensure that the function is loading as expected Next delete the For Next loop and add the following statements to the beginning of the temporary script:

Dim astrWordList(9) ‘Define an array that can hold 10 game words

FillArray()

Save this script again A little later, I’ll show you how to modify and use this temporary script to perform another test

Building the PlayTheGame() Function

The PlayTheGame()function, shown next, controls the play of the Hangman game When I developed this function, I wrote a few lines, stopped and tested it, and then wrote some more Specifically, each time I added a call to an external function I stopped, wrote the func-tion that I called, and then did a test to be sure that everything worked before continuing However, it would take me too long to guide you through every step along the way Instead,

I’ll leave it up to you to follow this basic process, and will instead focus on the development

of the other functions that make up the script, most of which are called from within the PlayTheGame()function

Function PlayTheGame()

‘Initialize variables displayed by the game’s initial pop-up dialog

intNoMisses = 0

intNoRight = 0

strWrongGuesses = “”

strRightGuesses = “”

‘Get the game a mystery word

strGameWord = RetrieveWord()

‘Call function that formats the initial pop-up dialog’s display string

strDisplayString = InitialDisplayString()

strTempStringOne = strGameWord

‘Let the player start guessing

Do Until intNoMisses = 6

‘Collect the player’s guess

strChoice = InputBox(vbCrLf & vbTab & strDisplayString & vbCrLf & _

vbCrLf & vbCrLf & “No of Misses: “ & intNoMisses & _

“ “ & vbTab & “Incorrect:” & strWrongGuesses & vbCrLf _

& vbCrLf & vbCrLf & _

“Type a letter and click on OK.” , cTitleBarMsg)

‘Determine if the player has quit

If strChoice = “” Then

Exit Function

End If

strProcessGuess = FirstLevelValidation()