GetInteger() - Crash-Free Integer Conversion

This section provides a tutorial example of writing a crash-free code logic to convert a user entered string into a Long integer value. The built-in function CLng() will crash with a string like '3.3e200'.

As a practical exercise of using variable inspection guidelines mentioned in previous sections, let's try to solve an coding issue in a real VBScript application world.

A common task of handling user input on a Web form is to convert user entered data into a long integer. For example, the data entered in the Order Quantity field on Web order form must be converted into a long integer before processing the entire order.

So what code logic should you use to convert the user input data into a Long value? This sounds like an easy task. You can you use a single statement to do this:

   quantity = CLng(string_entered)

But the above code will crash, your customer enters something like "3.3e200".

So converting a used entered string into a Long value is not a simple task, if you allow the user to type in anything. I have tried my best to write a crash-free code, GetInteger(), to convert the input data as much as possible into a long integer as shown in the following tutorial example, parsing_integer.html:

<!-- parsing_integer.html
 - Copyright (c) 1998 All Rights Reserved.
<script language="vbscript">

   document.writeln(" ")
   document.writeln("Converting variants to integers:")
   document.writeln("   777 = " & GetInteger(777))
   document.writeln("   ""777"" = " & GetInteger("777"))
   document.writeln("   3.14159 = " & GetInteger(3.14159))
   document.writeln("   ""3.14159"" = " & GetInteger("3.14159"))
   document.writeln("   ""Hello"" = " & GetInteger("Hello"))
   document.writeln("   True = " & GetInteger(True))
   document.writeln("   Empty = " & GetInteger(Empty))
   document.writeln("   Null = " & GetInteger(Null))
   document.writeln("   ""1+2"" = " & GetInteger("1+2"))
   document.writeln("   777777 = " & GetInteger(777777))
   document.writeln("   3.3e200 = " & GetInteger(3.3e200))
   document.writeln("   ""3.3e20000"" = " & GetInteger("3.3e20000"))

Function GetInteger(vAnyThing)
   If IsNumeric(vAnyThing) Then
'      GetInteger = CInt(vAnyThing) 'Error 1: overflow on 777777
'      GetInteger = CLng(vAnyThing) 'Error 2: overflow on 3.3e200
      GetInteger = CDbl(vAnyThing)
      If Abs(GetInteger) < 2147483647 Then
         GetInteger = CLng(GetInteger)
         GetInteger = -2147483648
      End If
      GetInteger = -2147483648
   End If 
End Function

Here is the output:

Converting variants to integers:
   777 = 777
   "777" = 777
   3.14159 = 3
   "3.14159" = 3
   "Hello" = -2147483648
   True = -1
   Empty = 0
   Null = -2147483648
   "1+2" = -2147483648
   777777 = 777777
   3.3e200 = -2147483648
   "3.3e20000" = -2147483648

Note that:

Table of Contents

 About This Book

 Introduction of VBScript - Visual Basic Scripting Edition

 Variant Data Type, Subtypes, and Literals

 Arithmetic Operations

 Numeric Comparison Operations and Logical Operations

 String Operations - Concatenation and Comparison

 Variable Declaration and Assignment Statement

 Expression and Order of Operation Precedence

 Statement Syntax and Statement Types

 Array Data Type and Related Statements

 Array References and Array Assignment Statements

 Conditional Statements - "If ... Then" and "Select Case"

 Loop Statements - "For", "While", and "Do"

 "Function" and "Sub" Procedures

 Built-in Functions

Inspecting Variables Received in Procedures

 Variable Inspection - Data Type Validation

 GetVarInfo() - Variable Inspection Example

GetInteger() - Crash-Free Integer Conversion

 Error Handling Flag and the "Err" Object

 Regular Expression Pattern Match and Replacement

 scrrun.dll - Scripting Runtime DLL Library

 Creating Your Own Classes

 IE Web Browser Supporting VBScript

 IIS ASP Server Supporting VBScript

 WSH (Windows Script Host)


 Full Version in PDF/EPUB