Variable Inspection - Data Type Validation

This section describes why variables need to be inspected when receiving it in a procedure and how to inspect a variable to determine its data type.

If are writing a procedure, and receiving a variable from the calling code through an argument, you can not always assume that value of the variable is of certain subtype. If you code your procedure with some assumptions, your code will crash if the calling code fails to meet those assumptions.

To better protect your code, you want to inspect the value first, and write your code based on the result of the inspection. Variable inspection can be performed at 3 different levels:

1. Determine the structure type of the variable. Is it an object, array, or scalar.

2. Determine the data subtype of the variable. If it is an object, check its properties; If it is an array, check its elements; If it is a scalar, check the subtype of the value: Byte, Integer, Long, Single, Double, Date, Currency, Boolean, or String.

3. Determine the status of the data. Is it Empty or Null.

VBScript offers a number of built-in functions to help you to inspect a variable:

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)

 References

 PDF Printing Version