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► KB ► To/From Guides ► VB.Net ► Data Structures

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Cross Ref > Data Structures

By Mike Prestwood

VB.Net versus ASP Classic: A side by side comparison between VB.Net and ASP Classic.

Data Structures

Data structures allow you to store and work with data. Common data structures include arrays, associative arrays, etc.

Array

[Other Languages]

Languages Focus

A data structure in which individual values (called elements or items) may be located by reference to one or more integer index variables, the number of such indices being the number of dimensions in the array.

Arrays can start with an index value of 0 or 1, sometimes referred to as 0 based or 1 based.

[Not specified yet. Coming...]

ASP Classic: x = Array()

Arrays in ASP Classic use a 0-based indice.

Use UBound to get the number of elements. UBound returns -1 if the array has no elements, 0 if it has 1, 1 if it has 2, etc.

Syntax Example: 1 certification question.

Dim MyArray, i

MyArray = Array("Mike", "Lisa", "Felicia", "Nathan")

If UBound(MyArray) > -1 Then
  For i = 0 to UBound(MyArray)

    Response.Write MyArray(i)

  Next

End If

Associative Array

[Other Languages]

A set of unique keys linked to a set of values. Each unique key is associated with a value. Think of it as a two column table. MyArray['CA'] = 'California' MyArray['AR'] = 'Arizona'

Languages Focus

Associative arrays are also known as a dictionary or a hash table in other languages.

VB.Net: Dictionary

An associative array links a set of keys to a set of values. In Visual Basic, associative arrays are implemented as Dictionaries.

This code produces a message box saying "Nevada."

Syntax Example: 1 certification question.

//Imports System.Collections.Generic
�

Dim States As New Dictionary(Of String, String)


States.Add("CA", "California")
States.Add("NV", "Nevada")

MsgBox(States("NV"))

Associative Arrays in Visual Basic (a Dictionary)

ASP Classic: Scripting.Dictionary

Use the scriptiing dictionary object which is available on later versions of ASP Classic (all still commonly in use).

Note: Both Access VBA and VB Classic use a collection for this but collections are not supported in ASP Classic.

Syntax Example:

Dim StateList

set StateList = Server.CreateObject("Scripting.Dictionary")
StateList.Add "CA", "California"
StateList.Add "NV", "Nevada"

Response.Write "I live in " & StateList.Item("CA")

ASP Classic Associative Array (Scripting.Dictionary)

Pointers

[Other Languages]

General Info: Pointers / References

A pointer is a variable type that allows you to refer indirectly to another object. Instead of holding data, a pointer holds the address to data -- the address of another variable or object. You can change the address value a pointer points to thus changing the variable or object the pointer is pointing to.

A reference is a type of pointer that cannot change and it must always point to a valid storage (no nulls).

VB.Net: None

VB.Net doesn't support pointers. The closest it comes is IntPtr which you use to get pointer handles on windows, files, etc.

C# does have better support for pointers and C++/CLI has extensive support. One solution when it's really needed in VB.Net is to code in C# or C++/CLI and add it to your project.

However, VB.Net does support references.

More Info / Comment 1 certification question.

ASP Classic: Not Supported

ASP Classic does not offer developer defined pointers.