A Simple Stack Class

Author: Chris Eastwood
Author’s WebSite: http://www.eastwood60.freeserve.co.uk

This class module functions as a simple stack that can be dropped straight into any project requiring a stack object.

The class contains an internal collection of objects (variants) – you can simply change the data types passed in through the Push method and returned from the Pop method to use any data type you like.

The Push / Pop functionality comes from using the internal Collections Add method with the underused ‘Before’ parameter set as 1.

Simply paste the code into a class module with a relevant name, eg. cStack and you can use it straight away in your projects :

option Explicit

'

' cStack.cls

'

' This class implements a simple stack structure - at the

' moment it only uses a variant item in the collection, but

' of course you can use any variable / object type you like !

'

' Our Internal Collection

'

private mStackCollection as Collection
private Sub Class_Initialize()

'

' Create the internal collection

'

    set mStackCollection = new Collection

End Sub
private Sub Class_Terminate()

'

' Kill off the internal collection

'

    set mStackCollection = nothing

End Sub
public Sub Push(byval vData as Variant)

'

' Push an item onto the stack

'
'

' If there's stuff already on the stack, then insert

' the new item before the first item

'

    If mStackCollection.Count > 0 then

        mStackCollection.Add vData, , 1

    else

'

' Otherwise, just add it to the stack as the first item

'

        mStackCollection.Add vData

    End If

End Sub
public Function Pop() as Variant

'

' 'Pop' an item off the stack

'

    If mStackCollection.Count > 0 then

        If IsObject(mStackCollection.Item(1)) then

            set Pop = mStackCollection.Item(1)

        else

            Pop = mStackCollection.Item(1)

        End If

'

' Don't forget to remove the item from the stack

' once it's been popped !

'

        mStackCollection.Remove 1

    else

        Err.Raise vbObjectError + 4999, "cStack::Pop", "Stack is empty"

    End If
End Function
public property get StackCount() as Long

'

' Number of items in stack

'

    StackCount = mStackCollection.Count

End property

'

'

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Posted On: 7-Jan-2000