If you plan to code your own hashing algorithm, you'll need a way to store data in nodes, and a method for referencing the nodes. This may be done by storing nodes in objects and arrays. I'll use a linked-list to illustrate each method.
References to objects are implemented as pointers in Visual Basic. One implementation simply defines the data fields of the node in a class, and accesses the fields from a module:
' in class CObj Public NextNode As CObj Public Value As Variant ' in module Main Private hdrObj As CObj Private pObj As CObj ' add new node to list Set pObj = New CObj Set pObj.NextNode = hdrObj Set hdrObj = pObj pObj.Value = value ' find value in list Set pObj = hdrObj Do While Not pObj Is Nothing If pObj.Value = value Then Exit Do Set pObj = pObj.NextNode Loop ' delete first node Set pObj = hdrObj.NextNode Set hdrObj = pObj Set pObj = Nothing
In the above code,
pObj is internally represented as a pointer to the class.
When we add a new node to the list, an instance of the node is allocated, and a pointer to
the node is placed in
pObj. The expression
pObj.Value actually de-references
the pointer, and accesses the
Value field. To delete the first node, we remove
all references to the underlying class.
An alternative implementation allocates an array of nodes, and the address of each node is represented as an index into the array.
' list header Private hdrArr As Long ' next free node Private nxtArr As Long ' fields of node Private NextNode(1 To 100) As Long Private Value(1 To 100) As Variant ' initialization hdrArr = 0 nxtArr = 1 ' add new node to list pArr = nxtArr nxtArr = nxtArr + 1 NextNode(pArr) = hdrArr hdrArr = pArr Value(pArr) = value ' find value in list pArr = hdrArr Do While pArr <> 0 If Value(pArr) = value Then Exit Do pArr = NextNode(pArr) Loop
Each field of a node is represented as a separate array, and referenced by subscripts instead of pointers. For a more robust solution, there are several problems to solve. In this example, we've allowed for 100 nodes, with no error checking. Enhancements could include dynamically adjusting the arrays size when nxtArr exceeds array bounds. Also, no provisions have been made to free a node for possible re-use. This may be accomplished by maintaining a list of subscripts referencing free array elements, and providing functions to allocate and free subscripts. Included in the download is a class designed to manage node allocation, allowing for dynamic array resizing and node re-use.