Binaryworld - StringBuilder Class. Very efficient way to append string ... [ VB -> String ]

Option Explicit

'
' ===============================================================================

' Name:   vbAccelerator cStringBuilder
' Author: Steve McMahon (steve@vbaccelerator.com)
' Date:   1 January 2002
'
' Copyright 2002 Steve McMahon for vbAccelerator
'
'-------------------------------------------------------------------------------

' Visit vbAccelerator - advanced free source code for VB programmers
' http://vbaccelerator.com
'
'
' VB can be slow to append strings together because of the continual
' reallocation of string size. This class pre-allocates a string in
' blocks and hence removes the performance restriction.
'
' Quicker insert and remove is also possible since string space does
' not have to be reallocated.
'
' Example:
' Adding "http://vbaccelerator.com/" 10,000 times to a string:
' Standard VB: 34s
' This Class:  0.35s
'
'

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDst As Any, pSrc As Any, ByVal ByteLen As Long)
Private m_sString As String
Private m_iChunkSize As Long
Private m_iPos As Long
Private m_iLen As Long

Public Property Get Length() As Long
Length = m_iPos \ 2
End Property

Public Property Get Capacity() As Long
Capacity = m_iLen \ 2
End Property

Public Property Get ChunkSize() As Long
' Return the unicode character chunk size:
ChunkSize = m_iChunkSize \ 2
End Property

Public Property Let ChunkSize(ByVal iChunkSize As Long)
' Set the chunksize. We multiply by 2 because internally
' we are considering bytes:
m_iChunkSize = iChunkSize * 2
End Property

Public Property Get ToString() As String
' The internal string:
If m_iPos > 0 Then
   ToString = Left$(m_sString, m_iPos \ 2)
End If
End Property

Public Property Let TheString(ByRef sThis As String)
Dim lLen As Long

' Setting the string:
lLen = LenB(sThis)
If lLen = 0 Then
   'Clear
   m_sString = ""
   m_iPos = 0
   m_iLen = 0
Else
   If m_iLen < lLen Then
     ' Need to expand string to accommodate:
     Do
      m_sString = m_sString & Space$(m_iChunkSize \ 2)
      m_iLen = m_iLen + m_iChunkSize
     Loop While m_iLen < lLen
   End If
   CopyMemory ByVal StrPtr(m_sString), ByVal StrPtr(sThis), lLen
   m_iPos = lLen
End If

End Property

Public Sub Append(ByRef sThis As String)
Dim lLen As Long

' Append an item to the string:
lLen = LenB(sThis)
If (m_iPos + lLen) > m_iLen Then
   m_sString = m_sString & Space$(m_iChunkSize \ 2)
   m_iLen = m_iLen + m_iChunkSize
End If
  CopyMemory ByVal UnsignedAdd(StrPtr(m_sString), m_iPos), ByVal StrPtr(sThis), lLen
m_iPos = m_iPos + lLen

End Sub

Public Sub AppendByVal(ByVal sThis As String)
Append sThis
End Sub

Public Sub Insert(ByVal iIndex As Long, ByRef sThis As String)
Dim lLen As Long
Dim lPos As Long
Dim lSize As Long

' is iIndex within bounds?
If (iIndex * 2 > m_iPos) Then
   Err.Raise 9
Else

   lLen = LenB(sThis)
   If (m_iPos + lLen) > m_iLen Then
     m_sString = m_sString & Space$(m_iChunkSize \ 2)
     m_iLen = m_iLen + m_iChunkSize
   End If

   ' Move existing characters from current position
   lPos = UnsignedAdd(StrPtr(m_sString), iIndex * 2)
   lSize = m_iPos - iIndex * 2

   ' moving from iIndex to iIndex + lLen
   CopyMemory ByVal UnsignedAdd(lPos, lLen), ByVal lPos, lSize

   ' Insert new characters:
   CopyMemory ByVal lPos, ByVal StrPtr(sThis), lLen

   m_iPos = m_iPos + lLen

End If

End Sub
Public Sub InsertByVal(ByVal iIndex As Long, ByVal sThis As String)
Insert iIndex, sThis
End Sub

Public Sub Remove(ByVal iIndex As Long, ByVal lLen As Long)
Dim lSrc As Long
Dim lDst As Long
Dim lSize As Long

' is iIndex within bounds?
If (iIndex * 2 > m_iPos) Then
   Err.Raise 9
Else
   ' is there sufficient length?
   If ((iIndex + lLen) * 2 > m_iPos) Then
     Err.Raise 9
   Else
     ' Need to copy characters from iIndex*2 to m_iPos back by lLen chars:
     lSrc = UnsignedAdd(StrPtr(m_sString), (iIndex + lLen) * 2)
     lDst = UnsignedAdd(StrPtr(m_sString), iIndex * 2)
     lSize = (m_iPos - (iIndex + lLen) * 2)
     CopyMemory ByVal lDst, ByVal lSrc, lSize
     m_iPos = m_iPos - lLen * 2
   End If
End If
End Sub

Public Function Find(ByVal sToFind As String, _
Optional ByVal lStartIndex As Long = 1, _
Optional ByVal compare As VbCompareMethod = vbTextCompare _
) As Long
Dim lInstr As Long
If (lStartIndex > 0) Then
   lInstr = InStr(lStartIndex, m_sString, sToFind, compare)
Else
   lInstr = InStr(m_sString, sToFind, compare)
End If
If (lInstr < m_iPos \ 2) Then
   Find = lInstr
End If
End Function

Public Sub HeapMinimize()
Dim iLen As Long

' Reduce the string size so only the minimal chunks
' are allocated:
If (m_iLen - m_iPos) > m_iChunkSize Then
   iLen = m_iLen
   Do While (iLen - m_iPos) > m_iChunkSize
     iLen = iLen - m_iChunkSize
   Loop
   m_sString = Left$(m_sString, iLen \ 2)
   m_iLen = iLen
End If

End Sub
Private Function UnsignedAdd(Start As Long, Incr As Long) As Long
' This function is useful when doing pointer arithmetic,
' but note it only works for positive values of Incr

If Start And &H80000000 Then 'Start < 0
   UnsignedAdd = Start + Incr
ElseIf (Start Or &H80000000) < -Incr Then
   UnsignedAdd = Start + Incr
Else
   UnsignedAdd = (Start + &H80000000) + (Incr + &H80000000)
End If

End Function
Private Sub Class_Initialize()
' The default allocation: 8192 characters.
m_iChunkSize = 16384
End Sub