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Fast append of strings

Fast append of strings

API Declarations


' * Programmer Name : Waty Thierry
' * Web Site : www.geocities.com/ResearchTriangle/6311/
' * E-Mail : [email protected]
' * Date : 13/10/98
' * Time : 10:24
' * Module Name : String_Module
' * Module Filename : String.bas
' **********************************************************************
' * Comments :
' * Fast append of strings
' **********************************************************************

Declare Function VarPtrArray Lib "msvbvm50.dll" Alias "VarPtr" (Ptr() As Any) As Long
Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDst As Any, pSrc As Any, ByVal ByteLen As Long)
Declare Function GetTickCount Lib "kernel32" () As Long





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' * Programmer Name  : Waty Thierry
' * Web Site         : www.geocities.com/ResearchTriangle/6311/
' * E-Mail           : [email protected]
' * Date             : 13/10/98
' * Time             : 10:24
' * Module Name      : String_Module
' * Module Filename  : String.bas
' **********************************************************************
' * Comments         :
' * Fast append of strings
' **********************************************************************

Private Sub Command1_Click()
   
   Dim g         As String
   
   Label1.Caption = ""
   u% = DoEvents
   tim& = GetTickCount
   '**************
   ' slow version
   '**************
   'note the second & is just to prove that joining to strings is
   'not inherently slow, only adding a string to itself g$ = g$ & extra
   
   For a% = 1 To 5000
      g = g & "str" & "g "
   Next
   
   '****
   Text1.Text = GetTickCount - tim&
   Label1.Caption = g
   
End Sub

Private Sub Command2_Click()
   Label1.Caption = ""
   u% = DoEvents
   tim& = GetTickCount
   Dim pos&
   Dim src As String
   Dim des As String
   '****************
   ' Fast Version
   '****************
   'Allocates a big string, then copies the smaller strings into it.
   'this means that VB does not need to perform the expensive
   'dynamic realocation of string memory!
   
   des = Space$(10000)
   
   src = "str" & "g "
   For a% = 1 To 5000
      If pos& + LenB(src) > LenB(des) Then des = des & Space$(10000)
      CopyMemory ByVal StrPtr(des) + pos&, ByVal StrPtr(src), LenB(src)
      pos& = pos& + LenB(src)
   Next
   
   des = Left$(des, pos& \ 2) 'trim back to size
   '**********
   Text2.Text = GetTickCount - tim&
   Label1.Caption = des
End Sub