Option Explicit

      ' For 16-bit products, uncomment the next three lines by removing the
      ' single quotes and add a single quote to comment out the following
      ' three lines.
      '  Const ConcatStr = "ABC"
      '  Const ccIncrement = 15000
      '  Declare Function GetTickCount Lib "USER" () As Long

         Const ConcatStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
         Const ccIncrement = 50000

         Private Declare Function GetTickCount Lib "KERNEL32" () As Long

      Dim ccOffset As Long

      Sub StdConcat(ByVal LoopCount As Long)
      Dim BigStr As String, I As Long, StartTick As Long
        StartTick = GetTickCount()
        For I = 1 To LoopCount
          BigStr = BigStr & ConcatStr
        Next I
        Debug.Print LoopCount; "concatenations took";
        Debug.Print GetTickCount() - StartTick; "ticks"
      End Sub

      Sub Test_Concat()
        Debug.Print "Using standard concatenation"
        StdConcat 1000
        StdConcat 2000
        StdConcat 3000
        StdConcat 4000
        StdConcat 5000
        Debug.Print
        Debug.Print "Using pre-allocated storage and pseudo-concatenation"
        MidConcat 1000
        MidConcat 2000
        MidConcat 3000
        MidConcat 4000
        MidConcat 5000
      End Sub

      Sub Concat(Dest As String, Source As String)
      Dim L As Long
        L = Len(Source)
        If (ccOffset + L) >= Len(Dest) Then
          If L > ccIncrement Then
            Dest = Dest & Space$(L)
          Else
            Dest = Dest & Space$(ccIncrement)
          End If
        End If
        Mid$(Dest, ccOffset + 1, L) = Source
        ccOffset = ccOffset + L
      End Sub

      Sub MidConcat(ByVal LoopCount As Long)
      Dim BigStr As String, I As Long, StartTick As Long
        StartTick = GetTickCount()
        ccOffset = 0
        For I = 1 To LoopCount
          Concat BigStr, ConcatStr
        Next I
        BigStr = Left$(BigStr, ccOffset)
        Debug.Print LoopCount; "pseudo-concatenations took";
        Debug.Print GetTickCount() - StartTick; "ticks"
      End Sub