Public Function StrReverse01(sExpression As String) As String
' by [traditional]
  Dim i As Integer
  For i = Len(sExpression) To 1 Step -1
    StrReverse01 = StrReverse01 & Mid$(sExpression, i, 1)
  Next
End Function

Public Function StrReverse02(sExpression As String) As String
' by [traditional]
  Dim i As Long
  Dim lenExpr As Long
  Dim charTmp As String
  
  lenExpr = Len(sExpression)
  StrReverse02 = sExpression
  
  For i = 1 To lenExpr \ 2
    charTmp = Mid$(StrReverse02, lenExpr - i + 1, 1)
    Mid$(StrReverse02, lenExpr - i + 1, 1) = Mid$(StrReverse02, i, 1)
    Mid$(StrReverse02, i, 1) = charTmp
  Next
  
End Function

Public Function StrReverse03(sExpression As String) As String
' by Donald, donald@xbeat.net, 20000913
  Dim i As Long
  Dim ubArr As Long
  Dim arrByte() As Byte
  Dim arrByteRev() As Byte
  
  If Len(sExpression) Then
    
    ' no need to ReDim
    arrByte = sExpression
    ubArr = UBound(arrByte)
    ReDim arrByteRev(ubArr)
    
    ' Step 2: it's Unicode
    For i = 0 To ubArr Step 2
      ' set double bytes pairwise
      ' eg. pos 01 = 67, 23 = 45, 45 = 23, 67 = 01
      arrByteRev(i) = arrByte(ubArr - i - 1)
      arrByteRev(i + 1) = arrByte(ubArr - i)
    Next
  
    StrReverse03 = arrByteRev
  
  End If
  
End Function

Public Function StrReverse04(sExpression As String) As String
' by Donald, donald@xbeat.net, 20000913
  Dim i As Long
  Dim ubArr As Long
  Dim arrByte() As Byte
  Dim arrByteRev() As Byte
  
  If Len(sExpression) Then
    
    ' no need to ReDim
    arrByte = StrConv(sExpression, vbFromUnicode)
    ubArr = UBound(arrByte)
    ReDim arrByteRev(ubArr)
    
    For i = 0 To ubArr
      arrByteRev(i) = arrByte(ubArr - i)
    Next
  
    StrReverse04 = StrConv(arrByteRev, vbUnicode)
  
  End If
  
End Function

' © G.Beckmann   eMail: G.Beckmann@NikoCity.de

Option Explicit

'// API
' VB5 -> msvbvm50.dll
Private Declare Function VarPtrArray& Lib "msvbvm60.dll" Alias "VarPtr" (ptr() As Any)
Private Declare Sub RtlMoveMemory Lib "kernel32" (dst As Any, src As Any, ByVal nBytes&)
Private Declare Sub RtlZeroMemory Lib "kernel32" (dst As Any, ByVal nBytes&)

Private Type SAFEARRAYBOUND
    cElements       As Long
    lLbound         As Long
End Type

Private Type SAFEARRAY1D
    cDims           As Integer
    fFeatures       As Integer
    cbElements      As Long
    cLocks          As Long
    pvData          As Long
    Bounds(0 To 0)  As SAFEARRAYBOUND
End Type


'// Locales
Private m_aIntSrc%()
Private m_aIntDst%()
Private m_pArrSrc&
Private m_pArrDst&
Private m_saSrc     As SAFEARRAY1D
Private m_saDst     As SAFEARRAY1D


Private Sub Class_Initialize()
    m_saSrc.cbElements = 2
    m_saSrc.cDims = 1
    m_saSrc.Bounds(0).cElements = &H7FFFFFFF
    m_saDst = m_saSrc
    
    m_pArrSrc = VarPtrArray(m_aIntSrc)
    m_pArrDst = VarPtrArray(m_aIntDst)
        
    RtlMoveMemory ByVal m_pArrSrc, VarPtr(m_saSrc), 4
    RtlMoveMemory ByVal m_pArrDst, VarPtr(m_saDst), 4

End Sub

Private Sub Class_Terminate()
    RtlZeroMemory ByVal m_pArrSrc, 4
    RtlZeroMemory ByVal m_pArrDst, 4
End Sub


' rev. 1.1 09/14/2000
Friend Function Reverse(s As String) As String
    Dim iLen&, c&
    
    iLen = Len(s)
    Reverse = Space$(iLen)
    
    m_saSrc.pvData = StrPtr(s)
    m_saDst.pvData = StrPtr(Reverse)
    
    iLen = iLen - 1
    For c = 0 To iLen
        m_aIntDst(c) = m_aIntSrc(iLen - c)
    Next c
End Function

Public Function StrReverse06(sExpression As String) As String
' by Peter Weighill, pweighill@btinternet.com, 000926
' [another traditional]
  Dim i As Long
  Dim lenExpr As Long

  lenExpr = Len(sExpression)
  StrReverse06 = sExpression

  For i = 1 To lenExpr
    Mid$(StrReverse06, lenExpr - i + 1, 1) = Mid$(sExpression, i, 1)
  Next i
  
End Function

Private Type OwnedInteger
    Owner As ArrayOwner
    pSA() As Integer
End Type
Private m_DerefInteger As OwnedInteger



Public Function StrReverse07(sExpression As String) As String
' by Matt Curland, mattcur@microsoft.com, www.PowerVB.com, 20001007
  Dim i As Long
  Dim cch As Long
  Dim iTemp As Integer
  If Len(sExpression) = 0 Then Exit Function
  StrReverse07 = sExpression
  With m_DerefInteger
      If .Owner.SA.cDims = 0 Then
          #If NOVBOOST = 0 Then
          If VBoost Is Nothing Then InitVBoost
          #End If
          InitArrayOwner .Owner, LenB(.pSA(0)), 0
      End If
      .Owner.SA.pvData = StrPtr(StrReverse07)
      cch = Len(StrReverse07)
      .Owner.SA.cElements = cch
      For i = 0 To cch \ 2 - 1
          iTemp = .pSA(i)
          .pSA(i) = .pSA(cch - i - 1)
          .pSA(cch - i - 1) = iTemp
      Next i
  End With
End Function

The code is a bit too long to be displayed here ... download it to have a look.

Private Type SafeArray1D
    cDims As Integer
    fFeatures As Integer
    cbElements As Long
    cLocks As Long
    pvData As Long
    cElements As Long
    lLBound As Long
End Type

Private Const FADF_AUTO As Long = &H1
Private Const FADF_FIXEDSIZE As Long = &H10

' unrem if not declared elsewhere:
'Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (dst As Any, src As Any, ByVal nBytes As Long)
'Private Declare Function VarPtrArray Lib "msvbvm60.dll" Alias "VarPtr" (Ptr() As Any) As Long



Public Function StrReverse09(Text As String) As String
' By Guy Gervais, ggervais@videotron.ca, 19 Nov 2001
'   - Requires a reference to the "Split03.tlb" type library

Dim iLTx        As Long         ' Length of "Text" parameter
Dim iInStr()    As Integer      ' Integer, since we will be flipping a Unicode string
Dim SAiInStr    As SafeArray1D
Dim iOutStr()   As Integer
Dim SAiOutStr   As SafeArray1D
Dim iBgn        As Long         ' Our pointer from the beginning
Dim iEnd        As Long         ' Our pointer from the end

    iLTx = Len(Text)
    If iLTx = 0 Then Exit Function  ' Reversing a null is FAST!

    ' Map Integer array to InString data
    With SAiInStr
        .cDims = 1
        .cbElements = 2&
        .cElements = iLTx
        .fFeatures = FADF_AUTO Or FADF_FIXEDSIZE
        .pvData = StrPtr(Text)
    End With
    CopyMemory ByVal VarPtrArray(iInStr), VarPtr(SAiInStr), 4&

    ' Alloc return string
    StrReverse09 = StringHelpers.SysAllocStringLen(ByVal 0&, iLTx)

    ' Map Interger array to OutString data
    With SAiOutStr
        .cDims = 1
        .cbElements = 2&
        .cElements = iLTx
        .fFeatures = FADF_AUTO Or FADF_FIXEDSIZE
        .pvData = StrPtr(StrReverse09)
    End With
    CopyMemory ByVal VarPtrArray(iOutStr), VarPtr(SAiOutStr), 4&

    ' Reverse the [in] str to the [out] str
    iBgn = 0&
    iEnd = iLTx - 1&
    Do
        iOutStr(iBgn) = iInStr(iEnd)
        iOutStr(iEnd) = iInStr(iBgn)
        iBgn = iBgn + 1&
        iEnd = iEnd - 1&
    Loop Until iBgn > iEnd

    ' Clean up
    CopyMemory ByVal VarPtrArray(iOutStr), 0&, 4&
    CopyMemory ByVal VarPtrArray(iInStr), 0&, 4&

End Function

Public Function StrReverse10(ByRef Text As String) As String
' By Guy Gervais, ggervais@videotron.ca, 21 Nov 2001

Dim iLTx    As Long         ' Length of "Text" parameter
Dim iStr()  As Integer
Dim SAiStr  As SafeArray1D
Dim iBgn    As Long         ' Our pointer from the beginning
Dim iEnd    As Long         ' Our pointer from the end
Dim iTmp    As Integer      ' Temp var for swap
    
    iLTx = Len(Text)
    If iLTx = 0 Then Exit Function

    StrReverse10 = Text

    With SAiStr
        .cDims = 1
        .cbElements = 2
        .cElements = iLTx
        .fFeatures = FADF_AUTO Or FADF_FIXEDSIZE
        .pvData = StrPtr(StrReverse10)
    End With
    CopyMemory ByVal VarPtrArray(iStr), VarPtr(SAiStr), 4

    iEnd = UBound(iStr)
    For iBgn = 0 To iEnd \ 2
        iTmp = iStr(iBgn)
        iStr(iBgn) = iStr(iEnd)
        iStr(iEnd) = iTmp
        iEnd = iEnd - 1
    Next

    SAiStr.pvData = 0

End Function