VBA: REGEX LOOKBEHIND MS ACCESS 2010 - regex

Question

I have a function that was written so that VBA can be used in MS Access
I wish to do the following
I have set up my code below. Everything before the product works perfectly but trying to get the information behind just returns "" which is strange as when i execute it within Notepad++ it works perfectly fine
So it looks for the letters MIP and one of the 3 letter codes (any of them)
StringToCheck = "MADHUBESOMIPTDTLTRCOYORGLEJ"
' PART 1
' If MIP appears in the string, then delete any of the following codes if they exist - DOM, DOX, DDI, ECX, LOW, WPX, SDX, DD6, DES, BDX, CMX,
' WMX, TDX, TDT, BSA, EPA, EPP, ACP, ACA, ACE, ACS, GMB, MAL, USP, NWP.
' EXAMPLE 1. Flagged as: MADHUBESOMIPTDTLTRCOYORGLEJ, should be MADHUBESOMIPLTRCOYORGLEJ
Do While regexp(StringToCheck, "MIP(DOM|DOX|DDI|ECX|LOW|WPX|SDX|DD6|DES|BDX|CMX|WMX|TDX|TDT|BSA|EPA|EPP|ACP|ACA|ACE|ACS|GMB|MAL|USP|NWP|BBX)", False) <> ""
' SELECT EVERYTHING BEFORE THE THREE LETTER CODES
strPart1 = regexp(StringToCheck, ".*^[^_]+(?=DOM|DOX|DDI|ECX|LOW|WPX|SDX|DD6|DES|BDX|CMX|WMX|TDX|TDT|BSA|EPA|EPP|ACP|ACA|ACE|ACS|GMB|MAL|USP|NWP|BBX)", False)
' SELECT EVERYTHING AFTER THE THREE LETTER CODES
strPart2 = regexp(StringToCheck, "(?<=(DOM|DOX|DDI|ECX|LOW|WPX|SDX|DD6|DES|BDX|CMX|WMX|TDX|TDT|BSA|EPA|EPP|ACP|ACA|ACE|ACS|GMB|MAL|USP|NWP|BBX).*", False)
StringToCheck = strPart1 & strPart2
Loop
The function i am using which i have taken from the internet is below
Function regexp(StringToCheck As Variant, PatternToUse As String, Optional CaseSensitive As Boolean = True) As String
On Error GoTo RefErr:
Dim re As New regexp
re.Pattern = PatternToUse
re.Global = False
re.IgnoreCase = Not CaseSensitive
Dim m
For Each m In re.Execute(StringToCheck)
regexp = UCase(m.Value)
Next
RefErr:
On Error Resume Next
End Function

Answer 1

Just do it in two steps:
Check if MIP is in the string
If it is, remove the other codes.
Like this:
Sub Test()
Dim StringToCheck As String
StringToCheck = "MADHUBESOMIPTDTLTRCOYORGLEJ"
Debug.Print StringToCheck
Debug.Print CleanupString(StringToCheck)
End Sub
Function CleanupString(str As String) As String
Dim reCheck As New RegExp
Dim reCodes As New RegExp
reCheck.Pattern = "^(?:...)*?MIP"
reCodes.Pattern = "^((?:...)*?)(?:DOM|DOX|DDI|ECX|LOW|WPX|SDX|DD6|DES|BDX|CMX|WMX|TDX|TDT|BSA|EPA|EPP|ACP|ACA|ACE|ACS|GMB|MAL|USP|NWP|BBX)"
reCodes.Global = True
If reCheck.Test(str) Then
While reCodes.Test(str)
str = reCodes.Replace(str, "$1")
Wend
End If
CleanupString = str
End Function
Note that the purpose of (?:...)*? is to group the letters in threes.
Since the VBScript regular expression engine does support look-aheads, you can of course also do it in a single regex:
Function CleanupString(str As String) As String
Dim reClean As New RegExp
reClean.Pattern = "^(?=(?:...)*?MIP)((?:...)*?)(?:DOM|DOX|DDI|ECX|LOW|WPX|SDX|DD6|DES|BDX|CMX|WMX|TDX|TDT|BSA|EPA|EPP|ACP|ACA|ACE|ACS|GMB|MAL|USP|NWP|BBX)"
While reClean.Test(str)
str = reClean.Replace(str, "$1")
Wend
CleanupString = str
End Function
Personally, I like the two-step check/remove pattern better because it is a lot more obvious and therefore more maintainable.

Answer 2

Non RE option:
Function DeMIPString(StringToCheck As String) As String
If Not InStr(StringToCheck, "MIP") Then
DeMIPString = StringToCheck
Else
Dim i As Long
For i = 1 To Len(StringToCheck) Step 3
Select Case Mid$(StringToCheck, i, 3)
Case "MIP", "DOM", "DOX", "DDI", "ECX", "LOW", "WPX", "SDX", "DD6", "DES", "BDX", "CMX", "WMX", "TDX", "TDT", "BSA", "EPA", "EPP", "ACP", "ACA", "ACE", "ACS", "GMB", "MAL", "USP", "NWP":
Case Else
DeMIPString = DeMIPString & Mid$(StringToCheck, i, 3)
End Select
Next
End If
End Function