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Modules: Validation with Regular Expressions

John Nurick
Function for "validating" entered data against a regular expression, which saves a lot of coding if the validation rules are at all complex. There are some sample regular expressions declared as globals at the bottom of this message (e.g. for US, Canadian and UK postal codes).

The function uses the VBScript regular expression object (v 5.5), with late binding to avoid complications with setting a reference in the project. Because of this and because it creates the object and compiles the regular expression every time it's called, it's a bit slow if called from a query or while iterating through a recordset, but it works happily in those circumstances with no sign of memory leaks after a million or so calls.

Typical call to check the format of a US phone number:

Private Sub txtPhone_BeforeUpdate(Cancel As Integer)
If Not rgxValidate(Me.ActiveControl.Text, "\(\d{3}\) \d{3}-\d{4}") Then
    MsgBox "I don't like " & Me.ActiveControl.Text & "."
    Cancel = True
End If
End Sub

Typical calls in Immediate window checking UK postcodes (against a regular expression declared as a constant at the bottom of this message):

?rgxValidate("BN22 0HX", rgxZIP_UK) 'returns True
?rgxValidate("BN22 O8X", rgxZIP_UK) 'returns False

'*******************CODE START***********************
                Function rgxValidate( _
                Target As Variant, _
                Pattern As String, _
                Optional CaseSensitive As Boolean = False, _
                Optional MatchWholeString As Boolean = True, _
                Optional FailOnError As Boolean = True) _
                As Boolean                
'Returns True if Target matches the regular 'expression Pattern.
'By John Nurick, October 2002 - January 2003 '2003 John Nurick
'Target will normally be a String. If Target is Null, 'rgxValidate returns False. Otherwise if Target cannot be 'converted to a string with CStr(), rgxValidate fails 'with Error 13, Type Mismatch.
'Pattern should be a VBScript regular expression. See VBScript 'help file and other documentation for information.
'CaseSensitive does the expected. 'MatchWholeString: if False, rgxValidate returns True if any 'substring of Target matches Pattern. If True or omitted, 'the function only returns True if the whole of Target 'matches Pattern. ' E.g. Target "12345" only matches Pattern "234" if ' MatchWholeString is False.
'FailOnError: if this is True or omitted, rgxValidate passes 'any run time error to the calling procedure. If it is False, 'the function returns True on a successful match and False if 'the match fails for any reason including a run time error.
'rgxValidate is suitable for use in data entry forms and the 'like. It can also be used in queries and in looping through
'recordsets, but because it creates a RegExp object and compiles 'the regular expression (Pattern) every time it is called, 'it is rather inefficient for repetitive operations.
'Constants for messages: Const rgxPROC_NAME = "rgxValidate" Const rgxERRMSG_CREATE = "Could not create VBScript.RegExp object: " Const rgxERRMSG_UNEXPECTED = "Unexpected error: "
'VBScript.Regexp error messages: Const rgxERRMSG_5017 = "Syntax error in regular expression" Const rgxERRMSG_5019 = "Expected ']' in regular expression" Const rgxERRMSG_5020 = "Expected ')' in regular expression"
Dim oRE As Object
rgxValidate = False 'Set default return value
If IsNull(Target) Then Exit Function
Set oRE = CreateObject("VBScript.RegExp")
'If we're here, the object has been created oRE.Global = False oRE.IgnoreCase = Not CaseSensitive oRE.Multiline = False
If MatchWholeString Then
'Add anchors at ends of Pattern '(doesn't matter if Pattern already has them)
oRE.Pattern = "^" & Pattern & "$" Else oRE.Pattern = Pattern
End If
'Do it! rgxValidate = oRE.Test(CStr(Target))
'If we're here, the match executed OK. Normal termination Set oRE = Nothing
Exit Function

ERRHANDLER: If FailOnError Then With Err Select Case .Number Case 5017: .Description = rgxERRMSG_5017 Case 5019: .Description = rgxERRMSG_5019 Case 5020: .Description = rgxERRMSG_5020 Case Else If oRE Is Nothing Then .Description = rgxERRMSG_CREATE & Err.Description Else .Description = rgxERRMSG_UNEXPECTED & Err.Description End If End Select Set oRE = Nothing Err.Raise Err.Number, , rgxPROC_NAME & "(): " & .Description End With Else 'Fail silently Err.Clear Set oRE = Nothing End If
End Function
'*******************CODE ENDS***********************

'**************CONSTANT DECLARATIONS******************
                'Some useful regular expressions:                
'Notes: 'Each of these regular expressions is wrapped in a (?: ) 'grouping pattern. This means that they can be OR'd by 'concatenating them with the pipe character "|". Thus ' rgxZIP_US & "|" & rgxZIP_CA 'will match either US or Canadian postal codes. ' 'Official formatting of postcodes and the like may change 'over time. Some of these expressions may need adjustment ' to bring them up to date.
'UK Postcode Public Const rgxZIP_UK = "(?:(?:A[BL]|B[ABDHLNRST]?|" _ & "C[ABFHMORTVW]|D[ADEGHLNTY]|E[CHNX]?|F[KY]|G[LUY]?|" _ & "H[ADGPRSUX]|I[GMPV]|JE|K[ATWY]|L[ADELNSU]?|M[EKL]?|" _ & "N[EGNPRW]?|O[LX]|P[AEHLOR]|R[GHM]|S[AEGKLMNOPRSTWY]?|" _ & "T[ADFNQRSW]|UB|W[ACDFNRSV]?|YO|ZE)" _ & "\d(?:\d|[A-Z])? \d[A-Z]{2})"
'A simpler expression that does not check for valid postcode areas: ' "(?:[A-Z]{1,2}\d(?:\d|[A-Z])? \d[A-Z]{2})"
'Zip or Zip+4 Public Const rgxZIP_US = "(?:\d{5}(?:-\d{4})?)"
'Canadian postal codes Public Const rgxZip_CA = "(?:[A-Z]\d[A-Z] \d[A-Z]\d)"
'Most European postal codes: Public Const rgxZIP_EU = "(?:NL-\d{4}(?: [A-Z][A-Z])|" _ & "(?:IS|FO)\d{3}|" _ & "(?:A|B|CH|CY|DK|EE|H|L|LT|LV|N)-\d{4}|" _ & "(?:BA|DE?|E|FR?|FIN?|HR|I|SI|YU)-\d{5}|" _ & "(?:CZ|GR|S|SK)-\d{3} \d{2}|PL-\d\d-\d{3}|" _ & "PT-\d{4}(?:-\d{3})?" _ & ")"
'A simpler expression that doesn't check the postcode 'format against the country code ' "(?:NL[- ]\d{4} [A-Z][A-Z]|" _ ' & "(?:[A-Z]{1,2}[- ])?\d{2,3}(?:\d\d?| \d\d|\d-\d{3}))"
'US States Public Const rgxSTATES_US = "(:?A[KLRZ]|C[AOT]|D[CE]|FL|" _ & "GA|HI|I[ADLN]|K[SY]|LA|M[ADEINOST]|N[CDEHJMVY]|" _ & "O[HKR]|P[AR]|RI|S[CD]|T[NX]|" _ & "UT|V[AIT]|W[AIVY])"
'Australian States Public Const rgxSTATES_AU = "(?:ACT|NSW|NT|QLD|SA|TAS|VIC|WA)"
'Canadian Provinces Public Const rgxPROVINCES_CA = "(?:AB|BC|MB|N[BLTSU]|ON|PE|QC|SK|YT)"
'Canonical phone number Public Const rgxPHONE_INTL = "(?:\+\d{1,4} ?(?:\(\d{0,5}\))?(?:\d+[-. ])*\d{2,})"
'***********************CONSTANTS END***********************

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