File extension validation - vba

Question

This searches for the end of a file name removes it's current file type of .docm and converts it to a .docx. Works great.
ActiveDocument.SaveAs2 Left(ActiveDocument.Name, InStrRev(ActiveDocument.Name, ".") - 1), WdSaveFormat.wdFormatXMLDocument
However, I noticed a little bug. If there is a . in the file name, it finds that first and obviously creates a file that is incorrect.
For example:
TestFileV1.2AlexTest.docm
Becomes the file
TestFileV.2AlextTest Where the new file type is a .2ALEXTEST file.
Kind of a funny error, but still a bug none the less.
Best course of action for validation?
Thanks!

Answer 1

Try the VBA.Strings.Split() function, which splits a string into an array.
Split the File name on '.' and the last element in the array will be your extension:
Public Function GetExtension(FileName As String) As String
'Returns a file's extension
' This does not go to the filesystem and get the file:
' The function parses out the string after the last '.'
' Useful for situations where a file does not yet exist
' Nigel Heffernan Excellerando.Blogspot.com
' **** THIS CODE IS IN THE PUBLIC DOMAIN ****
'Print GetExtension("C:\Temp\data.txt1.docx")
'Returns docx
Dim arrayX() As String
Dim iLast As Integer
arrayX = Split(FileName, ".")
iLast = UBound(arrayX)
GetExtension = arrayX(iLast)
Erase arrayX
End Function
If you don't care about readability, the quick-and-dirty answer is:
strExt = Split(strFile, ".")(UBound(Split(strFile, ".")))
However... I think you're looking for something more sophisticated than a string parser to extract the file extension.
Are you actually looking to validate the file extension?
I'm not coding up a registry lookup for the ShellExt application command to open your file, but I had a closely-related issue to yours a year or two ago, when I needed to populate a file dialog's filter list with a list of arbitrary file extensions.
It doesn't 'validate' as such, but unknown extensions will return a string containing 'unknown file type', and you can test for that:
VBA and the Registry: Returning a File Type from a File Extension
Public Function GetExtensionType(strExt As String) As String
' Return a file extension type descriptor, if the OS knows it
' Parses out the string after the last "." and reads the registry
' GetExtensionType("txt") Returns 'Text Document'
' GetExtensionType("SystemORA.user.config") 'XML Configuration File'
' GetExtensionType("Phishy.vbs") 'VBScript Script File'
' Nigel Heffernan Excellerando.Blogspot.com
' **** THIS CODE IS IN THE PUBLIC DOMAIN ****
On Error GoTo ErrSub
Dim strType As String
Dim strTyp1 As String
Dim strTyp2 As String
strExt = Trim(strExt)
' Set a default return: if an error is raised, return this value
GetExtensionType = Trim(strExt & " (unknown file type)")
strExt = Split(strExt, ".")(UBound(Split(strExt, "."))) '
If strExt = "" Then
Exit Function
End If
With CreateObject("WScript.Shell")
' This will go to error if there's no key for strExt in HKCR
strTyp1 = .RegRead("HKCR." & strExt & "\")
If strTyp1 = "" Then
strType = strExt & " File"
Else
' This value isn't very readable, eg: Access.ACCDEFile.14
' But we can use it to retrieve a descriptive string:
strTyp2 = .RegRead("HKCR\" & strTyp1 & "\")
If strTyp2 = "" Then
' So we didn't get a descriptive string:
' Parse some readability out of strType1:
strType = strTyp1
strType = Replace(strType, "File", " File")
strType = Replace(strType, ".", " ")
Else
strType = strTyp2
End If
End If
End With
If strType <> "" Then
GetExtensionType = strType
End If
ExitSub:
Exit Function
ErrSub:
Resume ExitSub
End Function
I made it error-tolerant but I didn't bother idiot-proofing it because someone, somewhere, is building a better idiot; and it's entirely possible that the user was actually right insofar as there really are files called that, and my system didn't have a registry entry for the file type in question.
There is an obvious source of errors in the code: GetExtensionType("docx") will give you 'Microsoft Word Document' on an English-Language workstation. If your user base are working with other languages and locales, they will see the descriptive name 'Microsoft Word Document' in their chosen language; and any validation logic you've coded up will fail to match that string (unless, of course, your string literals are internationalised in a conditional compiler block).
So any validation against a predefined application name or file type needs to be at the language-independent layer of the registry, using 'strTyp1' from the root instead of the locale-dependent strings passed into 'strTyp2'.

Answer 2

Use the FileSystemObject from the Scripting Runtime - it has a .GetBaseName() method to extract the basename from a file path:
'Early bound (reference to Microsoft Scripting Runtime):
Dim fso As New FileSystemObject
ActiveDocument.SaveAs2 fso.GetBaseName(ActiveDocument.Name), WdSaveFormat.wdFormatXMLDocument
'Late bound:
Dim fso As Object
Set fso = CreateObject("Scripting.FileSystemObject")
ActiveDocument.SaveAs2 fso.GetBaseName(ActiveDocument.Name), WdSaveFormat.wdFormatXMLDocument
You can also retrieve the extension with the .GetExtensionName() method, the path with .GetParentFolderName(), and the drive letter with GetDriveName() (which also works with UNC paths).
If you need to find the registered name of the extension in the current Windows install, you can either use the registry method #Nile answered with or an API call to AssocQueryStringA:
Const ASSOCSTR_FRIENDLYDOCNAME = 3
Private Declare Function AssocQueryString Lib "shlwapi.dll" _
Alias "AssocQueryStringA" ( _
ByRef Flags As Long, _
ByVal str As Long, _
ByVal pszAssoc As String, _
ByVal pszExtra As String, _
ByVal pszOut As String, _
ByRef pcchOut As Long) As Long
Sub Main()
Dim buffer As String
buffer = String$(255, " ")
Dim hresult As Long
hresult = AssocQueryString(0, ASSOCSTR_FRIENDLYDOCNAME, ".docm", _
vbNullString, buffer, 255)
If hresult = 0 Then
'Should be something like "Microsoft Word Macro-Enabled Document"
Debug.Print Trim$(buffer)
End If
End Sub
Note that you can also retrieve addition information about the associated file type by passing different values for the str parameter. See the ASSOCSTR enumeration.