Valid Windows Filename

[BruceG]

So I don't have to reinvent the wheel, does anyone have a function (or is there an API function) that checks to see if a given string is a valid Windows filename (which may contain a drive letter and a network or non-network path)? The file need not exist at the time of user entry. This is straight validation of a user-entered string, not using the Common Dialog or any of the file controls.

[MartinLiss]

Here is some code (very slightly modified) compliments of the VB5 setup program.

Private Sub Command1_Click()
 
    If fValidFilename(Text1.Text) Then
        MsgBox "OK"
    Else
        MsgBox "Nope"
    End If
 
End Sub
Public Function fCheckFNLength(strFilename As String) As Boolean
'
' This routine verifies that the length of the filename strFilename is valid.
' Under NT (Intel) and Win95 it can be up to 259 (gintMAX_PATH_LEN-1) characters
' long.  This length must include the drive, path, filename, commandline
' arguments and quotes (if the string is quoted).
'
    fCheckFNLength = (Len(strFilename) < 260)
End Function
Public Function fValidFilename(strFilename As String) As Boolean
'
' This routine verifies that strFileName is a valid file name.
' It checks that its length is less than the max allowed
' and that it doesn't contain any invalid characters..
'
    If Not fCheckFNLength(strFilename) Then
        '
        ' Name is too long.
        '
        fValidFilename = False
        Exit Function
    End If
    '
    ' Search through the list of invalid filename characters and make
    ' sure none of them are in the string.
    '
    Dim iInvalidChar As Integer
    Dim iFilename As Integer
    Dim strInvalidChars As String
    
    ' I changed this to allow for : and \
    strInvalidChars = "/*?""<>|" '"\/:*?""<>|"
    
    For iInvalidChar = 1 To Len(strInvalidChars)
        If InStr(strFilename, Mid$(strInvalidChars, iInvalidChar, 1)) <> 0 Then
            fValidFilename = False
            Exit Function
        End If
    Next iInvalidChar
    
    fValidFilename = True
    
End Function

[BruceG]

Thanks, Marty. This will be suitable with some modifications - such as, if the string contains ":", then it must only be part of the first two characters as a drive specification; also, if it contains two consecutive backslashes, then they must be the first two characters of the string. I was fairly sure of the rules (I thought the max length was 255 rather than 259, and I knew about the invalid characters). I was just wondering if there was any more to it. Thanks for the legwork.