Excel VBA efficient get file names function

Question

I need to get a collection of file names from a folder on a remote server using VBA in excel 2010. I have a function that works and in the majority of cases it would do the job, however the remote server frequently has terrible, terrible network performance issues. This means that looping through say 300 files to put their names into a collection can take 10 minutes, the number of files in the folder is likely to grow to thousands so this is not workable, I need a way to get all of the file names in a single network request and not looping. I believe its connecting to the remote server that is taking the time so a single request should be able to get all of the files in one pass fairly quickly.

This is the function I currently have in place:

Private Function GetFileNames(sPath As String) As Collection
'takes a path and returns a collection of the file names in the folder

Dim oFolder     As Object
Dim oFile       As Object
Dim oFSO        As Object
Dim colList     As New Collection

Set oFSO = CreateObject("Scripting.FileSystemObject")
Set oFolder = oFSO.GetFolder(folderpath:=sPath)

For Each oFile In oFolder.Files
    colList.Add oFile.Name
Next oFile

Set GetFileNames = colList

Set oFolder = Nothing
Set oFSO = Nothing

End Function

Answer 1

This one is lightning fast:

  Sub filesTest()
    Dim x() As String
    x = Function_FileList("YOUR_PATH_AND_FOLDER_NAME")
    Debug.Print Join(x, vbCrLf)
  End Sub

Which calls this function:

 Function Function_FileList(FolderLocation As String)
    Function_FileList = Filter(Split(CreateObject("wscript.shell").exec("cmd /c Dir """ & FolderLocation & """ /b /a-d").stdout.readall, vbCrLf), ".")
 End Function

Answer 2

Ok, I have found a solution that works for my situation and perhaps others will find it useful too. This soution uses the windows API and gets me the filenames in 1 second or less where as the FSO method was taking several minutes. It still involves a loop so i'm not certain why it is so much faster but it is.

This takes a path like "c:\windows\" and returns a collection of all the files (and directories) in that folder. The exact parameters I have used require windows 7 or newer, see the comments in the declarations.

'for windows API call to FindFirstFileEx
Private Const INVALID_HANDLE_VALUE = -1
Private Const MAX_PATH = 260

Private Type FILETIME
    dwLowDateTime   As Long
    dwHighDateTime  As Long
End Type

Private Type WIN32_FIND_DATA
    dwFileAttributes    As Long
    ftCreationTime      As FILETIME
    ftLastAccessTime    As FILETIME
    ftLastWriteTime     As FILETIME
    nFileSizeHigh       As Long
    nFileSizeLow        As Long
    dwReserved0         As Long
    dwReserved1         As Long
    cFileName           As String * MAX_PATH
    cAlternate          As String * 14
End Type

Private Const FIND_FIRST_EX_CASE_SENSITIVE  As Long = 1
'MSDN: "This value is not supported until Windows Server 2008 R2 and Windows 7."
Private Const FIND_FIRST_EX_LARGE_FETCH     As Long = 2

Private Enum FINDEX_SEARCH_OPS
    FindExSearchNameMatch
    FindExSearchLimitToDirectories
    FindExSearchLimitToDevices
End Enum

Private Enum FINDEX_INFO_LEVELS
    FindExInfoStandard
    FindExInfoBasic 'MSDN: "This value is not supported until Windows Server 2008 R2 and Windows 7."
    FindExInfoMaxInfoLevel
End Enum

Private Declare Function FindFirstFileEx Lib "kernel32" Alias "FindFirstFileExA" ( _
ByVal lpFileName As String, ByVal fInfoLevelId As Long, lpFindFileData As WIN32_FIND_DATA, _
    ByVal fSearchOp As Long, ByVal lpSearchFilter As Long, ByVal dwAdditionalFlags As Long) As Long
Private Declare Function FindNextFile Lib "kernel32" Alias "FindNextFileA" ( _
    ByVal hFindFile As Long, lpFindFileData As WIN32_FIND_DATA) As Long
Private Declare Function FindClose Lib "kernel32" (ByVal hFindFile As Long) As Long


Private Function GetFiles(ByVal sPath As String) As Collection

    Dim fileInfo    As WIN32_FIND_DATA  'buffer for file info
    Dim hFile       As Long             'file handle
    Dim colFiles    As New Collection

    sPath = sPath & "*.*"

    hFile = FindFirstFileEx(sPath & vbNullChar, FindExInfoBasic, fileInfo, FindExSearchNameMatch, 0&, FIND_FIRST_EX_LARGE_FETCH)

    If hFile <> INVALID_HANDLE_VALUE Then
        Do While FindNextFile(hFile, fileInfo)
            colFiles.Add Left(fileInfo.cFileName, InStr(fileInfo.cFileName, vbNullChar) - 1)
        Loop

        FindClose hFile
    End If

    Set GetFiles = colFiles

End Function