FindFirstFileEx() and Unicode

[Dave Kreskowiak]

treddie wrote:

But why do they declare strings in any function that accepts them?

Because you're definfing the TYPE of the pointer. What kind of object does it point to? What are the rules for incrementing that pointer if needed?? If you go back to C, a "string" in it's most basic form is just a pointer to an array of type char (character). Under Windows, you can have ASCII strings and wide-character strings. Incrementing the pointer for an ASCII character just adding 1 to the pointer, but, for multi-byte characters, such as Unicode, you increment the pointer by 2 or more.

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Dave Kreskowiak

[treddie]

That's logical.

[MicroVirus]

Actually, NTFS is not at all that limited. It's just that the kernel32.dll API interface is limited to those path limits. From MSDN, CreateFile page: In the ANSI version of this function, the name is limited to MAX_PATH characters. To extend this limit to 32,767 wide characters, call the Unicode version of the function and prepend "\\?\" to the path. For more information, see Naming Files, Paths, and Namespaces. By adding \\?\ you tell the kernel32 API to NOT do any parsing or processing on the path, and instead pass it directly on to the filesystem driver. From MSDN page on Naming Files, Paths, and Namespaces (Windows): For file I/O, the "\\?\" prefix to a path string tells the Windows APIs to disable all string parsing and to send the string that follows it straight to the file system. But not all functions can work with the extended paths, because some functions inherently need to do processing on the path.

[Dave Kreskowiak]

Yeah, I knew that. Slip of the brain when I typed it.

A guide to posting questions on CodeProject[^]
Dave Kreskowiak

[treddie]

OK, I'm finally getting this to work. I took the suggestion more seriously that GetLastError() might provide some insight into the problem. It wasn't anything that explicitly told me what was wrong, but it did cause me to take a much closer look at all of my declarations, and realizing that using "\\?\UNC\" was not correct...It needs to be just "\\?\". But also took to heart your comments on strings and pointers. In that regard, I found some typing problems here and there, and missed some lines that were still not rewritten for pointers. I'll post the resulting code here, shortly, after I copy my test code over to my final demo program and fix some remaining issues.

[TnTinMn]

Hi treddie, Based on my understanding of your code, I see no reason to use FindFirstFileEx versus FindFirstFile. Also, the directory filter flag option can fail silently if it is not supported and you need to check the attributes anyways if it was your intent to just recover directories. But it appears as your code is also doing these checks. Just a word of caution about interop examples you find on the web; many of these were originally done in VB6 and may not have been properly modified for DotNet types. Here are links to a reference and a tool that you may find useful in working with interop. Miscellaneous Marshaling (look at the links under "See Also") Samples[^] PInvoke Interop Assistant[^] I was bored so I tried putting together a simple TreeView file explorer that bypasses the 260 character limit. It may serve as an example for what you are trying to do. Just place a TreeView control on new WinForm project and paste this code. I used the command prompt "Subst" command to create a drive reference to a path that reached the 260 character barier and then added some more directories under that substituted drive to get to a file that had 400+ characters in it's path to test this. It appears to work. Edit: There appears to be a length limit on codeblock code.

Imports System.Runtime.InteropServices

Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
TreeView1.Nodes.Add(DriveToTreeNode("c"c))
End Sub

Private Sub TreeView1_AfterCollapse(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles TreeView1.AfterCollapse
e.Node.Nodes.Clear()
e.Node.Nodes.Add(New TreeNode With {.Tag = New NodeData With {.IsDirectory = True}}) ' add dummy node
End Sub

Private Sub TreeView1_BeforeExpand(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewCancelEventArgs) Handles TreeView1.BeforeExpand
' only directories can have nodes
e.Node.Nodes.Clear()
EnumerateDirectory(e.Node)
End Sub

Private Sub TreeView1_MouseDoubleClick(ByVal sender As Obje

[TnTinMn]

Here is the remainder of the code.

Private Shared Function GetShortPathName(ByVal path As String) As String
Dim sb As New System.Text.StringBuilder(1000)
Dim len As Int32 = GetShortPathName(LongPathPrefix & path, sb, sb.Capacity)
If len > sb.Capacity Then
sb.Capacity = len
GetShortPathName(LongPathPrefix & path, sb, sb.Capacity)
End If
Return sb.ToString().Replace(LongPathPrefix, "")
End Function

<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode), BestFitMapping(False)> _
Private Class WIN32_FIND_DATA
<MarshalAs(UnmanagedType.U4)> Public dwFileAttributes As IO.FileAttributes
<MarshalAs(UnmanagedType.U4)> Private ftCreationTime_dwLowDateTime As UInt32
<MarshalAs(UnmanagedType.U4)> Private ftCreationTime_dwHighDateTime As UInt32
<MarshalAs(UnmanagedType.U4)> Private ftLastAccessTime_dwLowDateTime As UInt32
<MarshalAs(UnmanagedType.U4)> Private ftLastAccessTime_dwHighDateTime As UInt32
<MarshalAs(UnmanagedType.U4)> Private ftLastWriteTime_dwLowDateTime As UInt32
<MarshalAs(UnmanagedType.U4)> Private ftLastWriteTime_dwHighDateTime As UInt32
<MarshalAs(UnmanagedType.U4)> Public nFileSizeHigh As UInt32
<MarshalAs(UnmanagedType.U4)> Public nFileSizeLow As UInt32
<MarshalAs(UnmanagedType.U4)> Public dwReserved0 As UInt32
<MarshalAs(UnmanagedType.U4)> Public dwReserved1 As UInt32

  ' Note: by changing the cFileName size constant from 260 to 32767 to handle long
  ' path names, it appears that cAlternateFileName always returns blank
  ' if the ShortPathName is needed, then use the GetShortPathName function
  ' http://msdn.microsoft.com/en-us/library/windows/desktop/aa364989%28v=vs.85%29.aspx
   <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=32767)> Public cFileName As String
   <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=14)> Public cAlternateFileName As String

  Public Function CreationTime() As DateTime
     Return DateTime.FromFileTime(MergeToInt64(ftCreationTime\_dwLowDateTime, ftCreationTime\_dwHighDateTime))
  End Function
  Public Function LastAccessTime() As DateTime
     Return DateTime.FromFileTime(MergeToInt64(ftLastAccessTim

[treddie]

But FindFirstFile() cannot handle Unicode, as far as MSDN seems to suggest.

[treddie]

One hickup...I need to deal with a C type, LPWSTR. When I research how to get this in vb.Net, I do not find any consistent explanation of how to deal with marshaling unmanaged types. There are no real-world examples and what MSDN offers is cryptic at best. Here is my best guess that does not show any syntax errors:

Dim LPWSTR As UnmanagedType
Dim MyUnicodePointer As New MarshalAsAttribute(LPWSTR)

[TnTinMn]

Where in the documentation does it suggest that? Quite the opposite is suggested in http://msdn.microsoft.com/en-us/library/windows/desktop/aa364418%28v=vs.85%29.aspx[^]

Quote:

In the ANSI version of this function, the name is limited to MAX_PATH characters. To extend this limit to 32,767 wide characters, call the Unicode version of the function and prepend "\\?\" to the path. For more information, see Naming a File.

[treddie]

Damn. I swear to gawd I saw it say you needed to use the Ex version to make it happen. Somewhere along the line I got messed up there. Too many questions all at once, I guess. But now that I know that, my overly-verbose usage should still work...I just have to keep track of extra arguments. Also, it is a good exercise in understanding both, since I may in the future need to use the Ex function. I haven't had a chance yet, today, to run your example.

[TnTinMn]

Quote:

Damn. I swear to gawd I saw it say you needed to use the Ex version to make it happen.

I blame it all on micro-blackhole that make one jump from one parallel universe to another just to screw with your mind when the minor differences bite you in the behind. :laugh: All I can say is that you are making an effort to learn and that is a rare and beautiful thing to see in a forum these days. :)

[treddie]

Thanks, man! It can be frustrating, but it is more frustrating to stay confused and not see the frikkin light! :)

[Dave Kreskowiak]

An LPWSTR is just a Long Pointer to a Wide character String. You're just marshalling a normal string from .NET to the function your calling. Usually, you don't have to do anything special in your function Declaration other than tell it that the paramter is a String.

A guide to posting questions on CodeProject[^]
Dave Kreskowiak

[treddie]

I'm confused. The function requires a pointer to a wide string, so you can't use 'As String' as a passed argument to the function FindFirstFileEx(). You have to use 'As LWPSTR' or, if I understand you correctly, 'As Long'. If that is true, then I have to wrap the string in a 'long' pointer, which for a 64bit platform would translate to Int32 (or rather, IntPtr), since a win32 function can only accept 32bits arguments and parameters. If that is true, then my existing marshal should be correct:

Dim MyStringPtr As Long = Marshal.StringToHGlobalAuto(MyString)

But when I pass MyStringPtr to FindFileEx(), I only get back the first character in a Unicode folder/file name, and then, only when the first character in the string happens to be in the ANSI range.

[Alan N]

I haven't read all of this thread but I don't see either the Auto or Unicode character set modifiers in your external procedure declarations, which means that the default of Ansi is being applied. This could be the root cause of your string problems as UTF16 encoded strings treated as Ansi will get truncated at the first null, i.e. after the first character. See Declare statement[^] and also Calling Windows APIs[^] for examples using both Declare and DllImport. Alan.

[treddie]

That basically has been my conclusion, though I don't know how to fix it yet. I figured SOMETHING had to be cutting the returned string short, and I know that the input string is getting to memory correctly, because I can retrieve it just fine. So that leaves the WIN32_FIND_DATA structure as the culprit. Documentation says the following declaration is required:

 Public cFileName As String

And for my string pointer, I used: Dim lpFileName_IntPtr As Long = Marshal.StringToHGlobalAuto(lpFileName_str) I experimented with changing MAX_PATH to 32767 rather than 260, but alone by itself it does nothing. And anyway, that is a max character length issue, not an ANSI vs. wide character issue. So I feel that the problem is with declaring cFileName, correctly. That was where I was at when I saw your post. I do not know how to squeeze some martialing in there to account for a wide string.

[treddie]

I built your project, but when run, the treeview stays blank.

[TnTinMn]

Edit: I deleted the upload, forgot I was in the middle of trying an ASCII version. Will repost a link once I get it back to Unicode. That's strange. I tried running it on a low privilege account and it run fine on Vista/32 bit. In case anything got messed up while I was trying to post the code(I had some issues) I've uploaded the project (VS2008) to: http://sdrv.ms/18SnASR This version is a bit different because I've been playing with it bit this evening. You will also find the syntax for the FindFirstFileEx function in the scraps.txt file. Try un-commenting the code in this block:

If hFile.DangerousGetHandle.ToInt32 = -1 Then
' just ignoring errors for this demo, most common is 5 - Access Denied
' System Error Codes
' http://msdn.microsoft.com/en-us/library/windows/desktop/ms681381(v=vs.85).aspx
Dim [error] As Int32 = Marshal.GetLastWin32Error()
Stop
Return
Else

and see what error code, if any, you are getting.

[TnTinMn]

Here is the updated project link that I mentioned in my previous post. http://sdrv.ms/13fhQi8[^]