[RESOLVED] Unicode problem: read binary file at spesific position with unicode path

[astralist]

i have a code like this:

Public Function GetBin(ByVal lpFileName As String, ByVal lpByteCount As Long, Optional ByVal StartByte As Long = 0) As String
On Error Resume Next
Dim Bin() As Byte
Dim ByteSum As Long
Dim i As Long

ReDim Bin(lpByteCount) As Byte

Open lpFileName For Binary As #1
    If StartByte = 0 Then
        Get #1, , Bin
    Else
        Get #1, StartByte, Bin
    End If
Close #1

For i = 0 To lpByteCount
    ByteSum = ByteSum + Bin(i)
Next i

GetBin = ByteSum

End Function

which can read spesific bytes within spesific position.
the problem is:

how to make it supports unicode path?

or..
is there any replacement for this function??

[Milk]

Can you help an idiot here by explaining what you mean by unicode path? Is lpFileName not unicode anyway?

[dilettante]

This probably refers to either files where the path is longer than MAXPATH (around 260) and/or where the full path name contains characters that can't be mapped from a VB6 (Unicode) String to the ANSI codepage for the current locale.

Almost everything VB6 does with its native I/O statements involves such translation to ANSI so that VB6 programs can still work on Win9X machines where Unicode was not natively supported.

To work with files using Unicode paths you usually have to resort to the wide-char ("Unicode") versions of system API calls with names ending in W instead of A. You would then generally have to prefix pathnames with "\\?\" as well, which tells the system you are supplying a Unicode path.

VB6's Open statement will accept names starting with "\\?\" but I don't think this means that unmappable characters or paths exceeding MAXPATH will actually work. Lots of other VB6 I/O functions (such as Dir$() and GetAttr()) may fail if you feed them a "\\?\" path too.


A long-winded way of saying I think the OP wants to use paths containing some characters that don't map to his default ANSI codepage. I could be wrong about this, and I suppose it is also possible that characters which do successfully map but exceed &H7F after mapping fail too (accented letters, etc.).

[LaVolpe]

CreateFileW, ReadFile & WriteFile APIs are unicode compatible. They have no problems with unicode path or file names. Once you have a file handle (CreateFileW), you can read the bytes into your array. Here's an example I use quite often, tweak to taste.

Note: I added the bUnicode variable in function below but never do that in my projects. I cache the value to a form-level variable in form load so the routines always know whether to use unicode or ansi APIs elsewhere in the project. Besides, caching it once is a bit faster vs testing every time.

Edited: For the GetFileHandle to work, the passed file name must be valid, it can't contain a path/filename like ?????. So if you are offering your customers an option to select a file, use a unicode version of the common dialog. A fair substitute example can be found in my signature below.

Private Function GetFileHandle(FileName As String, bRead As Boolean) As Long

    ' Function uses APIs to read/create files with unicode support

    Const GENERIC_READ As Long = &H80000000
    Const OPEN_EXISTING = &H3
    Const FILE_SHARE_READ = &H1
    Const GENERIC_WRITE As Long = &H40000000
    Const FILE_SHARE_WRITE As Long = &H2
    Const CREATE_ALWAYS As Long = 2
    Const FILE_ATTRIBUTE_ARCHIVE As Long = &H20
    Const FILE_ATTRIBUTE_HIDDEN As Long = &H2
    Const FILE_ATTRIBUTE_READONLY As Long = &H1
    Const FILE_ATTRIBUTE_SYSTEM As Long = &H4
    Const FILE_ATTRIBUTE_NORMAL = &H80&
    
    Dim Flags As Long, Access As Long
    Dim Disposition As Long, Share As Long, hFile As Long

    Dim bUnicode As Boolean
    bUnicode = Not (IsWindowUnicode(GetDesktopWindow) = 0&)
    
    If bRead Then
        Access = GENERIC_READ
        Share = FILE_SHARE_READ
        Disposition = OPEN_EXISTING
        Flags = FILE_ATTRIBUTE_ARCHIVE Or FILE_ATTRIBUTE_HIDDEN Or FILE_ATTRIBUTE_NORMAL _
                Or FILE_ATTRIBUTE_READONLY Or FILE_ATTRIBUTE_SYSTEM
    Else
        Access = GENERIC_READ Or GENERIC_WRITE
        Share = 0&
        If bUnicode Then
            Flags = GetFileAttributesW(StrPtr(FileName))
            If (Flags And FILE_ATTRIBUTE_READONLY) Then
                Flags = FILE_ATTRIBUTE_NORMAL
                SetFileAttributesW StrPtr(FileName), Flags
            End If
        Else
            Flags = GetFileAttributes(FileName)
            If (Flags And FILE_ATTRIBUTE_READONLY) Then
                Flags = FILE_ATTRIBUTE_NORMAL
                SetFileAttributes FileName, Flags
            End If
        End If
        If Flags < 0& Then Flags = FILE_ATTRIBUTE_NORMAL
        ' CREATE_ALWAYS will delete previous file if necessary
        Disposition = CREATE_ALWAYS
    End If
    
    If bUnicode Then
        hFile = CreateFileW(StrPtr(FileName), Access, Share, ByVal 0&, Disposition, Flags, 0&)
        If hFile = 0& Then hFile = INVALID_HANDLE_VALUE
    Else
        hFile = CreateFile(FileName, Access, Share, ByVal 0&, Disposition, Flags, 0&)
        If hFile = 0& Then hFile = INVALID_HANDLE_VALUE
    End If
    
    GetFileHandle = hFile

End Function

' changes to your routine
Public Function GetBin(ByVal lpFileName As String, ByVal lpByteCount As Long, Optional ByVal StartByte As Long = 0) As String
On Error Resume Next
Dim Bin() As Byte
Dim ByteSum As Long
Dim i As Long
Dim hFile As Long, lNrRead As Long

hFile = GetFileHandle(lpFileName, True)
If hFile = INVALID_HANDLE_VALUE Then
     MsgBox "Failed to access the passed file name"
Else
     ReDim Bin(lpByteCount) As Byte

     SetFilePointer hFile, 0&, 0&, ByVal 0& ' beginning of file
     ReadFile hFile, Bin(0), lpByteCount, lNrRead, ByVal 0&
     CloseHandle hFile
     If lpByteCount < lNrRead Then
         MsgBox "Not all data was read."
         ' Reasons: 1) StartByte > FileLength, 2) lbByteCount+StartByte > FileLength, 3) other
     Else
        For i = 0 To lpByteCount
            ByteSum = ByteSum + Bin(i)
        Next i
        GetBin = ByteSum
     End If
End If
End Function

Here are the API declarations. To get more details about the APIs recommend reading about them on MSDN or AllAPI.net

Private Declare Function IsWindowUnicode Lib "user32.dll" (ByVal hWnd As Long) As Long
Private Declare Function GetDesktopWindow Lib "user32.dll" () As Long
Private Declare Function ReadFile Lib "kernel32.dll" (ByVal hFile As Long, ByRef lpBuffer As Any, ByVal nNumberOfBytesToRead As Long, ByRef lpNumberOfBytesRead As Long, ByRef lpOverlapped As Any) As Long
Private Declare Function WriteFile Lib "kernel32" (ByVal hFile As Long, lpBuffer As Any, ByVal nNumberOfBytesToWrite As Long, lpNumberOfBytesWritten As Long, lpOverlapped As Any) As Long
Private Declare Function CreateFileW Lib "kernel32" (ByVal lpFileName As Long, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Private Declare Function DeleteFileW Lib "kernel32.dll" (ByVal lpFileName As Long) As Long
Private Declare Function DeleteFileA Lib "kernel32.dll" (ByVal lpFileName As String) As Long
Private Declare Function SetFileAttributesW Lib "kernel32.dll" (ByVal lpFileName As Long, ByVal dwFileAttributes As Long) As Long
Private Declare Function SetFileAttributes Lib "kernel32.dll" Alias "SetFileAttributesA" (ByVal lpFileName As String, ByVal dwFileAttributes As Long) As Long
Private Declare Function GetFileAttributesW Lib "kernel32.dll" (ByVal lpFileName As Long) As Long
Private Declare Function GetFileAttributes Lib "kernel32.dll" Alias "GetFileAttributesA" (ByVal lpFileName As String) As Long
Private Declare Function GetFileSize Lib "kernel32.dll" (ByVal hFile As Long, ByVal lpFileSizeHigh As Long) As Long
Private Declare Function SetFilePointer Lib "kernel32.dll" (ByVal hFile As Long, ByVal lDistanceToMove As Long, ByRef lpDistanceToMoveHigh As Long, ByVal dwMoveMethod As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Const INVALID_HANDLE_VALUE = -1&

[astralist]

WOW!

thanks a lot LaVolpe

[LaVolpe]

You are welcome. In order to use your optional StartByte parameter, suggest changing related line to:
SetFilePointer hFile, startByte, 0&, ByVal 0&