Porting from C++

I am porting an application from C++ to Visual Basic. Is wchar_t the same as a byte array in Visual Basic?

Sorry if this seems like an easy answer, but for the life of me - I can not find an answer anywhere.

wchar_t is going to be more like an array of integers. Or, you could just use a VB string, which is just an array of integers (shorts) internally.

Here is the problem I am encountering. I am playing around with a driver that does various things to files (kernel level). I have a C++ example of how to pass the file name. I tokHere it is:


_snwprintf( path, sizeofW( path ), L"\\??\\%s", argv[ i + 1 ] );
size = (DWORD)(( wcslen( path ) + 1 ) * 2);

DeviceIoControl(hDevice, ioctl, path, size, NULL, 0, &byteRet, NULL )


Internally, this is how I interpreted the code. It takes the argument passed, for example F:\test.exe, slaps on a prefix (\??\) and then passes it to DeviceIoControl. This works excellent.

So I try the following with Visual Basic


DeviceIoControl (lDevice, IOCTL, sFileName, Len(sFileName), ByVal 0&, 0, lBytesReturned, ByVal 0&)


And the driver either returns ERROR_INVALID_NAME or ERROR_BAD_PATHNAME which makes me assume that I am passing the wrong parameters. I tried copying the file name into a byte array using CopyMemory() and then tried to pass a pointer to the array and the size of the array. It fails as well.

Any ideas?

Try 2 * Len(sFileName)

lpInBuffer: \??\F:\test.exe
nInBufferSize: 30

ERROR_BAD_PATHNAME

:(

LenB would be acceptable too. What does your DeviceIoControl declare look like?

If you're using the "standard" declare from the API Viewer, then the string needs to be passed ByVal, as lpInBuffer As Any is ByRef.

Private Declare Function DeviceIoControl Lib "kernel32" (ByVal hDevice As Long, ByVal dwIoControlCode As Long, _
lpInBuffer As Any, ByVal nInBufferSize As Long, lpOutBuffer As Any, ByVal nOutBufferSize As Long, lpBytesReturned As Long, _
lpOverlapped As Any) As Long


And I have tried ByVal as well. Here is my current statement.


If DeviceIoControl(lDevice, IOCTL, ByVal sFileName, LenB(sFileName), ByVal 0&, 0, lBytesReturned, ByVal 0&) = 0 Then

Please provide more of the code. Specifically variable dimensioning and assignment.

Private Sub cmdTestFile_Click()
TestFile "\??\" & txtFile.Text
End Sub

Public Sub TestFile(sFileName$)
Dim lDevice&, lBytesReturned&

'Obtain handle to device
lDevice = CreateFile("\\.\MBAM_FILE_HANDLER", GENERIC_WRITE Or GENERIC_READ, _
FILE_SHARE_READ Or FILE_SHARE_WRITE, ByVal 0&, OPEN_EXISTING, _
FILE_ATTRIBUTE_NORMAL, 0&)

If lDevice > 0 Then
If DeviceIoControl(lDevice, IOCTL, ByVal sFileName, LenB(sFileName), ByVal 0&, 0, lBytesReturned, ByVal 0&) = 0 Then
MsgBox Err.LastDllError
End If

'Close device handle
CloseHandle lDevice
End If
End Sub


This is really the meat of the program. I create a service and delete it, but I have that in other projects and just copied and pasted the code. I use Option Explicit in all modules and forms. I am able to control the driver with all other control codes, for example:


DeviceIoControl(lDevice, IOCTL_VERSION, ByVal 0&, 0, lDeviceVersion, _
Len(lDeviceVersion), lBytesReturned, ByVal 0&)


This control code returns "2" for the internal version of the driver. I am also 100% positive the control code is correct because the C++ example can do this with the lines I stated above.

I wonder if the API wants a null terminator included in the length? Technically, BSTRs are already null terminated. Try this before the call:

sFileName = sFileName & vbNullChar

If that's not it, then supply your definition for IOCTL

I am doing 2 checks for errors now. One with a string buffer, one with a byte array buffer. As soon as I added the null terminator, instead of both being ERROR_BAD_PATHNAME, the byte array turned into ERROR_INVALID_NAME.

My definition for the controls is below.

Private Const IOCTL_VERSION As Long = -1737048060
Private Const IOCTL As Long = -1737047868

I have checked these in C++ the same way, so if the version one works, the other does as well.

Oops, I forgot you want to pass the unicode version of the string. ByVal sFoo is converted to ANSI. Use this instead:

If DeviceIoControl(lDevice, IOCTL, ByVal StrPtr(sFileName), LenB(sFileName), ByVal 0&, 0, lBytesReturned, ByVal 0&) = 0

Wow.

I tried StrPtr() and I tried ByVal, but never put them together. Turns out the null character is not needed. It works great now.

Thanks a lot for your help :)