Thread: Invalid parameter

HI!
Im trying to comunicating width my bluetooth usb divice.
After register the GUID, (information on inf file),
At this time, i can receive in my winproc a DBT_DEVICEARRIVAL: message.
In lParam the DBT_DEVTYP_DEVICEINTERFACE
width devInterface->dbcc_classguid== my register GUID IVT_BLUETOOTH.
Now, im trying to get all informatiom from device, and all works god,
just at :

DeviceHandle=CreateFile(detailData->DevicePath,0,FILE_SHARE_READ| FILE_SHARE_WRITE,
&SecurityAttributes,OPEN_EXISTING,FILE_ATTRIBUTE_N ORMAL,NULL);
DisplayLastError("CreateFile: ");
Attributes.Size = sizeof(Attributes);

after that, i have a error message 'Invalid parameter'.
I think the invalid parameter is DeviceHandle, but i dont now why.


HidD_GetAttributes(DeviceHandle,&Attributes);
DisplayLastError("HidD_GetAttributes: ");
sprintf(Buf,"0x%x",Attributes.VendorID);
_editVendorID.SetText(Buf);
sprintf(Buf,"0x%x",Attributes.ProductID);
_editProductID.SetText(Buf);
HidD_GetManufacturerString(DeviceHandle, Buffer, 126);
DisplayLastError("HidD_GetManufacturerString: ");
sprintf(Buf,"%ws",Buffer);
_editManufacturer.SetText(Buf);
HidD_GetProductString(DeviceHandle,Buffer,126);
DisplayLastError("HidD_GetProductString: ");
sprintf(Buf,"%ws",Buffer);
_editName.SetText(Buf);

Can you show me the way?
thanks in advance.

That's right... the error shows up later, the first time you try to actually access the opened file, because the file handle is invalid.

CreateFile() returns an error, not a handle, if it fails to open the file (or device) then your code just carries on with DeviceHandle == INVALID_HANDLE_VALUE which causes an access violation when you try to actually use the handle in your later function calls.

The thing is you don't know if there's an error or not... because you aren't testing the return value of CreateFile() before crashing along into your other code.

No you are not checking for errors.

Yes, I see your DisplayLastError() function...

The fact remains that you are NOT testing the returned value from CreateFile... you do not know if the handle is valid or not.

This correctly tests the handle returned by CreateFile()...

Code:

fHandle = CreateFile(...

if (fHandle == INVALID_HANDLE_VALUE)
  { messagebox(...
     // deal with error
   }

This does not...

Code:

DeviceHandle=CreateFile(...
DisplayLastError("CreateFile: ");

An invalid file handle with a reported error of 0 can and will slip right past that.

To make what you have work you need to do this...

Code:

DeviceHandle=CreateFile(...

if (DeviceHandle == INVALID_HANDLE_VALUE)
  { 
     DisplayLastError("CreateFile: ");
     // fix the error or exit()
  }

Read the MSDN specification for the return value of CreateFile()...

Originally Posted by MSDN

If the function succeeds, the return value is an open handle to the specified file, device, named pipe, or mail slot.

If the function fails, the return value is INVALID_HANDLE_VALUE. To get extended error information, call GetLastError.

Originally Posted by joseCarlos

you're right, but GetLastError() does not report any error, but I'll try DeviceHandler. thanks

That's what I've been trying to tell you... it is possible to have an invalid file handle without any reported error.

It is also possible that your error reporting mechanism might show an error message with a valid file handle.

The only way to know for sure is to test the actual handle ... i.e. the return value of CreateFile()