Accessing "Win32_DeviceBus" properties

[SandyS]

I'm using the MSDN sample code to get WMI Data from a local computer (http://msdn.microsoft.com/en-us/libr...23(VS.85).aspx), and everything works fine for Win32 classes with only scalar elements (like in Win32_Processor).

Now I want to access Win32_DeviceBus which is defined as

class Win32_DeviceBus : CIM_Dependency
{
Win32_Bus REF Antecedent;
CIM_LogicalDevice REF Dependent;
};

How do I access the Antecedent properties (like Antecedent.BusType)?

[Codeplug]

What's your end goal? Are you trying to determine the bus type of a particular device?

Win32_DeviceBus is an association class. Never used an association class myself, but you should be able to get the "Antecedent" property. The returned variant should be of type IUnknown - which is actually an IWbemClassObject interface.

gg

[SandyS]

The goal is to get a list if PCI devices, including the Bus/Device (and possibly) Function numbers, and it looks like I can find this in "Win32_DeviceBus".

I get the "Antecedent" like this:
...
IWbemClassObject *pclsObj;
VARIANT vtProp;
HRESULT hr = pEnumerator->Next(WBEM_INFINITE, 1, &pclsObj, &uReturn);
hr = pclsObj->Get(L"Antecedent", 0, &vtProp, 0, 0);

If "Antecedent" were a string, I could access it with "vtProp.bstrVal". But since it is a Variant, I guess I need to cast it (to Win32_Bus or IWbemClassObject?) before I can access its properties, but I don't know how.

Thanks!

[Codeplug]

IWbemClassObject *pWin32BusObj;
hr = vtProp.punkVal->QueryInterface(__uuidof(IWbemClassObject), (void**)&pWin32BusObj);

Don't forget to check hr, Release() your objects when you're done with them, and call VariantClear() on vtProp.

gg

[SandyS]

Still not quite there. The

hr = pclsObj->Get(L"Antecedent", 0, &vtProp, 0, 0);

call looks ok, hr = S_OK, and the debugger shows vtProp.BSTR set to seomething like
0x00170ebc "\\DOCKNB143\root\cimv2:Win32_Bus.DeviceID="PCI_BUS_0""

But the

hr = vtProp.punkVal->QueryInterface(__uuidof(IWbemClassObject), (void**)&pWin32BusObj);

call fails because of an access violation.
"vtProp" seems to be pointing to a valid address, so does "vtProp.punkVal". However, vtProp.punkVal._vfptr[0] = 0x00000000.

[Codeplug]

Sorry, looks like the "Antecedent" property is actually a string, not an IUnknown pointer.

So that string is an "object path", which describes a unique object instance. You use IWbemServices::GetObject() to get an object instance based on its path.

IWbemClassObject *pWin32BusObj;
hr = pSvc->GetObject(vtProp.bstrVal, WBEM_FLAG_RETURN_WBEM_COMPLETE, 0, 
                     &pWin32BusObj, 0);

http://msdn.microsoft.com/en-us/libr...09(VS.85).aspx
http://msdn.microsoft.com/en-us/libr...50(VS.85).aspx

gg