Variables & WMI

[Simoninman]

Hi everybody I am currently trying to create a C++ program that collects data from WMI through a function and then stores them into seperate variables so as it can be used later. However I am running into a snag, I think it might have something to do with the way I am assigning variables but unsure, i can get the results to my queries fine, but then when I try to display the variables later they do not make sense...
This is my function:

WCHAR* WMIQuery(char* QueryName, char* ClassName, char* PropertyName, char* QueryArgument)
{
	WCHAR* QueryResult;

	// Display Current Objective
	printf("Looking for %s...\n", QueryName);

	// Create BSTR variable containing query
	CComBSTR querystr(OLESTR("SELECT * FROM "));
	querystr.Append(ClassName);
	querystr.Append(QueryArgument);
	BSTR WQLQuery = querystr.Detach();

	// Create BSTR variable containt propertyname
	CComBSTR propertystr;
	propertystr.Append(PropertyName);
	BSTR NameQuery = propertystr.Detach();
	
	// Use the IWbemServices pointer to make requests of WMI
	printf("Query %s Class...\n", ClassName);
    IEnumWbemClassObject* pEnumerator = NULL;
    hr = pSvc->ExecQuery(
        BSTR(L"WQL"), 
        BSTR(WQLQuery),
        WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, 
        NULL,
        &pEnumerator);
    
    if (FAILED(hr))  // Program has failed.
    {
        cout << "Query failed. " << "Error code = 0x" << hex << hr << endl;
        pSvc->Release();
        pLoc->Release();
        CoUninitialize();
    }

    else
    { 
		printf("Getting Value of %s property from class...",PropertyName);
        IWbemClassObject *pclsObj;
        ULONG uReturn = 0;
   
        while (pEnumerator)
        {
            hr = pEnumerator->Next(WBEM_INFINITE, 1, &pclsObj, &uReturn);

            if(0 == uReturn)
            {
				break;
            }

            VARIANT vtProp;

            // Get the value of the Name property from class
            hr = pclsObj->Get(NameQuery, 0, &vtProp, 0, 0);

			// Display Resuly
			printf("Result: %ls\n",vtProp.bstrVal);
			
			// Copy result into a usable variable
			QueryResult = vtProp.bstrVal;
			
			// Clear vtprop
            VariantClear(&vtProp);
        }

    }
	return QueryResult;
}

This is my call:

	WCHAR* WS_Name = WMIQuery("Computer Name", "Win32_ComputerSystem", "Name", ""); // Computer Name
	WCHAR* WS_Domain = WMIQuery("Domain Name", "Win32_ComputerSystem", "Domain", ""); // Domain Name

	printf("Display ALL Results...\n");
	printf("Machine Name: %ls\n", WS_Name);
	printf("Domain Name: %ls\n", WS_Domain);

but my results look like this:

Looking for Computer Name...
Query Win32_ComputerSystem Class...
Getting Value of Name property from class...Result: Home-11
Result: Home-11

Looking for Domain Name...
Query Win32_ComputerSystem Class...
Getting Value of Domain property from class...Result: home.local
Result: home.local

Display ALL Results...
Machine Name: Domain
Domain Name: home.local

Sorry its long, but any help would be greatly appreciated, I know i'm overlooking something stupid :-(

[VictorN]

This is my function:

WCHAR* WMIQuery(char* QueryName, char* ClassName, char* PropertyName, char* QueryArgument)
{
	WCHAR* QueryResult;
	...
	return QueryResult;
}

You return a pointer to WCHAR that is defined locally within the WMIQuery() function.
But it goes out of scope just before this function returns, so the return value points to some garbage!

Either return CString (or std::wstring) objects or add additional parameter (WCHAR* QueryResult) in the argument list of the function.

[GCDEF]

I'm not really up on the code he's using, but it seems that the code here probably contributes.

VARIANT vtProp;
...
QueryResult = vtProp.bstrVal;
...
VariantClear(&vtProp);
...
return QueryResult;

Looks more like he's returning a pointer to a variant that's getting cleared then going out of scope.

[VictorN]

...
Looks more like he's returning a pointer to a variant that's getting cleared then going out of scope.

You are probably right.
And sorry, I didn't have enough time to analyze the function body. I only looked at the how return value was defined.

[Simoninman]

Thank you for your help, Still new to all the variable types, so didn't see that :-s
Thank you again