QCoreApplication QApplication with WMI

Question

I found some WMI C++ Application Examples in MSDN website.

I have tried the code form the below link

http://msdn.microsoft.com/en-us/library/aa390423%28v=VS.85%29.aspx

when I copied and run the application as win32 console application it worked well.

the same code I put into the Qt application ,

When I use QApplication anApplication ( argc, argv ); in my code it is not working

But if I use QCoreApplication anApplication ( argc, argv ); it is working

shows me error like "when i change QCoreApplication to QApplication The below source code not works and gives me error like " Failed to initialize COM library. Error code = 0x80010106 "

Any suggestions or help

#define _WIN32_DCOM
#include <iostream>
using namespace std;
#include <comdef.h>
#include <Wbemidl.h>

# pragma comment(lib, "wbemuuid.lib")

// Qt Includes
#include <QtCore>
#include <QtGui>


 //----------------------------------------------------------------------------

// Main Function
int main( int a_argc, char *a_argv[] )
//************************************
{
    // initialize the application
    QApplication anapplication( a_argc, a_argv );

    HRESULT hres;

    // Step 1: --------------------------------------------------
    // Initialize COM. ------------------------------------------

    hres =  CoInitializeEx(0, COINIT_MULTITHREADED); 
    if (FAILED(hres))
    {
        cout << "Failed to initialize COM library. Error code = 0x" 
            << hex << hres << endl;
        return 1;                  // Program has failed.
    }

    // Step 2: --------------------------------------------------
    // Set general COM security levels --------------------------
    // Note: If you are using Windows 2000, you need to specify -
    // the default authentication credentials for a user by using
    // a SOLE_AUTHENTICATION_LIST structure in the pAuthList ----
    // parameter of CoInitializeSecurity ------------------------

    hres =  CoInitializeSecurity(
        NULL, 
        -1,                          // COM authentication
        NULL,                        // Authentication services
        NULL,                        // Reserved
        RPC_C_AUTHN_LEVEL_DEFAULT,   // Default authentication 
        RPC_C_IMP_LEVEL_IMPERSONATE, // Default Impersonation  
        NULL,                        // Authentication info
        EOAC_NONE,                   // Additional capabilities 
        NULL                         // Reserved
        );


    if (FAILED(hres))
    {
        cout << "Failed to initialize security. Error code = 0x" 
            << hex << hres << endl;
        CoUninitialize();
        return 1;                    // Program has failed.
    }

    // Step 3: ---------------------------------------------------
    // Obtain the initial locator to WMI -------------------------

    IWbemLocator *pLoc = NULL;

    hres = CoCreateInstance(
        CLSID_WbemLocator,             
        0, 
        CLSCTX_INPROC_SERVER, 
        IID_IWbemLocator, (LPVOID *) &pLoc);

    if (FAILED(hres))
    {
        cout << "Failed to create IWbemLocator object."
            << " Err code = 0x"
            << hex << hres << endl;
        CoUninitialize();
        return 1;                 // Program has failed.
    }

    // Step 4: -----------------------------------------------------
    // Connect to WMI through the IWbemLocator::ConnectServer method

    IWbemServices *pSvc = NULL;

    // Connect to the root\cimv2 namespace with
    // the current user and obtain pointer pSvc
    // to make IWbemServices calls.
    hres = pLoc->ConnectServer(
         _bstr_t(L"ROOT\\CIMV2"), // Object path of WMI namespace
         NULL,                    // User name. NULL = current user
         NULL,                    // User password. NULL = current
         0,                       // Locale. NULL indicates current
         NULL,                    // Security flags.
         0,                       // Authority (e.g. Kerberos)
         0,                       // Context object 
         &pSvc                    // pointer to IWbemServices proxy
         );

    if (FAILED(hres))
    {
        cout << "Could not connect. Error code = 0x" 
             << hex << hres << endl;
        pLoc->Release();     
        CoUninitialize();
        return 1;                // Program has failed.
    }

    cout << "Connected to ROOT\\CIMV2 WMI namespace" << endl;


    // Step 5: --------------------------------------------------
    // Set security levels on the proxy -------------------------

    hres = CoSetProxyBlanket(
       pSvc,                        // Indicates the proxy to set
       RPC_C_AUTHN_WINNT,           // RPC_C_AUTHN_xxx
       RPC_C_AUTHZ_NONE,            // RPC_C_AUTHZ_xxx
       NULL,                        // Server principal name 
       RPC_C_AUTHN_LEVEL_CALL,      // RPC_C_AUTHN_LEVEL_xxx 
       RPC_C_IMP_LEVEL_IMPERSONATE, // RPC_C_IMP_LEVEL_xxx
       NULL,                        // client identity
       EOAC_NONE                    // proxy capabilities 
    );

    if (FAILED(hres))
    {
        cout << "Could not set proxy blanket. Error code = 0x" 
            << hex << hres << endl;
        pSvc->Release();
        pLoc->Release();     
        CoUninitialize();
        return 1;               // Program has failed.
    }

    // Step 6: --------------------------------------------------
    // Use the IWbemServices pointer to make requests of WMI ----

    // For example, get the name of the operating system
    IEnumWbemClassObject* pEnumerator = NULL;
    hres = pSvc->ExecQuery(
        bstr_t("WQL"), 
        bstr_t("SELECT * FROM Win32_USBControllerDevice"),
        WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, 
        NULL,
        &pEnumerator);

//ExecQuery(L"WQL", L"SELECT * FROM Win32_LogicalDisk", WBEM_FLAG_FORWARD_ONLY, NULL, &iter);

    if (FAILED(hres))
    {
        cout << "Query for operating system name failed."
            << " Error code = 0x" 
            << hex << hres << endl;
        pSvc->Release();
        pLoc->Release();
        CoUninitialize();
        return 1;               // Program has failed.
    }

    // Step 7: -------------------------------------------------
    // Get the data from the query in step 6 -------------------

    IWbemClassObject *pclsObj;
    ULONG uReturn = 0;

    while (pEnumerator)
    {
        HRESULT hr = pEnumerator->Next(WBEM_INFINITE, 1, 
            &pclsObj, &uReturn);

        if(FAILED(hr)||0 == uReturn)
        {
            break;
        }

        VARIANT vtProp;

        // Get the value of the Name property
        /*hr = pclsObj->Get(L"VolumeName", 0, &vtProp, 0, 0);
        wcout << " VolumeName : " << vtProp.bstrVal << endl;
        VariantClear(&vtProp);*/


        if (FAILED(pclsObj->Get(L"Antecedent", 0, &vtProp, 0, 0)))
        {
            cout<<"The specified property is not found."<<endl;
        }
        else
        {
            wcout <<vtProp.bstrVal << endl;
        }

        pclsObj->Release();
    }

    // Cleanup
    // ========

    pSvc->Release();
    pLoc->Release();
    pEnumerator->Release();
   // pclsObj->Release();
    CoUninitialize();


   // return 0;   // Program successfully completed.

    //execute the application
    int anInt = anapplication.exec();

    return anInt;
}
//-----------------------------------------------------------------------------

Answer 1

The error you are receiving is due to the fact that COM is already initialized. QApplication calls OleInitialize in its constructor, but QCoreApplication does not, so that's why you get the error 0x80010106 (RPC_E_CHANGED_MODE) when you use QApplication. For further reading, see the documentation for CoInitializeEx. The following article should provide more insight.

Answer 2

At first I have used this code

hres =  CoInitializeEx(0, COINIT_MULTITHREADED);

if (hres == RPC_E_CHANGED_MODE) {
    OleUninitialize();
    hres =  CoInitializeEx(0, COINIT_MULTITHREADED);
}

When I get error "Failed to initialize COM library(0x80010106)

I just call OleUninitialize to deal with OleInitialize() in QApplication, but that could break some qt functionality.

As I found the best is to use flag COINIT_APARTMENTTHREADED for CoInitializeEx

MSDN

Generally, a thread that creates a window should use the COINIT_APARTMENTTHREADED flag, and other threads should use COINIT_MULTITHREADED. However, some COM components require a particular threading model. The MSDN documentation should tell you when that is the case.

For me it`s a black magic, but it helped me