CoCreateInstance failing for COM initializing for windows XP...

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I have a MFC application. It initializes COM through following code (part of that code):

BOOL WMIInterface::ConnectWMI()
{
    LOG_API(CommonLogger::cmpPrintChannelSerializer,"WMIInterface::ConnectWMI()");

    HRESULT hres;
    int PrJobsCount =0;

    hres = CoCreateInstance(
        CLSID_WbemLocator,             
        0, 
        CLSCTX_INPROC_SERVER, 
        IID_IWbemLocator, (LPVOID *) &pLocation_);
 
    if (FAILED(hres))
    {
		LOG_API_MSG("CoCreateInstance() failed..");
        return FALSE;       // Program has failed.
    }
........

As you can see it have no CoInitializeEx.... My assumption was it should fail CoCreateInstance, but it not failing in WINDOWS 7, it fails for Windows XP...

C++

HRESULT hres;
// Initialize COM. ------------------------------------------
hres =  CoInitializeEx(0, COINIT_MULTITHREADED);
if (FAILED(hres))
{
    LOG_API(CommonLogger::cmpSmc, "CMultiplePrinterDlg::OnRun - CoInitializeEx Failed...Can't proceed..");
    return;
}

...

Any clue why?

Posted 6-Dec-12 0:31am

debdipta_ghosh

Updated 6-Dec-12 1:58am

armagedescu

v2

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[no name] 6-Dec-12 8:23am

For win 7 it is returnong S_OK....for win xp is returning NULL....

Jochen Arndt 6-Dec-12 9:02am

There is no difference between S_OK and NULL. Both are defined as 0 (zero).

ThatsAlok 6-Dec-12 21:32pm

thats why MS recommend FAILED or SUCCESS macro to check for validation

[no name] 6-Dec-12 23:22pm

Actually my dev PC is Win7...so I don't got any error....but during testing in WinXP this prob revealed through log.....It is very interesting problem...

2 solutions

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miro10 · Answer 1 · 2013-11-12T06:42:00

Solution 1

You should look at the hres code. For example, assign the hres to the m_sc member of an COleException and then call GetErrorMessage on the exception object. This probably tells you more about the root cause.

Posted 12-Nov-13 6:42am

miro10

JJMatthews · Answer 2 · 2013-11-19T23:50:00

I never have a problem with CoInitializeEx myself, after reading MSDN it says:

Return Values<br />
This function supports the standard return values E_INVALIDARG, E_OUTOFMEMORY, and E_UNEXPECTED, as well as the following: <br />
S_OK <br />
The COM library was initialized successfully on the calling thread. <br />
S_FALSE <br />
The COM library is already initialized on the calling thread. <br />
RPC_E_CHANGED_MODE<br />
<br />
A previous call to CoInitializeEx specified a different concurrency model for the calling thread, or the thread that called CoInitializeEx currently belongs to the neutral threaded apartment. <br />

so perhaps you are mistaking an "already initialized" return code for an "error" return code.

Here is a function to retrieve an error message from a HRESULT:

C#

CString CApp::GetErrorText(HRESULT hr)
{
    if(FACILITY_WINDOWS == HRESULT_FACILITY(hr))
        hr = HRESULT_CODE(hr);
    TCHAR* szErrMsg;

    if(::FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM,
        NULL, hr, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR)&szErrMsg, 0, NULL) != 0)
    {
        LocalFree(szErrMsg);
    }
    else
    {
        _stprintf(szErrMsg, _T("Unkown Error: %#x"), hr);
    }

    return CString(szErrMsg);
}