How to tell if there's no default file extensi

Question

Going back to the days of Windows XP one could use the following code to tell if there's no file association existed for an extension:

TCHAR buffPath[MAX_PATH] = {0};
DWORD dwszBuffPath = MAX_PATH;

HRESULT hR = ::AssocQueryString(
    ASSOCF_NOFIXUPS | ASSOCF_VERIFY, 
    ASSOCSTR_EXECUTABLE,
    _T(".weirdassextension"),
    NULL,
    buffPath,
    &dwszBuffPath);

if(hR != S_OK &&
    hR != E_POINTER)
{
    //Association does not exist
}

But since Windows 8, the AssocQueryString API returns S_OK and buffPath is set to something like C:\WINDOWS\system32\OpenWith.exe if it doesn't find anything.

Is there a better way now to determine that file extension has no Shell association?

PS. I do not want to just compare the file name to OpenWith.exe. What if there's a legit executable called just that... There must be a better way.

Answer 1

I think I got it. The trick was to use the correct flags. This seems to work from XP and up:

WCHAR wbuffPath[MAX_PATH] = {0};
DWORD dwszBuffPath = MAX_PATH;
HRESULT hR = ::AssocQueryStringW(ASSOCF_INIT_IGNOREUNKNOWN, 
    ASSOCSTR_EXECUTABLE,
    L".weirdassextension",
    NULL,
    wbuffPath,
    &dwszBuffPath);

if(hR == 0x80070483)   // HRESULT_FROM_WIN32(ERROR_NO_ASSOCIATION)
{
    //The association is missing
}

There's one other trick there, that took me some time to figure out -- DO NOT use AssocQueryStringA(). The shim for AssocQueryStringA() that converts its passed string parameters to Unicode has a bug in XP (and evidently in Vista as well) that will make that API fail on those OS. So, if you do your own ANSI-to-Unicode conversion and call AssocQueryStringW() the problem will go away (Evidently 14 years is not enough time for Microsoft to fix that bug?).