Re: WMI question

Hi John,

On Sat, Dec 4, 2010 at 02:21, John Smith <[email protected]> wrote:
>
> I just found out that google will not let me attach a lib file that is
> needed for the project. the file is WbemUuid.lib, if your SDK's are up to
> date, you should have it already.
>

            VARIANT vtProp;

            // Get the value of the Name property
            hres = pclsObj->Get(L"Name", 0, &vtProp, 0, 0);
            wcout<< "Data Name : " << vtProp.bstrVal<< endl;   //changing
vtProp.bstrVal to one of the other 'dot' member
            VariantClear(&vtProp);   //variables seems to keep it from
crashing, but the data
        }   //that is reported is garbage...

I think the BSTR you get back may not be zero-terminated. They are
apparently supposed to be, see [1], but I seem to recall the rule was that
they may be but aren't required to, since the length is already available in
the prefix.

I'd try and wrap it in a _bstr_t and call its conversion operator to a wide
string;

  wcout<< "Data Name : " << (const wchar_t*) _bstr_t(vtProp.bstrVal) <<
endl;

Also, when you get a VARIANT out of a COM method, it's always a good idea to
check its type before attempting to use it. Try and inspect the vtProp.vt
member in your debugger, and compare it to the VT_ flags in wtypes.h. If the
type is anything other than VT_BSTR, the bstrVal member is not valid.

So, you may need to change the type of the value into a string before
printing it, using VariantChangeType(Ex).

Hope that helps,
- Kim

[1] http://msdn.microsoft.com/en-us/library/ms221069.aspx

- BSTRs are length-prefixed and wide strings are zero-terminated
- BSTRs MAY BE zero-terminated but aren't required to be, since the length
is available from the prefix