Re: WMI question

Hi Kim,
  I think you're on to something here, I used a query that normally causes
the program to crash and I commented out the
wcout<< "Data Name : " << vtProp.bstrVal<< endl;   line and although the
program didn't print any information, it also did not crash, which is a
positive sign. I did try casting the bstr to a const wchar_t* but it didn't
seem to help, I wonder if I could load the data into an array and step
through it in a for loop just to see what information is actually there
before it is sent to wcout( )? I'll keep working and see what I can come up
with. Thanks again for your help.


John

On Sat, Dec 4, 2010 at 12:38 AM, Kim Gräsman <[email protected]> wrote:

>
>
> 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
>
>  
>