should i do SysFreeString here?

i'm just doing some wrap class for msxml and got some problem?

i'm using the raw interface in msxml.h, not smart pointer. (visual studio
2003)

sample code like this:
//--start-------------------------------------------
{
IXMLDOMDocument* pDoc = NULL;
HRESULT hr = ::CoCreateInstance(CLSID_DOMDocument, NULL,
CLSCTX_INPROC_SERVER, IID_IXMLDOMDocument, (void**) &pDoc);

hr = pDoc->put_async(VARIANT_FALSE);
hr = pDoc->put_validateOnParse(VARIANT_FALSE);
hr = pDoc->put_resolveExternals(VARIANT_FALSE);

CComVariant varFile(_T("c:\\aa.xml"));
VARIANT_BOOL status;
hr = pDoc->load(varFile, &status);

BSTR bstrXML = NULL;
pDoc->get_xml(&bstrXML);

//***********************
// doing some processing for bstrXML;
// ...
//
SysFreeString(bstrXML); //should i do SysFreeString here?
//***********************

pDoc->Release();
}
//--end---------------------------------------------


i have used _CrtDumpMemoryLeaks() and
_CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF )
to detect memory leak.
but whether i do SysFreeString or not, there is no memory leak detected.

i believe use SysFreeString() here is a good behave.
and i have viewed some code from others. someone use, someone not.

i am very confused that is it necessary to do SysFreeString here?
and anyone can help me?

thanks!

Jeff
Wed Jun 01 23:35:17 CDT 2005

"aotin" <aotin@discussions.microsoft.com> wrote in message
news:3855E3CA-B224-48EB-8419-8584DA6165E9@microsoft.com...
>
> BSTR bstrXML = NULL;
> pDoc->get_xml(&bstrXML);
>
> //***********************
> // doing some processing for bstrXML;
> // ...
> //
> SysFreeString(bstrXML); //should i do SysFreeString here?

Yes.
--
Jeff Partch [VC++ MVP]

aotin
Thu Jun 02 00:40:02 CDT 2005



"Jeff Partch [MVP]" wrote:

> "aotin" <aotin@discussions.microsoft.com> wrote in message
> news:3855E3CA-B224-48EB-8419-8584DA6165E9@microsoft.com...
> >
> > BSTR bstrXML = NULL;
> > pDoc->get_xml(&bstrXML);
> >
> > //***********************
> > // doing some processing for bstrXML;
> > // ...
> > //
> > SysFreeString(bstrXML); //should i do SysFreeString here?
>
> Yes.
> --
> Jeff Partch [VC++ MVP]
>
>
>

but why?
even i don't do that, there is no memory leak be detected?
can you show me more details about that.

thanks.

Jochen
Thu Jun 02 00:53:58 CDT 2005

Hi aotin!

>>>BSTR bstrXML = NULL;
>>>pDoc->get_xml(&bstrXML);
>>>
>>>//***********************
>>>// doing some processing for bstrXML;
>>>// ...
>>>//
>>>SysFreeString(bstrXML); //should i do SysFreeString here?
>>
>>Yes.

>
> but why?
> even i don't do that, there is no memory leak be detected?
> can you show me more details about that.

Who should detect the leak?
This is not an CRT-Allocation, so CRT does not detect it...
And the allocation occurs inside the COM-Stub, so I do not know if tools
like Purify or other will detect the allocation...

--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/

aotin
Thu Jun 02 01:44:03 CDT 2005

>
> Who should detect the leak?
> This is not an CRT-Allocation, so CRT does not detect it...
> And the allocation occurs inside the COM-Stub, so I do not know if tools
> like Purify or other will detect the allocation...
>
> --
> Greetings
> Jochen
>


Oh. i see.

_CrtDumpMemoryLeaks() cannot detect the memory leak in com object.

i have tried another case:

//---------------------------------------
_CrtDumpMemoryLeaks();
{
BSTR bstrTMP = SysAllocString(L"ABCDEFG");
//...
//without: SysFreeString(bstrTMP);
}
_CrtDumpMemoryLeaks();
//---------------------------------------

_CrtDumpMemoryLeaks() also cannot detect the memory leak here.

so, in my first Q, the answer is:

The SysFreeString(bstrXML) is necessary to call by user to free the buffer.

thanks all of you guys.

Rodrigo
Thu Jun 02 04:56:20 CDT 2005

This document could be interesting for you

http://www.winwonk.com/writing/commemory/


--
Un saludo
Rodrigo Corral González [MVP]

FAQ de microsoft.public.es.vc++
http://rcorral.mvps.org

Simon
Thu Jun 02 05:37:13 CDT 2005

One method for checking for COM memory leaks (including BSTRs) is the
IMallocSpy method. Have a look at

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wcedcom/html/cerefimallocspy.asp
and
http://www.microsoft.com/msj/0699/visualprog/visualprog0699.aspx

cheers

Simon

"aotin" <aotin@discussions.microsoft.com> wrote in message
news:F6B2A02A-FCF5-4632-97C6-0BF007C4B4E9@microsoft.com...
> >
> > Who should detect the leak?
> > This is not an CRT-Allocation, so CRT does not detect it...
> > And the allocation occurs inside the COM-Stub, so I do not know if tools
> > like Purify or other will detect the allocation...
> >
> > --
> > Greetings
> > Jochen
> >
>
>
> Oh. i see.
>
> _CrtDumpMemoryLeaks() cannot detect the memory leak in com object.
>
> i have tried another case:
>
> //---------------------------------------
> _CrtDumpMemoryLeaks();
> {
> BSTR bstrTMP = SysAllocString(L"ABCDEFG");
> //...
> //without: SysFreeString(bstrTMP);
> }
> _CrtDumpMemoryLeaks();
> //---------------------------------------
>
> _CrtDumpMemoryLeaks() also cannot detect the memory leak here.
>
> so, in my first Q, the answer is:
>
> The SysFreeString(bstrXML) is necessary to call by user to free the
buffer.
>
> thanks all of you guys.
>

Jochen
Thu Jun 02 06:09:31 CDT 2005

> One method for checking for COM memory leaks (including BSTRs) is the
> IMallocSpy method. Have a look at
>
> http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wcedcom/html/cerefimallocspy.asp
> and
> http://www.microsoft.com/msj/0699/visualprog/visualprog0699.aspx

You can also use my leak-finder:

http://blog.kalmbachnet.de/?postid=13


--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/

aotin
Thu Jun 02 22:09:24 CDT 2005

"Rodrigo Corral [MVP]" wrote:

> This document could be interesting for you
>
> http://www.winwonk.com/writing/commemory/
>
>
> --
> Un saludo
> Rodrigo Corral González [MVP]
>
> FAQ de microsoft.public.es.vc++
> http://rcorral.mvps.org
>
>


it is a good article!

thanks a lot!!!

aotin
Thu Jun 02 22:36:01 CDT 2005

"Jochen Kalmbach [MVP]" wrote:

> > One method for checking for COM memory leaks (including BSTRs) is the
> > IMallocSpy method. Have a look at
> >
> > http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wcedcom/html/cerefimallocspy.asp
> > and
> > http://www.microsoft.com/msj/0699/visualprog/visualprog0699.aspx
>
> You can also use my leak-finder:
>
> http://blog.kalmbachnet.de/?postid=13
>
>
> --
> Greetings
> Jochen
>
> My blog about Win32 and .NET
> http://blog.kalmbachnet.de/
>

all of you are great. thanks a lot!