Thread: MSXML driving me insane!

Code:

#import <msxml6.dll>
int main()
{
    ::CoInitialize(NULL);
    MSXML2::IXMLDOMDocumentPtr doc;
    doc.CreateInstance(__uuidof(MSXML2::DOMDocument));
    doc->validateOnParse = true;
    if (doc->load("c:\\test.xml"))
    {
    }
    ::CoUninitialize();
}

i'm getting a memory access violation in comip.h at the following code:

Code:

void _Release() throw()
{
    if (m_pInterface != NULL) {
        m_pInterface->Release();
    }
}

the test.xml is a valid XML file. is there some funky magic happening in the background i should know about? thanks.

i did more digging and now i'm very confused....haha...

both of the following versions will not throw the memory access violation anymore.

version A:

Code:

int main()
{
  ::CoInitialize(NULL);
  MSXML2::IXMLDOMDocumentPtr doc;
  doc.CreateInstance(__uuidof(MSXML2::DOMDocument));
  doc.Release();
  ::CoUninitialize();
}

version B:

Code:

class CXmlDocument
{
private:
    MSXML2::IXMLDOMDocumentPtr mp_Document;
public:
    CXmlDocument()
    {
        ::CoInitialize(NULL);
        mp_Document.CreateInstance(__uuidof(MSXML2::DOMDocument));
    }
    ~CXmlDocument()
    {
        mp_Document = 0;
        ::CoUninitialize();
    }
    MSXML2::IXMLDOMDocumentPtr operator->() { return mp_Document; }
};

int main()
{
  CXmlDocument doc;
}

if i use Release() in CXmlDocument's destructor, i will get a memory access violation. can someone please explain what's happening? i just want to make sure i understand so there's no memory leaks due to my ignorance. thanks.

>> i'm getting a memory access violation
The object "doc" is going out of scope (invoking destructors) after ::CoUninitialize(). Version A and B are working because you are calling Release() prior to ::CoUninitialize().

>> if i use Release() in CXmlDocument's destructor, i will get a memory access violation
"mp_Document = 0" is the same as calling Release(). Just do it while the COM sub-system is still running

gg

ok, it makes more sense now.

since _com_ptr_t is a smart pointer, i shouldn't need to call the Release() function at any time right? and the problems i'm having are because the Release(), whether manually or automatically, are called after CoUninitialize?

>> i shouldn't need to call the Release() function at any time right?
You can rely on _com_ptr_t's destructor if you like - yes.

>> and the problems i'm having are because the Release() ... called after CoUninitialize?
That's definitely the problem with post #1.

gg