FIX: Interfaces Not Released by _com_ptr_t::CreateInstance()

• Microsoft Visual C++, 32-bit Editions, version 5.0

SYMPTOMS

Smart pointers object creation (using _com_ptr_t::CreateInstance() ) does not release interface pointers to local or remote servers on failure.

RESOLUTION

For local and remote servers, use the CoCreateInstance() API instead of the function, _com_ptr_t::CreateInstance(). Then use the smart pointer wrapper to call methods on the object by calling _com_ptr_t::Attach(). Once the smart pointer goes out of scope, Release() is called for the interface pointer.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

This bug was corrected in Microsoft Visual C++, version 6.0.

MORE INFORMATION

For local and remote servers, call CoCreateInstance() directly, as in the following sample code:

HRESULT hr = CoCreateInstance(..., ..., IID_IUnknown, (LPVOID*)&pUnk);
if (FAILED(hr))
    //Do error handling.

hr = OleRun(pUnk);

if (FAILED(hr)) {
    pUnk->Release();
    //Do error handling
}

// Query for the required interface, such as IFoo.
hr = pUnk->QueryInterface( IID_IFoo, pFoo);

if (FAILED(hr)) {
    pUnk->Release();
    //Do error handling
} 

// Declare the smart pointer for the IFoo interface.
IFooPtr m_pFoo;

// Attach the raw interface pointer which you got above
// to the smart pointer wrapper.
m_pFoo.Attach(pFoo); 

REFERENCES

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Jaganathan Thangavelu, Microsoft Corporation.

Additional query words: Smart pointers

Keywords : kbCOMt kbVC500bug kbVC600fix
Version : winnt:5.0
Platform : winnt
Issue type : kbbug