FIX: CComEnumImpl<>::Skip() Doesn't Handle Overflow Correctly (218829)

The information in this article applies to:

The Microsoft Active Template Library (ATL) 3.0, when used with:
- Microsoft Visual C++, 32-bit Enterprise Edition 6.0
- Microsoft Visual C++, 32-bit Professional Edition 6.0
- Microsoft Visual C++, 32-bit Learning Edition 6.0

This article was previously published under Q218829

SYMPTOMS

If an argument passed into CComEnumImpl<>::Skip() is a negative number, then the pointer to the current enumeration may not be set correctly.

CAUSE

Following is the implementation of CComEnumImpl<>::Skip():

template <class Base, const IID* piid, class T, class Copy>
STDMETHODIMP CComEnumImpl<Base, piid, T, Copy>::Skip(ULONG celt)
{
	m_iter += celt;
	if (m_iter <= m_end)
		return S_OK;
	m_iter = m_end;
	return S_FALSE;
}

M_iter points to the current enumeration. If celt is a negative number, Skip() is supposed to set m_iter back "celt" items. If "m_iter + celt" results in a value that is less than m_begin, then this case is not handled and m_iter is set to an invalid pointer.

RESOLUTION

This bug has been fixed in Visual Studio 6.0 Service Pack 3.

STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.

This bug was corrected in Visual Studio 6.0 Service Pack 3. For more information about Visual Studio service packs, please see the following articles in the Microsoft Knowledge Base:

194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

Modification Type:	Major	Last Reviewed:	2/24/2004
Keywords:	kbBug kbCollectionClass kbfix kbVS600sp3fix KB218829