Re: STL - Debug assertion failure, vector iterator not dereferencable

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Wed, 10 Oct 2007 13:20:03 -0400

Message-ID:

<ufimMH2CIHA.5228@TK2MSFTNGP05.phx.gbl>

John <John@discussions.microsoft.com> wrote:

I recently converted a visual studio .net project to visual studio
2005 project. After
the conversion I am now having runtime errors on a collection that is
composed of a vector of CComVariants.

std::vector<CComVariant> m_vecResults;

More specifically it gives me a Debug assertion failure, vector
iterator not dereferencable in my get__NewEnum method on the Init
statement in the following
code;

STDMETHODIMP get__NewEnum(IUnknown** ppUnk)
{
   typedef CComObject<CComEnum<IEnumVARIANT, &IID_IEnumVARIANT,
        VARIANT, _Copy<VARIANT> > > enumVariant;
   enumVariant* pEnum = new enumVariant;
   HRESULT hr = pEnum->Init(&*m_vecResults.begin(),
                              &*m_vecResults.end(),
                              0,
                              AtlFlagCopy );

This code exhibits undefined behavior, and could only ever work by
accident. Specifically, *m_vecResults.end() is illegal - an end()
iterator is not dereferenceable. Try this:

CComVariant* pStart = 0;
CComVariant* pEnd = 0;
if (!m_vecResults.empty()) {
pStart = &m_vecResults.front();
pEnd = pStart + m_vecResults.size();
}
pEnum->Init(pStart, pEnd, ...);

So I modified my code to the following the following to not use
begin/end and it
seemed to of fix the problem.

STDMETHODIMP get__NewEnum(IUnknown** ppUnk)
{
      typedef CComObject<CComEnum<IEnumVARIANT, &IID_IEnumVARIANT,
         VARIANT, _Copy<VARIANT> > > enumVariant;
     size_t nSize = m_vecResults.size();
     enumVariant* pEnum = new enumVariant;
     HRESULT hr = pEnum->Init(&m_vecResults[0],
&m_vecResults[nSize-1], NULL,
        AtlFlagCopy);

This a) doesn't work when the vector is empty, and b) always leaves the
last element out.

Now I have another piece of code that uses a priority queue;

typedef priority_queue< CRfItem, vector< CRfItem >, CRfItem::greater >
RfQueue;
RfQueue m_QueueAllPoints;

I am experiencing the same error again in the following code segment
on the top()
statment;

RfQueue::value_type temp = m_QueueAllPoints.top();

Is the queue empty at this point, by any chance?
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925