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

From:

=?Utf-8?B?Sm9obg==?= <John@discussions.microsoft.com>

Newsgroups:

microsoft.public.vc.atl

Date:

Wed, 10 Oct 2007 10:47:02 -0700

Message-ID:

<43D8B925-EC5C-4406-BFC1-70D1DBD54DD7@microsoft.com>

Thanks for the explanation Igor,

I tried the code you supplied and it worked but this brings up another
question what does one return when the vector is empty E_FAIL?

As for the other problem, as it turns out the vector is empty on that
statement. I am using recursion in this routine so I will need to track down
the bug. It's odd that these routines both used to work before converting
them to 2005. Microsoft must have improved the error trapping in their STL.

"Igor Tandetnik" wrote:

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