I have a method as follows (from a class than implements TBB task interface - not currently multithreading though) My problem is that two ways of accessing a vector are causing quite different behaviour - one works and the other causes the entire program to bomb out quite spectacularly (this is a plugin and normally a crash will be caught by the host - but this one takes out the host program as well! As I said quite spectacular)

void PtBranchAndBoundIterationOriginRunner::runOrigin(int origin, int time) const // NOTE: const method
{
    BOOST_FOREACH(int accessMode, m_props->GetAccessModes())
    {
        // get a const reference to appropriate vector from member variable
        // map<int, vector<double>> m_rowTotalsByAccessMode;
        const vector<double>& rowTotalsForAccessMode = m_rowTotalsByAccessMode.find(accessMode)->second;

        if (origin != 129) continue; // Additional debug constrain: I know that the vector only has one non-zero element at index 129

        m_job->Write("size: " + ToString(rowTotalsForAccessMode.size()));
        try {
            // check for early return... i.e. nothing to do for this origin 
            if (!rowTotalsForAccessMode[origin])    continue; // <- this works
            if (!rowTotalsForAccessMode.at(origin)) continue; // <- this crashes
        } catch (...) {
            m_job->Write("Caught an exception"); // but its not an exception
        }

        // do some other stuff
    }
}

I hate not putting in well defined questions but at the moment my best phrasing is : "WTF?"

I'm compiling this with Intel C++ 11.0.074 [IA-32] using Microsoft (R) Visual Studio Version 9.0.21022.8 and my implementation of vector has

const_reference operator[](size_type _Pos) const
{   // subscript nonmutable sequence

#if _HAS_ITERATOR_DEBUGGING
    if (size() <= _Pos)
    {
        _DEBUG_ERROR("vector subscript out of range");
        _SCL_SECURE_OUT_OF_RANGE;
    }
#endif /* _HAS_ITERATOR_DEBUGGING */
    _SCL_SECURE_VALIDATE_RANGE(_Pos < size());

    return (*(_Myfirst + _Pos));
}

(Iterator debugging is off - I'm pretty sure) and

const_reference at(size_type _Pos) const
{   // subscript nonmutable sequence with checking
    if (size() <= _Pos)
        _Xran();
    return (*(begin() + _Pos));
}

So the only difference I can see is that at calls begin instead of simply using _Myfirst - but how could that possibly be causing such a huge difference in behaviour?