crash when using stl vector at instead of operator[]
- by Jamie Cook
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?
