Question

I created a program, and it uses the vector.h #include, and iterators, etc… But when I run the program, under certain circumstances (I’m still trying to figure out what those would be) I get an assertion error refering me to line 98 of vector.h. I went to line 98 of vector.h and got this:

 #if _HAS_ITERATOR_DEBUGGING
        if (this->_Mycont == 0
            || _Myptr < ((_Myvec *)this->_Mycont)->_Myfirst
            || ((_Myvec *)this->_Mycont)->_Mylast <= _Myptr)
            {
            _DEBUG_ERROR("vector iterator not dereferencable");
            _SCL_SECURE_OUT_OF_RANGE;
            }

Can somebody please tell me what this means and what in my program is causing this assertion?

NB: Line 98, for the record, is the one that begins “_DEBUG_ERROR(“vect…”

NB: This is the code in my program that I BELIEVE triggered the error, I’m not entirely sure, though.

CODE:

for(aI = antiviral_data.begin(); aI < antiviral_data.end();)
    {
        for(vI = viral_data.begin(); vI < viral_data.end();)
        {
            if((*aI)->x == (*vI)->x && (*aI)->y == (*vI)->y)
            {
                vI = viral_data.erase(vI);
                aI = antiviral_data.erase(aI);
            }
            else
            {
                vI++;
            }
        }
        if((*aI)->x >= maxx || (*aI)->x < 0 || (*aI)->y >= maxy || (*aI)->y < 0)
        {
            aI = antiviral_data.erase(aI);
        }
        else
        {
            aI++;
        }
    }

Answer 1

The runtime is detecting that you are dereferencing an iterator that is before begin() or after end().

Imagine if you delete the last item in the antiviral_data vector in line 7:

aI = antiviral_data.erase(aI);

aI gets set to antiviral_data.end(), and when you dereference it in line 14:

if((*aI)->x >= maxx ...

and also in line 5:

if((*aI)->x == (*vI)->x

You are dereferencing an out of bounds iterator.

The fix is to check that aI != antiviral_data.end() after the erase call to make sure you haven’t hit the end of the vector before you continue on using it.