Question

The following code snippet gives the error message at run time of:

Debug assertion failed: Vector iterator not dereferenceable

 for(it=stat1vec.begin(); *(it)>=investigated_stat; it++, positioner++)
    {


        if(*it==investigated_stat)
            equalwith++;

    }

When changed to:

for(it=stat1vec.begin(); *(it)==investigated_stat; it++, positioner++)
        {


            if(*it==investigated_stat)
                equalwith++;

        }

The code works perfectly.

All the has been done is to change >= to ==

Why is this?

Thanks very much

Answer 1

You should test for the iterator to be a valid iterator before dereferencing it. Your loop will continue until *it < investigated_stat but it won’t stop when none of the elements are >= investigated_stat and you iterate past the end of the vector.

The test in the for loop should be

it != stat1vec.end() && *it >= investigated_stat

Which makes the slightly modified for:

for(it = stat1vec.begin(); it != stat1vec.end() && *it >= investigated_stat; ++it, ++positioner)
    if(*it == investigated_stat)
        ++equalwith;