iterators can't access problems properly

Question

I am trying to access the element of a vector using the iterator. But I get strange outputs.

std::vector<int> ivec{ 7, 6 , 8, 9} ; 

std::vector<int>::iterator beg = ivec.begin(); 
std::vector<int>::iterator last = ivec.end(); 

std::cout << *beg << *last << std::endl; 

But, In the above case the program shows me error: debug assertion failed. Vector iterator not dereferencable. and this error is particularly for *last. If I just print *beg that seems to wrong fine. But can't dereference the last one.

Other problem I get with iterator is during increment.

std::vector<int>::iterator beg = ivec.begin(); 

cout << *(beg++) ;  // in this case it prints me value of 7
cout << *(++beg) ;  // in this case it print me the right value of second place i.e. is 6
cout << *(beg+=1) ; // in this case we also print the second value i.e. 6 

Answer 1

end iterators are not iterators that you can de-reference. They point past the last element into the container. There's a good reason why this needs to be true; but long and short, the end iterator does not actually point to any element. If you want the last element, you need to decrement the end iterator.