Comparing two iterator of different containers

Question

Hi

I was informed that comparing two iterator of different containers will either crash or result into undefined behaviour.

I have a case where above statement is false.

Please refer code below:

I know iterator is almost a pointer and points to actual data within container. As v1 and v2 is different, itr1 and itr2 points to different memory location. Hence, itr1 == itr2 will be false and same is shown in output as well.

So, just want to confirm that this output is always same and it is not undefined behaviour.
https://sololearn.com/compiler-playground/c69473vKMc7H/?ref=app

Answer 1

Ketan Lalcheta It depends on the compiler settings and how the iterator for the container implements the overload of the == operator.

Most compilers will usually yield a compiler warning about the comparison.
If the compiler is set to be forgiving, it might allow the comparison but it will always be false.

Since each container represents a different memory space, it will always be impossible for the 2 iterators to ever be equal.

Answer 2

Your implementation is a valid way to check if two iterators are the same and it cannot lead to undefined behaviour

If you're doing any container operations like push_back() etc, then you should always remember to recheck v1 and v2 again

Answer 3

Thanks RuntimeTerror and Shardis Wolfe