Assignment of a Singular Iterator

Question

A \"Singular Iterator\" is defined as an:

iterators that are not associated with any sequence. A null pointer, as well as a default-constructed pointer (

Answer 1

Question 2 is: Does working with a result that is "undefined" constitute Undefined Behavior?

Answer is: Definitely Yes. Working on UB is UB.

It seems to run fine for you since it is undefined. It can do anything, this includes working as expected, as well as working not as expected.

Answer 2

Regarding the example for the second question, it works fine because and is well-defined, because you don't actually dereference the pointer foo. The variable foo is initialized, all you are doing is initializing a variable with another initialized variable. It's no different from e.g.

int foo = 0;
auto bar = foo;

However, if you did e.g.

int* foo = nullptr;
auto bar = *foo;

that would be UB because you dereference a null pointer.

Also, Undefined behavior is, well, undefined... It might seem to run fine but in reality it's really not.