Is it correct for comparing with an initialized value iterator?

Question

Does the following program perform undefined behavior?

#include <iostream>
#include <iterator>

int main(int argc, char* argv[])
{
    for (auto it = std::istream_iterator<std::string>(std::cin);
         it != std::istream_iterator<std::string>();
         ++it)
    {
        std::cout << *it << " ";
    }

    return 0;
}

This 4 year old question says they cannot be compared:

Iterators may also have special values ​​that are not associated with any container. [Example: after declaring an uninitialized pointer x (as for int * x;), x should always be considered that the singular value of the pointer. ] The results of most expressions are undefined for singular values; the only exception is the assignment of a non-singular value to an iterator that has a singular value.

But another answer for the C ++ 14 standard:

However, iterators initialized by initialization can compare and compare equal to other iterators with initialization values ​​of the same type.

Answer 1

.

istream_iterator - , , ++ 14, , . istream_iterator , . , (§24.6.1 [istream.iterator])

istream_iterator() - , , . [...]

. . , .

( ) ++ 14. , . . - . undefined ++ 14:

std::list<int> l;

if(l.begin() == std::list<int>::iterator())
    foo();
else 
    bar();