Question

In an algorithm I’m currently implementing, I need to manipulate a std::list of struct T.
T holds a reference to another instance of T, but this reference can also be “unassigned”.
At first, I wanted to use a pointer to hold this reference, but using an iterator instead makes it easier to remove from the list.

My question is : how to represent the equivalent to null pointer with my iterator?

I read general solution is to use myList.end(), but in my case, I need to test whether the iterator is “null” or not, and I may add or remove elements to the list between the moment when I store the iterator and the moment I remove it from list… Should I make the iterator point to a known list containing the “null” element? Or is there a more elegant solution?

Answer 1

According to this (emphasis by me):

Compared to the other base sequence
containers (vector and deque), lists
are the most efficient container doing
insertions at some position other than
the beginning or the end of the
sequence, and, unlike in these, all of
the previously obtained iterators and
references remain valid after the
insertion and refer to the same
elements they were referring before.

The same applies to erasure (with the obvious exception of iterators referring to a deleted element becoming invalidated). So yes, obtaining end() will always point to the same “invalid” element and should be safe to use.