Keeping std::list iterators valid through insertion

Question

Note: This is not a question whether I should \"use list or deque\". It\'s a question about the validity of iterators in the face of insert().

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Answer 1

I was indeed being dense. The standard gives us all the tools we need. Specifically, the sequence container requirements 23.2.3/9 say:

The iterator returned from a.insert(p, i, j) points to the copy of the first element inserted into a, or p if i == j.

Next, the description of list::insert says (23.3.5.4/1):

Does not affect the validity of iterators and references.

So in fact if pos is my current iterator inside the list which is being consumed, I can say:

auto it = buf.insert(buf.end(), newdata.begin(), newdata.end());

if (pos == buf.end()) { pos = it; }

The range of new elements in my list is [it, buf.end()), and the range of yet unprocessed elements is [pos, buf.end()). This works because if pos was equal to buf.end() before the insertion, then it still is after the insertion, since insertion does not invalidate any iterators, not even the end.