Is it OK to have a nested iterator like the following?
for (vector<type>::iterator i = list.begin(); i != list.end(); ++i) {
for (vector<type>::iterator j = i; j != list.end(); ++j) {
...
}
}
Note that j starts at i, and not list.begin(). Since the iterator is random access, can I guarantee that both i and j will have the same order? is there a better way of doing this?
Your code is correct.
Both iterators will have the same order and incrementing j doesn't affect i as long as you don't make any operation that invalidates iterators (for example erasing from or pushing to vector).
This is absolutely fine as long as you don't do anything inside the loops that might invalidate iterators.
(As an aside, list is a questionable name for a std::vector in my opinion.)
That's perfectly fine. Random access doesn't mean random order. It means that you can jump through the container by using additive operators (+ and -) on your iterator. For example, with a random access iterator it, you can do it + 10. For an non-random access iterator, you would have to do it++ 10 times to achieve the same effect. (the std::advance function will encapsulate this for you though)
This should work fine. Vector stores elements in order, and both iterators will obey this order.
来源：https://stackoverflow.com/questions/14924612/c-nested-iterators