Surprisingly, C++98 and C++11 didn’t say that you can compare a iterator with a const_iterator. This leads to LWG issue 179 and LWG issue 2263. Now in C++14, this is explicitly permitted by § 23.2.1[container.requirements.general]p7 In the expressions i == j i != j i < j i <= j i >= j i > … Read more
If nothing else, a const_iterator reads better, since it tells anyone reading the code “I’m just iterating over this container, not messing with the objects contained”. That’s a great big win, never mind any performance differences.
There is a solution with constant time complexity in C++11: for any sequence, associative, or unordered associative container (including all of the Standard Library containers), you can call the range-erase member function with an empty range: template <typename Container, typename ConstIterator> typename Container::iterator remove_constness(Container& c, ConstIterator it) { return c.erase(it, it); } The range-erase member … Read more
There is no performance difference. A const_iterator is an iterator that points to const value (like a const T* pointer); dereferencing it returns a reference to a constant value (const T&) and prevents modification of the referenced value: it enforces const-correctness. When you have a const reference to the container, you can only get a … Read more
It’s quite simple. Say I have a vector: std::vector<int> vec; I fill it with some data. Then I want to get some iterators to it. Maybe pass them around. Maybe to std::for_each: std::for_each(vec.begin(), vec.end(), SomeFunctor()); In C++03, SomeFunctor was free to be able to modify the parameter it gets. Sure, SomeFunctor could take its parameter … Read more
Choose type of iterator which fits your container: input, output, forward etc. Use base iterator classes from standard library. For example, std::iterator with random_access_iterator_tag.These base classes define all type definitions required by STL and do other work. To avoid code duplication iterator class should be a template class and be parametrized by “value type”, “pointer … Read more
http://www.cplusplus.com/reference/std/iterator/ has a handy chart that details the specs of § 24.2.2 of the C++11 standard. Basically, the iterators have tags that describe the valid operations, and the tags have a hierarchy. Below is purely symbolic, these classes don’t actually exist as such. iterator { iterator(const iterator&); ~iterator(); iterator& operator=(const iterator&); iterator& operator++(); //prefix increment … Read more