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
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
The elements of the set will be in sorted order. If you are allowed to modify an element, then this sorting order can not be maintained. Hence you can not modify the item. You need to erase the existing element and insert a new one.
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 ยง 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