c++11 foreach syntax and custom iterator

Question

I am writing an iterator for a container which is being used in place of a STL container. Currently the STL container is being used in many places with the c++11 foreach syn

Answer 1

To be able to use range-based for, your class should provide const_iterator begin() const and const_iterator end() const members. You can also overload the global begin function, but having a member function is better in my opinion. iterator begin() and const_iterator cbegin() const are also recommended, but not required. If you simply want to iterate over a single internal container, that's REALLY easy:

template< typename Type>
class SomeSortedContainer{

    std::vector m_data; //we wish to iterate over this
    //container implementation code
public:
    typedef typename std::vector::iterator iterator;
    typedef typename std::vector::const_iterator const_iterator;

    iterator begin() {return m_data.begin();}
    const_iterator begin() const {return m_data.begin();}
    const_iterator cbegin() const {return m_data.cbegin();}
    iterator end() {return m_data.end();}
    const_iterator end() const {return m_data.end();}
    const_iterator cend() const {return m_data.cend();}
};    

If you want to iterate over anything custom though, you'll probably have to design your own iterators as classes inside your container.

class const_iterator : public std::iterator{
    typename std::vector::iterator m_data;
    const_iterator(typename std::vector::iterator data) :m_data(data) {}
public:
    const_iterator() :m_data() {}
    const_iterator(const const_iterator& rhs) :m_data(rhs.m_data) {}
     //const iterator implementation code
};

For more details on writing an iterator class, see my answer here.