Question

I need help understanding some C++ operator overload statements. The class is declared like this:

template <class key_t, class ipdc_t> class ipdc_map_template_t : public ipdc_lockable_t {     ...     typedef map<key_t,             ipdc_t*,             less<key_t>> map_t;     ... 

The creator of the class has created an iterator for the internal map structure:

struct iterator : public map_t::iterator {     iterator() {}     iterator(const map_t::iterator & it)         : map_t::iterator(it) {}     iterator(const iterator & it)         : map_t::iterator(             *static_cast<const map_t::iterator *>(&it)) {}     operator key_t() {return ((this->operator*()).first);}           // I don't understand this.     operator ipdc_t*() const {return ((this->operator*()).second);}  // or this.  }; 

And begin() and end() return the begin() and end() of the map:

iterator begin() {IT_ASSERT(is_owner()); return map.begin();} iterator end() {return map.end();} 

My question is, if I have an iterator, how do I use those overloads to get the key and the value?

ipdc_map_template_t::iterator iter;     for( iter = my_instance.begin();              iter != my_instance.end();          ++iter )     {         key_t my_key = ??????;         ipdc_t *my_value = ??????;      } 

Answer 1

These are typecast operators, so you can do this:

{     key_t   key = iter;     ipdc_t *val = iter; } 

Or, since ipdc_map_template::iterator is a subclass of std::map::iterator, you can still use the original accessors (which I find more readable):

{     key_t   key = (*iter).first;     ipdc_t *val = (*iter).second;      // or, equivalently     key_t   key = iter->first;     ipdc_t *val = iter->second;  }