C++ Standard: Unexpected const_iterator in multiset

Question

I recently ran into an odd issue where I\'d get a const_iterator instead of the expected iterator when iterating through a multiset. It turned out

Answer 1

How to fool the compiler for std::set::iterator?

I have struct

struct _item {
  int a;
  int b;
  bool operator <(const _item& x) const {return a

I want change only member b (b is irrelevant for sorting in set, only member a is compared).

std::set<_item> data;
std::set<_item>::iterator iter=data.begin();
iter->b=0;  // error !!!

Avada Kedavra !

struct _item {
  int a;
  int b;
  _item* self;
  _item() {self=this;} 
  bool operator <(const _item& x) const {return aself->b=0; // Success !! Tested on VC10

Of course more C + + correctly

struct _item {
  int a;
  int b;
 private:
  _item* self;
 public:
  _item() {self=this;} 
  bool operator <(const _item& x) const {return ab;}
};
std::set<_item> items;
std::set<_item>::iterator iter=items.begin();
iter->bReference()=0; // Success !! Tested on VC1