class A
{
public:
char * name;
};

template < class Key, class Compare = less<Key>,
           class Allocator = allocator<Key> > class set;

template<typename _Key, typename _Val, typename _KeyOfValue,
           typename _Compare, typename _Alloc>
    typename _Rb_tree<_Key, _Val, _KeyOfValue,
              _Compare, _Alloc>::iterator
    _Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::
    find(const _Key& __k)
    {
      iterator __j = _M_lower_bound(_M_begin(), _M_end(), __k);
      return (__j == end()
          || _M_impl._M_key_compare(__k, _S_key(__j._M_node))) ? end() : __j;
    }

struct comparator : std::binary_function<A,A,bool> {
   bool operator()( A const& lhs, A const& rhs ) const;
};

a == b  <==>  !(a < b) && !(b < a)

set<Item*> itemSet;

Item* item = new Item();

if (itemSet.count(item) == 0)
{
    std::cout<<"not found"
}
//or
if (itemSet.find(item) == itemSet.end())
{
    std::cout<<"not found"
}