Re: Problem with defining operator<< for std::ostream_iterator

I cannot compile the code which defines a std::map type consisting of
built in types and operator<< overload for std::map::value_type.
See the code below - I attach a full example.

Note: if I define map type with my new type (structure) everything is
OK. All compileres I've cheked report an error so I think it is a
problem with my code.

#include <algorithm>
#include <cstddef>
#include <fstream>
#include <iterator>
#include <map>

class A
{
        struct S // behavior similar to built-in int
        {
                int i;
                S( int _i ) : i( _i ) {}
        };

        typedef std::map< int, int > Map1;
        typedef std::map< int, S > Map2;

// the function below cannot be found by
// std::ostream_iterator< Map1::value_type >
friend std::ostream &operator<<(
  std::ostream &_ostr,
  const Map1::value_type &_value
)
  {
    return _ostr << _value.first << ' ' << _value.second;
  }