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;
    }

    friend std::ostream &operator<<( std::ostream &_ostr, const
Map2::value_type &_value )
    {
        return _ostr << _value.first << ' ' << _value.second.i;
    }

    Map1 m_map1;
    Map2 m_map2;

public:
    A(
        const int *_keyStart,
        const int *_valueStart,
        const std::size_t _size
        )
    {
        for ( std::size_t i = 0; i < _size; i++ )
        {
            m_map1.insert( Map1::value_type( _keyStart[i], _valueStart[i] ) );
            m_map2.insert( Map2::value_type( _keyStart[i],
S( _valueStart[i] ) ) );
        }
    }

    ~A()
    {
        std::ofstream out( "test" );

        out << "#### Map1 ####" << std::endl;
                                // this call does not compile
        std::copy(
            m_map1.begin(),
            m_map1.end(),
            std::ostream_iterator< Map1::value_type >( out, "\n" )
            );

        out << "\n#### Map2 ####" << std::endl;
        std::copy(
            m_map2.begin(),
            m_map2.end(),
            std::ostream_iterator< Map2::value_type >( out, "\n" )
            );
    }
};

int main()
{
    int tab1[] = { 1, 3, 5, 2, 0 };
    int tab2[ sizeof tab1 / sizeof *tab1 ] = { 1, 2, 3, 4, 5 };

    A a( tab1, tab2, sizeof tab1 / sizeof *tab1 );
}