Question about overloading operator >> in STL.

[George2]

Hi, everyone!

I meet with some trouble when debugging the following
codes dealing with overloading operator >> in STL.
I have tried my best to resolve it but still failed.
My IDE is VC6.0.

Source Codes:

--------
#include <iostream>
#include <map>
#include <set>

using namespace std;

class employee_data {
public:
	employee_data() : name (""), skill(0), salary(0) {}
	employee_data(string n, int s, long sa) : 
	   name (n), skill (s), salary (sa) {}

	string	name;
	int 	skill;
	long	salary;

   friend ostream& operator<< (ostream& os, const employee_data& e);
};

ostream& operator<< (ostream& os, const employee_data& e) {
	os << "employee: " << e.name << " " << e.skill << " " << e.salary;
	return os;
}

class employee {
public: 
   employee (int i, employee_data e) :
      identification_code (i), description (e) {}

	int identification_code;	// key expression to identify an employee
	employee_data description;

	bool operator< (const employee& e) const {
	  return identification_code < e.identification_code; }
};

int main()
{
	set  <employee, less<employee> > employee_set;

	multiset  <employee, less<employee> > employee_multiset;

	employee_data ed1 ("john", 1, 5000);
	employee_data ed2 ("tom", 5, 2000);
	employee_data ed3 ("mary", 2, 3000);

	employee e1 (1010, ed1); 
	employee e2 (2020, ed2); 
	employee e3 (3030, ed3); 

	pair<set <employee, less<employee> >::iterator, bool>
		result = employee_set.insert (e1);

	if (result.second) cout << "insert ok"; else cout << "not inserted";
	cout << endl << (*result.first).description.name << endl;

	result = employee_set.insert (e1);
	if (result.second) cout << "insert ok"; else cout << "not inserted";
	
	return 1;
}
--------

Error messages:
--------
C:\Program Files\Microsoft Visual Studio\MyProjects\testMap1\testMap1.cpp(22) : error C2679: binary '<<' : no operator

defined which takes a right-hand operand of type 'const class std::basic_string<char,struct std::char_traits<char>,class

std::allocator<char> >' (or there is no acceptable conversion)
C:\Program Files\Microsoft Visual Studio\MyProjects\testMap1\testMap1.cpp(56) : error C2679: binary '<<' : no operator

defined which takes a right-hand operand of type 'class std::basic_string<char,struct std::char_traits<char>,class

std::allocator<
char> >' (or there is no acceptable conversion)
--------

How to resolve them?


Thanks in advance,
George

[Gabriel: added CODE tags]