What's wrong with overloading of "<<"?

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C++

#include<vector>
#include<iostream>

class mytype
{
private:

	int cor[2];

public:

	mytype();
	mytype(int x , int y);
	
	~mytype(){}

	mytype (const mytype & m);
	mytype & operator = (const mytype & m);

	friend std::ostream & operator << (std::ostream os , const mytype & m);

};

mytype::mytype()
{

	cor[0]=0;
	cor[1]=0;

}

mytype::mytype(int x , int y)
{

	cor[0]=x;
	cor[1]=y;

}

mytype::mytype(const mytype & m)
{

	cor[0]=m.cor[0];
	cor[1]=m.cor[1];

}

mytype & mytype::operator = (const mytype & m)
{

	cor[0]=m.cor[0];
	cor[1]=m.cor[1];
	return * this;

}

std::ostream & operator << (std::ostream & os , const mytype & m)
{

	os << m.cor[0] << "," << m.cor[1];
	return os;

}

I overload "<<" with a friend fun in mytype class.But when I define it , the compiler say that I can't access the member of m. I don't know why! Who can tell me what's wrong with it?