关于操作符重载的问题

在重载时为什么用#include<iostream>头文件重载<<,>>,==操作符时  明明已经把重载函数申明位友元了，但是在重载函数定义时却不能调用私有成员？把头文件改成#include<iostream.h> 注释掉using namespace std;就可以了呢？  但是在用了#include<iostream.h>后string类又出问题了    请高手指点

#include<iostream>
using namespace std;


class C
{
public:
    C():x(0),y(1){}
    friend ostream &operator << (ostream &,const C &);
private:
    int x;
    int y;
};

ostream &operator << (ostream &out,const C &c1)
{
    out<<c1.x<<" "<<c1.y<<endl;
    return out;
}

int main()
{
    C cc;
    cout<<cc;
    return 0;
}


编译错误
:\program files\microsoft visual studio\myprojects\iostream\io.cpp(17) : error C2248: 'x' : cannot access private member declared in class 'C'
        g:\program files\microsoft visual studio\myprojects\iostream\io.cpp(11) : see declaration of 'x'
g:\program files\microsoft visual studio\myprojects\iostream\io.cpp(17) : error C2248: 'y' : cannot access private member declared in class 'C'
        g:\program files\microsoft visual studio\myprojects\iostream\io.cpp(12) : see declaration of 'y'
g:\program files\microsoft visual studio\myprojects\iostream\io.cpp(24) : error C2593: 'operator <<' is ambiguous


但是头文件改成#include<iostream.h>却可以呢