C++重载输入输出运算符重载在VC6.0中通不过编译

#include <iostream>
using namespace std;

class CBase
{
private:
 int m_a;
protected:
 int m_pp;
public:
 CBase(int a,int pp): m_a(a),m_pp(pp){}
 friend ostream& operator<<(ostream &out, const CBase &b);
};

ostream& operator<<(ostream &out, const CBase &b)
{
 out<<b.m_a<< " "<<b.m_pp<<endl;
 return out;
}

编译时，却提示

error C2248: 'm_a: cannot access private member declared in class CBase

error C2248: 'm_pp: cannot access private member declared in class CBase

 

这就奇怪了，友元函数不是能访问类的私有成员变量吗？怎么就不行了。

后来得知，原来我用的是VC++6.0编译器，在vs2005上就没问题了。或者把头文件包含写成

#include <iostream.h>

//using namespace std

就可以了。