C++ 左移重载的 套路

.

必须全局方式

要用到友元

用到引用

#include 
using namespace std;
class Person
{
    friend ostream& operator<<(ostream& out, const Person& p);
private :
    int m_A;
    int m_B;
public:    
    Person(int a, int b) :m_A(a), m_B(b) {};
};
// 左移重载 必须全局方式，成员方式实现不了
ostream& operator<<(ostream &out,const Person &p)
{
    out << p.m_A << " " << p.m_B << endl;
    return out;
}
int main()
{
    Person p(1,2);

    cout << p << endl;
    return 0;
}