掌握类模板配合友元函数的类内实现和类外实现。

全局函数类内实现：直接在类内声明友元函数即可（推荐使用这种）

#include <iostream>
#include <Windows.h>
#include <string>using namespace std;template<typename T1, typename T2>
class Person
{
private:T1 m_Name;T2 m_Age;
public:Person(T1 name, T2 age){m_Name = name;m_Age = age;}// 全局函数类内实现，直接声明为类的友元函数friend void showPerson(Person<T1, T2> person){cout << "姓名：" << person.m_Name << " 年龄：" << person.m_Age << endl;}
};void test()
{Person<string, int> p("张三", 18); showPerson(p);
}int main(void)
{test();system("pause");return 0;
}

全局函数类外实现：需要让编译器提前知道全局函数的存在

#include <iostream>
#include <Windows.h>
#include <string>using namespace std;template<typename T1, typename T2>
class Person;template<typename T1, typename T2>
void showPerson(Person<T1, T2> person);template<typename T1, typename T2>
class Person
{
private:T1 m_Name;T2 m_Age;
public:Person(T1 name, T2 age){m_Name = name;m_Age = age;}// 全局函数类外实现，需要让编译器提前知道全局函数的存在// 添加空模板参数列表 <>friend void showPerson<>(Person<T1, T2> person);
};template<typename T1, typename T2>
void showPerson(Person<T1, T2> person)
{cout << "姓名：" << person.m_Name << " 年龄：" << person.m_Age << endl;
}void test()
{Person<string, int> p("张三", 18); showPerson(p);
}int main(void)
{test();system("pause");return 0;
}