为使程序中某些特殊函数或类可以访问到私有属性，采用友元技术
.1全局函数做友元
将全局函数声明前加friend 放在类内即可
class Person {
friend void test(Person &p); //该全局函数可访问私有属性b
public:
private:
int b;
};
.2 类做友元
class Person {
//友元声明，fri类可以访问本类的私有属性
friend class fri;
public:
Person() {
name = "zzh";
nickname = "zc";
}
public:
string name;
private:
string nickname;
};
class fri {
public :
fri() {
p = new Person; //在堆区为Person指针开辟内存空间
}
void acknow() {
cout << "姓名：" << p->name << endl;
cout << "绰号：" << p->nickname << endl; //调用私有属性 需要friend声明
}
private:
Person * p; //一个指向Person的指针
};
void test( ) {
fri wang;
wang.acknow();
}
.3成员函数作友元 + （成员函数类外实现的规范）
只需在函数声明加上作用域即可 类名::
#include <iostream>
#include <string >
using namespace std;
class Person;
class fri {
public :
fri ();
void acknow1(); //允许访问私有属性
void acknow2(); //不允许访问私有属性
private:
Person * p;
};
class Person {
friend void fri::acknow1();
public:
Person();
string name;
private:
string nickname;
};
//类外成员函数实现
fri::fri() {
p=new Person;
}
Person::Person() {
name = "zzh";
nickname = "zc";
}
void fri::acknow1() {
cout << "姓名：" << p->name << endl;
cout << "绰号：" << p->nickname << endl;
}
void fri::acknow2(){
cout << "姓名：" << p->name << endl;
//cout << "绰号：" << p->nickname << endl;
}
void test( ) {
fri wang;
wang.acknow1();
wang.acknow2();
}
int main() {
test();
system("pause");
return 0;
}
