友元
关键字:friend
友元的目的:让友元的函数或类能够访问本类中的private变量或函数。
- 全局函数做友元
friend 返回值 函数(参数);
例:friend int swap(int &a, int &b);
- 类做友元
friend class 类名;
例:friend class student;
- 成员函数做友元
friend 返回值 类名::函数名(参数);
例如: friend void student::visit(int a);
一、全局函数做友元
class Building { //告诉编译器 goodGay全局函数 是 Building类的好朋友,可以访问类中的私有内容 friend void goodGay(Building * building); public: Building() { this->m_SittingRoom = "客厅"; this->m_BedRoom = "卧室"; } public: string m_SittingRoom; //客厅 private: string m_BedRoom; //卧室 }; void goodGay(Building * building) { cout << "好基友正在访问: " << building->m_SittingRoom << endl; cout << "好基友正在访问: " << building->m_BedRoom << endl; } void test01() { Building b; goodGay(&b); } int main(){ test01(); system("pause"); return 0; }
二、类做友元
class Building; class goodGay { public: goodGay(); void visit(); private: Building *building; }; class Building { //告诉编译器 goodGay类是Building类的好朋友,可以访问到Building类中私有内容 friend class goodGay; public: Building(); public: string m_SittingRoom; //客厅 private: string m_BedRoom;//卧室 }; Building::Building() { this->m_SittingRoom = "客厅"; this->m_BedRoom = "卧室"; } goodGay::goodGay() { building = new Building; } void goodGay::visit() { cout << "好基友正在访问" << building->m_SittingRoom << endl; cout << "好基友正在访问" << building->m_BedRoom << endl; } void test01() { goodGay gg; gg.visit(); } int main(){ test01(); system("pause"); return 0; }
三、成员函数做友元
class Building; class goodGay { public: goodGay(); void visit(); //只让visit函数作为Building的好朋友,可以发访问Building中私有内容 void visit2(); private: Building *building; }; class Building { //告诉编译器 goodGay类中的visit成员函数 是Building好朋友,可以访问私有内容 friend void goodGay::visit(); public: Building(); public: string m_SittingRoom; //客厅 private: string m_BedRoom;//卧室 }; Building::Building() { this->m_SittingRoom = "客厅"; this->m_BedRoom = "卧室"; } goodGay::goodGay() { building = new Building; } void goodGay::visit() { cout << "好基友正在访问" << building->m_SittingRoom << endl; cout << "好基友正在访问" << building->m_BedRoom << endl; } void goodGay::visit2() { cout << "好基友正在访问" << building->m_SittingRoom << endl; //cout << "好基友正在访问" << building->m_BedRoom << endl; } void test01() { goodGay gg; gg.visit(); } int main(){ test01(); system("pause"); return 0; }