C++:友元

友元

(1)全局函数做友元

class Building {
	//添加友元，即可访问全局函数中的私有属性
	friend void goodGay(Building *building);
public:
	Building() {
		m_SittingRoom = "客厅";
		m_BedRoom = "卧室";
	}
public:
	string m_SittingRoom;
private:
	string m_BedRoom;
};

void goodGay(Building *building) {
	cout << "全局函数 正在访问：" << building->m_SittingRoom << endl;
	cout << "全局函数 正在访问：" << building->m_BedRoom << endl;
}

void test() {
	Building building;
	goodGay(&building);
}
int main() {
	test();
}

运行结果：

全局函数 正在访问：客厅
全局函数 正在访问：卧室

(2)类做友元

class Building {
	friend class GoodGay;
public:
	Building(); //构造函数
	string m_SittingRoom; //客厅

private:
	string m_BedRoom; //卧室
};

//类外写成员函数
Building::Building() {
	m_SittingRoom = "客厅";
	m_BedRoom = "卧室";
}

class GoodGay {
public:
	GoodGay();
	void visit(); //访问Building中的属性

	Building *building;

};

GoodGay::GoodGay() {
	//创建建筑物对象
	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 test() {
	GoodGay gg;
	gg.visit();
}

int main() {
	test();
}

运行结果：

好基友正在访问客厅
好基友正在访问卧室

(2)成员函数做友元

class Building;

class GoodGay {
public:
	GoodGay(); //构造函数
	void visit1(); //访问Building中的属性
	void visit2();

private:
	Building *building;

};

class Building {
	friend void GoodGay::visit1();
public:
	Building(); //构造函数
	string m_SittingRoom; //客厅

private:
	string m_BedRoom; //卧室
};

//类外写成员函数
Building::Building() {
	m_SittingRoom = "客厅";
	m_BedRoom = "卧室";
}



GoodGay::GoodGay() {
	//创建建筑物对象
	building = new Building;
}

void GoodGay::visit1() {
	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 test() {
	GoodGay gg;
	gg.visit1();
}
int main() {
	test();
}

运行结果：

好基友正在访问客厅
好基友正在访问卧室