目录
1 全局函数做友元
2 类做友元
3 成员函数做友元
在程序中有些私有属性，也想让类外特殊的一些函数或者类进行访问，这就需要用到友元技术，友元的目的就是让一个函数或者类访问另外一个类中的私有成员。
友元的关键字为friend
友元的三种实现方式：
全局函数做友元类做友元成员函数做友元
1 全局函数做友元
class Building
{
//goodGay全局函数是Building的好朋友，可以访问Building 中的私有成员
friend void goodGay(Building* building);
public:
Building()
{
m_SittingRoom = "keting";
m_Bedroom = "woshi";
}
public:
string m_SittingRoom;
private:
string m_Bedroom;
};
//全局函数
void goodGay(Building *building)
{
cout << "好基友全局函数 正在访问" << building->m_SittingRoom << endl;
cout << "好基友全局函数 正在访问" << building->m_Bedroom << endl;
}
2 类做友元
class Building
{
friend class GoodGay;
public:
Building();
public:
string m_SittingRoom;
private:
string m_BadRoom;
};
//类外写成员函数
Building::Building()
{
m_SittingRoom = "客厅";
m_BadRoom = "卧室";
}
class GoodGay
{
public:
GoodGay();
public:
void visit();//参观函数，访问Building中的属性；
Building* building;
};
GoodGay::GoodGay()
{
building = new Building;
}
void GoodGay::visit()
{
cout << "好基友正在访问你的" << building->m_SittingRoom << endl;
cout << "好基友正在访问你的" << building->m_BadRoom << endl;
}
void test01()
{
GoodGay gg;
gg.visit();
}
int main()
{
test01();
system("pause");
return 0;
}
3 成员函数做友元
class Building;
class GoodGay
{
public:
GoodGay();
public:
void visit();//参观函数，访问Building中的属性；
void visit1();
Building* building;
};
class Building
{
friend void GoodGay::visit();
public:
Building();
public:
string m_SittingRoom;
private:
string m_BadRoom;
};
Building::Building()
{
m_SittingRoom = "客厅";
m_BadRoom = "卧室";
}
GoodGay::GoodGay()
{
building = new Building;
}
void GoodGay::visit()
{
cout << "好基友正在访问你的" << building->m_SittingRoom << endl;
cout << "好基友正在访问你的" << building->m_BadRoom << endl;
}
void GoodGay::visit1()
{
cout << "好基友正在访问你的" << building->m_SittingRoom << endl;
//cout << "好基友正在访问你的" << building->m_BadRoom << endl;
}
Building的顺序很重要，需要先声明Building，再定义GoodGay
