友元的目的：让一个函数或者类访问一个类中的私有成员
关键字： friend
1. 全局函数做友元
class Building
{
//goodFriend函数可以访问私有成员
friend void goodFriend(Building &build); //全局函数做友元
public:
string m_SittingRoom; //客厅
Building();
private:
string m_BedRoom; //卧室
};
Building::Building()
{
m_SittingRoom = "客厅";
m_BedRoom = "卧室";
}
//全局函数
void goodFriend(Building &build)
{
cout << "好朋友正在访问: " << build.m_SittingRoom << endl;
cout << "好朋友正在访问: " << build.m_BedRoom << endl;
}
2. 类做友元
class Building
{
//GoodFriend类做友元
friend class GoodFriend;
public:
string m_SittingRoom; //客厅
Building();
private:
string m_BedRoom; //卧室
};
Building::Building()
{
m_SittingRoom = "客厅";
m_BedRoom = "卧室";
}
////////////////////////////////////////////////
class GoodFriend
{
public:
GoodFriend();
Building * building;
void visit(); //访问building中的属性
private:
};
GoodFriend::GoodFriend()
{
//创建建筑物对象
building = new Building;
}
////////////////////////////////////////////////
void GoodFriend::visit()
{
cout << "好朋友类正在访问: " << this->building->m_SittingRoom << endl;
cout << "好朋友类正在访问: " << this->building->m_BedRoom << endl;
}
3. 成员函数做友元
class Building;
class GoodFriend
{
public:
GoodFriend();
void visit(); //访问building中的属性
Building * building;
};
class Building
{
//GoodFriend::visit()成员函数做友元
friend void GoodFriend::visit();
public:
string m_SittingRoom; //客厅
Building();
private:
string m_BedRoom; //卧室
};
GoodFriend::GoodFriend()//注意构造函数的位置，用到了Building类，再Building之后再实现
{
//创建建筑物对象
building = new Building;
}
Building::Building()
{
m_SittingRoom = "客厅";
m_BedRoom = "卧室";
}
void GoodFriend::visit()
{
cout << "好朋友类正在访问: " << this->building->m_SittingRoom << endl;
cout << "好朋友类正在访问: " << this->building->m_BedRoom << endl;
}
void test()
{
GoodFriend f1;
f1.visit();
}
