友元函数

全局函数做友元函数

友元函数目的是访问类中的私有成员属性

格式：

friend type 函数名 (参数...);
在类中加入 friend 函数声明

例：

class Building {
//void goodGay(Building* building)函数声明
    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
};
//友元函数 
void goodGay(Building* building)
{
cout<<building->m_SittingRoom<<endl;
cout<<building->m_BedRoom<<endl;
}

成员函数做友元函数

例：

class Building;

class goodGay
{
public:
    goodGay();
    void visit();
private:
    Building* building;

};
class Building {
//友元成员函数
    friend void goodGay::visit();
public:
    Building();

public:
    string m_SittingRoom;//客厅
private:
    string m_BedRoom;//卧室
};
goodGay::goodGay()
{
    building = new Building;
}
//构造
Building::Building()
{
    this->m_SittingRoom = "客厅";
    this->m_BedRoom = "卧室";
}
void goodGay::visit()
{
    cout << this->building->m_SittingRoom << endl;
    cout << this->building->m_BedRoom << endl;
}

友元类

格式：

在类中加入友元类声明

friend class classname;

例：

class Building;

class goodGay
{
public:
    goodGay();
    void visit();
private:
    Building* building;

};
class Building {
//友元类
    friend class goodGay;
public:
    Building();

public:
    string m_SittingRoom;//客厅
private:
    string m_BedRoom;//卧室
};
goodGay::goodGay()
{
    building = new Building;
}
//构造
Building::Building()
{
    this->m_SittingRoom = "客厅";
    this->m_BedRoom = "卧室";
}
void goodGay::visit()
{
    cout << this->building->m_SittingRoom << endl;
    cout << this->building->m_BedRoom << endl;
}