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友元的三种实现

• 全局函数做友元
• 类做友元
• 成员函数做友元

#include <iostream>
#include <string>
using namespace std;//友元的三种实现
//
//* 全局函数做友元
//* 类做友元
//* 成员函数做友元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(){m_S = "客厅";m_B = "卧室";}
public:string m_S;
private:string m_B;
};void goodGay(Building* building)
{cout << "好基友正在访问：" << building->m_S << endl;cout << "好基友正在访问：" << building->m_B << endl;}
void test01()
{Building b;goodGay(&b);
}int main()
{test01();return 0;
}

类做友元

#include <iostream>
#include <string>
using namespace std;//友元的三种实现
//
//* 全局函数做友元
//* 类做友元
//* 成员函数做友元
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类中的私有内容friend class goodGay;
public:Building();
public:string m_S;
private:string m_B;
};Building::Building()
{m_S = "客厅";m_B = "卧室";
}goodGay::goodGay()
{building = new Building;
}
void goodGay::visit()
{cout << "好基友正在访问" << building->m_S << endl;cout << "好基友正在访问" << building->m_B << endl;
}void test01()
{goodGay gg;gg.visit();
}int main()
{test01();return 0;
}

成员函数做友元

#include <iostream>
#include <string>
using namespace std;//友元的三种实现
//
//* 全局函数做友元
//* 类做友元
//* 成员函数做友元
class Building;
class goodGay
{public:goodGay();void visit();void visit2();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类中的私有内容friend void goodGay::visit();//friend void goodGay::visit2();public:Building();
public:string m_S;
private:string m_B;
};Building::Building()
{m_S = "客厅";m_B = "卧室";
}goodGay::goodGay()
{building = new Building;
}
void goodGay::visit()
{cout << "好基友正在访问" << building->m_S << endl;cout << "好基友正在访问" << building->m_B << endl;
}
void goodGay::visit2()
{cout << "好基友正在访问" << building->m_S << endl;//cout << "好基友正在访问" << building->m_B << endl; //-- 没有友元，没法访问
}
void test01()
{goodGay gg;gg.visit2();
}int main()
{test01();return 0;
}