目錄
在程序中有些私有屬性,也想讓類外特殊的一些函數或者類進行訪問,這就需要用到友元技術,友元的目的就是讓一個函數或者類訪問另外一個類中的私有成員。
友元的關鍵字爲friend
友元的三種實現方式:
- 全局函數做友元
- 類做友元
- 成員函數做友元
1 全局函數做友元
class Building
{
//goodGay全局函數是Building的好朋友,可以訪問Building 中的私有成員
friend void goodGay(Building* building);
public:
Building()
{
m_SittingRoom = "keting";
m_Bedroom = "woshi";
}
public:
string m_SittingRoom;
private:
string m_Bedroom;
};
//全局函數
void goodGay(Building *building)
{
cout << "好基友全局函數 正在訪問" << building->m_SittingRoom << endl;
cout << "好基友全局函數 正在訪問" << building->m_Bedroom << endl;
}
2 類做友元
class Building
{
friend class GoodGay;
public:
Building();
public:
string m_SittingRoom;
private:
string m_BadRoom;
};
//類外寫成員函數
Building::Building()
{
m_SittingRoom = "客廳";
m_BadRoom = "臥室";
}
class GoodGay
{
public:
GoodGay();
public:
void visit();//參觀函數,訪問Building中的屬性;
Building* building;
};
GoodGay::GoodGay()
{
building = new Building;
}
void GoodGay::visit()
{
cout << "好基友正在訪問你的" << building->m_SittingRoom << endl;
cout << "好基友正在訪問你的" << building->m_BadRoom << endl;
}
void test01()
{
GoodGay gg;
gg.visit();
}
int main()
{
test01();
system("pause");
return 0;
}
3 成員函數做友元
class Building;
class GoodGay
{
public:
GoodGay();
public:
void visit();//參觀函數,訪問Building中的屬性;
void visit1();
Building* building;
};
class Building
{
friend void GoodGay::visit();
public:
Building();
public:
string m_SittingRoom;
private:
string m_BadRoom;
};
Building::Building()
{
m_SittingRoom = "客廳";
m_BadRoom = "臥室";
}
GoodGay::GoodGay()
{
building = new Building;
}
void GoodGay::visit()
{
cout << "好基友正在訪問你的" << building->m_SittingRoom << endl;
cout << "好基友正在訪問你的" << building->m_BadRoom << endl;
}
void GoodGay::visit1()
{
cout << "好基友正在訪問你的" << building->m_SittingRoom << endl;
//cout << "好基友正在訪問你的" << building->m_BadRoom << endl;
}
Building的順序很重要,需要先聲明Building,再定義GoodGay