C++类与对象深入之静态成员与友元及内部类详解

class Person
{
public:
	static int m_A; //静态成员变量
private:
	static int m_B; //静态成员变量也是有访问权限的
};
int Person::m_A = 10;
int Person::m_B = 10;
void test01()
{
	//静态成员变量两种访问方式
	//1、通过对象
	Person p1;
	p1.m_A = 100;
	cout << "p1.m_A = " << p1.m_A << endl;
	Person p2;
	p2.m_A = 200;
	cout << "p1.m_A = " << p1.m_A << endl; //共享同一份数据
	cout << "p2.m_A = " << p2.m_A << endl;
	//2、通过类名
	cout << "m_A = " << Person::m_A << endl;
	//cout << "m_B = " << Person::m_B << endl; //私有权限访问不到
}
int main() {
	test01();
	system("pause");
	return 0;
}

class Person
{
public:
	static void func()
	{
		cout << "func调用" << endl;
		m_A = 100;
		//m_B = 100; //错误，不可以访问非静态成员变量
	}
	static int m_A; //静态成员变量
	int m_B; // 
private:
	//静态成员函数也是有访问权限的
	static void func2()
	{
		cout << "func2调用" << endl;
	}
};
int Person::m_A = 10;
void test01()
{
	//静态成员变量两种访问方式
	//1、通过对象
	Person p1;
	p1.func();
	//2、通过类名
	Person::func();
	//Person::func2(); //私有权限访问不到
}
int main() {
	test01();
	system("pause");
	return 0;
}

class A
{
public:
	A(){
		++_count1;
	}
	A(const A& aa){
		++_count2;
	}
	// 成员函数也可以是静态，static成员函数没有this指针
	static int GetCount1(){
		return _count1;
	}
	static int GetCount2(){
		return _count2;
	}
//private:
	// 静态成员变量属于整个类，所以类的所有对象
	static int _count1;
	static int _count2; // 声明
};
// 定义
int A::_count1 = 0;
int A::_count2 = 0;
A Func(A a)
{
	A copy(a);
	return copy;
}
int main()
{
	A a1;
	A a2 = Func(a1);
	cout << a1._count1 << endl;
	cout << a2._count1 << endl;
	cout << a1._count2 << endl;
	cout << a2._count2 << endl;
	cout << A::_count1 << endl;
	cout << A::_count2 << endl;
	cout << a1.GetCount1() << endl;
	cout << a2.GetCount2() << endl;
	cout << A::GetCount1() << endl;
	cout << A::GetCount2() << endl;
	system("pause");
	return 0;
}

class B
{
public:
	B(int b = 0)
		:_b(b)
	{}
	int _b;
};
class A
{
public:
	//A()//其实是编译器自己生产的默认构造函数用缺省值初始化
	//	:a(10)
	//	, b(20)
	//	, p((int*)malloc(4))
	//{}
	void Print()
	{
		cout << a << endl;
		cout << b._b << endl;
		cout << p << endl;
		cout << n << endl;
	}
private:
	// 非静态成员变量，可以在成员声明时给缺省值。
	int a = 10;
	B b = 20;//单参数的构造函数，支持隐式类型的转换
	int* p = (int*)malloc(4);
	static int n;
	//非静态成员变量定义在构造函数
	//静态在类外
};
int A::n = 0;
int main()
{
	A a;
	a.Print();
	system("pause");
	return 0;
}

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(){
		this->m_SittingRoom = "客厅";
		this->m_BedRoom = "卧室";
	}
public:
	string m_SittingRoom; //客厅
private:
	string m_BedRoom; //卧室
};
void goodGay(Building * building){
	cout << "好基友正在访问： " << building->m_SittingRoom << endl;
	cout << "好基友正在访问： " << building->m_BedRoom << endl;
}
void test01(){
	Building b;
	goodGay(&b);
}
int main(){
	test01();
	system("pause");
	return 0;
}

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类中私有内容
	friend class goodGay;
public:
	Building();
public:
	string m_SittingRoom; //客厅
private:
	string m_BedRoom;//卧室
};
Building::Building(){
	this->m_SittingRoom = "客厅";
	this->m_BedRoom = "卧室";
}
goodGay::goodGay(){
	building = new Building;
}
void goodGay::visit(){
	cout << "好基友正在访问" << building->m_SittingRoom << endl;
	cout << "好基友正在访问" << building->m_BedRoom << endl;
}
void test01(){
	goodGay gg;
	gg.visit();
}
int main(){
	test01();
	system("pause");
	return 0;
}

class Building;//提前声明
class goodGay
{
public:
	goodGay();
	void visit(); //只让visit函数作为Building的好朋友，可以发访问Building中私有内容
	void visit2(); 
private:
	Building *building;
};
class Building
{
	//告诉编译器  goodGay类中的visit成员函数 是Building好朋友，可以访问私有内容
	friend void goodGay::visit();
public:
	Building();
public:
	string m_SittingRoom; //客厅
private:
	string m_BedRoom;//卧室
};
Building::Building(){
	this->m_SittingRoom = "客厅";
	this->m_BedRoom = "卧室";
}
goodGay::goodGay(){
	building = new Building;
}
void goodGay::visit(){
	cout << "好基友正在访问" << building->m_SittingRoom << endl;
	cout << "好基友正在访问" << building->m_BedRoom << endl;
}
void goodGay::visit2(){
	cout << "好基友正在访问" << building->m_SittingRoom << endl;
	//cout << "好基友正在访问" << building->m_BedRoom << endl;
}
void test01(){
	goodGay  gg;
	gg.visit();
}
int main(){  
	test01();
	system("pause");
	return 0;
}

// 内部类
class A
{
private:
	static int k;
	int h;
public:
	// 内部类
	class B // B天生就是A的友元
	{
	public:
		void foo(const A& a)
		{
			cout << k << endl;//OK
			cout << a.h << endl;//OK
		}
	private:
		int _b;
	};

	// A不是B的友元
	
};
int A::k = 1;
int main()
{
	A aa;
	cout << sizeof(A) << endl;
	A::B bb;
	return 0;
}