1、虚基类与虚继承

class A
{
public:

	virtual void func()
	{
		cout << "call A ::func()" << endl;
	}

	void operator delete(void* ptr)
	{
		cout << "operator delete ptr " << ptr << endl;
		free(ptr);

	}
private:
	int ma;

};

class B :virtual public A
{
public:
	virtual void func()
	{
		cout << "call B ::func()" << endl;
	}

	void* operator new(size_t size)
	{
		void* p = malloc(size);
		cout << "operator new p:" << p << endl;
		return p;
	}
private:
private:
	int mb;
};

/*
A a;4
B b:8;ma,mb;
*/


int main()
{
	//基类指针指向的派生类对象，永远指向派生类的地址
	B b;
	A* p = &b; //栈上自己会析构
	//A* p = new B();
	cout << "mian p :" << p << endl;
	p->func();
	//delete p;
	return 0;

	/*
	vbptr
	*p 释放了从这边开始 释放出错
	vfptr
	*/
}

2、菱形继承的问题

解决方法：虚继承

虚继承之后报错：
严重性 代码 说明 项目 文件 行 禁止显示状态 详细信息
错误 C2512 “A::A”: 没有合适的默认构造函数可用 Primer_cpp5 P:\qiniu_basic_learn\first_parase\Primer_cpp5\test.cpp 678
因为ma靠近d了，需要d自己初始化
代码：

/*多重继承
菱形继承的问题


*/

class A
{
public:
	A(int data) :ma(data) { cout << "A()" << endl; }
	~A() { cout << "~A()" << endl; }
protected:
	int ma;
};

class B : virtual public  A
{
public:
	B(int data) :A(data), mb(data) { cout << "B()" << endl; }
	~B() { cout << "~B()" << endl; }

protected:
	int mb;
};

class C :virtual public A
{
public:
	C(int data) :A(data), mc(data) { cout << "C()" << endl; }
	~C() { cout << "~C()" << endl; }

protected:
	int mc;
};


class D :public B, public C
{
public:
	D(int data) :A(data), B(data), C(data), md(data) { cout << "D()" << endl; }
	~D() { cout << "~D()" << endl; }
protected:
	int md;
};
int main()
{
	D d(10);
	return 0;
}

3、四种类型的转换

class Base
{
public:
	virtual void func() = 0;
};

class Derive1 :public Base
{
public:
	void func() { cout << "call Dervivel::func" << endl; }
};

class Derive2 :public Base
{
public:
	void func() { cout << "call Derive2::func" << endl; }
	//sDerive2实现新功能的API接口函数
	void derive02func()
	{
		cout << "call Derive2::derive02func" << endl;
	}
};

void showFunc(Base* p)
{
	//dynamic_cast会检查p是否指向的是一个Derive2类型的对象
	//p->vfptr->vftable  RTTI信息 如果是，dynamic_cast转型成功
	//返回Derive2对象的地址，给p2，否则返回nullptr
	Derive2* p2 = dynamic_cast<Derive2*>(p);
	if (p2 != nullptr)
	{
		p2->derive02func();
	}
	else
	{
		p->func(); //动态绑定  *p的类型 Derive2 derive02func

	}
}
int main()
{

	Derive1 d1;
	Derive2 d2;
	showFunc(&d1);
	showFunc(&d2);
	//const int a = 10;
	//int* p1 = (int*)&a;
	//int* p2 = const_cast<int*>(&a);
	//cout << *p2 << endl;


	//int b = const_cast<int>(a); 不支持必须是指针或者引用类型
	//int& b = const_cast<int&>(a);
	//cout << b << en dl;

	/*int a = 95;
	char b = static_cast<int>(a);
	cout << b << endl;*/
	//基类 《=》派生类 能不能用static_cast
	//int* p = nullptr;
	//double* b = (double*)p;
	return 0;
}