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nullptrDerive2* 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;
}