深入解析C++中多态性和虚函数使用原理

#include<iOStream>
using std::cout;
using std::endl;
class A{
public:
  void f() const{
    cout<<"class A's function"<<endl;
  }
};
class B : public A{
public:
  void f() const{
    cout<<"class B's function"<<endl;
  }
};
int main(){
  B b;
  A *ptr_a = &b;
  A &ref_a = b;
  ptr_a->f();//print: class A's function
  ref_a.f();//print: Class A's function
}

class A{
public:
  virtual void f() const{
    cout<<"class A's function"<<endl;
  }
};

class A{
public:
  virtual void do() = 0; 
};

void A::do(){
  //一些公共代码
}
class B : public A{
public:
  void do() {
    A::do();
    //其他代码
  }
};

#include<iostream>
using namespace std;
class Base1{
public:
  ~Base1(){cout<<"~Base1()"<<endl;}
};
class Base2{
public:
  virtual ~Base2(){cout<<"~Base2()"<<endl;}
};
class Derived1 : public Base1{
public:
  ~Derived1(){cout<<"~Derived1()"<<endl;}
};
class Derived2 : public Base2{
public:
  ~Derived2(){cout<<"~Derived2()"<<endl;}
};
int main(){
  Base1* pd1 = new Derived1();
  Base2* pd2 = new Derived2();
  delete pd1;
  delete pd2;
}

class A{
public:
  virtual ~A() = 0;
};
A::~A(){ }

class B:public A{
//不一定需要重定义析构函数，根据需要
}

#include<iostream>
using namespace std;
class Base{
public:
  virtual ~Base(){cout<<"~Base()"<<endl;f();}
  virtual void f(){cout<<"Base::f()"<<endl;}
};
class Derived : public Base{
public:
  ~Derived(){cout<<"~Derived()"<<endl;}
  void f(){cout<<"Derived::f()"<<endl;}
};
int main(){
  Base * pb = new Derived();
  delete pb;
}