C++分析如何用虚析构与纯虚析构处理内存泄漏

#include <iostream>
#include <string>
using namespace std;
class Animal{
  public:
    Animal(){
        cout<<"Animal-构造"<<endl;
    }
      ~Animal(){
        cout<<"Animal-析构"<<endl;
    }
    virtual void Run()=0;  //纯虚函数无需实现，只需声明
};
class Cat:public Animal{
  public:
  string *s_name;
  Cat(string name){
      s_name = new string(name);//在堆区创建内存
      cout<<"Cat-构造"<<endl;
  }
  void Run()
  {
      cout<<*s_name<<"->"<<"Cat-Run"<<endl;
  }
  ~Cat(){
      cout<<"Cat-析构"<<endl;
      if(s_name!=NULL){
          delete s_name;
          s_name=NULL;
      }
  }
};
int main()
{
    Animal *a;
    a = new Cat("Tom");
    a->Run();
    delete a;   //父类指针析构的时候，不会调用子类析构函数
    return 0;
}

   virtual ~Animal(){
        cout<<"Animal析构"<<endl;
    }

class Animal{
  public:
    Animal(){
        cout<<"Animal-构造"<<endl;
    }
    //虚析构
     /*virtual ~Animal(){
        cout<<"Animal析构"<<endl;
    }*/
    //纯虚析构
    virtual ~Animal()=0;
    virtual void Run()=0;  //纯虚函数无需实现，只需声明
};
//需要有声明，也需要有实现
Animal::~Animal(){
    cout<<"纯虚析构"<<endl;
}