析构函数问题？

       //v.h
#include <iostream>
using namespace std;
#include<string.h>

class Person                                //基类：Person
{
protected:
    char *name;
public:
    Person(char *n)                        //构造函数
    {
        name=new char[strlen(n)+1];
        strcpy(name,n);
        cout<<"调用Person构造函数."<<endl;
    }
    virtual ~Person()    {                    //虚析构函数
        delete[]name;
        cout<<"调用Person析构函数."<<endl;
    }
    virtual void display()                    //虚函数
    {
        cout<<"姓名："<<name<<endl;
    }
};

class Student:public Person                //派生类：Student
{
protected:
    char *major;
public:
    Student(char *n,char *m):Person(n)      //派生类的构造函数
    {
        major=new char[strlen(m)+1];
        strcpy(major,m);
        cout<<"调用Student构造函数."<<endl;
    }
    ~Student()                            //派生类析构函数
    {
        delete[]major;
        cout<<"调用Student析构函数."<<endl;
    }
    void display()                        //虚函数
    {
        Person::display();
        cout<<"专业："<<major<<endl;
    }
};
         //g.cpp

#include "v.h"
void main()
{
    Person *p1=new Person("李清");   
    p1->display();
    delete p1;
    cout<<endl;

    Person *p2=new Student("田农","环境科学");   
    p2->display();
    delete p2;   
    cout<<endl;

    Student *p3=new Student("丁一健","计算机科学技术");     
    p3->display();
    delete p3;   
    cout<<endl;
}
析构函数不是自动调用的吗？那为什么要手动delete p1,p2,p3？那为何一手动删除p1，p2，p3会自动调用各个析构函数呢？



[ 本帖最后由 q345918550q 于 2010-4-27 10:10 编辑 ]