C+=析构函数应当是虚函数，除非类不用作基数。

1. 

//基数student的析构函数不是vi
#include <iostream>
#include <stdio.h>
using namespace std;

class student{
public:
    student(){
        printf("%s constructor\n", __FUNCTION__);
    }
    ~student(){
        printf("%s destructor\n", __FUNCTION__);
    }
    //virtual void study();
private:
    string m_name;
};

class studentLeader:public student{
public:
    studentLeader() {
        printf("%s constructor\n", __FUNCTION__);
    }
    ~studentLeader(){
        printf("%s destructor\n", __FUNCTION__);
    }
    //virtual void study();
};

int main(int argc, char **argv)
{
    studentLeader *sl = new studentLeader();
    delete sl;
    return 0;
}

./a.out
student constructor
studentLeader constructor
~studentLeader destructor
~student destructor

出现问题了。
student的析构函数不是virtual,编译器对其使用静态联编,根据指针类型(student*)，只调用student的析构函数

int main(int argc, char **argv)
{
    student *s = new studentLeader();
    delete s;
    return 0;
}

./a.out
student constructor
studentLeader constructor

~student destructor

2. 基数的析构函数使用virtual
原则：析构函数应当是虚函数，除非类不用作基数。

#include <iostream>
#include <stdio.h>
using namespace std;

class student{
public:
    student(){
        printf("%s constructor\n", __FUNCTION__);
    }
    virtual ~student(){
        printf("%s destructor\n", __FUNCTION__);
    }
    //virtual void study();
private:
    string m_name;
};

class studentLeader:public student{
public:
    studentLeader() {
        printf("%s constructor\n", __FUNCTION__);
    }
    ~studentLeader(){
        printf("%s destructor\n", __FUNCTION__);
    }
    //virtual void study();
};

int main(int argc, char **argv)
{
    //指针类型是基数
    student *s = new studentLeader();
    delete s;
    return 0;
}

./a.out
student constructor
studentLeader constructor
~studentLeader destructor //关键
~student destructor