关于子对象的派生类的一个小迷惑

[老猫也很爱吃鱼]

请问大家，为什么书上一个正常派生类和基类需要写析构函数，而包含子对象的派生类和基类的构造函数就不用写析构函数了呢？？？求指点

[转角天边]

都要写，没写只是用编译器默认生成的

[老猫也很爱吃鱼]

 class student
 {
public :
        student(int n,string nam,char s):num(n),name(nam),sex(s){}
        ~student(){}//派生类析构函数
protected :
        int num;
        string name;//c++字符串类型
        char sex;
};
class student1:public student
{
public :
        student1(int n,string nam,char s,int a,string ad):student(n,nam,s)
        {
                age=a;
                add=ad;
        }
        student1(int n,string nam,char s,int a,string ad):student(n,nam,s),age(a),add(ad){}
        void show();
        ~student1(){}//派生类析构函数
private :
        int age;
        string add;
};

---------------------------------------------------------------------------------------------------------------------------------------------------------

#include <iostream>
#include <string>
using namespace std;
class student
{
public :
       student(int n,string nam):num(n),name(nam){}
       void dis();
protected:
        int num;
        string name;
};
void student::dis()
{
        cout<<num<<endl<<name<<endl;
}
class student1: public student
{
public :
        student1(int n,string nam,int n1,string nam1,int a,string ad):student(n,nam),monitor(n1,nam1),age(a),add(ad){}
        void dis_()
        {
            cout<<age<<endl<<add<<endl;
            dis();
        }
private :
        student monitor;
        int age;
        string add;
};

请问这两个代码为什么一个需要写一个不需要写呢

[paschen]

引用 4 楼 weixin_35755166 的回复:

 class student
 {
public :
        student(int n,string nam,char s):num(n),name(nam),sex(s){}
        ~student(){}//派生类析构函数
protected :
        int num;
        string name;//c++字符串类型
        char sex;
};
class student1:public student
{
public :
        student1(int n,string nam,char s,int a,string ad):student(n,nam,s)
        {
                age=a;
                add=ad;
        }
        student1(int n,string nam,char s,int a,string ad):student(n,nam,s),age(a),add(ad){}
        void show();
        ~student1(){}//派生类析构函数
private :
        int age;
        string add;
};

---------------------------------------------------------------------------------------------------------------------------------------------------------

#include <iostream>
#include <string>
using namespace std;
class student
{
public :
       student(int n,string nam):num(n),name(nam){}
       void dis();
protected:
        int num;
        string name;
};
void student::dis()
{
        cout<<num<<endl<<name<<endl;
}
class student1: public student
{
public :
        student1(int n,string nam,int n1,string nam1,int a,string ad):student(n,nam),monitor(n1,nam1),age(a),add(ad){}
        void dis_()
        {
            cout<<age<<endl<<add<<endl;
            dis();
        }
private :
        student monitor;
        int age;
        string add;
};

请问这两个代码为什么一个需要写一个不需要写呢

上面的也可以不写

[paschen]

如果不写编译器会生成一个默认的

[qq_32953509]

那要看你用没用动态变量，用了就要重写，没用一般系统有默认的