C++语言基础 例程 派生类的构造函数和析构函数

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一个简单派生类的定义

#include <iostream>
#include<cstring>
using namespace std;
class Student  //声明基类Student
{
public:
    Student(int n,string nam,char s):num(n),name(nam),sex(s) {}  //基类构造函数
    ~Student( ) { }                    //基类析构函数
    void show( )
    {
        cout<<"num: "<<num<<endl;
        cout<<"name: "<<name<<endl;
        cout<<"sex: "<<sex<<endl<<endl;
    }
protected:     //保护部分
    int num;
    string name;
    char sex ;
};

class Student1: public Student //声明派生类Student1
{
public:
    //在函数体中只对派生类新增的数据成员初始化
    //派生类构造函数
    Student1(int n,string nam,char s,int a,string ad):Student(n,nam,s),age(a),addr(ad) {}
    void show1( )
    {
        cout<<"num: "<<num<<endl;
        cout<<"name: "<<name<<endl;
        cout<<"sex: "<<sex<<endl;
        cout<<"age: "<<age<<endl;
        cout<<"address: "<<addr<<endl<<endl;
    }
    ~Student1( ) { }        //派生类析构函数
private:                    //派生类的私有部分
    int age;
    string addr;
};

int main( )
{
    Student1 stud1(10010,"Wang-li",'f',19,"115 Beijing Road,Shanghai");
    Student1 stud2(10011,"Zhang-fun",'m',21,"213 Shanghai Road,Beijing");
    Student stud3(20010,"He-xin",'m');
    stud1.show1( );         //输出第一个学生的数据
    stud2.show( );          //输出第二个学生的数据
    stud3.show( );          //输出第二个学生的数据
    return 0;
}

构造函数的写法

#include <iostream>
#include<string>
using namespace std;
class Student//声明基类Student
{
public:
    Student(int n,string nam,char s);   //基类构造函数
    ~Student( ) { }                    //基类析构函数
protected:                             //保护部分
    int num;
    string name;
    char sex ;
};

Student::Student(int n,string nam,char s)   //基类构造函数
{
    num=n;
    name=nam;
    sex=s;
}

class Student1: public Student    //声明派生类Student1
{
public:                           //派生类的公用部分
    Student1(int n,string nam,char s,int a,string ad);//声明
    void show( );
    ~Student1( ) { }        //派生类析构函数
private:                    //派生类的私有部分
    int age;
    string addr;
};

Student1::Student1(int n,string nam,char s,int a,string ad):Student(n,nam,s)
{
    age=a;                  //在函数体中只对派生类新增的数据成员初始化
    addr=ad;
}

void Student1::show( )
{
    cout<<"num: "<<num<<endl;
    cout<<"name: "<<name<<endl;
    cout<<"sex: "<<sex<<endl;
    cout<<"age: "<<age<<endl;
    cout<<"address: "<<addr<<endl<<endl;
}

int main( )
{
    Student1 stud1(10010,"Wang-li",'f',19,"115 Beijing Road,Shanghai");
    Student1 stud2(10011,"Zhang-fun",'m',21,"213 Shanghai Road,Beijing");
    stud1.show( );          //输出第一个学生的数据
    stud2.show( );          //输出第二个学生的数据
    return 0;
}

构造函数和析构函数执行的顺序

#include<iostream>
using namespace std;
class Base
{
protected:
    Base()
    {
        cout<<'A';
    }
    Base(char c)
    {
        cout<<c;
    }
};
class Derived: public Base
{
public:
    Derived(char c)
    {
        cout<<c;
    }
};
int main()
{
    Derived d1('B');
    return 0;
}

有子对象的派生类的构造函数

#include <iostream>
#include <string>
using namespace std;
class Student//声明基类
{
public:                                  //公用部分
    Student(int n, string nam ):num(n), name(nam) {} //基类构造函数，与例相同
    void display( )                           //成员函数，输出基类数据成员
    {
        cout<<"num:"<<num<<endl<<"name:"<<name<<endl;
    }
protected:                                //保护部分
    int num;
    string name;
};

class Student1: public Student              //声明公用派生类Student1
{
public:
    Student1(int n, string nam,int n1, string nam1,int a, string ad):
        Student(n,nam),monitor(n1,nam1),age(a),addr(ad) {}               //派生类构造函数
    void show( )
    {
        cout<<"This student is:"<<endl;
        display();                               //输出num和name
        cout<<"age: "<<age<<endl;                //输出age
        cout<<"address: "<<addr<<endl<<endl;     //输出addr
    }

    void show_monitor( )                        //成员函数，输出子对象
    {
        cout<<endl<<"Class monitor is:"<<endl;
        monitor.display( );                       //调用基类成员函数
    }
private:                                      //派生类的私有数据
    Student monitor;                          //定义子对象(班长)
    int age;
    string addr;
};

int main( )
{
    Student1 stud1(10010,"Wang-li",10001,"Li-sun",19,"115 Beijing Road,Shanghai");
    stud1.show( );                       //输出学生的数据
    stud1.show_monitor();                //输出子对象的数据
    return 0;
}

多层派生时的构造函数

#include <iostream>
#include<string>
using namespace std;
class Student//声明基类
{
public:                                  //公用部分
    Student(int n, string nam )            //基类构造函数
    {
        num=n;
        name=nam;
    }
    void display( )                           //输出基类数据成员
    {
        cout<<"num:"<<num<<endl;
        cout<<"name:"<<name<<endl;
    }
protected:                                //保护部分
    int num;                                //基类有两个数据成员
    string name;
};

class Student1: public Student               //声明公用派生类Student1
{
public:
    Student1(int n,string nam,int a):Student(n,nam)//派生类构造函数
    {
        age=a;
    }                         //在此处只对派生类新增的数据成员初始化
    void show( )                               //输出num，name和age
    {
        display( );                               //输出num和name
        cout<<"age: "<<age<<endl;
    }
private:                                   //派生类的私有数据
    int age;                                  //增加一个数据成员
};

class Student2:public Student1               //声明间接公用派生类Student2
{
public:
    //下面是间接派生类构造函数
    Student2(int n, string nam,int a,int s):Student1(n,nam,a)
    {
        score=s;
    }
    void show_all( )                              //输出全部数据成员
    {
        show( );                                    //输出num和name
        cout<<"score:"<<score<<endl;               //输出age
    }
private:
    int score;                                   //增加一个数据成员
};

int main( )
{
    Student2 stud(10010,"Li",17,89);
    stud.show_all( );                            //输出学生的全部数据
    return 0;
}