C++——派生类的构造函数实例

1、简单的派生类构造函数

声明形式：派生类构造函数名（总参数列表）：基类构造函数名（参数列表）{派生类中新增加成员初始化语句}

#include<iostream>
#include<string>
using namespace std;
class student
{
  public:
     student(int n=0,string nam="null",char s='F'):num(n),name(nam),sex(s){}
     ~student(){}
     void show();
  protected:
     int num;
     string name;
     char sex;
};

void student::show()
{
    cout<<num<<" "<<name<<" "<<sex<<endl;
}

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(){}
        void show1();
     private:
        int age;
        string add;
};

void student1::show1()
{    cout<<"==========================================="<<endl;
     cout<<"    num:"<<num<<endl;
     cout<<"   name:"<<name<<endl;
     cout<<"    sex:"<<sex<<endl;
     cout<<"    age:"<<age<<endl;
     cout<<"address:"<<add<<endl;
}

int main()
{
     student1 s(10001,"zhangtong",'M',25,"Wuxi NewDistrict ZhongShanRoad 8#");
     s.show();
     s.show1();
     return 0;
}

2、含子对象的派生类构造函数

声明形式：派生类构造函数名（总参数列表）：基类构造函数名（参数列表），子对象名（参数列表）{派生类中新增加成员初始化语名句}

#include<iostream>
#include<string>
using namespace std;
class student
{
  public:
     student(int n=0,string nam="null",char s='F'):num(n),name(nam),sex(s){}
     ~student(){}
     void show();
  protected:
     int num;
     string name;
     char sex;
};

void student::show()
{
     cout<<"    num:"<<num<<endl;
     cout<<"   name:"<<name<<endl;
     cout<<"    sex:"<<sex<<endl;
}

class student1:public student
{
     public:
        student1(int n,string nam,char s,int n1,string nam1,char s1,int a,string ad):student(n,nam,s),monitor(n1,nam1,s1),age(a),add(ad){}
        ~student1(){}
        void show1();
     private:
        student monitor;
        int age;
        string add;
};

void student1::show1()
{    cout<<"This Student is:"<<endl;
     show();
     cout<<"    age:"<<age<<endl;
     cout<<"address:"<<add<<endl<<endl;
     cout<<"The Monitor is:"<<endl;
     monitor.show();
}

int main()
{
     student1 s(10001,"zhangtong",'M',10008,"limeng",'F',25,"Wuxi NewDistrict ZhongShanRoad 8#");
     s.show1();
     return 0;
}

运行结果：
This Student is:
    num:10001
   name:zhangtong
    sex:M
    age:25
address:Wuxi NewDistrict ZhongShanRoad 8#

The Monitor is:
    num:10008
   name:limeng
    sex:F
Press any key to continue...


3、多层派生时的构造函数

#include<iostream>
#include<string>
using namespace std;
class student
{
  public:
     student(int n=0,string nam="null"):num(n),name(nam){}
     ~student(){}
     void show();
  protected:
     int num;
     string name;
};

void student::show()
{
     cout<<"num : "<<num<<endl;
     cout<<"name: "<<name<<endl;
}

class student1:public student
{
     public:
        student1(int n,string nam,int a):student(n,nam),age(a){}
        ~student1(){}
        void show1();
     protected:
        int age;
};

void student1::show1()
{    cout<<"This Student is:"<<endl;
     show();
     cout<<"age : "<<age<<endl;
}

class student2:public student1
{
     public:
         student2(int n,string nam,int a,float s):student1(n,nam,a),score(s){}
         void show2();
     private:
         float score;
};

void student2::show2()
{
     show1();
     cout<<"score: "<<score<<endl;
}

int main()
{
     student2 s2(10001,"zhangtong",25,98.52);
     s2.show2();
     return 0;
}

    说明：如果在基类或子对象中定义了带参数的构造函数，则在派生类中必须显式地定义派生类构造函数，并写出基类或子对象
的构造函数及参数表。


习题：
有以下程序，请写出运行结果：（注意构造函数的用法！）

#include<iostream>
using namespace std;
class A
{
  public:
     A(){a=0;b=0;}
     A(int i){a=i;b=0;}
     A(int i,int j){a=i;b=j;}
     void display(){cout<<"a="<<a<<" "<<"b="<<b<<" ";}
  private:
     int a,b;
};
class B:public A
{
   public:
      B(){c=0;}
      B(int i):A(i){c=0;}
      B(int i,int j):A(i,j){c=0;}
      B(int i,int j,int k):A(i,j),c(k){}
      void display1()
          {
             display();
             cout<<"c="<<c<<endl;
          }
   private:
      int c;
};

int main()
{
   B b1;
   B b2(1);
   B b3(1,3);
   B b4(1,3,5);
   b1.display1();
   b2.display1();
   b3.display1();
   b4.display1();
   return 0;
}


运行结果：

a=0 b=0 c=0
a=1 b=0 c=0
a=1 b=3 c=0
a=1 b=3 c=5
Press any key to continue...