c++继承与派生

继承的作用是减少代码冗余，通过协调来减少接口和界面。

1.派生类的定义

<1>吸收基类成员

<2>改造基类成员

一是依靠派生类的继承方式来控制基类成员的访问、二是对基类成员或成员函数的覆盖。

<3>添加新的成员

2.类的继承方式

 

<1>.公有继承

#include <iostream>
using namespace std;
class vehicle
{
private:
    float weight;
    int wheels;
public:
    vehicle(int in_wheels,float in_weight)
    {
        wheels=in_wheels;
        weight=in_weight;
    }
    int get_wheels()
    {
        return wheels;
    }
    float get_weight()
    {
        return weight;
    }

};
class car:public vehicle
{
private:
    int passenger_load;
public:
    car(int in_wheels,float in_weight,int people=5):vehicle(in_wheels,in_weight)
    {
        passenger_load=people;
    }
    int get_passenger()
    {
        return passenger_load;
    }
};
int main()
{
    car bm(4,100);
    cout<<bm.get_wheels()<<endl;
    cout<<bm.get_weight()<<endl;
    cout<<bm.get_passenger()<<endl;
    return 0;
}

结果：

4

100

5

<2>.私有继承

#include <iostream>
using namespace std;
class vehicle
{
private:
    float weight;
    int wheels;
public:
    vehicle(int in_wheels,float in_weight)
    {
        wheels=in_wheels;
        weight=in_weight;
    }
    int get_wheels()
    {
        return wheels;
    }
    float get_weight()
    {
        return weight;
    }

};
class car:private vehicle
{
private:
    int passenger_load;
public:
    car(int in_wheels,float in_weight,int people=5):vehicle(in_wheels,in_weight)
    {
        passenger_load=people;
    }
    int get_passenger()
    {
        return passenger_load;
    }
    int get_wheels()
    {
        return vehicle::get_wheels();
    }
    int get_weight()
    {
        return vehicle::get_weight();
    }
};
int main()
{
    car bm(4,100);
    cout<<bm.get_wheels()<<endl;
    cout<<bm.get_weight()<<endl;
    cout<<bm.get_passenger()<<endl;
    return 0;
}

结果：

4

100

5

<3>.保护继承

#include <iostream>
using namespace std;
class vehicle
{
private:
    int wheels;
protected:
    float weight;
public:
    vehicle(int in_wheels,float in_weight)
    {
        wheels=in_wheels;
        weight=in_weight;
    }
    int get_wheels()
    {
        return wheels;
    }
    float get_weight()
    {
        return weight;
    }

};
class car:protected vehicle
{
private:
    int passenger_load;
public:
    car(int in_wheels,float in_weight,int people=5):vehicle(in_wheels,in_weight)
    {
        passenger_load=people;
    }
    int get_passenger()
    {
        return passenger_load;
    }
    int get_wheels()
    {
        return vehicle::get_wheels();
    }
    int get_weight()
    {
        return weight;
    }
};
int main()
{
    car bm(4,100);
    cout<<bm.get_wheels()<<endl;
    cout<<bm.get_weight()<<endl;
    cout<<bm.get_passenger()<<endl;
    return 0;
}

结果：

4

100

5

 3.派生类的构造函数和析构函数

4.派生类对基类成员的继承

 通过访问声明调整访问域

<1>访问声明仅仅调整名字的访问，不可为它说明任何类型；成员函数在访问声明时，也不准说明任何参数

<2>对重载函数的访问声明将调整基类中具有该名得所有函数的访问域

<3>若派生类中具有与基类同名的函数，则基类中的此函数不能在派生类中进行访问声明

5.多重继承

<1>二义性和支配原则

作用域规则、支配规则

一个派生类中的名字将优先于它的基类中相同的名字

<2>赋值兼容原则

6.虚基类

例子：

#include <iostream>
using namespace std;
class Furniture{
public:
    Furniture(){
        cout<<"2333"<<endl;
    }
    void SetWeight(int i){
        weight=i;
    }
    int GetWeight(){
        return weight;
    }
protected:
    int weight;
};
class Bed:virtual public Furniture{
public:
    Bed(){
        cout<<"2444"<<endl;
    }
    void Sleep(){
        cout<<"Sleeping...
";
    }
};
class Sofa:virtual public Furniture{
public:
    Sofa(){
        cout<<"2555"<<endl;
    }
    void WatchTV(){
        cout<<"Watch TV
";
    }
};
class SleeerpSofa:public Bed,public Sofa{
public:
    SleeerpSofa():Sofa(),Bed(){
    }
    void FoldOut(){
        cout<<"Fold out the sofa. 
";
    }
};
int main(){
    SleeerpSofa ss;
    ss.SetWeight(20);
    cout<<ss.GetWeight()<<endl;
    return 0;
}

结果:

233

2444

2555

20

 7.类模板

理解类模板与模板类的关系:类模板+特定的数据类型=模板类

例题:

#include <iostream>
using namespace std;
template<class T>
class tem{
    T *data;
    int size;
public:
    tem(int);
    ~tem(){
        delete []data;
    }
    T& operator[](int i){
        return data[i];
    }
        
};
template<class T>
tem<T>::tem(int n){
    data=new T[n];
    size=n;
}
int main(){
    tem<int> x(5);
    int i;
    for(i=0;i<5;i++)
        x[i]=i;
    for(i=0;i<5;i++)
        cout<<x[i]<<' ';
    cout<<endl;
    return 0;
}

结果：

0 1 2 3 4