C++知识点案例 笔记-4

1.纯虚函数

2.抽象类

3.内部类

4.运算符重载

5.类的函数重载

6.友元的函数重载

1.纯虚函数

==纯虚函数==

//有时基类中无法给出函数的具体体现，定义纯虚函数可以为派生函数保留一个函数接口
#include <iostream>
#include <cstring>
using namespace std;
class Animal
{
public:
    Animal(char *name);
    void print_name();
    virtual void print_color() = 0;
    virtual ~Animal();
private:
    char *m_Name;

};
Animal::Animal(char *name)
{

    m_Name = new char[strlen(name)+1];
    strcpy(m_Name,name);
}
Animal::~Animal()
{
   cout<<"Animal diluting !!!"<<endl;
   if(m_Name)
   {
       delete[]m_Name;
   }
}
void Animal::print_name()
{
    cout<<"name: "<<m_Name<<endl;
}
class Cat:public Animal
{
public:
    Cat(char *name,char *color);
    virtual void print_color();
    virtual ~Cat();
private:
    char *m_Color;
};
Cat::Cat(char *name,char *color):Animal(name)
{
    m_Color = new char[strlen(color)+1];
    strcpy(m_Color,color);
}
void Cat:: print_color()
{
    cout<<"Cat color :"<<m_Color<<endl;
}
Cat::~Cat()
{
    cout<<"Cat diluting !!!"<<endl;
    if(m_Color)
    {
        delete[]m_Color;
    }
}
int main()
{
    Animal *p;
    p = new Cat("catmimi","yellow");
    p->print_name();
    p->print_color();
    delete p;
    return 0;

}

2.抽象类

==抽象类==

//含有纯虚函数的基类，若派生类继承后仍有纯虚函数也为抽象类，直至无纯虚函数为止
#include<iostream>
#include<cstring>
using namespace std;
const double IP = 3.1415926;
class Shapes
{
public:
    Shapes(int x,int y = 0);
    virtual ~Shapes();
    virtual void disp() = 0;
protected:
    int m_X,m_Y;
};
Shapes::Shapes(int x,int y)
{
    m_X = x;
    m_Y = y;
}
Shapes::~Shapes()
{
    cout<<"Shapes diluting !!!"<<endl;
}
class Squre:public Shapes
{
public:
    Squre(int squre_x,int squre_y);
    virtual void disp();
    virtual ~Squre();

};
Squre::Squre(int squre_x,int squre_y):Shapes(squre_x,squre_y)
{

}
void Squre::disp()
{
    cout<<"The squre area:"<<m_X*m_Y<<endl;
}
Squre::~Squre()
{
    cout<<"Squre diluting !!!"<<endl;
}
class Circle:public Shapes
{
public:
    Circle(int R);
    virtual void disp();
    virtual ~Circle();
};
Circle::Circle(int R):Shapes(R)
{

}
void Circle::disp()
{
    cout<<"The circle area : "<<IP * m_X * m_X<<endl;
}
Circle::~Circle()
{
    cout<<"Circle diluting !!!"<<endl;
}
int main()
{
    Shapes *p[2];
    p[0] = new Squre(5,10);
    p[0] ->disp();
    p[1] = new Circle(2);
    p[1] ->disp();
    for(int i;i<2;i++)
    {
        delete p[i];
    }
    return 0;
}

3.内部类

==内部类==

//在（基）类内部定义的类叫做内部类，（基）类相当于该类的外部类
#include <iostream>
using namespace std;
class Outer
{
public:
    class Inner{
    private:
        int Inner_n;
    public:
        void set_outer_n(Outer &ref_outer){ref_outer.outer_n = 100;}
        void set_inner_n(){Inner_n = 666;}
        void show(Outer &ref_outer)
        {
            ref_outer.show();
            cout<<"Inner: "<<Inner_n<<endl;
            }
    };
   void show(){cout<<"Out: "<<outer_n<<endl;}
private:
    int outer_n;
};
int main()
{
    Outer outer_ojb;
    Outer::Inner inner_ojb;

    inner_ojb.set_outer_n(outer_ojb);
    inner_ojb.set_inner_n();
    inner_ojb.show(outer_ojb);
    return 0;
}

4.运算符重载

==运算符重载==
//如对象的相加，把特殊符号定义为函数易于表达
#include<iostream>
using namespace std;
class Q
{
private:
    int x,y;
public:
    Q(int x1=0,int y1=0):x(x1),y(y1){}
    void show() const;
    Q operator + (const Q&a)const ;###########重载+运算符
    Q operator - (const Q&a)const ;
};
void Q::show() const
{
    cout<<"(x,y)="<<"("<<x<<","<<y<<")"<<endl;
}
Q Q::operator + (const Q&a)const
{
    return Q(x + a.x,y + a.y);
}
Q Q::operator - (const Q&a)const
{
    return Q(x - a.x,y - a.y);
}
int main()
{
    Q a1(7,2);
    Q a2(5,1);
    Q a;
    Q b;
    a = a1 + a2;
    b = a1 - a2;
    cout<<"a1:";
    a1.show();
    cout<<"a2:";
    a2.show();
    cout<<"a:";
    a.show();
    cout<<"b:";
    b.show();
    cout<<"a1+a2:";
    a.show();
    cout<<"a1-a2:";
    b.show();
    return 0;

}

5.类的函数重载

==类的函数重载==

#include<iostream>
using namespace std;
class V
{
private:
    int a,b;
public:
    V(int a1 = 0,int b1 = 0):a(a1),b(b1){}
    void show() const;
    V operator ++();
    V operator ++(int);

};
void V::show() const
{
    cout<<"(a,b)="<<"("<<a<<","<<b<<")"<<endl;
}
V V::operator ++()  //++前置函数
{
    ++a;
    ++b;
    return *this;
}

V V::operator ++(int)  //"k=i++"：后缀++表示先k=i之后i自增
{
    V a = *this;
    ++(*this);          //调用前置函数
    return a;
}
int main()
{
    V m(1,1);
    V n(0,0);
    (m++).show();
    (++n).show();
    return 0;
}

6.友元的函数重载

==友元的函数重载==

//定义时不用指明函数位置，方便私有数据成员的调用
#include<iostream>
using namespace std;
class G
{
private:
    int m,n;
public:
    G(int m1 = 0,int n1 = 0):m(m1),n(n1){}
    void show() const;
    friend G operator + (const G&a1,const G&a2);
    friend G operator - (const G&a1,const G&a2);

};
void G::show() const
{
    cout<<"(m,n)="<<"("<<m<<","<<n<<")"<<endl;
}
G operator + (const G&a1,const G&a2)
{
    return G(a1.m +a2.m , a1.n +a2.n);
}
G operator - (const G&a1,const G&a2)
{
    return G(a1.m - a2.m, a1.n - a2.n);
}
int main()
{
    G j(2,2);
    G k(1,1);
    G a;

    j.show();
    k.show();
    a.show();

    a = j + k;
    a.show();
    a = j - k;
    a.show();

    return 0;

}