程式設計與演算法（三）C++面向物件程式設計第三週相關筆記

阿新 • • 發佈：2021-10-20

1、this指標的運用

指向當前函式作用類的指標

相當於翻譯為C語言，r.run() = run(test * this)

#include<bits/stdc++.h>
using namespace std;
class test{
    private:
        double real,imag;
    public:
        test(double r,double i):real(r),imag(i)
        {}
        void add_one(){
            this->real ++;
        }
         
void get_(){
            cout<<this->real<<" "<<this->imag<<endl;
        }
};
int main(){
    test a(1,2);
    a.add_one();
    a.get_();

}

View Code

#include<bits/stdc++.h>
using namespace std;
class test{
    private:
        double real,imag;
    public:
        test( 
double r,double i):real(r),imag(i)

        void out(){
            cout<<"Hello"<<endl;
        }
};
int main(){
    test* p = NULL;
    p->out();

}

View Code

2、靜態成員

分為靜態成員函式，靜態成員變數

相當於全域性函式，全域性變數

定義靜態成員變數需要先說明

int CRectangle::nTotleArea = 0;

靜態成員函式內不能訪問非靜態變數與非靜態函式

#include<bits/stdc++.h>
using 
 namespace std;
class Rectangle{
    private:
        int w,h;
        static int total_area;
        static int total_number;
    public:
        Rectangle(int _w,int _h){
            w = _w;
            h = _h;
            total_area += w*h;
            total_number++;
        }
        Rectangle(Rectangle& r){
            w = r.w;
            h = r.h;
            total_area += w*h;
            total_number++;
        }
        ~Rectangle(){
            total_area -= w*h;
            total_number--;
        }
        static void out(){
            cout<<total_number<<" "<<total_area<<endl;
        }
};
int Rectangle::total_number = 0;
int Rectangle::total_area = 0;


int main(){
    Rectangle r1(1,2);
    Rectangle* r2 = new Rectangle(2,4);
    Rectangle r3(2,3);
    Rectangle::out();
    delete r2;
    Rectangle::out();
    Rectangle r4 = r1;
    Rectangle::out();
    return 0;
}

輸出:
3 16
2 8
3 10

View Code

新增建構函式後預設無參建構函式消失

但是複製建構函式依然在

3、成員物件與封閉類

有成員物件的類叫做封閉類

封閉類的建構函式與解構函式的執行順序相反

建構函式都是先生產成員物件，在操作封閉類

解構函式先操作封閉類先操作成員物件

#include<bits/stdc++.h>
using namespace std;
class tyre{
public:
    tyre(){
        cout<<"tyre constructor"<<endl;
    }
    ~tyre(){
        cout<<"tyre destructor"<<endl;
    }
};
class engine{
public:
    engine(){
        cout<<"engine constructor"<<endl;
    }
    ~engine(){
        cout<<"engine destructor"<<endl;
    }
};
class Car{
    tyre t;
    engine e;
    public:
        Car(){
            cout<<"car constructor"<<endl;
        }
        ~Car(){
            cout<<"car destructor"<<endl;
        }
};


int main(){
    Car c;
    return 0;
}

輸出：
tyre constructor
engine constructor
car constructor
car destructor
engine destructor
tyre destructor

View Code

封閉類的複製建構函式還是呼叫其成員的物件的複製建構函式

pass

4、友元 friend

一個類友元函式可以訪問該類的私有成員

一個類友元類可以訪問該類的私有成員

#include<bits/stdc++.h>
using namespace std;

class Car{
    int a = 1,b = 2;
    public:
        friend void get_(Car c);
};
//改成指標也可
//class 也行
void get_(Car c){
    cout<<c.a<<" "<<c.b<<endl;
}

int main(){
    Car c;
    get_(c);
    return 0;
}