c++派生类中构造函数和析构函数执行顺序、判断对象类型、抽象类、虚函数

一、

代码：

 1 #include<stdio.h>
 2 #include<string.h>
 3 #include<algorithm>
 4 #include<iostream>
 5 using namespace std;
 6 class A
 7 {
 8 public:
 9     int a,b;
10     A();
11     A(int x,int y);
12     ~A();
13 };
14 A::A()
15 {
16     printf("调用A类构造函数\n");
17 }
18 A::A(int x,int y)
19 {
20     a=x;
21     b=y;
22     printf("调用A类构造函数\n");
23 }
24 A::~A()
25 {
26     printf("调用A类析构函数\n");
27 }
28 class B:public A
29 {
30 public:
31     int aa,bb;
32     B()
33     {
34         printf("调用B类构造函数\n");
35     }
36     B(int x,int y)
37     {
38         aa=x;
39         bb=y;
40         printf("调用B类构造函数\n");
41     }
42     ~B()
43     {
44         printf("调用B类析构函数\n");
45     }
46 };
47 class C:public B
48 {
49 public:
50     int aaa,bbb;
51     B one;
52     C(int x,int y)
53     {
54         aaa=x;
55         bbb=y;
56         one.aa=x;
57         one.bb=y;
58         printf("调用C类构造函数\n");
59     }
60     ~C()
61     {
62         printf("调用C类析构函数\n");
63     }
64 };
65 int main()
66 {
67     C first(0,0);
68     printf("%d %d %d %d\n",first.aaa,first.bbb,first.one.aa,first.one.bb);
69     return 0;
70 }

二、

  1 #include<stdio.h>
  2 #include<string.h>
  3 #include<algorithm>
  4 #include<iostream>
  5 using namespace std;
  6 class Base
  7 {
  8 public:
  9     Base(int x,int y)
 10     {
 11         a=x;
 12         b=y;
 13     }
 14     virtual void show()  //声明了虚函数，那么指针指向哪个对象就用那个对象的函数
 15     {     //否则的话，声明指针是什么类型就会用那个类型的函数
 16         cout<<"基类内容show打印"<<endl;
 17         cout<<"a:"<<a<<"b:"<<b<<endl;
 18     }
 19     void prinf()
 20     {
 21         cout<<"基类内容prinf打印"<<endl;
 22         cout<<"a:"<<a<<"b:"<<b<<endl;
 23     }
 24 private:
 25     int a,b;
 26
 27 };
 28 class One:public Base
 29 {
 30 public:
 31
 32     One(int x,int y):Base(x,y)
 33     {
 34         aa=x;
 35         bb=y;
 36     }
 37     void show()
 38     {
 39         cout<<"派生类内容show打印"<<endl;
 40         cout<<"aa:"<<aa<<"bb:"<<bb<<endl;
 41     }
 42     void prinf()
 43     {
 44         cout<<"派生类内容prinf打印"<<endl;
 45         cout<<"aa:"<<aa<<"bb:"<<bb<<endl;
 46     }
 47 private:
 48     int aa,bb;
 49 };
 50 int main()
 51 {
 52     Base mb(100,200),*pc;
 53     One mc(200,300);
 54     pc=&mc;
 55     pc->show();
 56     pc->prinf();
 57     pc=&mb;
 58     pc->show();
 59     pc->prinf();
 60     return 0;
 61 }
 62
 63 //2、
 64 #include<stdio.h>
 65 #include<string.h>
 66 #include<algorithm>
 67 #include<iostream>
 68 using namespace std;
 69 class Shape   //抽象类定义是只要里面有一个纯虚函数那他就是抽象类，
 70 {   //抽象类不需要什么关键字来定义，且它的派生类必须覆盖重写他的纯虚方法
 71 public :
 72     double a;
 73     Shape(double x)
 74     {
 75         a=x;
 76     }
 77     virtual void area()=0;
 78     virtual void show()=0;
 79 };
 80 class Circle:public Shape
 81 {
 82 public:
 83     Circle(double x):Shape(x)
 84     {
 85
 86     }
 87     void area()
 88     {
 89         cout<<"the circle area is :"<<endl;
 90         cout<<3.14*a*a<<endl;
 91     }
 92     void show()
 93     {
 94         cout<<"a:"<<a<<endl;
 95     }
 96 };
 97 int main()
 98 {
 99     Shape *ptr;
100     Circle r(6);
101     ptr=&r;
102     ptr->area();
103     ptr->show();
104     return 0;
105 }
106
107 //3、
108 #include<stdio.h>
109 #include<string.h>
110 #include<algorithm>
111 #include<iostream>
112 #include<typeinfo>
113 using namespace std;
114 class Sqare
115 {
116 public :
117     double a;
118     Sqare(double x)
119     {
120         a=x;
121     }
122 };
123 class Circle
124 {
125 public :
126     double a;
127     Circle(double x)
128     {
129         a=x;
130     }
131 };
132 int main()
133 {
134     Sqare one(1);
135     Circle two(2);
136     if(typeid(one)==typeid(Sqare))  //判断对象类型
137     {
138         cout<<"它是Sqare对象"<<endl;
139     }
140     else
141     {
142         cout<<"它是Circle对象"<<endl;
143     }
144
145     if(typeid(two)==typeid(Sqare))
146     {
147         cout<<"它是Sqare对象"<<endl;
148     }
149     else
150     {
151         cout<<"它是Circle对象"<<endl;
152     }
153     return 0;
154 }

原文地址：https://www.cnblogs.com/kongbursi-2292702937/p/11775093.html