1     #include <iostream>
 2 
 3     using namespace std;
 4 
 5     class A
 6     {
 7         public:
 8             A(int n = 0) { num = n; }       //在构造函数内使用 n 初始化const型数据成员 num
 9             void showNum() { cout<<"num = "<<num<<endl; }
10         private:
11             const int num;            //const 型数据成员
12     };
13 
14     int main()
15     {
16         A a(10);
17         a.showNum();
18 
19         return 0;
20     }

        error: uninitialized member 'A::num' with 'const' type 'const int'
        error: assignment of read-only data-member 'A::num'

 1     #include <iostream>
 2 
 3     using namespace std;
 4 
 5     class A
 6     {
 7         public:
 8             A(int n = 0):num(n) { }       //使用初始化表达式对const型数据成员进行初始化
 9             void showNum() { cout<<"num = "<<num<<endl; }
10         private:
11             const int num;
12     };
13 
14     int main()
15     {
16         A a(10);
17         a.showNum();
18 
19         return 0;
20     }

 1     #include <iostream>
 2 
 3     using namespace std;
 4 
 5     class A
 6     {
 7         public:
 8             A(int &rn):rNum(rn) { }       //使用初始化表达式对引用型数据成员进行初始化
 9             void showNum() { cout<<"num = "<<rNum<<endl; }
10         private:
11             int &rNum;      //引用类型
12     };
13 
14     int main()
15     {
16         int x = 10, &rx = x;
17         A a(rx);        //传递引用类型
18         a.showNum();
19 
20         return 0;
21     }

    private:
        int xPos(10, 20);
        int yPos(100, 200);

 1         #include <iostream>
 2 
 3         using namespace std;
 4 
 5         class Point
 6         {
 7             public:
 8                 void printPoint() { cout<<"("<<xPos<<", "<<yPos<<")\n"; }
 9                 int xPos;   //public类型的 xPos 和 yPos
10                 int yPos;
11         };
12 
13         class Line
14         {
15             public:
16                 Line(int x1, int y1, int x2, int y2)
17                 {
18                     M.xPos = x1; M.yPos = y1;       //在构造函数内完成类对象的初始化
19                     N.xPos = x2; N.yPos = y2;
20                 }
21                 void printLine() { M.printPoint(); N.printPoint(); }
22             private:
23                 Point M;        //类对象成员, M和N
24                 Point N;
25         };
26 
27         int main()
28         {
29             Line L(10, 20, 100, 200);
30             L.printLine();
31 
32             return 0;
33         }

            (10, 20)
            (100, 200)

            Process returned 0 (0x0)   execution time : 0.500 s
            Press any key to continue.

 1         #include <iostream>
 2 
 3         using namespace std;
 4 
 5         class Point
 6         {
 7             public:
 8                 Point(int x, int y) { xPos = x; yPos = y; }
 9                 void printPoint() { cout<<"("<<xPos<<", "<<yPos<<")\n"; }
10             private:
11                 int xPos;   //private类型的 xPos 和 yPos
12                 int yPos;
13         };
14 
15         class Line
16         {
17             public:
18                 Line(int x1, int y1, int x2, int y2):M(10, 20), N(100, 200) { ; }   //借助初始化表达式完成对M,N的初始化
19                 void printLine() { M.printPoint(); N.printPoint(); }
20             private:
21                 Point M;        //类对象成员, M和N
22                 Point N;
23         };
24 
25         int main()
26         {
27             Line L(10, 20, 100, 200);
28             L.printLine();
29 
30             return 0;
31         }

 1     #include <iostream>
 2 
 3     using namespace std;
 4 
 5     class Book
 6     {
 7         public:
 8             Book() { ibookNumber++; }           //通过构造函数访问static型数据ibookNumber并使其自增1
 9             ~Book() { ibookNumber--; }          //对象在被撤销时将static型数据ibookNumber并使其自减1
10             void showNum() { cout<<"Book number = "<<ibookNumber<<endl; }
11         private:
12             static int ibookNumber;             //static类型数据成员 ibookNumber
13     };
14 
15     int Book::ibookNumber = 0;        //在类外对static类型的数据成员进行初始化
16 
17     int main()
18     {
19         Book A; Book B; Book C; Book D; Book E;     //创建一些对象
20         A.showNum();        //使用对象A查看当前对象个数
21         B.showNum();        //使用对象B查看当前对象个数
22         cout<<"销毁一些对象...\n";
23         B.~Book(); C.~Book();   //将B、C对象进行撤销
24         D.showNum();            //使用D对象查看剩余对象个数
25         E.showNum();            //使用E对象查看剩余对象个数
26 
27         return 0;
28     }

        Book number = 5
        Book number = 5
        销毁一些对象...
        Book number = 3
        Book number = 3

        Process returned 0 (0x0)   execution time : 0.266 s
        Press any key to continue.