1 #include
2 #include
3 #include
4 #include
5
6 using std::cout;
7 class Grand
8 {
9 private:
10 int hold;
11 public:
12 Grand(int h=0):hold(h){}
13 virtual void Speak() const {cout << "I am a grand class!\n";} 14 virtual int Value() const {return hold;} 15 }; 16 17 class Superb:public Grand 18 { 19 public: 20 Superb(int h=0):Grand(h){} 21 void Speak() const {cout << "I am a superb class!\n";} 22 virtual void Say() const 23 { 24 cout << "I hold the superb value of " << Value() << "!\n"; 25 } 26 }; 27 28 class Magnificent:public Superb 29 { 30 private: 31 char ch; 32 public: 33 Magnificent(int h=0, char c='A') : Superb(h),ch(c){} 34 void Speak() const {cout << "I am a magnificent class!!!\n";} 35 void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "!\n";} 36 }; 37 38 Grand * Getone(); 39 40 int main() 41 { 42 std::srand(std::time(0)); 43 Grand * pg; 44 Superb * ps; 45 for(int i=0;i<5;i++) 46 { 47 pg=Getone(); 48 cout << "Now processing type " << typeid(*pg).name() << ".\n"; 49 pg->Speak();
50 if(ps=dynamic_cast(pg))
51 ps->Say();
52 if(typeid(Magnificent)==typeid(*pg))
53 cout << "Yes, you're really magnificent.\n";
54 }
55 return 0;
56 }
57
58 Grand * Getone()
59 {
60 Grand * p;
61 switch(std::rand()%3)
62 {
63 case 0: p=new Grand(std::rand()%100);
64 break;
65 case 1:p=new Superb(std::rand()%100);
66 break;
67 case 2:p=new Magnificent(std::rand()%100,'A'+std::rand()%26);
68 break;
69 }
70 return p;
71 }

1 #include
2 #include
3 #include
4 #include
5
6 using std::cout;
7 class Grand
8 {
9 private:
10 int hold;
11 public:
12 Grand(int h=0):hold(h){}
13 virtual void Speak() const {cout << "I am a grand class!\n";} 14 virtual int Value() const {return hold;} 15 }; 16 17 class Superb:public Grand 18 { 19 public: 20 Superb(int h=0):Grand(h){} 21 void Speak() const {cout << "I am a superb class!\n";} 22 virtual void Say() const 23 { 24 cout << "I hold the superb value of " << Value() << "!\n"; 25 } 26 }; 27 28 class Magnificent:public Superb 29 { 30 private: 31 char ch; 32 public: 33 Magnificent(int h=0, char c='A') : Superb(h),ch(c){} 34 void Speak() const {cout << "I am a magnificent class!!!\n";} 35 void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "!\n";} 36 }; 37 38 Grand * Getone(); 39 40 int main() 41 { 42 std::srand(std::time(0)); 43 Grand * pg; 44 Superb * ps; 45 for(int i=0;i<5;i++) 46 { 47 pg=Getone(); 48 cout << "Now processing type " << typeid(*pg).name() << ".\n"; 49 pg->Speak();
50 if(ps=dynamic_cast(pg))
51 ps->Say();
52 if(typeid(Magnificent)==typeid(*pg))
53 cout << "Yes, you're really magnificent.\n";
54 }
55 return 0;
56 }
57
58 Grand * Getone()
59 {
60 Grand * p;
61 switch(std::rand()%3)
62 {
63 case 0: p=new Grand(std::rand()%100);
64 break;
65 case 1:p=new Superb(std::rand()%100);
66 break;
67 case 2:p=new Magnificent(std::rand()%100,'A'+std::rand()%26);
68 break;
69 }
70 return p;
71 }

1 #include
2 #include
3 #include
4 #include
5
6 using std::cout;
7 class Grand
8 {
9 private:
10 int hold;
11 public:
12 Grand(int h=0):hold(h){}
13 virtual void Speak() const {cout << "I am a grand class!\n";} 14 virtual int Value() const {return hold;} 15 }; 16 17 class Superb:public Grand 18 { 19 public: 20 Superb(int h=0):Grand(h){} 21 void Speak() const {cout << "I am a superb class!\n";} 22 virtual void Say() const 23 { 24 cout << "I hold the superb value of " << Value() << "!\n"; 25 } 26 }; 27 28 class Magnificent:public Superb 29 { 30 private: 31 char ch; 32 public: 33 Magnificent(int h=0, char c='A') : Superb(h),ch(c){} 34 void Speak() const {cout << "I am a magnificent class!!!\n";} 35 void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "!\n";} 36 }; 37 38 Grand * Getone(); 39 40 int main() 41 { 42 std::srand(std::time(0)); 43 Grand * pg; 44 Superb * ps; 45 for(int i=0;i<5;i++) 46 { 47 pg=Getone(); 48 cout << "Now processing type " << typeid(*pg).name() << ".\n"; 49 pg->Speak();
50 if(ps=dynamic_cast(pg))
51 ps->Say();
52 if(typeid(Magnificent)==typeid(*pg))
53 cout << "Yes, you're really magnificent.\n";
54 }
55 return 0;
56 }
57
58 Grand * Getone()
59 {
60 Grand * p;
61 switch(std::rand()%3)
62 {
63 case 0: p=new Grand(std::rand()%100);
64 break;
65 case 1:p=new Superb(std::rand()%100);
66 break;
67 case 2:p=new Magnificent(std::rand()%100,'A'+std::rand()%26);
68 break;
69 }
70 return p;
71 }

typeid运算符能够确定两个对象是否为同种类型。它与sizeof有些相像，可以接受两种参数：

类型；

结果为对象的表达式。

typeid运算符返回一个对type_info对象的引用，其中，type_info是在头文件typeinfo中定义的一个类。type_info类重在了==和！==运算符，以便可以使用这些运算符来对类型进行比较。例如，如果pg指向的是一个Magnificent对象，则下述表达式返回true,否则为false:

typeid(Magnificent)==typeid(*pg)

如果pg是一个空指针，程序将引发bad_typeid异常。

type_info类的实现随厂商而异，但包含一个name()成员，该函数返回一个随实现而异的字符串，通常为类的名称。本程序返回的是类的名称长度+类的名称。