1 #include <iostream> 2 #include <cstdlib> 3 #include <ctime> 4 #include <typeinfo> 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! ";} 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! ";} 22 virtual void Say() const 23 { 24 cout << "I hold the superb value of " << Value() << "! "; 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!!! ";} 35 void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "! ";} 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() << ". "; 49 pg->Speak(); 50 if(ps=dynamic_cast<Superb *>(pg)) 51 ps->Say(); 52 if(typeid(Magnificent)==typeid(*pg)) 53 cout << "Yes, you're really magnificent. "; 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 <iostream> 2 #include <cstdlib> 3 #include <ctime> 4 #include <typeinfo> 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! ";} 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! ";} 22 virtual void Say() const 23 { 24 cout << "I hold the superb value of " << Value() << "! "; 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!!! ";} 35 void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "! ";} 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() << ". "; 49 pg->Speak(); 50 if(ps=dynamic_cast<Superb *>(pg)) 51 ps->Say(); 52 if(typeid(Magnificent)==typeid(*pg)) 53 cout << "Yes, you're really magnificent. "; 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 <iostream> 2 #include <cstdlib> 3 #include <ctime> 4 #include <typeinfo> 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! ";} 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! ";} 22 virtual void Say() const 23 { 24 cout << "I hold the superb value of " << Value() << "! "; 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!!! ";} 35 void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "! ";} 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() << ". "; 49 pg->Speak(); 50 if(ps=dynamic_cast<Superb *>(pg)) 51 ps->Say(); 52 if(typeid(Magnificent)==typeid(*pg)) 53 cout << "Yes, you're really magnificent. "; 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。