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RTTI之typeid运算符
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!\n";}14 virtual int Value() const {return hold;}15 };16 17 class Superb:public Grand18 {19 public:20 Superb(int h=0):Grand(h){}21 void Speak() const {cout << "I am a superb class!\n";}22 virtual void Say() const23 {24 cout << "I hold the superb value of " << Value() << "!\n";25 }26 };27 28 class Magnificent:public Superb29 {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<Superb *>(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 <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!\n";}14 virtual int Value() const {return hold;}15 };16 17 class Superb:public Grand18 {19 public:20 Superb(int h=0):Grand(h){}21 void Speak() const {cout << "I am a superb class!\n";}22 virtual void Say() const23 {24 cout << "I hold the superb value of " << Value() << "!\n";25 }26 };27 28 class Magnificent:public Superb29 {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<Superb *>(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 <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!\n";}14 virtual int Value() const {return hold;}15 };16 17 class Superb:public Grand18 {19 public:20 Superb(int h=0):Grand(h){}21 void Speak() const {cout << "I am a superb class!\n";}22 virtual void Say() const23 {24 cout << "I hold the superb value of " << Value() << "!\n";25 }26 };27 28 class Magnificent:public Superb29 {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<Superb *>(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。
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