RTTI之typeid运算符

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <typeinfo>

using std::cout;
class Grand
{
    private:
        int hold;
    public:
        Grand(int h=0):hold(h){}
        virtual void Speak() const {cout << "I am a grand class!
";}
        virtual int Value() const {return hold;}
};

class Superb:public Grand
{
    public:
        Superb(int h=0):Grand(h){}
        void Speak() const {cout << "I am a superb class!
";}
        virtual void Say() const
        {
            cout << "I hold the superb value of " << Value() << "!
";
        }
};

class Magnificent:public Superb
{
    private:
        char    ch;
    public:
        Magnificent(int h=0, char c='A') : Superb(h),ch(c){}
        void Speak() const {cout << "I am a magnificent class!!!
";}
        void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "!
";}
};

Grand * Getone();

int main()
{
    std::srand(std::time(0));
    Grand * pg;
    Superb * ps;
    for(int i=0;i<5;i++)
    {
        pg=Getone();
        cout << "Now processing type " << typeid(*pg).name() << ".
";
        pg->Speak();
        if(ps=dynamic_cast<Superb *>(pg))
            ps->Say();
        if(typeid(Magnificent)==typeid(*pg))
            cout << "Yes, you're really magnificent.
";
    }
    return 0;
}

Grand * Getone()
{
    Grand * p;
    switch(std::rand()%3)
    {
        case 0: p=new Grand(std::rand()%100);
                break;
        case 1:p=new Superb(std::rand()%100);
               break;
        case 2:p=new Magnificent(std::rand()%100,'A'+std::rand()%26);
               break;
    }
    return p;
}

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <typeinfo>

using std::cout;
class Grand
{
    private:
        int hold;
    public:
        Grand(int h=0):hold(h){}
        virtual void Speak() const {cout << "I am a grand class!
";}
        virtual int Value() const {return hold;}
};

class Superb:public Grand
{
    public:
        Superb(int h=0):Grand(h){}
        void Speak() const {cout << "I am a superb class!
";}
        virtual void Say() const
        {
            cout << "I hold the superb value of " << Value() << "!
";
        }
};

class Magnificent:public Superb
{
    private:
        char    ch;
    public:
        Magnificent(int h=0, char c='A') : Superb(h),ch(c){}
        void Speak() const {cout << "I am a magnificent class!!!
";}
        void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "!
";}
};

Grand * Getone();

int main()
{
    std::srand(std::time(0));
    Grand * pg;
    Superb * ps;
    for(int i=0;i<5;i++)
    {
        pg=Getone();
        cout << "Now processing type " << typeid(*pg).name() << ".
";
        pg->Speak();
        if(ps=dynamic_cast<Superb *>(pg))
            ps->Say();
        if(typeid(Magnificent)==typeid(*pg))
            cout << "Yes, you're really magnificent.
";
    }
    return 0;
}

Grand * Getone()
{
    Grand * p;
    switch(std::rand()%3)
    {
        case 0: p=new Grand(std::rand()%100);
                break;
        case 1:p=new Superb(std::rand()%100);
               break;
        case 2:p=new Magnificent(std::rand()%100,'A'+std::rand()%26);
               break;
    }
    return p;
}

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <typeinfo>

using std::cout;
class Grand
{
    private:
        int hold;
    public:
        Grand(int h=0):hold(h){}
        virtual void Speak() const {cout << "I am a grand class!
";}
        virtual int Value() const {return hold;}
};

class Superb:public Grand
{
    public:
        Superb(int h=0):Grand(h){}
        void Speak() const {cout << "I am a superb class!
";}
        virtual void Say() const
        {
            cout << "I hold the superb value of " << Value() << "!
";
        }
};

class Magnificent:public Superb
{
    private:
        char    ch;
    public:
        Magnificent(int h=0, char c='A') : Superb(h),ch(c){}
        void Speak() const {cout << "I am a magnificent class!!!
";}
        void Say() const {cout << "I hold the character " << ch << " and th e integer " << Value() << "!
";}
};

Grand * Getone();

int main()
{
    std::srand(std::time(0));
    Grand * pg;
    Superb * ps;
    for(int i=0;i<5;i++)
    {
        pg=Getone();
        cout << "Now processing type " << typeid(*pg).name() << ".
";
        pg->Speak();
        if(ps=dynamic_cast<Superb *>(pg))
            ps->Say();
        if(typeid(Magnificent)==typeid(*pg))
            cout << "Yes, you're really magnificent.
";
    }
    return 0;
}

Grand * Getone()
{
    Grand * p;
    switch(std::rand()%3)
    {
        case 0: p=new Grand(std::rand()%100);
                break;
        case 1:p=new Superb(std::rand()%100);
               break;
        case 2:p=new Magnificent(std::rand()%100,'A'+std::rand()%26);
               break;
    }
    return p;
}

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。