学步园

cpp中typeid举例：

#include <iostream>
#include <typeinfo>  //for 'typeid'

using namespace std;

class Person {
public:
   // ... Person members ...
   virtual ~Person() {}
};

class Employee : public Person {

   // ... Employee members ...
};

int main()
{
   Person person;
   Employee employee;
   Person *ptr = &employee;
   Person &ref = employee;
   // The string returned by typeid::name is implementation-defined
   std::cout << typeid(person).name() << std::endl;   // Person (statically known at compile-time)
   std::cout << typeid(employee).name() << std::endl; // Employee (statically known at compile-time)
   std::cout << typeid(ptr).name() << std::endl;      // Person * (statically known at compile-time)
   std::cout << typeid(*ptr).name() << std::endl;     // Employee (looked up dynamically at run-time
                                                      //           because it is the dereference of a
                                                      //           pointer to a polymorphic class)
   std::cout << typeid(ref).name() << std::endl;      // Employee (references can also be polymorphic)

   Person* p = 0;
   try {
        typeid(*p); // not undefined behavior; throws std::bad_typeid
                  // *p, *(p), *((p)), etc. all behave identically
   }catch (...){
        cout << "NULL pointer!"<<endl;
   }

  Person& pRef = *p; // undefined behavior, dereferences null
  typeid(pRef);        // does not meet requirements to throw std::bad_typeid

  Employee e;
  Person pp;
  Person &per_ref = pp;
  try{
    Employee & em_ref = dynamic_cast<Employee&>(per_ref);
  }catch(bad_cast e){
    cout << "bad cast : not valid type reference !" <<endl;
  }catch(...){
    cout << "not valid type reference !" <<endl;
  }                    // because the expression for typeid is not the result
                      // of applying the unary * operator; behavior is undefined
}