typeid 키워드

typeid 키워드는 런타임에 오브젝트의 클래스를 결정하기 위해 사용 된다. std::type_info 오브젝트를 리턴한다.( 프로그램 종료까지 유지 되는 값 ) 단순히 class 정보만이 필요할 경우에, dynamic_cast<class_type> 보다는 typeid 를 사용하는 것을 선호한다.( typeid 의 수행속도가 짧음 )

#include <iostream>    // cout
#include <typeinfo>  //for 'typeid'
 
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 = nullptr;
   try {
      typeid(*p); // not undefined behavior; throws std::bad_typeid
                  // *p, *(p), *((p)), etc. all behave identically
   }
   catch (...)
   {}
 
   Person& pRef = *p; // Undefined behavior: dereferencing null
   typeid(pRef);      // does not meet requirements to throw std::bad_typeid
                      // because the expression for typeid is not the result
                      // of applying the unary * operator
}

Output (exact output varies by system):

Person
Employee
Person*
Employee
Employee

출처 : http://en.wikipedia.org/wiki/Typeid