C++ Runtime Type Identification(RTTI)

What is RTTI for?

The intent of RTTI is to provide a standard way for a program to determine the type of object during runtime.

How Does RTTI Work?

• The dynamic_cast operator generates a pointer to a derived type from a pointer to a base type, if possible. Otherwise, the operator returns 0, the null pointer.
• The typeid operator returns a value identifying the exact type of an object.
• A type_info structure holds information about a particular type.

Caution

RTTI works only for classes that have virtual functions.

class Grand{has virtual methods};
class Superb: public Grand{...};
class Magnificent : public Superb{...};

Grand* pg = new Grand;
Superb * pm = dynamic_cast<Superb *>(pg); 
// This code asks whether the pointer pg can be type cast safely to the type Superb*. If it can, the operator renturns the address of the object. Otherwise it returns 0, the null pointer. 

You can invoke the Say() function safely:

if(ps = dynamic_cast<Superb *>(pg))
    ps->Say();

The typeid operator and type_info Class

The typeid operator returns a reference to a type_info object, where type_info is a class defined in the typeinfo header file (formerly typeinfo.h). The type_info class overloads the == and != operators so that you can use these operators to compare types.
For example, the following expression evalluates to the bool value true if
pg points to a magnificent object and to false otherwise:

typeid(Magnificent) == typeid(*pg);
// if pg happens to be a null pointer, the program throws a bad_typeid exception.

cout<< typeid(*pg).name() <<"\n";

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来源： https://blog.csdn.net/lilele12211104/article/details/111239599