19.2. Run-Time Type Identification

Run-time type identification (RTTI) is provided through two operators:

• The typeid operator, which returns the type of a given expression

• The dynamic_cast operator, which safely converts a pointer or reference to a base type into a pointer or reference to a derived type

When applied to pointers or references to types that have virtual functions, these operators use the dynamic type (§ 15.2.3, p. 601) of the object to which the pointer or reference is bound.

These operators are useful when we have a derived operation that we want to perform through a pointer or reference to a base-class object and it is not possible to make that operation a virtual function. Ordinarily, we should use virtual functions if we can. When the operation is virtual, the compiler automatically selects the right function according to the dynamic type of the object.

However, it is not always possible to define a virtual. If we cannot use a virtual, we can use one of the RTTI operators. On the other hand, using these operators is more error-prone than using virtual member functions: The programmer must know to which type the object should be cast and must check that the cast was performed successfully.